Fwd: Saji's Fukushima Update (169, Dec 9-16)

[Pieter Franken]

FYI.

Interesting personal comments on the sorry state of openness around the disaster.

Pieter

Begin forwarded message:

From: Ko-ichi Nakamura <koichi....@aist.go.jp>

Subject: FW: Saji's Fukushima Update (169, Dec 9-16)

Date: December 18, 2011 5:19:44 PM GMT+09:00

To: Ko-ichi Nakamura <koichi....@aist.go.jp>

Greetings, I am forwarding Dr. Saji's latest daily update (Dr. Saji is Ex-Secretariat of Nuclear Safety Commission, Japan). He is now retired, independent from any government or industry group.

   I put all of your e-mail addresses in BCC. If you would not like to receive this e-mail further, please let me know. Otherwise, I am forwarding this e-mail to you. Also, if you wish me to add someone in the addressee of this e-mail, do not hesitate to let me know.

   I put only one latest updates in this e-mail, because the reports became bigger than before.  If anyone needs reports before #168, please let me know. You could also request me the past updates by numbers or by approximate date.

Best regards,
Ko-ichi Nakamura

-------------------------------------

From: Genn Saji

Subject: Earthquake (169, Dec 9-16)

Date: Sun, 18 Dec 2011 15:32:44 +0900

   I am thinking of reducing this series of periodical update, making it nonscheduled, perhaps starting early next year. A frequency of interesting news releases, scientifically and technically important, have decreased much in these days. It indicates that the disaster is now going into a new phase calling for deeper scientific research investigations. That will take tens of years of time, calling for devotion of thousands of motivated scientists and engineers. Although there are many new research topics I am interested to investigate in the future, obviously I cannot do all of them in my life and have to entrust them to the future generation people. In addition, most of the the reports released recently became too bulky for me to review timely for the periodical updates. I intend to change to be "event-driven", by introducing major findings or important releases, whenever I found interesting. A new corner stone is in sight for me, to reconsider how to continue the update beyond this year. I am also thinking of returning back to my previous research fields, hopefully sometimes next year.

   Sometimes I feel it was almost a miracle that I could continue my independent activity for nine months until now. Although I have not decided what I should be doing next year, I intend to continue this series non-periodically best I can, until around the time of reviewing the projected release of final reports of several organizations, including Investigation Committee on the Accident at the Fukushima Nuclear Power Stations established by the Government, as well as a similar committee inaugurated by the Diet, although both of them are intentionally excluding Japanese nuclear safety specialists, who are considered responsible for failing to prevent the Fukushima disaster, responsible for inducing a great confusion soon after the accident.

   I am well aware that the updates were not deep enough for scientific publication, but too much specialized for general scientific readers. They contain too much of information, without focusing on some specific topics, written periodically with time constraints without being able to go through technical editing for improvement in English. For me, being able to continue my series of Earthquake updates, without disturbances, has been my first priority. Also, please understand that sending my e-mail updates was possible, only because it was written in English. As long as in English, most of the Japanese people do not pay much attention. The freedom of information as well as human right is not necessarily respected in the real society in Japan, through demanding a subtle and unwritten social consensus. As a matter of fact, I am suffering from a discrimination of a branch of Atomic Energy Society of Japan, who distributed libel bashings through internet, since I refused to participate in a closed group (Team "F" of Senior Network) for exchange of scientific information pertaining to the disaster.  (Ko-ichi's comment: precise expression of "through internet" should be "by e-mails in the mailing list of Senior Network of AESJ". Dr. Saji was suddenly excluded from the mailing list in April.) Currently in Japan, politicians of the ruling DPJ (Democratic Party of Japan) are trying to control the Fukushima disaster politically, even trying to control scientific assessments and discussions in a loathsome way. For example, they are insisting that the news released from NISA should first be informed to the politicians before press interviews. This, in effect, resulted in censoring the press releases, although the Government does not realize what they are doing.  This is intimidating "salaried" scientists in addressing their real opinions. In other words, no other Japanese could have sent the daily update type reports written from a pure scientific point of view, without getting an internal consensus during which removal of all of the pointed arguments tend to occur. Such a negative effect was clearly visible in the recent TEPCO's report of internal investigation committee as introduced in Earthquake (168, Dec 2-9), where many of the TEPCO's engineers appear to have changed their views on the 1F1 core status in order to support their MAAP results.

Dear Colleagues:

273rd - 280the day!

