The international Press is focusing on news reports out of Japan about recriticality in the damaged fuel of reactor #2 at Fukushima Daiichi. The Japanese Press is calling for a complete revision of the “cold shutdown” criteria, and the world’s Press is drooling over it. As it turns out, what was discovered and reported to the Press has nothing to do with the process known as “criticality”. The whole mess could have been avoided if it were not for the ineptitude of TEPCO’s public information staff, exacerbated by speculations made by some of TEPCO’s remarkably naïve nuclear officials.
All uranium-based fuel experiences the process of spontaneous fission. It’s a property of elements with atomic masses greater than 232, where the nucleus of the atom will split all by itself. The probability of spontaneous fission is extremely low for U-238, but not too low to be detectable. Uranium is not the only element in nuclear fuel that spontaneously fissions at a detectable level. The other is Curium.
Curium is not a naturally-existing element. It is produced in small quantities during reactor operation and slowly builds up in the fuel pins (~20 grams per ton of spent fuel). Here’s a summary of the production process…U-238 has a tiny probability of fission, but it does absorb neutrons. U-238 neutron absorption transmutes it into the element Plutonium through natural radioactive decay (Alpha and Beta). Some Plutonium is isotope 239, some Pu-240, and some more Pu-241. It is the Pu-241 which further absorbs neutrons and subsequently transmutes into Curium. Curium isotopes 242 and 244 have a probability of spontaneous fission.
All fissions produce any of about 42 possible elements (see “Nuclear Waste : Is it?”), which are known as fission products. One of the most probable fission products is Xenon, and its two most probable isotopes are Xe-133 and Xe-135. Xenon is an inert gas, which chemically combines with nothing, so it has little trouble migrating out of the fuel and into the surrounding environment, in this case the inside of the Primary Containment of unit #2 at Fukushima. The tiny amounts of Xenon discovered by TEPCO on Wednesday strongly indicate the process of spontaneous Uranium and Curium fission, with Curium’s probability 10-50 times greater than Uranium’s. Recriticality would have produced Xenon in volumes 1,000 to 10,000 times greater.
When they told the Press, TEPCO let everything get out of control from the very start. They said the Xenon having come from recriticality is “unlikely” due to all the boric acid in the water injections, when actually the source had nothing to do with criticality and could not be inhibited by boric acid. In other words, the notion of recriticality was not “unlikely”, it was unquestionably impossible! TEPCO has yet to learn two of the basic nuclear facts of life. First, anything that can be misinterpreted to the extreme, will be. The word “unlikely” means “possible” to the Press and their readers. In some cases it is taken to mean “inevitable”. Second, never release information through people who haven’t got a clue, and the TEPCO Press staff has repeatedly shown a high degree of “cluelessness” with respect to nuclear realities since March 11. The same can be said for some of TEPCO’s officials who make public statements about things they obviously know nothing about.
The following updates exemplify what we are saying…
- On Wednesday, TEPCO spokesperson Hiroki Kawamata said ““We cannot rule out the possibility of a small nuclear fission reaction.” Thus, the Press assumed that fissioning had resumed inside RPV #2. (Japan Today)
- Junichi Matsumoto, acting director of TEPCO’s Nuclear Power and Plant Siting Division, told a press conference a small scale fission reaction is likely to have occurred in RPV #2. “We don’t believe criticality has been maintained,” Matsumoto said. Which led the newspaper to speculate “TEPCO suspects a nuclear fission chain reaction took place caused by existing neutrons within the reactor or that very local criticality took place as the water temperature in the reactor decreased and water density increased, due to the recent increase of water injection.” (Yomiuri Shimbun)
- Mainichi Shimbun’s lead editorial on Thursday calls for a complete revision of the cold shutdown criteria, based entirely on the re-criticality issue. The editorial first says, “The government and Tokyo Electric Power Co., the operator of the tsunami-hit Fukushima No. 1 Nuclear Power Plant, should step up their monitoring of the plant’s reactors to check whether nuclear fission is occurring and provide good explanations of the situation in the reactors to the public…we mustn’t let down our guard. The government and TEPCO need to find out why the fission has occurred and take appropriate responses.” Then later concludes, “The government and TEPCO have announced their intention to bring forward the timing of achieving a so-called “cold shutdown” of the crippled reactors in their roadmap to bringing the nuclear plant under control…However, the discovery of xenon in the No. 2 reactor’s containment vessel suggests nuclear fission is occurring even though the temperature at the bottom of the pressure vessel is thought to be below 100 degrees Celsius. It raises questions as to whether such a reactor can be considered stable, even if it is under that temperature threshold.”
