Fukushima: 224th-231tst day!

Dear Colleagues: 224th-231tst day! I. Update of EPZ (Part 1) I touched on this issue in earthquake (161, Oct 14-21) in a short introduction of "A set of JNES's safety assessment released from NISA" . This seems to have called attention of Professor. A. Dave Rossin by responding "I have not heard of any decision to extend the EPZ. We understand "Planning Zone" but would be surprised if any further evacuations or restrictions were announced now that radiation contamination data are widely available. Can you clarify?" I apologize for my incomplete explanation about this very important safety issue. Since the current EPZ was specified by assuming a release from a single reactor accident in Japan, a concern was raised against its appropriateness in protecting the public. The scoping assessments performed by JNES I introduced was intended to provide some reference, by extending the data and method used in specifying the EPZ by simply increasing the source terms. In view of significant impacts on to the ution of accident management, the expansion of the EPZ was not implemented. Instead, a series of evacuation orders were issued as follows: Fukushima-Daiichi Fukushima-Daiini Restriction R 20mSv/y. II. Update of EPZ (Part 2) On October 20, Nuclear Safety Commission (NSC) held the Working Group meeting for Disaster Prevention to discuss a new policy for prevention of disasters of nuclear power plants. It appears that it is to respond partially to concerns of local municipal governments with NPP sites. Currently those NPPs off-power are going through the stress tests as specified by NISA on July 22. However, some of the local governments (i.e. Fukui Prefecture) are demanding to perform a comprehensive safety review after completely revising the safety criteria of NPPs as a requirement of restarting. The discussion on new policy for prevention of disasters of nuclear power plants seems to be well accepted by the local governments. The discussion started with potential adaptation of GS-R-2, Preparedness and Response for a Nuclear or Radiological Emergency, REQUIREMENTS, in IAEA SAFETY STANDARDS SERIES (2002); together with GSG-2, Criteria for Use in Preparedness and Response for a Nuclear or Radiological Emergency, General Safety Guide, in IAEA Safety Standards ((2011). The GS-R-2, combined with GSG-2, has many things in common with US NRC's Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear Power Plants: Guidance for Protective Action Recommendations for General Emergencies (NUREG-0654/FEMA-REP-1, Supplement 3, Revision 1, SAND2010-0293, Draft Report for Comment). The main idea was formulated as early as in 1980 http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0654/ with the last reviewed/updated Sunday, March 13, 2011. Since GS-R-2 was issued more than ten years ago, one of the focal point of discussion should be whether it is applicable for the severe accident situation experienced through Fukushima-Daiich. The safety principle in GSG-2 specifies; PAZ (Precautionary Action Zone) should be provided to prevent the development of severe deterministic effects for very high levels of doses such as provided in Table 2 of GSG-2. UPZ (Urgent Protective action Planning Zone) should be provided to reduce the occurrence of stochastic effects in the population at present and in the future such as by referring to Table 3 of GSG-2, which is compatible with reference levels within a range of 20-100 mSv. The IAEA's system of generic criteria and operational criteria is as shown in Fig. 1: The default OILs are listed in Table 8 and Emergency Classifications are summarized in Table 12 of GSG-2. The size of zones are not clearly defined by IAEA, although the US NRC provides a guidance of 10 miles (16 km) for EPZ-plime and 50 miles (89 km) for EPZ-ingestion). NSC is discussing 3-5 km for PAZ and 5-30km for UPZ, plus un-specified PPZ (Plume Passage Zone) based on international practices as well as analysis of Fukushima-Daiichi. By expanding the EPZ to 30 km radius, the number of municipal districts is said to increase to over 130 from the current 44. I believe more in-depth study should be made in designating there zones, especially through integration of risks to account for the densely populated characteristics of EPZ in Japan. In this connection, I recall a pioneering approach for siting criteria that provided all the essential components of a PSA [Farner, F.R. Siting Criteria – A New Approach, Proc, Symp. On the Containment and Siting of NPPs, SM-89/34, IAEA, April 3-7, 1967 and FR FARMER, Reactor Safety and Siting: A Proposed Risk Criterion, Nuclear Safety, 8 (1967), pp. 539-548]. Since many countries with dense populations had begun to accept the major role of nuclear power, Farmer’s objective was to realize the power plant’s full economies of scale by strategically building new power plants where there was the greatest demand for electricity. By extending his approach as well as incorporating the lessons learned from the Chernobyl accident, I once published a new approach for safety goals [G. Saji, Safety goals in the framework of INES,” Rel. Eng. and Sys. Safety, 2003, Vol. 80-2, pp. 143-161]. A similar approach is needed in specifying EPZ as proposed by Farmer. Also, I noticed that designation of EPZ for restriction of ingestion by distance form the NPPs was proven almost impossible due to very complicated plume passage characteristics not only in Fukushima, but also in surrounding prefectures and cities. III. JNES's Assessment on Status of 1F1, 1F2 and 1F3 On October 21, JNES (Japan Nuclear Energy Safety Organization) released their MELCORE (Method of Estimation of Leakages and Consequences of Releases) sresults for estimation of of 1F1, 1F2 and 1F3 (in Japanese). http://www.jnes.go.jp/content/000119740.pdf This assessment was performed to check TEPCO's calculation by using MAAR (Modular Accident Analysis Program). The basic conditions of analyses followed the TEPCO's calculation, such as TEPCO's chronology, supplemented with some sensitivity assessments. In particular; 1F1: RCV leakage (from atmospheric portion) due to approximately 7 cm2 at 18 hours after the reactor trip, enlarged to 40 cm2 after 50 hours. Loss of IV upon station blackout 1F2: RCV leakage due to 80 cm2 hole 21 hours after the reactor trip and another 80 cm2 hole on March 15 at the gas phase of Suppression Chamber 1F3: Followed TEPCO's chronology These two calculations generally support each other, especially in (1) time of exposure of reactor core, (2) start of fuel failure and (3) time of RCV failure. The in-vessel retention of corium is achieved both in 1F2 and 3, but not in 1F1, which is predicted to fail in 5 hours in the JNES's calculation, 15 hours in the TEPCO's calculation. This early melt-through is coming from their assumption that the core cooling by IC (Isolation Condenser) was lost before arrival of the tsunami, at 15:03 of March 11, together with termination of HPCI which should have injected water into the Reactor Pressure Vessel. This very conservative assumption was made since their operation could not be confirmed from the faulty indicator ramps of the control panels. However, the assumption of large holes in the RCV need to be substantiated, such as by comparing the leak rates of nitrogen gas injection currently being performed. I do not think the observed low leakage rates as well as the sampling data of the gas inside of the RCV support such a large hole nor existence of corium out of the reactor vessel. The truth is expected to be demonstrated soon, in a matter of a few months, when a robot could get inside of the RCV. While looking through this report, I noticed that the analyses of the transition phase, a phase between the station blackout to the initiation of core melt, is absent in the current analyses. Unlike in the case of LOCA, the development of the event sequence occurs gradually after the initiation of station blackout. During this phase, operator actions as well as availability of instrumentation and control systems and behavior of crippled safety systems such as through loss of DC power or flooding of essential DC power/control centers should have induced significant differences before going into the severe accident phase. The decay heat decreases rapidly during this phase also, followed with a gradual change in water levels inside of the Reactor Pressure Vessel. The severe accident codes, such as MELCORE ands MARP, simulate severe accident phase, often starting with "leakages". (Recall that an initial motivation of developing MELCORE was to integrate RELAP and CONTAIN ) More appropriate code system for assessment of the transition phase after the station blackout should be applied, I believe. I also noticed a very strange situation in these two assessments. They paid no attention to a potential "feed and bleed" operation soon after the station blackout. Each of these reactors seem to have provisions to enable the "feed and bleed" operation by releasing high pressure steam from the PRV into the suppression pool through several mechanical action function portion of Release and Safety Valves (The "release" action is pneumatic using electromagnetic valves). Even after losing the high pressure water injection, the cores should have been cooled for several hours by sacrificing water inventory inside of the PCV. What was essential was the high pressure water injection. When the battery power was lost, it was necessary to depressurize the PCV to be able to inject water through the fire fighting pump or fire engines. This seems to have been achieved by using temporary auto batteries to open the release valves. I believe "feed and bleed" operation is one of the most important lessons learned from the TMI accident. However, it appears that this concept did not spread into the Japanese BWR community, perhaps since it was originally developed for PWRs such as given in http://dspace.mit.edu/handle/1721.1/15437. This wide-spread omission seems to be not limited to the JNES's severe accident calculation. I