(October 29, 1999) More sloppy work at the Tokai-Mura uranium processing plant and inadequate measures after the accident became known. The radius of the evacuation zone was decreased due to fear that panic would arise. STA had not carried out a legally- prescribed site inspection for 10 years!
(520.5100) WISE Amsterdam - The union of the employees of JAERI (Japan Atomic Energy Research Institute) worked out an independent estimation of the total radiation dose at 17 monitoring points around the JCO Tokai accident site. The result of their calculation was reported in Mainich Newspaper on October 16 and 17 nationwide. It unequivocally shows that evacuation of at least 600m radius zone (rather than the actual evacuation of 350m zone) should have been encouraged, as it was revealed that the annual dose limit of 1mSv had been reached even at a 400m point.
It has also been revealed that the government's emergency responce unit (headed by the Prime Minister Obuchi) was about to issue the evacuation order for 500m zone, but it was not issued since it was after midnight (i.e. early hours of October 1) and it was raining (so a panic could easily be caused). As a result, the population in 350m to 600m zone was left in the neutron bombard. Evacuation of 350m radius was no doubt insufficient, and the evacuation started only after 4 or 5 hours after the criticality sparked. Greenpeace Japan requested in writing that STA should conduct follow-up surveys on the health of the nearby residents.
Earlier, a spokesman of JCO, the operator of the plant, disclosed individual radiation exposure doses of the workers who had engaged in the dangerous operation to control the criticality. One member of the first team who approached the building to take photographs of the pipe systems they were going to work on was dosed with 20mSv, according to this original JCO statement.
On October 15, it was revealed that the workers wore 2-digit type neutron recorders, i.e . the meter is reset to "00" when the count is over 99. So, "20mSv" was actually 120mSv! (119.79mSv to be exact; neutron plus gamma, mostly consisting of neutron dose.) The fact was reported by STA (the governmentþs Science and Technology Agency) to the accident investigation unit of NSC (Nuclear Safety Commission).
JCO admitted that a limited amount (twice the allowed limit!) of radioactive iodine-133 had been kept going out into atmosphere after the accident via exhaust system of the building in which the criticality occurred. The exhaust system switch was on until October 11. More than 10 days after the accident, JCO hastily sealed up the windows of the building in question in order to avoid further release. (More workers exposed during the operation!) But at a press conference on October 15, JCO admitted that radioactive I-131 was still leaking. They had no filter to trap iodine gas in the exhaust system. They said they would put additional filters the next day (Oct 16) to reduce the emission of radioactivity into atmosphere. The problem is that STA knew all this all the time. STA should have ordered JCO to do this much earlier. Critics say that STA and JCO may be expecting to reduce the contamination inside the building by releasing the contaminants out into atmosphere, so that liquidating work can be started as early as possible. JCO Company plans to shield the accident site (i.e. building) with concrete blocks 30cm thick and 300cm high.
On October 22, JCO and STA extracted 40cc (or 50cc according to certain insider information) of the uranium nitrate solution out of the precipitation tank (sediment basin) in which the uncontrolled criticality occurred. Radiochemically speaking, retrieving the solution is of crucial significance in understanding the nature and extent of the accident. Qualitative and quantitative analysis of the fission products (such radionuclides as barium, ruthenium, molybdenum, cerium, etc.) that are contained in the solution will render an exact estimation of the number of nuclear fissions (thus the number of neutrons and energy generated).
However, JCO did not stir the solution before they took sample of it. They claim that the stirring mechanism (which is a part of the precipitation tank in question) was malfunctioning. They only managed to extract the sample from the surface of the uranium solution that was in the tank. Whatever the reasons or technical constraints may be, the fact flatly means that the result of the analysis of the extracted sample may be incorrect (most probably an underestimation) as regards the number of fissions and the quantity of the fission products generated.
It was also confirmed that there was only less than 20 liters of the uranium solution in the tank. It had been earlier estimated that there were some 40 liters. The JCO workers said they had poured seven bucketfuls of the uranium solution into the tank, each bucket containing 6.5 liters, before unexpectedly triggering the chain reaction. If the volume of the solution in the tank (i.e. the substance which went into criticality) was really less than 20 liters, it means that the workers could have been unlawfully handling nitrate solution with much higher fissile uranium concentration than the prescribed 18.8%. As a matter of fact, the JCO plant has an STA license to deal with up to 20kg of 50% U-235. It is just incredible (and outrageous!) that a plant with such a license had no safety measure or contingency plan for a criticality control failure.
On October 3, STA sent a site-inspection team to the JCO plant. This is the very first time in 10 years that a site inspection, which is legally prescribed, at this plant is carried out. It was also revealed that STA had conducted no site inspection either at Tokai Reprocessing Plant (operated by JNC) or at Rokkasho-mura Enrichment Plant (operated by JNFL) over six years. STA claims they were too busy. According to press reports IAEA officials were at the plant (in an adjacent room!) when the accident occurred. Later, there were reports that IAEA denied the presence of a team. On October 12 the IAEA sent an fact-finding mission to Japan for a three-day visit. They are preparing an internal report.
Sources:
- MagpieNews, 15, 16, 18 and 24 October
- UPI, 14 October
- E-mail WISE Hiroshima 15 October
- IAEA press release, 12 October 1999
Contact: Citizens' Nuclear Information Center (CNIC),
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