I. Prime Minister's declaration of completion of Step 2 of Roadmap to Recovery

   On December 16, Mr. Noda, the Prime Minister, declared completion of Step 2 of the road map.  In addition to a press interview held in the evening, the Organization of Nuclear Emergency Response Headquarters released a set of technical reports which technically support the prime minister's declaration in Japanese. The main text of 60 pages is appended with six appendices of 115 pages total. This report is written in the framework of Roadmap to Recovery, which was first issued on April 17. At that time, the Roadmap was divided into two steps, the first step covered the planning for approximately 3 months to achieve the effluent releases in a declining trend, followed with the second step for approximately six to nine months to place the effluent releases under control at a substantially reduced level. The Step 1 was completed on July 17 and now the Step 2 is declared completed. Many important agenda were introduced for the next step which will cover Intermediate Step lasting for approximately 3 years.     It is reported as long as 40 years will be necessary for final decommissioning.

   As can be seen, the Roadmap was developed as a kind of project management tool integrated with a kind of "work breakdown structure" and does not represent a scientific "acceptance criteria" of the TEPCO's achievement of safety, nor it is a check sheet for performance of the Government. Therefore, I think it is not appropriate to discuss TEPCO's achievement from a political point of view. Although TEPCO identified the following ten issues at the end of Step I, some of them have not been achieved or approaches were modified.

(1) Damaged core cooling

   TEPCO was initially trying to achieve the "cold shutdown" by bringing the plants into a "water sarcophagas" status and installing closed cooling lines with air coolers for RPVs. However, the reactor cooling still depends on the temporary water treatment system by employing a total of about four kilometers of vulnerable "plastic horses." TEPCO appears to have given up the closed cooling option. This continues to increase generation of the highly contaminated water accumulated in the building. Nevertheless, by bringing its temperature below the boiling point, the current cold state substantially helped in reducing radioactive effluent releases. Now the estimated dose rate is around 0.1 mSv/y at the site boundary, 0.0002 to 0.002 mSv/y at 20 km.

(2) SFP cooling

   The closed-circuit and air-cooled loops have been successfully installed in all SFPs, 1F1 through 1F4. The removal of debris from the 1F3 and 1F4 SFP areas are now being performed by employing remote-operaion civil engineering vehicles.

(3) Reduction of the volume of highly contaminated water

   At one time, TEPCO was hoping to drain all of the highly contaminated water from the basements of both reactor buildings as well as from the turbine halls by the end of this year. Although the water levels have been kept under control, further reduction is not in sight, perhaps due to an in-flow of underground water. As of December 16, the total volume of the processed water reached 190.000 m3, however, the water level does not go lower than around OP+3m, likely due to the underground water seepage.

   Although not mentioned in the report, there is a growing concern in the capacity of temporary storage tanks, which might be filled up by the next March. Although TEPCO sounded a possibility of releasing the very low level processed water as well as the contaminated accumulated water (likely due to the underground water) from 1F5 and 6, the local union of fishing industries violently opposed the TEPCO's plan of discharge into the ocean. However, TEPCO will have to establish a viable solution for disposal of very low level water within a few months.

   In the TEPCO's water treatment facility, removal of cesium and iodine (in early phase) was their primary objectives by selecting zeolite type sobers. These sobers are designed for selectively remove cesium and iodine, by optimizing the molecular sieve size of zeolite. It appears to have low sorption capability for other species, including strontium among all. The strontium can be removed by the reverse osmosis (RO) process or evaporation process, however, tritium will not. As a matter of fact, a significant concentration of these beta emitters are detected at the outlet of the RO process as well as of evaporators.

   In general, disposal of wastes into the ocean, including radioactive wastes, is prohibited by Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972, usually dubbed as London Convention. In case of radioactive wastes, only those below the clearance level specified by the IAEA is allowed. Since the clearance level is specified in concentration, the liquid waste is usually diluted with a large volume of sea water, following the "drinking water criteria" at the discharge point, for example. However, such a volume of sea water may not be available for disposal of treated water. Therefore, a feasibility of releasing the treated water should all depend on whether the tritium concentration is below the IAEA's clearance level or not. I do not know whether such clearance level has been specified by IAEA for liquid wastes or not, although for solid waste, IAEA-TECDOC-8S5, Clearance levels for radionuclides in solid materials is well known. In this document, TABLE I. DERIVED UNCONDITIONAL CLEARANCE LEVELS specifies 1000 to 10,000 Bq/g for tritium, which is now specified as IAEA recommendations (IAEA, 2004) for the clearance limits (Bq/g) of 100 Bq/g for tritium. However, the clearance levels depend on exposure scenario and cannot be directly extended to liquid wastes, I believe. Perhaps, it is necessary to follow the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (the BSS), which are based on information on the detrimental effects attributed to radiation exposure provided by the United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR (United Nations, 2000), as well as on the recommendations of the International Commission on Radiological Protection, ICRP (ICRP, 1991). In addition, liquid waste disposal in an event of accident, has not been studied until this time.