have not found any description in other Japanese document so far, although I have never worked for BWRs in my life. IV. Disclosure of TEPCO's "Operational Procedure Manual". TEPCO finally disclosed the "Operational Procedure Manual for Accidents" and associated documents on October 24, in response to an order from Special Committee for Promotion of Innovation of Science and Engineering, House of Representatives. http://www.meti.go.jp/press/2011/10/20111024003/20111024003.html For last two months, they have be resisting to disclose this document on the ground that it contains their intellectual properties. Previously they only disclosed tables of contents, by masking all the contents in black. NISA was also considered protecting TEPCO, by saying they can look it at any time. Their closed position was attacked by medias, by saying that both of them do not take recognition of responsibility of gigantic damages induced by the disaster, not just limited to Japan, but throughout the world. At present, the disclosure was limited to only a part of the manual for the 1F1, to be followed with other plants' version. It helps much for understanding the accident sequences. There are Operational Procedure Manuals in "Event-Base"- "Symptom-Base" and "Severe Accident." Only a portion of first and third was released this time, together with Appendix 3, which explains how the actual operator actions complied with the procedures specified. The Appendix 3 is readable in understanding the bases of the operator actions, in particular, how operators were confused with a lack of reliable water level in the core, induced by a loss of power to the central control panel. The event-base manual is organized in 4 parts: Reactor Accidents Reactor Scram, LOCA, Pipe Ruptures, Loss of Feed Water Flow, Fuel Failures, Accidents in Recirculation System, CRDM Accident, Reactor System Failures, Turbine and Electric Power Accident Turbine Trip, Anomalies in Turbine Generator trip, External Transmission Line Failures (12-4 Station Blackout), Loss of Control Power, Generator Troubles Fires Cable Routing Rooms, Generator Fires, Fires in DG rooms, In-house Oil Storage Rooms, Oil Storage Tanks and Transformer Fires, 6.9 kV Metal- Clad Switch Gears, 480V Power Centers, Natural Disasters Large Earthquakes Tsunami Among them, the following sections were released this time. 1-1 Reactor Scram 12-4 Station Blackout 2-3. System-wize AM (Accident Management) Procedures (After Core Damage) for Inert Gas System (Improved Venting) The following remarks, quoted from 12-4, might be interesting. (1) It is essential to recover electric power as soon as possible, since it is indispensable to secure at lease one Emergency bus for reactor safety. (2) Motor operated valves and pneumatic valves wii become inoperable, except DC-driven valves (3) It is possible to prevent the core damage, if the external power source or emergency DGs could be recovered within 10 hours. Thus Isolation condenser should not be inadvertently tripped. In connection with Point (2), I consulted with the planned released battery discharge curves. The battery power should have lasted longer than 10 hours, since the station blackout followed approximately one hour after the loss of off site power. Since emergency diesel generators worked as planned for an hour, the plants have gone through the DC power demanding first one hour, without draining the battery power. However, the Fukushima Daiichi went into un-operable soon after tsunami, due to flooding of essential DC power/control centers as well as batteries due, presumably, to flooding. It was one of the largest design flaw to layout these essential electrical component for control of reactors in the basements where flooding threat exist, not only from the tsunami, but also from pipe break of the sea water pipes. Even if the external power could have been recovered early, most of the essential systems could not have become operable without closing the contacters/breakers which need battery power to drive. Although most of the media commented that the manual does not postulate the extended station blackout, I got an impression that the manual provides ultimate procedures closely relevant to what has happened in the course of the accident. The actual accident sequence of Fukushima-Daiichi proceeded in combination of several different "postulated" event sequences. However, let me point out some of the notable omissions in the procedures: (1) No provision for removal of hydrogen gas after reactor isolation, which was accumulated through water radiolysis, upon the station blackout. This should have been closely related with the early hydrogen explosion. (2) No provision to depressurize the Reactor Pressure Vessel without DC power to enable the low pressure water injection upon loss of the DC power. This should have restricted the "feed and bleed" operation after switching to an alternative low pressure water injection line. (3) No manuals released yet dealing with water flooding threat in the basement. (4) No manual for the "internal hydrogen explosion/pipe break as occurred in Hamaoka Unit 1 as well as 8 other cases inside TEPCO V. Update of Radiological Safety Evaluation Report (draft) by Food Safety Commission I introduced this subject first in Earthquake (141) on August 8, followed with Earthquake (149, Sept 2-6). The Food Safety Commission (FSC, http://www.fsc.go.jp/english/index.htm) compiled and posted, for public comments, a draft Evaluation Report on Assessment of Radioactive Materials Contained in Foods (in Japanese, 226 pages). It is very interesting to read that the FSC is trying to introduce a cutoff dose rate for low level radiation risk at 100 mSv. The report invited 3,089 public comments from all levels of Japanese people, from concerned mothers to very knowledgeable scientists. I also submitted several comments. On October 27 , the final report was posted in the FSC's website. The report is in 221 pages in Japanese, accompanied with a one page summary, Q&A and summary of public comments. http://www.fsc.go.jp/sonota/emerg/radio_hyoka.html The conclusion states the following three key points: (1) Potential health effects of radiation at more than 100 mSv of life-time additional accumulated dose for assessment of health effect through ingestion (2) It is impossible to address health effects below 100 mSv, based on our current knowledge (3) Criteria for restrictive values for food should be made in consideration of the risk management, which is based on the assessment of life-time additional accumulated dose, while taking into account of radiation detection situation as well as ingestion conditions. This indicates that FSC is now addressing only the potential health effects through intake of radioactivities through ingestion, instead of the total dose, which combines external and internal (ingestion, inhalation and skin intake) exposures. I think this is more realistic, since the internal exposure through inhalation, especially due to radioactive iodines, has already occurred and there is no way to reduce the resultant thyroid doses. External exposures, especially through Cs134 + Cs-137 cannot be mitigated by regulation of foods. The report relies heavily on epidemiology, which is criticized much by some scientists who favors cellular effects, such as damage to DNA and cellular damages. Deep knowledge of these mechanisms are indispensable for understanding causes of health effects, however, I believe epidemiology is more practical since final judgement should weigh more on health effects to human. Unfortunately this position left some of the key issues behind, and still inviting comments that no epidemiological data does not prove that there is not health effect. I have once proposed the following approach in my previous paper (G. Saji, 2002. Safety goals in the framework of INES,” Rel. Eng. and Sys. Safety, 2003, Vol. 80-2, pp. 143-161). "Below 0.005–0.25 Gy is considered as ‘zero dose’ group, although it does not mean that there is no effect below this level. It indicates that the health effect of radiation cannot be isolated, and are masked by confounding factors below this level." I glanced through the public comments and noticed the following points. (1) A condensed explantation of the Fukushima-Daiichi release and potential effect is necessary (2) A concise explanation of the concept of life-time accumulated dose is necessary. Many public misunderstood that FSC is trying to raise the current public dose limit of 1 mSv/y to 100 mSv. (3) Many people are asking to include information as presented in: ECRR 2010: The Health Effects of Ionising Radiation Exposure at Low Doses and Low Dose Rates for Radiation Protection Purposes: Regulators’ Edition ( http://www.euradcom.org/2011/ecrr2010.pdf ) and Chernobyl: Cnsequences of the Catastrophe for people and the Environment, Alexey Yablokov, New York Academy of Sciences 2009 VI. Testing of a filtered venting system for 1F2 On October 27, TEPCO announced that a filtered venting system for 1F2 RPV (Reactor Containment System) has been installed and tested as shown in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111027_01-e.pdf. It consists of gas cooler/heat-radiaters, replaceable filters and exhaust fans, which released filtered atmosphere to the external environment. It was reported that the hydrogen gas concentration of the gas discharge is around 1%. There is no secondary confinement system (cover) recovered in 1F2, but TEPCO appears to have decided to purify atmosphere of the RCV first. In 1F1, a filtered exhaust line was installed to keep the atmosphere in negative pressure to reduce radioactive effluent release. TEPCO announced that the 1F1 cover (a kind of secondary confinement barrier) is now completed. VII. A set of illustrative pictures of the water treatment system. On October 22, TEPCO released a set of 15 illustrative drawings and photos of the water purification system in: http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111022_02-e.pdf VIII. Thirty years for de-comissioning