The latest JAIF posting of pressures and temperatures inside the three damaged RPVs at Fukushima continues to suggest that only unit #1 experienced a complete core-relocating meltdown. Units #2 and #3 RPV temperatures indicate severe melting of core materials, but not a full meltdown in either case. Here’s why. The faster water flows through any heat producing system, the lesser the amount of heat the water removes as it passes through. The slower the flow, the greater the amount of heat absorbed as it passes through. With the entire fuel cell of unit #1 completely melted and relocated, there is literally nothing to obstruct the flow of water through the core barrel where the fuel used to be. It’s not there anymore. The water flows through rather rapidly and picks up minimal heat from the corium (solidified mixture of uranium and other core metals). Please keep in mind that unit #1 has 60% less fuel in its core than units #2 and #3, and decay heat has dropped to perhaps one MWth. Unit #1 RPV temperature is at 26oC. On the other hand, unit #2 temperature is at 52oC and unit #3 temperatures are between 47-55oC. The higher temperatures strongly indicate there are some pretty severe flow restrictions in and around the core barrel. This demonstrates that for units #2 and #3 some or most of the damaged fuel has not relocated and remains in its original position! The unmelted portion in each RPV is unquestionably deformed, blocking possible water flow pathways. This slows the flow and allows the water itself to pick up more heat than would otherwise be the case. Thus, government, TEPCO, and news media reports of full, core-relocating meltdowns for all three reactors are probably incorrect. With unit #1…without a doubt! With units #2 and #3…possibly not.

There are relatively few updates to follow because of a very heavy focus on our first entry by all Japanese news services…

  • Soon after the explosions at Fukushima Daiichi, Prime Minister Kan requested the chairman of the Japan Atomic Energy Commission to draft a worst case scenario for potential evacuations. At the end of the first week of the accident, Kan told the Press he particularly feared he might have to evacuate Tokyo but never said why he felt that way. Behind the scenes, he wanted something to use as evidence and asked the JAEC for assistance. The report was given to Kan on March 25 which postulated mandatory evacuations out to 170km and voluntary evacuations out to 250km. Chairman Shunsuke Kondo based his assumptions on a second hydrogen explosion at unit #1 forcing a complete abandonment of the power complex. He felt abandonment would result in full meltdowns in units #2 and #3, along with full melting of stored fuel cells in the unit #4 SPF. The SPF meltdown would cause complete collapse of its supporting structure. The entire scenario would release high volumes of volatile fission products from all four buildings. During and after the on-site destruction occurred, winds were assumed to carry airborne contamination at a constant velocity towards the locations with greatest population density. Local topography was not included in the contamination prediction. Kondo pointed out that his full worst case worst case calculations were not realistic. As a result of these improbable conjectures, Kondo wrote that the numbers were very rough and should not be used to assume how large the contaminated areas would actually be. The computer system for such predictions, SPEEDI, was not used by Kondo, probably because of P.M. Kan’s staff’s decision to ignore SPEEDI beginning March 16. In conclusion, Kondo re-emphasized his postulations were not intended to be detailed and taken with a high degree of confidence. (Japan Times) We have used the Times as a reference because it first reported this story on Thursday. All other news media posted today. (Friday) First come…first serve.
  • Nuclear disaster Minister Goshi Hosono has announced the Tokyo government wants to enact a law limiting nuclear power plant life-span to forty years. This is the first such limit on the duration of a Japanese nuclear plant’s operating period, ever. The regulatory limit can be extended after 40 years if certain conditions are met. The two conditions for extension reported by Hosono are (1) relative obsolescence of the facility and (2) the degree of appropriate maintenance taken over the 40 year period. (NHK World) The United States has a similar limit, but extensions in America are commonplace. Hosono says actual lifetime extensions in Japan will be “very rare” under the suggested rules of the proposed law. The new bill will also require nuclear plant operators to take measures to prepare for severe accidents that could result in damage to the reactor core. Current regulations place no licensing limit on the duration of nuclear plant operation and leave severe nuclear accident mitigation to the discretion of the companies owning the nukes. (Mainichi Shimbun)
  • The municipal government of Kashiwa has once again stopped all waste incineration because of ash constipation. The problem is not the incineration itself, but rather storage space for the ash containing more than 8,000 becquerels/kg of radioactivity. Existing storage space for 200 tons of ash is satiated and 30 tons of ash remains in the high-efficiency incinerators. Kashiwa has tried to get the cities of Abiko and Inzai to allow temporary storage, but local opposition keeps it from happening. Until the waste disposal issues based on public radiation fears are resolved, there is no place where the stored materials can be moved. Some older, less efficient incineration facilities will be re-started to handle garbage produced by city residents. (Mainichi Shimbun) NIMBY strikes again!
  • By the end of 2011, the Great Tohoku Earthquake of March 11 had produced nearly 7,000 aftershocks which were felt by people. Across Japan, 9,723 earthquakes and aftershocks were felt last year. This number is seven times more than in 2010, mostly because of the March 11 quake aftershocks. (NHK World)