   From this point of view, the most recent sampling analysis by TEPCO is showing 5.5E+03 Bq/cm3 for H3 at the outlet of the Evaporation Water Treatment Facility, according tohttp://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111212_01-e.pdf. Other nuclear species are not detectable, except for total beta showing 0.22 Bq/cm3. This indicates that approximately two orders of magnitude dilution is going to be necessary for discharge even for the final evaporation-purified water. The total beta concentration is in a borderline level. Perhaps the only way for disposal is atmospheric/steam discharge by evaporating the purified water once more, although it is more like a desperate resort.  I think the dilution and ocean discharge should induce less radiological effects, as being done in practically all nuclear power plants. A violent public reaction is anticipated in either of these two methods.

(4) Prevention of leakage of the highly contaminated water through the subsurface routes.

   Although TEPCO close-off seawater intake and discharge area, it is still not clear whether this is sufficient. At least, it is not effective in prevention of the ground water flowing into the basement areas. I believe construction of a pipe line is more practical to directly discharge the fresh underground water flowing along the ancient buried and hidden valley leading from the Abkuma Highland into the site.

(5) Reduction of re-suspension of radioactive dust

   Prevention of increase of dose rates off-site, by preventing re-suspension of radioactive dust from the site. It is now being demonstrated that the effluent release from the damaged plant is substantially decreased. This should result in reduction of doses around the site. However, in reality, it is now confirmed that the dose rates increases when the wind direction is coming from the Fukushima Daiichi, when monitored　as far as a few hundred kilometers from the site. This seems to be due to a combination of ground shine of already deposited radioactivities, as well as re-suspension of dust from off-site areas around the site, such as within 20 km zone. It is becoming important to identify where the high dose contribution are coming from, not just limited to on-site, but also the heavily contaminated areas surrounding Fukushima Daiichi.

(6) Radiation monitoring and decontamination
   Obviously, one of the largest tasks is amelioration and decontamination, which are obviously almost an endless task from now on.

(7) Prevention of further damages due to another natural disaster
   TEPCO seems to have made ready for a potential large after shock-induced tsunami by constructing a temporary a tide embarkment along the coast line, as well as finished fortification of damaged load bearing wall of 1F4.

(8) Health care of recovery workers

(9) Training of health physics personnel

   The last two issues have been improved reasonably well.

II. "Facility operational plan" for mid-term safety assurance of 1F1 to 1F4

   TEPCO's "facility operational plan for mid-term safety assurance of 1F1 to 1F4" was recently approved by the regulatory authority and is now ready to be applied for amelioration activities necessary after achieving "cold-shutdown status." This is equivalent to SAR (Safety Analysis Report) submitted to regulatory bodies for obtaining an construction and operational license of new plants. Since Fukushima Daiichi is damaged substantially, a new regal framework became necessary for amelioration of the damaged plants and integration of new safety provisions. The FAC (facility operational plan) consists of the following chapters:

(1) Reactor containment vessel (RCV)
(2) Disposal of contaminated solid debris
(3) Removal of spent fuels from the Spent Fuel Pools (SFP)

(4) Restoration  of existing Common Spent Fuel Storage Pool

(5) Temporary dry cask storage of spent fuels

(6) Monitoring and control room

   As can be seen from the table of contents, this phase of FAC addresses up to firstly recovery of the secondary containment boundary (cover) for 1F3 and 1F4, secondary, disposal and storage of contaminated debris in site, and thirdly, planning of removal of spent fuels from the damaged SFPs. The current version of FAC covers a time span of several months to at most a year or so, for those amelioration activities that are in sight by knowing details of dose rates, for example. Re-entry into the RCVs nor removal of reactor top covers is still not in sight.