On October 28, a Technical Committee on Mid- and Long Term Measures of Atomic Energy Commission drafted a initial planning of decommissioning of Fukushima-Daiich as follows: 2011, end - Achieving the "cold shutdown" state, launching decommissioning activities - decontamination and removal of debris - installation of fuel handling cranes 2014, end - Start of evacuation of fuels from the spent fuel pools - remediation of RCV failures - flooding the reactor pressure vessels, inspection inside of the PCV 2021 - Starting removal of damaged fuels - start disassembly of reactors 2041 Completion of de-comissioning Well, let me stop here tonight! Genn Saji ____________________________________________________________________________________________________ (Previous e-mail sent on Oct 22 as Earthquake (161, Oct 14-21)) Dear Colleagues: 217th-224th day! This week, I was traveling in Hokkaido for four days and came back on Thursday. I could not cover some of the important information in this update. I will include them in the next issue. I. Progress of "Roadmap towards Restoration from the Accident at Fukushima Daiichi Nuclear Power Station" as of October 17 TEPCO released a overview report on the status of "Roadmap towards Restoration from the Accident at Fukushima Daiichi Nuclear Power Station" as of October 17. http://www.tepco.co.jp/en/press/corp-com/release/11101703-e.html Perhaps, the summary report in English may be convenient to glance through. http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111017e2.pdf II. Mid-Term Safety for Units 1 to 4 at Fukushima Dai-ichi NISA defined the basic guidelines and requirements for securing safety at the Fukushima Dai-ichi NPS, TEPCO, during the preparation period (within nearly three years) until the operation is initiated for decommissioning after the completion of Step 2 of “Roadmap towards Restoration from the Accident. For that, it is necessary to 1) control and mitigate the release of radioactive materials, 2) properly remove the decay heat, 3) prevent criticality, and 4) prevent hydrogen explosion. On October 17, TEPCO submitted reports on the equipment related to the circulating injection cooling system, http://www.nisa.meti.go.jp/english/press/2011/10/en20111020-2.pdf According to the TEPCO's Press Release of October 17, *We (TEPCO) have provided Japanese press release version of the instructions received from NISA. However, at this time we have reserved the right to not provide an English version due to potential misunderstandings that may arise from an inaccurate rendering of the original Japanese text."　　”We may provide the English translation that NISA releases in our press releases. However, in principle we would advise you to visit the NISA website for timely and accurate information.” The report looks equivalent to PSAR (Preliminary Safety Analysis Report) commonly provided for construction and alteration of NPPs in Japan. A probabilistic safety assessment was performed in Chapter 8 for water injection system. The highest risk-worth events were another large tsunami (62%) and failures of the water injection pipe lines (38%). This conclusion is reasonable, since the "hoses" have been experienced to be vulnerable for reliable operation. III. A set of JNES's safety assessment released from NISA On October 15, a set of 39 memos, which summarize safety assessment performed by JNES (Japan Nuclear Energy Safety Organization http://www.jnes.go.jp/english/index.html) was released by NISA (Nuclear and Industrial Safety Agency). These quick safety analyses were performed during March 15 to July 11, including the active phase (generally around 10 days) of the severe accidents occurred in the Fukushima-Daiichi. Copies of FAX, which were sent from JNES to staffs of NISA in the Emergency Center, were compiled. Since they are quick assessment, the results are summarized, only with short explanation of methodologies used in the assessment. Nevertheless, some of the memos were used as technical bases for making very important judgement, such as classifying Level 7 in INES. It appears that NISA/JNES does not intend to issue these memos in English. Although it is welcome to disclose these memos, some of the contents are masked in black by saying that such caution was necessary for protection of personal information. However, the masked information is nothing to do with personal information, including dimensions of spent fuel racks, size and number of fuel assemblies in cores, volume of reactor pressure vessels and primary containment vessels, etc. They do not seem to be related with security reasons. Let me introduce some of the notable issues from this report. (1) Discussions on INES levels through estimation of fuel damage fractions. They used the estimated relationship of CAMS dry-well dose rates with respect to release fraction of rare gases, as well an postulated hydrogen concentration at the time of explosion (4%〜75% in volume) assuming a total conversion through Zr + 2H2O -> ZrOP2 + 2H2. The dose rates correspond to 50% in 1F1, 35% in 1F2 and 30% in 1F3. When 4% hydrogen concentration is applied, the amount of Zr consumption corresponds to 5.6% in 1F1, 4% in 1F2 and 5.6% in 1F3. Although NESA concluded Level 5 from these estimations at the early phase, I think it is not appropriate, since the original INES levels were generally classified in terms I-131 releases from a point of view of off-site impacts, onsite impacts and defense-in-depth degradation. That is, INES off-site impacts are defined in terms of releases from the containment vessel and not the fuel damage fraction, I believe. In any case, NESA should not have made such a hasty decision based on scant information. (2) Estimation of release fraction from a remote monitoring station in Fukushima An revers engineering estimation was made by using a monitoring data of March 15-20, which was obtained near City of Fukushima, located approximately 60 km from Fukushima-Daiichi. The results were 13%/unit. (3) MCCI study On March 25, an study was made for possibility of molten-core-concrete-interaction, by assuming 100% of corium placed on the pedestal floor, when the corium flows down slowly, instantaneously as well as in a jet stream. By reviewing the plant status, it was concluded that slowly ejected corium should solidify, without inducing CCI. For their assessment, a report by S. Lomperski et al. of ANL (OECD MCCI Project report, OECD/MCCI-2005-Tr03) was used. They also performed for the case of total amount of molten core onto the pedestal and concluded that it is unlikely the corium will penetrated the concrete. An estimated release from the PCV was around 1% for rare gas and 0.6 % in CsI, indicating no need to extend the current EPZ. (4) EPZ Possible extension of EPZ (Emergency Planning Zone) to account for multiple reactor failure was investigated by performing a dispersion calculation. The results indicated that additional 19 km was necessary from the current 5.5 km for the whole body doses. Further parametric studies were performed for a case of 2 times and 2.5 times of the single release. (5) Possibility of hydrogen explosion due to water-radiolysis Approximately 10% of the FP inventory was assumed to be ejected from the primary containment vessel and estimated an amount of environmental release. The results indicated 6.5% for the release fraction. (6) Response to US NRC US NRC seems to have recommended to perform MELCOR calculation, by assuming early termination of RCIC. The critical point was how long the RCIC survived until the battery power drained. The time duration is not clarified yet but JNES is saying "several hours" after the station blackout. (7) Detection of neutrons during March 14-15 JNES investigated a possibility of re-criticality, release of volatile delayed neutron precursors, as well as leakage of neutrons from spent fuel pools. They conclude that a leakage of the volatile delayed neutron precursors, such as Br-87 (55.7 d), Cs-141 (24.9s), I-137 (24.5 s) Te-136 (19.0s) and Br--86 (16,0s) may be the cause. This is an interesting conclusion, since the reactor in shutdown is still in a sub-critical state, with very small fission reactions persisting through subcritical multiplication, although it appears that JNES had not performed a quantitative study. I thought the neutrons were due to small release of fuel particles containing spontaneous fission species. Obviously, further study is needed to explain which mechanist can explain the neutron detection during March 14-15. (8) Reconstruction of dose rates starting from off-site environmental monitoring data Due to the station blackout, there has been no off-site environmental monitoring data recovered until March 17, nearly six days after the accident. In view of this, theoretical dose reconstruction was performed, by performing reverse engineering in terms of time and distance, to estimate time-dependent dose distribution maps within 20 km zone, dating back to March 14. An effect of dose reduction through evacuation was also estimated. They conclude that the evacuation performed on March 12 should have evaded the giant release occurred starting March 14 to 17. This result is interesting, however, I am still concerned that dose rates measured at the monitoring car on the site nor meteorological data (wind direction data) measured on-site by the monitoring car do not correlate well. The dose rates should have become high when the plume flew in the direction of the monitoring car. The quoted dose rates in time are not showing the amount of releases. In addition, the inhalation exposure before evacuation should be estimated, since it is needed to account for thyroid doses. The areal dose rates are now available from data taken by airplane as well as soil sampling. IV. Exploring damaged core status through LFCM On October 19, TEPCO released the results of exploitation of a damaged core status by sending electric signals from a control panel which detects signals from neutron detectors (LPRM: Local Power Range Monitor) in a central control room. The