August 7, 2014

Aug 7, 2014 | Fukushima Accident Updates

  • Tepco revised their unit #3 estimates of equipment failure and core damage. The equipment failure topic focuses on Reactor Core Isolation Cooling (RCIC) system. Although only designed for four hours of operation, it lasted for some 20 hours before stopping. RCIC uses steam from the reactor to spin a turbine connected to a pump that injects water into the reactor pressure vessel (RPV) during an emergency condition. The system will run as long as there is sufficient steam pressure and an adequate supply of water to be injected. There was more than enough water in the condensate storage supply tank when unit #3 RCIC automatically shut down. Thus it was assumed some sort of system failure had occurred. However, it now seems that RCIC automatically ceased because of high turbine exhaust pressure. Why this happened with unit #3 RCIC, and not with unit #2 RCIC remains to be understood. With respect to core damage, Tepco’s newest computer simulation suggests that the meltdown began as early as 5:30am on March 13th. This is about 5 hours earlier than prior estimates. Because of the earlier assumed onset of meltdown, Tepco now believes that most of the molten core ate its way through the bottom of the RPV and fell to the steel-reinforced concrete floor beneath. Some of the melted fuel is believed to still be inside of the RPV, however. The escaped molten mass would have been 0.85 meters thick and penetrated the base-mat up to a depth of 0.68 meters. Nearly a meter of concrete would have remained before the mass could have burned through and fell to the outer steel shell of the containment. Government researchers directing the Tepco engineering team said the reason for the higher core damage estimates is the improper shutdown of the High Pressure Coolant Injection system. http://www.tepco.co.jp/en/press/corp-com/release/2014/1240141_5892.html — http://www.tepco.co.jp/en/press/corp-com/release/betu14_e/images/140806e0101.pdf  For a representative news media report, see… NHK World; Meltdown at Fukushima reactor 3 worse than thought; 8/6/14
  • Tepco wants decontaminated groundwater releases locally approved. The company wishes to pump water out of 27 existing sub-drains that surround the basements of units 1 through 4, plus 15 more which are in the planning stage. Tepco feels they might reduce groundwater in-seepage to the contaminated basements by as much as 200 tons per day. Before discharge to the sea, the waters would be passed through the advanced isotopic purification system (ALPS) and have only small amounts of Tritium remaining. The existing ALPS system, which has been fully operational for several weeks, will be upgraded with additional processing streams by this fall. Tepco also says their shoreline barricades have reduced the estimated groundwater seepage to the sea by about 50%, and is now believed to be 200 tons per day. Another iron barrier is being installed to provide further out-flow protection, also on-schedule for a fall completion. NHK World; TEPCO plans to release treated water to ocean; 8/7/14 — http://jen.jiji.com/jc/eng?g=eco
  • Yomiuri Shimbun says using actual dosimeter exposures for repopulation is realistic. Japan’s largest newspaper believes that “setting realistic targets to lower radiation exposure doses is essential” for expediting decontamination work needed for Fukushima exclusion zone repopulation. The prior use of airborne monitoring to assume approximate exposures is subject to variances and over-estimation. Personal dosimeter measurements have shown that airborne monitoring estimates can be as much as double the actual amounts. Thus dosimeter-based exposure levels is the viable option for setting decontamination criteria. In addition, the Yomiuri argues that using dosimeter-based values is not enough. The 1 millisievert per year “goal” is often interpreted as a “threshold of safety and danger”, but this is neither true nor practical. The 1 mSv/year goal has made many who have been allowed to return home, reject the opportunity because radiation doses are believed to be too high to be safe. Thus, “The 1-millisievert benchmark, set by the former Democratic Party of Japan-led government to meet requests of local residents that decontamination work be carried out thoroughly, still hampers reconstruction of the affected areas.” The Yomiuri believes that the IAEA guideline of 20 mSv/year is “tolerable” and should be used as the criterion for repopulation. http://the-japan-news.com/news/article/0001475240
  • Miyagi Prefecture will allow a radioactive waste disposal siting study. Miyagi Gov. Yoshihiro Murai will notify Environment Minister Nobuteru Ishihara of the decision. Tokyo has announced three candidate sites in Miyagi, but needed prefectural permission to proceed. The local officials of the three sites had voiced opposition, but it seems two have reconsidered. On July 25th, Ishihara asked Gov. Murai asked the mayors of 35 municipalities to cooperate with the ministry for a site-selection survey for a final disposal facility for “specially designated” waste, as defined by the Ministry. The Mayors could not reach a consensus, so the governor was left with making the decision unilaterally, which he was reluctant to do. On August 4th, Murai emphasized the need for a positive decision, saying “A massive amount of specially designated waste is stored at various areas of the prefecture, and needs to be disposed of at an early date. To dispel the three municipalities’ concerns, it’s inevitable for us to accept a detailed survey.” Thus, Kurihara Mayor Isamu Sato and Taiwa Mayor Hajimu Asano decided to accept the survey. Kami Mayor Inomata continued his dissent, and some other mayors agreed with him. But, most said local communities should support the siting survey and continue open discussion on the matter, providing the consensus the governor sought. In response, Mayor Inomata said local residents may try to block the surveys, “A survey shouldn’t be conducted without local residents’ understanding. If the national government is to forcibly start its survey, it would cause confusion.” The studies will include checks on unground geology and groundwater infiltration levels. http://mainichi.jp/english/english/newsselect/news/20140805p2a00m0na007000c.html
  • The groundwater bypassing effort at F. Daiichi shows improving results. Last week, the Press reported that one well had merely dropped 4 centimeters in level as result of the process. However, they failed to mention that levels in three other wells had dropped 10 centimeters. As of June 25th, the “pumped –up” water discharged to the Pacific totaled nearly 16,000 tons, all of which met the self-imposed limits set by Tepco which are roughly 10 times less than national standards. The company reiterated that heavy rainfalls the past few months may well have limited the impact of the bypassing effort because in-seepage from the surface has been high. http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1407137706P.pdf
  • The head of Tokyo’s nuke watchdog agency says Tepco is not doing a good job with groundwater management. Shunichi Tanaka, Nuclear Regulation Authority chairman, said, “The biggest risk is the trench water. Until that matter is addressed, it will be difficult to proceed with other decommissioning work. It appears that they are getting off track” because of the parallel work being done to upgrade ALPS. His rationale seems predicated on yet another worst-case scenario, “It would be the best if you can keep all contamination from spreading. But what if another tsunami hits the plant and the highly contaminated water in the trench is discharged while you are trying to do everything [else]?” http://blogs.wsj.com/japanrealtime/2014/08/07/fukushima-watch-regulator-says-tepco-must-focus-on-trench-water/