(1) Reactor containment vessel (RCV)

   TEPCO's radiation safety assurance of RCV depend heavily on the "Gas Management System", which is a de-hymidified/filtered venting system with various sampling and monitoring system. It has a capacity to cope with the nitrogen gas charging system to keep the RCV pressure closed to the atmospheric pressure. Such an unit has already been installed and in operation in 1F2 since October 28 as introduced in Earthquake (162, Oct 21-28). Currently a similar system is being constructed in 1F1but no schedule has been released for 1F3. Removal of radioactivity will be performed by HEPA filters (with 99% particulate removal efficiency) and charcoal filters.

(2)Disposal of contaminated solid debris

   The debris so far collected from ground with a contact dose rate higher than 100 microSv/h, being classified as "low level wastes", will be stored inside of temporary buildings, however, those with lower dose rate will be piled up outdoor with restricted access. The debris to be removed from the damaged reactor buildings are generally much higher in dose rate and will be further classified with respect to the contact dose rate and characteristics of debris (e.g., metallic, concrete, etc.) . For classification, a benchmark of 1 Sv/h, 10 mSv/h and 100 microSv/h will be applied. The ultimate disposal of the solid debris is yet undecided.

(3) Removal of spent fuels from the Spent Fuel Pools (SFP)

   Currently, removal of contaminated debris from the upper portion of damaged reactors, in particular 1F3 and 1F4, are in progress. After that, it is necessary to restore fuel handling cranes for transfer spent fuels from the SFP into a cask, which is going to be transported to the Common Spent Fuel Storage Pool. The fuel handing operation will be performed by constructing a temporary cover (secondary confinement system) on top of the reactor building.  No schedule has been released at this time. For 1F1 and 1F2, detailed planning is in progress but not ready. For 1F3 and 1F4, the planning has not been even started, since it is necessary to have the dose rate information after removal of the debris.

(4) Restoration of existing Common Spent Fuel Storage Pool

   This facility also suffered from the "station blackout" combined with "loss of ultimate heat sink". At one time, the pool water temperature was as high as 73 deg C, however, by installing a temporary power source, as well as repairing a part of water purification and supply system, the pool temperature has been brought down to 25 deg C. This facility will play a pivotal role for removal of spent fuels after the Step II operation.

(5) Temporary dry cask storage of spent fuels

   Due to the tsunami damage, the existing building for the dry cask storage cannot be used. Because of this, a new temporary building will be constructed.

(6) Monitoring and control room

   One of the controversial issue is monitoring of re-criticality. It has been a recent interest by detection of short half-life rare gases in 1F2 PCV as introduced in Earthquake (163, Oct 28-Nov 4) as to whether there can be a re-criticality threat or not. As I introduced in Earthquake (162, Oct 21-28), on October 27, TEPCO announced that a filtered venting system has been installed and tested as shown in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111027_01-e.pdf. The system is incorporated with a "gas sampling system dust radiation monitor" and now it became possible to detect radioactive species contained inside of the PCV (Primary Containment Vessel) with a high sensitivity. Although the initial data taken on October 28 did not detected neither Kr nor Xe species, however, on November 1, a small amount of Kr-85 (T1/2=10.4y), Xe-131m (T1/2=12d), Xe-133 (T1/2=5.27d) and Xe-135 (T1/2=9.13h) was detected as reported in:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111102_04-e.pdf

The detection of Kr-85 is not surprising, since it is likely a residual radioactive rare gas escaped from the breached fuel rods, considering its long half life. However, sudden detection of the radioactive Xe isotopes of the short half-life puzzled TEPCO. To prevent a possible re-criticallity TEPCO injected boron into the PCV on November 2. TEPCO as well as NISA soon concluded that the phenomenon is due to spontaneous fission of Cm-242. 244. I do not understand why they have to go so far to curium, since the discharge uranium fuels contains many spontaneous fission Pu isotopes, including Pu-236 Pu-239, Pu-240 and Pu-242.