signals enables to estimate soundness between LPRM and cables, and judge a possibility to estimate a situation of lower part or inside of Reactor Pressure Vessel (RPV). http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111019_01-e.pdf. The results showed that there were no undamaged detectors since all detectors were short-circuited or disconnected between connector to detector at the bottom of reactor and the penetration to PCV. Usually, the cables connected to the in-vessel detectors are mineral-insulated (MI) cables, which withstand high temperature and radiation. However, the cables appear to be connected to plastic insulated cables at the bottom of the RPV using "Connectors to Detectors". As in the case of CRDM position indicator probes (PIP) as introduced in Earthquake (153, Sept 16-20), unfortunately, it is difficult to specify the status of the bottom part of RPV from this survey. The Nuclear Safety Commission (NSC) is asking TEPCO to clarify core status, however, it should be extremely difficult to accomplish this, since the most desirable way should be somehow inserting VIDEO camera inside of the RPV. Well, let me stop here tonight! Genn Saji __________________________________________________________________________________________ (Previous e-mail sent on Oct 14 as Earthquake (160, Oct 11-14)) Dear Colleagues: 214th-217th day! Starting next week, I will reduce this series of update to once a week, on every Friday night in principle. I may provide an intermediate one in case there are urgent issues or too many reportable events. I noticed substantial slowing down in events announcements and press releases this week. I. Installation of the roof panel of the cover for the 1F1 reactor building On October 14, TEPCO announced completion of the final roof panel installation of the cover (the secondary confinement system) for the 1F1 Reactor Building as shown in ( http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111014_02-e.pdf ). Each panel is constructed with steel frames covered with a plastic sheet. The assembly of the panels were made by using two remote-controlled cranes without using bolts and nuts. It is said to be an application of building classical wooden buildings in Japan, without using a single nail. When a filtered ventilation system is installed, it will prevent environmental release of radioactive effluent. 1F1 is also waiting for the installation of recirculation cooling system for the damaged core. Also, last June, a steam discharge was observed from a floor of the reactor building above the pressure suppression room, indicating a presence of break somewhere. The recent PackBot examination confirmed that the steam ejection has stopped as shown in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111014_03-e.pdf Since the temperature of the primary reactor vessel is below the boiling point, in a "cold shutdown" state, no steam ejection is understandable. II. Update of detection of Sr and Pu in Fukushima I introduced this topic in Earthquake (156, Sept 27-30). On September 30, MEXT released the detailed soil sampling results of Pu and Sr in http://radioactivity.mext.go.jp/ja/distribution_map_around_FukushimaNPP/0002/5600_0930.pdf It is important to point out that a corridor of Pu is also observed at the middle of the highly contaminated corridor of radioactive plume passage, stretching NW direction from Fukushima-Daiichi. The corridor was contaminated with heavy deposits of Ce-137+Cs-140. The concentration of Pu is a little bit (0.33-2.2 times) above the previous radiation fallout from the weapon tests mainly performed by the US in the cold war days. As shown in attachment 2-1 of the document, the consistency of the Pu corridor with the Cs corridor indicates that this contamination should have been induced by a single puff release, such as with a hydrogen explosion, instead of superposition of multiple releases. This observation is also generally supported with maps for Sr-89 and Sr-90 in attachment 2-2, where the ratio of Sr-90 to Cs-137 was 1.6E-04~5.8E-02 (average:2.6E-03). I once calculated this value back in May and obtained ration of Sr-90/Cs-137 was 7E-05 to 1.6E-03, which agrees reasonably well. In spite of relatively small release fraction, I was surprised to read a news report on October 13 that notable strontium contamination was identified in Yokohama, approximately 250 km SWS of Fukushima-Daiichi. A resident of a condo sampled sludge from the roof and sent to a private radiation assessment organization, who reported 195 Bq/kg of Sr-90. The City of Yokohama is in a process of independent check of the measurement. Since it is well known that assessment of strontium (as well as plutonium) is difficult, this news motivated me to revisit how the strontium was measured by MEXT in the map I referred in Earthquake (156, Sept 27-30). Unfortunately, no detailed information is available. The report only mentions that "radiochemical analysis" was performed in 30 gram of soil samples. Radiation was measured for 60 minutes by using a low-background beta detector. Detection limits are 300 Bq/m2 for Sr-89 and 40 Bq/m2 for Sr-90." The radiation assessment was performed by Japan Chemical Analysis Center (http://www.jcac.or.jp/index2.html, no English home page), who has ISO/IEC17025 certificate, including analysis of environmental samples of radioactive strontium. Although this organization is trusted in Japan, this kind of insufficient disclosure of essential scientific information may result in dubious feeling among the public. I believe this is about the time that MEXT should organize an international benchmark exercise for environmental radiation assessment of strontium- and plutonium isotopes to improve transparency, by inviting some of the most experienced institutes who established the land contamination density maps at the time of Chernobyl accident; in particular, Dr. B. Burakov, V.G. Khlopin Radium Institute, St. Petersburg, Russia and Dr. V. A. Kashparov, Ukrainian Institute of Agricultural Radiology, Kiev, Ukraine. III. Radiation hazard evaluation, applied to Fukushima recovery-workers I introduced related radiation protection issues for PUBLIC in Earthquake (157, Sept 30-Oct 4), followed with Earthquake (158, Oct 4-7) and Earthquake (159, Oct 7-11). In view of an importance of dose limit issues both for radiation workers as well as the public, let me introduce a very interesting paper recently published by B.R. Scott, 2011. (In: Journal of American Physicians and Surgeons Volume 16 Number 3 Fall 2011. pp. 75-78.) Dr. Scott is a senior scientist at Lovelace Respiratory Research Institute, who specializes in radiation risk and benefit assessment. Since he distributed his paper among the US colleagues whose mailing addresses are included in one of my primary distribution list, let me attach his paper to make sure other audience can read his paper. He is discussing the deterministic radiation effects, based on his central estimates of the median lethal gamma dose in Gy for different mammalian species (rats, mice, swine, dogs, goats, human, and sheep) as a function of the average dose rate in Gy/h (0.01, 0.1, 1, 10, 100 Gy/h) to bone marrow, based on research reported elsewhere. The illustrated feature, pasted below, of the approaching an asymptotic value significantly >0 as the dose rate becomes very high is called the Ainsworth phenomenon in honor of the late John Ainsworth, who first reported the observation. The formalism he used is applicable to either lethality (i.e., LD ) or morbidity. He concludes: From personal dosimetry and a standard hazard-function model, risk of deterministic effects of ionizing radiation on exposed recovery workers can be calculated. Barring an exceptional event that caused the 250 mSv/y limit to be greatly exceeded, such effects in Fukushima workers are unlikely. The discredited LNT risk model should not be used to project cancer deaths in down-wind populations with low-dose and low-dose rate exposures. Let me add some information as to the recent radiation exposure situation of radiation workers so far engaged in the recovery work at Fukushima-Daiichi. According to the reported statistics as of end June, approximately 13,000 workers engaged in emergency recovery activities. Those who received more than 100 mSv (external + internal) were 135. The most exposed individuals occurred among operators, since masks with charcoal filters were not sufficiently provided during the first few days. They were even taking food by removing masks in the control room. Two of them, males in their age of 30th and 40th, stayed in the control room until March 14. During this time, radiation monitoring was performed only by personal dosimeters. TEPCO tried to limit to 50 mSv during this time, but failed to account for internal exposure. Because of this, they received the following doses: total (external + internal) internal Note A (30th) 678.08 mSv 590 mSv may have taken iodine pills on March 14 B (40th) 643.07 540 may have taken iodine pills on March 13 C (50th) 352.08 6 additional >250 Here, I feel very uncomfortable in using mSv for the internal exposure, in line with the current ICRP Pub. 103. Assuming the tissue weighing factor of 0.04 and most of the internal exposure is due to radioactive iodine (I-131 (8.04 d); I-132 (2.08 h); I-133 (20.8 h); I-134 (52.6 min); I-135 ( 6.61 h), the thyroid dose can be as high as 15 Gy. I believe this high level of thyroid exposure cannot be treated as stochastic. However, the highly exposed Fukushima radiation workers are not comparable with the doses exposed among the Chernobyl "liquidators". I saw a video of the liquidation, in which young soldiers were shoveling the smoldering graphite blocks, piled on the roof of turbine building, without radiation protection suits. I was shocked at this scene in watching at the National Chernobyl Museum in Kiev, Ukraine. I remember they were raising the flag of ВС СССР. It appears that radiation monitoring was not performed ahead of such a dangerous operation. On the contrary, except