- Thursday, TEPCO did its best to recover from its PR gaffe, but the damage was already done… “The Tokyo Electric Power Company, or TEPCO, said on Thursday that the small amount of xenon-135 it detected in gas taken from the reactor’s containment vessel was the result of the spontaneous nuclear fission of radioactive curium-242 and -244.” (NHK World) But… Japan Today writes “The operator of Japan’s
crippled Fukushima nuclear plant on Thursday played down fears of an uncontrolled chain reaction at the site, despite the discovery of evidence of recent nuclear fission.” TEPCO spokeswoman Chie Hosoda said the amount of Xenon detected was about 10,000 times less than what would be found with re-fissioning or recriticality. The Japan Today report immediately reminds the reader that this contradicts TEPCO’s announcement the day before.
Before we relate some other updates, we want to point out that for enough Xenon to be released into the Primary Containment to be detectable, it is improbable that the source is a completely melted fuel cell. If completely melted, the re-solidified corium material would bee too massive and dense to allow sufficient Xenon migration for detectability of the type found Wednesday. On the other hand, a partially, if not severely melted fuel cell would have enough exposed surface area to emit detectable levels of Xenon. Just one more clue that unit #2 might not have fully melted.
Now, for other updates…
- The radioactive bottle of Radium buried outside a Tokyo supermarket was broken and its contents mixed liberally with the surrounding soil. After all bottle shards and surrounding soil were removed, the radiation field dropped from the initial 40 millisieverts down to 25 microsieverts, a reduction factor of more than 1,000. (Asahi Shimbun)
- The discovery of two hot spots not due to Fukushima has brought a warning from the Tokyo government. “Because many radioactive materials had not been under control before the country set up a law, there could be an increasing number of such cases”, one official said. Tokyo advises anyone finding what appears
to be a new hot spot should report it to the Ministry of Science as soon as possible. (Japan Times)
- Although the government tried to collect all Radium quantities from 1965 to 1974, it is now obvious they missed some. Most of the privately held vials and jars of Radium were given up voluntarily during that period, but some were not because the owners had either personal or sentimental attachments. “In some cases people stored them away carefully, saying they were family treasures. It remained a fact that the  law hadn’t seeped in,” said Yoshihide Nakamura, an official from the Japan Radioisotope Association. In addition, prior to 1965, government inventories of Radium were not well documented. But, it might not only be Radium, “There are a lot of old substances, such as those that university professors purchased overseas and left behind when they retired without others realizing,” said Takao Nakaya, head of the Radiation Regulation Office of the Ministry of Education, Culture, Sports, Science and Technology. (Mainichi Shimbun) What do people do when they want to get rid of something strange? Either toss it in the garbage or bury it somewhere. Thus, the Japanese are finding hot spots, and the process will continue.
- Japan Times runs an editorial Q&A about the biological effects of radiation exposure. Unfortunately, it’s the same old song and dance about the effects of low level exposure being unknown, concluding, “Experts
just don’t know the effect on humans below 100 millisieverts.” Perhaps the most heinous fallacy concerns mention of the studies done on the high-background Kerala region of India. The Times first states, “No correlation was found between the ambient radiation and the risk of cancer,” then follows with, “Just
because studies haven’t found a statistically significant increase in risk doesn’t necessarily prove there is no chance of an increase in the cancer rate.” The Times tries to justify their spin by evoking BEIR VII (2006) which uses the mentally-confounding notion of relative risk derived from the statistically-corrupt Linear/ No Threshold concept. Why? Because Kerala has an annual exposure rate higher than most of the communities inside the Fukushima evacuation zone, like Iitate and Namie, which might lessen public fears. There is no mention whatsoever of Mortazavi’s discoveries with Ramsar, Iran, where natural backgrounds are greater than 250 millisieverts per year, up to 5 times the exposure levels found inside the no-go zone. But then, we’re dealing with fear of radiation in Japan, which has become very good business for their Press and food for the rest of the world’s Press that loves nuclear energy. Loves nuclear energy? Yes! Any and all scary-sounding nuclear stuff makes immediate headlines. It’s an automatic money-maker. Of course they love it.