   However, the re-criticality issue also renewed my interest, in the light of the studies made in the late 1980th at Oak Ridge National Laboratory, lead by Dr. Stephen A. Hodge and L. J. Ott, in

"Boiling Water Reactor Severe Accident Technology (BWRSAT) Program." I made a quick web search and came across with the following papers:

http://www.osti.gov/bridge/servlets/purl/6343189-Nf9EJg/6343189.pdf
http://www.osti.gov/bridge/servlets/purl/6124656-R8y05j/6124656.pdf

http://www.ornl.gov/info/reports/1989/3445606042920.pdf

   They pointed out the following assessment. "The presence of B4C powder within the core region has two important ramifications with respect to the BWR response under severe accident conditions. First, the stainless steel sheath and absorber rod walls have a lower melting temperature than the Zircaloy of the channel box walls and fuel cladding. Thus, severe accident calculations predict control blade structural failure and relocation while the fuel assemblies remain standing in the uncovered region of the core [3]. This early relocation of the control blade was also observed in the DF-4 experiment in the ACRR at Sandia National Laboratories and clearly raises the question of recriticality should reactor vessel water injection capability be restored after partial core degradation has occurred. The effect is aggravated by the tendency of the B4C powder to form a lower-melting-temperature mixture with the surrounding stainless steel, causing an even earlier blade relocation than that which is predicted by consideration of the melting temperature of stainless steel : (1672 K)."

   Their argument further continues, "As the relocated core material accumulates in the BWR reactor vessel bottom head, it is expected that the composition of the quenched debris bed would vary with height. Lowermost in the bed would be the mostly metallic debris (control blades, canisters, candled clad and dissolved fuel) that had either accumulated on the core plate before local core plate failure or had subsequently relocated downward above the core plate failure locations before fuel pellet stack collapse. Higher, within the middle region of the bed, would be the collapsed fuel and Zr02 from the central region of the core. The initial local core plate structural failures would cause temporary bursts of steaming as the relocated metallic debris was quenched; however, with the collapse of the central core fuel pellet stacks, a constant heat source (the decay heat associated with the pellets) would be introduced to the lower plenum reservoir, initiating a rapid continuous boiloff of the lower plenum water."

   Their vision of the core debris formation, where the first to melt should be the metallic components, including B4C containing stainless steel control blades, has occurred at the Chernobyl accident. As introduced in Earthquake (107) on June 27, Professor Burakov and his colleagues of Radium Institute. ( B.E. BURAKOV et al. , 1996. The Behavior of Nuclear Fuel in First Days of the Chernobyl Accident, MRS 1996 Fall Meeting, Boston, MA, USA. Symposium II, December 2, 1996, Scientific Basis for Nuclear Waste Management XX", Mat. Res. Soc. Symp. Proc. Vol. 465 (1997), pp. 1297-1308). They studied various types of Chernobyl fuel containing masses named black "lava", brown "lava", porous "ceramic" and "hot" particles that formed during first days of the accident at the Chernobyl NPP 4th Unit by methods of optical and electron microscopy, microprobe and X-ray diffraction.  One of the most important lessons learned was that the meltdown sequence follows the melting points of the structural materials involved in forming the corium.

   If I apply their findings to the Fukushima Daiichi, the following sequence can be predicted during the meltdown, although I believe this kind of sequence occurs when the water inside of the reactor vessel is completely dried out.

(1) The first structural material started to melt must have been the stainless steel components in core, including control rods and poison

curtain with the melting temperature of 1371-1400 deg C for SUS 316 (Ko-ichi's note, "SUS" is the Japanese abbreviation of stainless steel). In the Chernobyl reactor, the spacer grids were made from the stainless steel,

therefore, among the initially released hot particles by the steam explosion, some of them were found entrapped in the Fe-Cr-Ni melts.

(2) When the temperature reached as high as 1900 deg C, zirconium started to melt with its melting temperature of 1852 deg C. This should be the initial source of corium together with the molten stainless steel. Into the mass of molten metals, some fraction of fuel particles should have been included. By melting the fuel cladding, the fuel assembly loses the self-standing configuration, and piled up on the core support plate by forming a non-uniform mixture of "cold" structural and "hot" fuel materials with the melt in the zone of direct contact, as in the Chernobyl accident.

(3) Since the melting point of UO2 is around 2800 deg C, the melting of fuel matrix is less likely just by the decay heat. It was confirmed with the Chernobyl lava that the temperature of the silicate melt in the Chernobyl lava" center did not exceed 1660-1700 deg C the limit of zircon's thermal stability.

   Even if the re-criticality has occurred during the active phase of 10 days in Fukushima, it was definitely not a nuclear explosion, since the RPV as well as PCV are found degraded but not shattered. Even if I were to concede as much as possible, a close to re-criticality may be a possibility in 1F3, where the hydrogen explosion was the most severe one. Losing the shutdown margin through the control blades melting and increase in subcritical multiplication may have substantially increase the radiation decomposition of water, releasing a large amount of hydrogen gas.

Well, let me stop here today!

Genn Saji

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