at the most critical phase of the first few days, TEPCO health physics staffs performed the dose monitoring, at least before entry of workers. Nevertheless, during the first few months, the radiation monitoring was not adequate, resulting in several cases of unplanned exposures. Currently, it appears to be generally well under control. It is planned to reduce the worker dose limit to 100 mSv, starting November. Even though radiological protection of workers has been much improved, the actual working environment seems continue to be very stressful, since many of them are unanimously appealing for improvement. IV. Installation of "Gas Management System" to 1F2 Primary containment Vessel. TEPCO released a schematic diagram of "Gas Management System" planned to be installed for cleaning the atmosphere inside of 1F2 Primary containment Vessel. The system consists of dehumidifier, exhaust blower and a filter. http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111012_01-e.pdf Installation of "Gas Management System" is being performed in all 1F1 - 1F3 in parallel. V. A safety assessment of the water injection system I hesitated to include this information in this update. On October 1, TEPCO released a handout which explains the time margins available when some malfunctions are postulated. "Reactor and Fuel Status in Case of a Reactor Water Injection System Malfunction" http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111001_03-e.pdf This assessment was regarded as a waring by some media and dispatched a news as an imminent potential remelting of the core. I felt such a safety assessment should not go into core melt analysis, since it is in a level of transient analysis. To demonstrate that sea water injection can be established in a due time, TEPCO performed an emergency drill to establish an alternate water injection line, which took approximately one hour for setting up an alternate cooling function. http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111012_02-e.pdf. Well, let me stop here tonight! Genn Saji __________________________________________________________________________________________________ (Previous e-mail sent on Oct 12 as Earthquake (159, Oct 7-11)) Dear Colleagues: 210th-214th day! In this update, some of the notable findings are summarized from Proceedings of the Atomic Energy Society (AESJ) fall meeting (Sept 19-22). I intend to cover the Fukushima-Daiichi related research topics in 2-3 commentaries. In this second series, papers dealing with decontamination issues are selected. My reviews are sketchy, since each presentation is limited to just one page. I. Government's revised decontamination policy On October 10, the Committee of Environmental Recovery of MENV (Ministry of Environment) discussed the Government's policy for decontamination of the Fukushima-Daoochi disaster. The minutes of the meeting has not been posted yet, but according to media reports, the committee agreed on the following policy; (1) The Government shall provide cost of decontamination for those contaminated areas with dose rates higher than 1 mSv/y (seems to mean the whole body dose). The dose rates of areas below 20 mSv/y shall be reduced by 50% for dwellings and 60% for schools and parks, in about two years. The total areas exceeding the 20 mSv/y benchmark shall be reduced as small as reasonably achievable in consideration of radiation worker doses. (2) The Government will take responsibility of decontamination of high dose areas, such as "Vigilance (Off-limit)" Zone and "Scheduled (and Organized) Evacuation" Zone, in about three years. Less contaminated areas shall be decontaminated following the planning established by local governments in about two fiscal years. (3) The Government shall take responsibility for securing sites and construction of "intermediate facilities," as well as final depositories. for storage of contaminated decontamination and sewage discharges. The Government's revised policy, in effect, expanded the goal of dose rates for decontamination to 1 mSv/y from the previous 5 mSv/y. This is expected to decontaminate practically all housings in Fukushima Prefecture. II. Update of dose limits for the public I started to introduce this subject in Earthquake (157, Sept 30-Oct 4), followed with Earthquake (158, Sept Oct 4-7). This issue is closely linked to the issue introduced above. Since this is a very important topic, Dr. Joyce Sloof and Dr. Joost Woittiez of Isotopics (isotopics@kpnplanet.nl) called my attention to their excellent memo: Note 2011-05: Fukushima and radiation protection policy posted in their website as http://www.isotopics.nl/wp-content/uploads/Isotopics-Note-2011-05.pdf . Since I felt it was a joy to read this kind of lucent explanation of radiation protection, let me introduce his website. He explained the bases of radiation protection from Dose, Risks, Dose limits and Radiation protection policy. Being inspired with their memo, let me add some of my opinions. (1) Dose I have been feeling very uncomfortable in following radiation protection related subjects here in Japan, since all are using mSv instead of Gy, even in discussion of internal exposure such as thyroid doses. This is making radiation effects unclear in discussing internal exposure of children. I was curious why Japanese scientists changed to discuss in terms of effective doses. In my understanding, it is rooted on Dr. Clarke's initiative in revising ICRP Pub. 60, ICRP 1991 Recommendations of the International Commission on Radiological Protection ICRP Publication 60; Ann. ICRP 21 (1–3). He considered that the radiation protection principles were matured enough waiting for simplification. This seems to resulted in suppressing the discussion using the absorbed dose, which is converted into an effective dose by multiplying with the tissue weighing factor (0.04 for the case of thyroid) and add all the tissue doses into a single effective dose value, in a sense assuming a homogeneous model. However, as isotopics points out, "for many radionuclides, (bio)chemical considerations, such as specific binding to bio- molecules, availability, precipitation, cell membrane transport, storage, etc., do not a priori support the homogeneity assumption. Since the new ICRP Pub. 103 is being used as an international standard in Japan, I have been following this tendency. When looking at the detriment suffered by thyroid-removed Chernobyl children, my heart sores with their quality of life, that cannot be converted just by applying a magic number of 0.04. Recently I was very interested in reading a book on Chernobyl: Consequences of the Catastrophe for People and the Environment" by Alexey V. Yablokov, former Adviser for Ecology and Public Health to Russian President Mikhail Gorbachev; Vasilly B. Nesterenko, Director of the Belarussian Insitute of Radioactive Safety (now deceased), and Alexy V. Nesterenko, the Institute’s senior scientist. Dec. 2009, 335 pages, published by the New York Academy of Sciences http://www.llrc.org/epidemiology/subtopic/alexeybook.htm Throughout this book, practically no discussion on doses are made in their epidemiological studies, but they used the land contamination density of cesium as an equivalent dose parameter. Knowing there are so much uncertainties in dose estimation, this scale makes their report robust, without relying on "transfer factors" very commonly used in Russia. However, for further scientific discussion, conversion of the land contamination densities into doses are still necessary, I believe. For such a purpose, I once tried to convert the land contamination densities into thyroid doses as attached. This presentation was originally prepared for my lecture at the Radium Institute in St. Petersburg on: Dose Reconstruction and Health Impact of theChernobyl Accident, June 9, 2006. This was expanded on top of the presentation at: International Topical Meeting on Probabilistic Safety Analysis, PSA’05 11-15 September 2005, San Francisco, California, USA. I made some updating to incorporate the recent statistics of thyroid cancer cases this time. I believe a similar methodology should be also developed for radiological assessment of Fukushima Daiichi. (2) Risks, dose limit and policy It is becoming clear in Japan that the concept of risk does not apply in the already existing exposure situation such as in Fukushima. Many people are looking for a radiologically safe dose limit, however, only the affected people can decide up to what extent the residual risks can be tolerable after being informed of the true magnitude of risk. The current discussions on the achievable decontamination level are exactly for finding the acceptable risk level for the public. III. A set of pictures showing the current status of Fukushima-Daiichi On October 8, TEPCO released a set of new pictures, which are showing the current status of Fukushima-Daiichi through: http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111008_02-e.pdf IV. Update of high concentration of hydrogen detected inside 1F1 PCV I introduced this issue in Earthquake (154, Sept 20-23), Earthqake (155, Sept 23-27) and Earthquake (156, Sept 27 - Oct 1). TEPCO reported surprisingly high hydrogen concentration values measured at two different locations, 61% and 63% in a pipe (a portion of the spray system pipe) to be used for cleaning the atmosphere of 1F1 containment vessel. Although the residual gas is nitrogen, TEPCO has been trying to purge the hydrogen through a temporary nitrogen purge line as illustrated in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111008_01-e.pdf Through this illustration, we can Guess that TEPCO is trying to purge only the piping system, although there is a high possibility that the total volume of the containment system can be filled with hydrogen gas. As a matter of fact the purging operation performed on October 8 resulted in gradual increase in hydrogen concentration in just two hours. TEPCO tried the nitrogen gas purge operation again on late October 9 and completed cutting the pipes at two locations as shown in the photos (http://www.tepco.co.jp/en/news/110311/index-e.html). The illustration also leads us to conclude that the filtering of the atmospheric will be performed without replacing the total volume of the gas in the containment vessel into nitrogen. However, it should be replaced with nitrogen eventually, before allowing a robot to get inside for further inspection. Perhaps TEPCO judged that releasing the filtered gas, even consisting mostly hydrogen, may not induce notable radiation exposure to the public, since the measured concentration of the atmosphere was surprisingly low. V. Long range monitoring of thyroid diagnoses started in Fukushima children Starting October 9, long term monitoring of ultrasonic thyroid diagnoses started to cover 360 thousands children (under 18 y.o. at the time of the accident) at Fukushima Medical University ( http://www.fmu.ac.jp/index-e.html ). The children will be monitored for every two years until age 18, followed with every five years for their entire life span. The first diagnoses are planned to be completed within two years, by the end of the 2013 fiscal year. In the rehearsal performed in October 8, it took only five minutes per children. If a "stiffness" was detected, the secondary medical examination will be performed, including blood chemistry tests. VI. Update of dispersion calculation (from AESJ-fall Proceedings) There were irregularities in my previous commentary by including the K45 presentation performed by scientists of Nagoya University. K45 Release Rate Estimation of Fission Products Discharged from the Fukushima Nuclear Power Plant into the Atmosphere using Environmental Monitoring Data K46 Estimation sea surface deposition of Cs-137 from Fukushima Daiichi NPP In K45, the release rates were estimated by using environmental monitoring data, measured at Tsukuba, Tokyo, Gumma and Chiba. The estimated amount of total release was 1.2E+17 Bq. A continuous release of 1 TBq/h was assumed in their calculation starting 4:00 PM on March 12 to April 1. In K46, an amount of Cs-137 deposition on the surface of ocean through atmospheric dispersion was assumed to be a fraction of 13 PBq (ref. Chino,M. et al., J. Nucl. Sci. Technol. 48[ 7], 1129–1134 (2011)), which should be compared with approximately 1 PBq release into the marine environmental through leakage of the highly contaminated underground water disclosed from TEPCO. Their estimation of the Cs-137 deposition through the atmospheric dispersion is 1.1 PB, comparable to the direct leakage of highly contaminated water. The largest fraction of marine surface deposition occurred on March 15, together with the land deposition, according to their assessment. This seems to predict that the most of the release was deposited on the ground. This conclusion should be checked by other scientists, since it is a very important conclusion. As I introduced in Earthquake (61) on May 11, I estimated a release fraction using the DOE/NNEA land contamination data ( http://energy.gov/news/10194.htm ). Zone Cs-total (Bq/m2) area (km2) Cs-134+137 V 6E+06 - 3E+07 151 4.53E+15 IV 3E+06 - 6E+06 116 7.00E+14 III 1E+06 - 3E+06 483 1.45E+15 II 6E+05 - 1E+06 379 3.80E+14 I 3E+05 - 6E+05 965 5.80E+14 ---------------------------------------------------------------------------------- Total 2094 7.64E+15 The total integrated amount of Ce-134+Cs--137 release was 7.64 PBq, and an estimated total land deposition of Cs-137 was 4.5 PBq. Although these values agree in an order of magnitude level, further justification is necessary to confirm that the major deposition should have occurred on the land instead of onto the sea. In this connection, Technology Analysis Sub-Committee of AESJ (Atomic Energy Society of Japan) released their assessment of the TEPCO's Live Camera Pictures re-posted recently in http://www.youtube.com/watch?v=y5FtdES8of0. Their assessment, which was posted on http://www.aesj.or.jp/information/fnpp201103/chousacom/gb/gbcom_fukuichikamera20111003.pdf is summarized below: March 12 15:00 Steam releases towards west are visible from the common stack for 1F1/1F2, confirming success of venting operations. March 13 10:00 Faint steam releases towards east are visible from the common stack for 1F3/1F4. This support the reported success of opening a large valves for venting form 1F3 suppression chamber vent line. No live picture was available at night. No release of steam is visible until the hydrogen explosion occurred around 11:00 of the next morning. March 15 06:00 A substantial white smoke is visible from 1F4, although the building of 1F4 is still standing. 07:00 A substantial amount of white smoke is visible, muffling the upper portion of the 1F4 building. This may indicate that the hydrogen explosion occurred between 06:00-07:00. It is puzzling not to see other ejection of smoke on March 15. The steam is coming only from 1F4.. The sub-committee also compared with RCV pressure transients, concluding that: 1F1 An decrease of the RCV is likely due to success of venting, however, the sudden pressure decrease after 15:14 of March 12, indicates a leakage from the RCV. 1F2 Although RCV pressure suddenly decreased from 750kPa at 7:30 ti 155jOa at 11;25, no corresponding steam release can be identified in the picture of the 1F1/1F2 common stuck. This may indicate a possibility of direct leakage from the RCV. 1F3 Venting seems to be successfully performed around 10:00 of March 13. However, the incomplete venting proceeded. Since no clear venting success was confirmed, the depressurization is likely due to direct leakage of the RCV. In the conclusion by AESJ, there were cases of successful venting, as well as unsuccessful venting. It i important to be able to vent when needed. V. Some of the important findings on amelioration/decontamination (from AESJ-fall Proceedings) Many research people in academia as well as research institutes engaged in urgent investigation of characterization as well as amelioration of contamination due to radioactive releases. Through reading their presentations, the following characteristics can be extracted in the environment surrounding Fukushima-Daiichi. (1) Majority of cesium in the contaminated soil is generally contained in the first few centimeters from the surface (2) The radioactive cesium is (chemically) bound in fine particles of clay in the soil, whose transfer to the plants through roots is very small. (3) In plants, most of the cesium is distributed in leaves which were grown at the time of the accident. Practically no cesium was found in newer leaves grown after the accident. Concentration of cesium in the trunk of tree is very small. The following 3 papers were reported from Kinki University group. K47 Survey of Radioactive Contaminations in cities at Fukushima-Nakadori area K48 Environmental radiation research in Kawamata-machi, Fukushima-ken (1) Outline of the survey and Radioactivity in soil K49 Environmental Radiation Research in Kawamata-machi, Fukushima Pref. (2) Reduction of Air Dose Rate by Removing Surface Soil In K47, groval variation of aerial dose rates were measured by using a GPS coupled NaI survey meter by a car. It was found that the contamination in the un-paved areas was several times larger compared with un-paved areas. The weathering of the soil samples was very small during April to June. In K48, (1) aerial dose rates by using GPS coupled NaI survey meter measurement was measured on foot, (2) soil and vegetation sampling and radiation measurement by using Ge detector and (3) confirmation of effect of removal of surface soils up to 0.5 centimeter. It is concluded that ninety percent of the cesium fallouts are distributed within the first centimeter from the surface. This result is interesting. The decontamination activities using ordinary civil engineering vehicle to remove the surface soil seldom achieve this much of decontamination by removing as deep as 5 cm of soil from the school ground. Perhaps the school grounds are usually covered with a layer of sand which does not absorb cesium. Also there should be more efficient way of removing the surface soils throughly such as done by TEPCO by developing a giant vacuum cleaner as shown in: http://www.tepco.co.jp/en/news/110311/index-e.html http://www.tepco.co.jp/en/news/110311/images/111001_12.jpg In connection with this, The Japanese Society of Turfgrass Science released their study that it is not necessary to remove the turfgrass completely for decontamination. A large scale amelioration experiment has been performed in Ouse Prke in Fukushima as shown (in Japanese) http://wwwsoc.nii.ac.jp/jsts/events/110930fukushima3.pdf They tested special machine for construction and maintenance of lawns. It appears that reduction of dose rate by an order of magnitude appears to be very difficult in practice, due to generally high environmental dose rates of the park. Well, let me stop here tonight! Genn Saji ____________________________________________________________________________________________________________________ (Previous e-mail sent at 0:15 AM on Oct 4 as Earthquake (158, Sept Oct 4-7)) Dear Colleagues: 207th - 210th day! In this update, some of the notable findings are summarized from Proceedings of the Atomic Energy Society (AESJ) fall meeting (Sept 19-22). I intend to cover the Fukushima-Daiichi related research topics in 2-3 commentaries. In this update, papers dealing with dose reconstruction and dispersion calculation issues are selected. My reviews are sketchy, since each presentation is limited to just one page. I. Update of dose limits for the public I started to introduce this subject in Earthquake (157, Sept 30-Oct 4). On the morning of October 6, the Committee of Fundamental Radiation Protection Policy, a MEXT's advisory committee established for unification of radiation protection issues, held its 41st meeting. The main agenda was in adaptation of ICRP Pub. 103, 2007 recommendations of the International Commission on Radiological Protection (ICRP). It was urgently convened in view of various dose guidelines being used by different organizations. It was further motivated since the recent wide range land contamination maps clearly indicates that it will be impossible to decontaminate all of the areas down to 1 mSv/y (0.1 microSv/h) level. It is reported that the committee agreed to introduce an intermediate/interim reference level between 1-20 mSv/y. This policy seems to be agreed upon in the context of emergency and existing exposure situations ‘for the restriction on dose or risk, above which it is judged to be inappropriate to plan to allow exposures to occur, and below which optimisation of protection should be implemented’ (ICRP Pub. 103). According to the framework of dose constraints and reference levels as shown in Table 5, which is copied from ( http://iopscience.iop.org/0952-4746/28/2/R02/pdf/0952-4746_28_2_R02.pdf ) the 1-20 mSv/y is a similar situation of the "reference level for radon in dwellings". I share the reality of inevitable difficulties of achievable level of decontamination, however, I think the committee as well as ICRP Pub. 103 is not responding to the most concerned question of Japanese mothers as to the radiation risk of children. It is not clear whether the 1-20 mSv bands of effective dose can be applied for children or not. It is because there have never been a large cohort of exposed children, large enough to be able to investigate stochastic effect of radiation, except for the children of Chernobyl although the duration of followup is limited to only 20 years. I think the committee should show their view on low level radiation exposure. In my view, the ICRP's reference level is for a hypothetical reference male and reference female, both of them are adults, I believe. If my understanding is correct, the reference radiation level for children should be lowered by a weight ratio of tissues to address age dependent effects. Or, said another way, we do not know the effect of prolonged low level radiation to children. II, Update of land contamination maps being constructed for wider areas (for each Prefecture) I introduced this issue in Earthquake (152, Sept 13-16) and Earthquake (156, Sept 27-30). The remote dosimetry by using the method provided by the US DOE/NNEA has proven very useful. In view of the valuable information obtained by this method, MEXT (Ministry of Education, Culture, Sport, Science and Technology) is currently extending this activity to cover all of the affected Prefectures. On October 6, the new data, covering TOKYO Metropolitan Districts as well as Kanagawa Prefecture were released through: http://radioactivity.mext.go.jp/ja/1910/2011/10/1910_100601.pdf Although the entire text is in Japanese, let me attach the document, since results are shown in several maps. Let me also paste one of the map, which shows aerial dose distribution map at 1 m above the ground level. It was very lucky that that these two very highly populated regions were almost free from contamination, except at the extreme E and W corners of Tokyo and some hot spots in a west portion of Kanagawa Prefecture , perhaps due to meteorological and geographical conditions. In these hot spot areas, the aerial dose rates are 0.1-0.2 microSv/h. It is necessary to decontaminate even these areas when the Government is going to keep the 1 mSv/y as the reference level. Personally, I live in Yokohama, Kanagawa Prefecture, approximately 260 km SWS of Fukushima Daiichi. It was reported recently that a rain water gutter in a nearby middle school was found contaminated with cesium deposited on fallen leaves. In the map, the corresponding hot spot is hardly visible, although it appears there exist some needle point hot spots. The parents of the school immediately clean the rain gutter and simply disposed the fallen leaves as a burnable household waste, collected by the City. III. Dose reconstruction with protective measures for the Fukushima Daiichi Nuclear Power Plant Accident (from AESJ-fall Proceedings) A series of JAEA reports were presented consisting of: K36 Averted doses by evacuation measures K37 Internal exposure in the public due to inhalation exposure K38 External exposure of the public due to deposited nuclear species K39 Public exposure due to ingestion pathways K40 Averted doses due to restriction of drinking water In paper K37, inhalation doses were estimated in consideration of re-suspention effects, by calibrating with the environmental monitoring data measured by MEXT. For re-suspention, Lasey's method was used ( K. R. Lassey (1980), “The possible importance of short-term exposure to resuspended radionuclides,” Health physics 38, p.749-761). The results indicate that the exposure through re-suspention is an order of magnitude larger for cesium, however, it is of the same order of magnitude for I-131. It is perhaps due to the short half life of I-131, I believe. However, I am not comfortable as to the "environmental monitoring data." I believe it is very difficult to distinguish the aerial doses from ground shine coming from the land-deposited source and effluents. A similar confusion occurred at the time of the Chernobyl accident, concluding that there is no correlation in the I-131/Cs-137 ratio. Only at the Tyfoon Observatory in Obninsk, the aerosol filters were replaced every day to measure both I-131 and Cs-137, showing excellent linear relationship. In the paper K38, the whole body doses were estimated from land deposition density of nuclear species at Namie-machi, 30 km from Fukushima-Daiichi. The effect of weathering was included through Gale's method (Gale et al., 1964, “Weathering of Caesium-137 in soil,” Nature, No. 4916, 257-261). The effective dose rates agreed well with the measured dose rates. The aerial dose rates will decrease to 1/3 of the first year in the third year, perhaps mainly due to decay of short half-life species. In paper K39, averted effective thyroid doses were estimated for effect ob restriction of marketing spinach in Fukushima. The results are as large as 0.84 mSv for adults and 1.9 for infants. In paper K40, averted effective thyroid doses of drinking water were computed. At Iidate-mura, 1.7 mSv was averted, and 8 mSv for infants. IV. Followup dispersion calculation by JAEA (from AESJ-fall Proceedings) Due to the station blackout, the emergency environmental monitoring data around Fukushima-Daiichi were not available for dose information, which was planned to be supplied by SPEEDI. JAEA's team is currently trying to reconstruct dispersion of radioactive species by using WSPEEDI, which is being developed to predict the radiological impact of nuclear accident abroad on Japan by quick calculations of air concentration, surface deposition, and radiological doses. Technical explanation of WSPEEDI has been presented (in Japanese) in http://www.aesj.or.jp/publication/TAESJ2008/No.3/7_3_257-267.pdf The code system is formulated to use global meteorological forecast data (GPV) released 4 times a day from Japan Meteorological Agency. Their current horizontal mesh near the ground level is 20 km x 20 km, since it is for global weather forecast. To interpolated finer space information, a nesting technology was adapted from MM5; ( Ref. G. A. Grell, J. Dudhia, D. R. StauŠer, A Description of the Fifth-generation Penn State/NCAR Mesoscale Model (MM5), NCAR Tech. Note, NCAR/TN398+STR, National Center for Atmospheric Research (1994) in its meteorological prediction package. The dispersion calculation is performed with GEARN, which is a Lagrange model package, also integrated with the nesting technology. Using the WSPEEDI-II, the following 4 presentations were given. K41 Overview of dispersion analysis by JAEA for radionuclides discharged from the Fukushima Daiichi Nuclear Power Plant into the environment K42 Local-scale atmospheric dispersion simulation of radionuclides discharged from Fukushima Daiichi nuclear power plant by WSPEEDI-II K43 Atmospheric Dispersion Simulation of Radionuclides in the Eastern Japan Region K44 Radionuclides migration forecast in the off Fukushima region General approaches are introduced in K41. In the dispersion calculation, it is indispensable to have reliable release data at the discharge point, however, this critical data was not available at Fukushima-Daiichi. The source data was estimated from a temporary environmental monitoring station combined with the dispersion calculation by SPEEDI, by assuming 1 Bq/h. (I am not comfortable in this method, since the radiation monitoring data measured by monitoring cars are all showing sharp peaks of dose increase (such as in the case of the "puff release" or "mushroom cloud release." The releases were not prolong leakage type that can be expressed in Bq/h. This may have resulted in an overestimation of release fraction.) In K42, it is explained that an amount of the giant release occurred on March 15 was estimated with WSPEEDI and was able to reproduce the highly contaminated corridor stretching NW direction of Fukushima Daiichi, especially in the afternoon when there was a rainfall. As to the input data of the release rate, a temporary assessment by Chino was used. ( M. Chino et al., J. Nucl. Sci. Technol. 48, 1129-1134 (2011). In K43, adequacy of the WSPEEDI-II was investigated by comparison of the wider environmental monitoring data throughout Japan, using the release data by Chino et al. In K44, marine dispersion calculations, by using SEA-GELAN, were combined with the atmospheric dispersion to account for deposition of radioactive species directly onto the surface of the ocean. The results reproduces the concentration of radioactivities in sea water samples. The early ocean contamination is through atmospheric dispersion/deposition, followed with a later discharge of the highly contaminated water directly into the sea. In K45, the release rates were estimated by using environmental monitoring data, measured at Tsukuba, Tokyo, Gumma and Chiba. The estimated amount of total release was 1.2E+17 Bq. Well, let me stop here tonight! Genn Saji ____________________________________________________________________________________________________________________ (Previous e-mail sent at 0:15 AM on Oct 4 as Earthquake (157, Sept 30-Oct 4)) Dear Colleagues: 203rd - 207th day! I. TEPCO's internal committee for investigation of nuclear disaster - No hydrogen explosion in 1F2? TEPCO has organized an internal committee for investigation of nuclear disaster in June. An interim report of the committee was recently drafted for review by external specialists. The draft seems to have sent out informally to news media, although it has not been posted in their web site. According to the news reports, the explosion in 1F2 was concluded not due to hydrogen explosion. This conclusion is based on an indication of an temporally installed solar power-driven seismograph, which recorded a small ground motion likely induced from the hydrogen explosion in 1F4 but no corresponding ground oscillation was record for another hydrogen explosion in 1F2. Although no technical details of this news is available for me, this finding is interesting. Please recall the robot Qunce video which is showing there is no remarkable debris inside of the 1F2 Reactor Building. The video was distributed by TEPCO on July 17: http://www.tepco.co.jp/en/news/110311/indexold-e.html Download • Investigation of the status in the Reactor Building, Unit 2, Fukushima Daiichi Nuclear Power Station by Quince(ZIP 18.1MB) (videoed on July 8, 2011) Also, more recent photo is available in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110924_01-e.pdf In contrast to 1F2 the corresponding videos of 1F3 are showing wealth of evidences of explosion with scattered debris, shuttered ducts, blown away structures, panels, etc. The 1F3 videos were released on July 28: Download • Video by Quince Robot within Fukushima Daiichi Nuclear Power Station Unit 3 reactor building(ZIP 12.6MB) (video on July 26, 2011) Another videos are also released on July 27: Download Fukushima Daiichi Nuclear Power Station Reactor Building of Unit3 Site Investigation by Quince • Staircase from 2nd floor to 3rd floor (pictured on July 26, 2011) • Grating at the valve of Core Spray System (pictured on July 26, 2011) • Valve of Water Supplement (pictured on July 26, 2011) • [Reference] Fukushima Daiichi Nuclear Power Station Reactor Building of Unit3 Site Investigation by Quince (PDF 95.4KB) More recent video was released on September 29 through: http://www.tepco.co.jp/en/news/110311/images/110928_02.wmv Download • JAEA-3, inside of Reactor Building of Unit 2, Fukushima Daiichi Nuclear Power Station (11.2 MB) (video on September 23, 2011) (I noticed something is wrong with this video.) • Inside of Reactor Building of Unit 3, Fukushima Daiichi Nuclaer Power Station (47.4 MB) (video on September 24, 2011) http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110924_02-e.pdf Comparing these videos, it indicates the following: (1) The 1F2 event is different from the 1F3, which are shown with ample evidence of explosion, likely due to hydrogen detonation. (2) There must have been an over-ressure event in the 1F2 Reactor Building, since a part of the building was damaged and operators heard some dull thumping noise around the pressure suppression room area. An increase in dose rate was observed, resulting in TEPCO to allow evacuation of some of the staffs to Fukushima Daiini. (3) Severe contamination was recently measured as reported in: http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110927_02-e.pdf I renewed my suspicion that the "internal hydrogen explosion" as occurred in Hamaoka Unit can be also a possibility as reported in the following reference. (1) M. Naito et al., Analysis on Pipe Rupture of Steam Condensation Line at Hamaoka-1, (I) Accumulation of Non-condensable Gas in a Pipe, Journal of NUCLEAR SCIENCE and TECHNOLOGY, Vol. 40, No. 12, p. 1041–1051 (December 2003). (2) M. Naito et al., Analysis on Pipe Rupture of Steam Condensation Line at Hamaoka-1, (II) Hydrogen Combustion and Pipe Deformation, Journal of NUCLEAR SCIENCE and TECHNOLOGY, Vol. 40, No. 12, p. 1041–1051 (December 2003). II. Giant vacuum cleaner for contaminated dust removal TEPCO introduced a set of photos of a giant vacuum cleaner system recently completed: http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111001_02-e.pdf. An achievable DF values are also in the handout. It is going to be used for cleaning up the roads and lots inside of the Fukushima-Daiichi site. III. Effects of low doses between 1-5 mSv/y. Although no official announcement has been made yet, the Government was using 5 mSv/y for the lowest level of intervention by the Government, such as for decontamination. This values has appeared in several reports in committee meetings. However, local governments are all unhappy about this, by interpreting that the national government will not financially support decontamination activities being performed by the municipal governments to reduce the dose rate to less than 5 mSv/y, even lower than 1 mSv/y. Mr. Hosono, Minister in charge of nuclear disasters recently assured that the Government will support the decontamination activities for those areas between 1 - 5 mS/y. The confusion seems to also came from a cutoff dose limit for children. The 5 mSv/y guideline, which is intrinsically specified by the government, seems to come from political decisions made not to deny cause and effect of cancers among radiation workers who received accumulated doses as low as 20 mSv in four years in certain cases. Also, in other countries, much attention has been given to studies of large numbers of radiation workers who were chronically exposed to low radiation doses. ( Cardis E, Vrijheid M. Blettner M., et al. "Risk of cancer after low doses of ionising radiation: retrospective cohort study in 15 countries." BMJ (2005) 9;331(7508): 77【PubMed】) Through this study, involving 407 391 workers individually monitored for external radiation with a total follow-up of 5.2 million person years, it was concluded that 1-2% of deaths from cancer among workers in this cohort ( the average individual cumulative dose was 19.4 mSv) may be attributable to radiation. However, this conclusion should be also qualified, since majority of radiation workers received less than 10 mSv, bringing the average accumulated dose significantly lower. The workers received high doses may be contributing to the cancer cases. In my understanding the current public dose limit of 1 mSv/y was specified by the ICRP to supplement their dose constraint system which is to limit exposures from well identified individual radiation sources. The public dose limit is to be prepared for unidentified radiation exposures. From this point of view, the radiation exposure through the Fukushima-Daiichi disaster should be included as a dose constraint system and the proposed Food Safety Commission's 100 mSv limit for a life-spen exposure is consistent with the ICRP's a life-span exposure limit of 1 Sv, if it is limited to the exposures through the Fukushima-Daiichi disaster. Here, it is a common practice to perform radiological assessment for the most exposed individuals among the public. There can be some children who are born in Fukushima, raised there and continued to live in Fukushima. For safety of those children, it is logical to ask for decontamination of public facilities, such as schools, day nurseries, parks and their homes as low as reasonably achievable, aiming 1 mSv/y. Since this target is not easy to achieve throughout Japan, perhaps a logical approach is to keep the 1 mSv/y for additional doses anticipated to be received after re-settlement, but the accumulated doses received before evacuation should be included among the 100 mSv life-span dose constraint system. Further discussion from a point of view of constrained optimization is indispensable. IV. Update of an official estimation of the total amount of damages induced by the Fukushima-Daiichi disaster The Government has installed the Investigation Committee on Management and Finance Affairs to support TEPCO for compensating the induced damages caused by the Fukushima-Daiichi disaster. The committee has been investigating TEPCO's financial situation as well as the amount of damages induced by the disaster. Their report was released on October 3. The committee estimated the following amount of damages; Tentative (for the first year + years after) compensation necessary for Fukushima-Daiichi accident Damages due to evacuation ordered by the Government 1.9245 trillion yen Damages caused by rumors 1.3039 trillion yen Indirect damage through business connections 1.3118 trillion yen ------------------------------------------------------------------------------------------------------------ Subtotal 4.5402 trillion yen Tentative cost for de-commissionig (referring to the TMI accident case) Cost of normal decommissioning 1867 billion yen Additional cost due to accident 8950 billion yen Up to "cold shut down" (2650) Up to mid to long term cost (6300) Miscellaneous 693 ----------------------------------------------------------------------------------------------------------- Subtotal 1.1510 trillion yen Since the characteristics of damages are much different from TMI, the final cost can be greatly different. It should depend on extent of melting of the core debris. The committee has also performed simulation studies, for the cases: (1) The un-affected NPPs should return back to the grid in: (i) Starting next fiscal year (ii) One year after (iii) No NPP option (3) Increase in sales price of electric power to cover an increase in costs of fossil fuels (a) non (b) 5% (c) 10% In an worst case with (1)-(iii) + (2)-(a), TEPCO may face with a deficit of 8.6427 trillion yen (approx. 110 billion USD). As you can see, the current Government policy is not let TEPCO go into a bankrupt, considering its social responsibility as an electric power supplier. The Government is trying to achieve this through "Corporation in support of Compensation for Nuclear Damage," for which the government may supply financing to TEPCO as needed. Well, let me stop here tonight! Genn Saji