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Magpie Country Nukes Headliner
nuclear issues news brief from Japan
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Criticality accident at Tokai uranium processing plant

17th REPORT

INADVERTENT CRITICALITY CONTINUED OVER 20 HOURS;
ACCIDENT LEVEL 5 ADMITTED BY STA;
IMMEDIATE SURVEY OF RADIOACTIVE SALT REQUESTED

7 October 1999

Citizens' Nuclear Information Center (CNIC) held a well-attended press conference yesterday (6 Oct) and presented their statement on the JCO Tokai accident.

It was pointed out that the accident was not only the worst-ever accident in the Japanese history of nuclear development, but also the worst-ever criticality accident so far in the world, in that the criticality had been maintained for over 20 hours.

**In previous reports of MagpieNews, we wrote that the criticality was being repeated intermittently. Now it has become clear that it actually went on without stopping.

This was confirmed by the neutron monitoring records at a research labo of Japan Atomic Energy Research Institute (JAERI) in Naka Town, 2km west of the accident point. There, the first wave of neutron shower (0.26microSv/h, as against the normal level of 0.01microSv/h) was recorded at 10:37am, 30 September, i.e. the same time as the three JCO workers was knocked down by radiation. Then abnormally high level of neutron radiation (at around 0.02-0.03microSv/h) continued without intermission until 6am the next day, i.e. roughly the time when other workers managed to break the chain reaction by draining coolant waters that had been conditioning the flux of neutron in favor of the criticality (see 10th Report).

CNIC also released a revised and updated assessment of the amount of radiation released: Around 0.1g of U-235 underwent fission; the amount of fission product (radioactive materials) produced by the chain reactions is 10E16 to 10E17, mainly rare gas, plus other radionuclides such as iodine and cesium, of which all the rare gas was released together with considerable percentage of volatile gas. The quantity of radioactive materials released into atmosphere is estimated conservatively at around 10E16 to 10E17.

**These figures are a bit smaller than the tentative calculation results that we reported previously (cf. 13th Report), but it is still large enough to rank the Tokai accident at Level 5 on the International Nuclear Event Scale (INES), in other words as severe as Three Mile Island accident 1979.

According to insider reports, STA officials are going to admit this (i.e. Level 5, rather than Level 4) and revise their report to IAEA accordingly.

CNIC also warned that there was still a danger of the remaining fission products, which is now confined inside the building (and most likely inside the precipitation basin), could be released outside the facility. So it is too early to consider that the residents around the JCO facility have a safety guarantee.

CNIC strongly accused the almost chronic irrensponsibilities of the Japanese nuclear industry, and concluded that (1) all the nuclear fuel processing facilities in the country should be suspended immediately and thourough safety inspection must be carried out by an independent body, and (2) MOX utilization program should be totally suspended.

In the meantime, Greenpeace conducted independent fieldwork and confirmed that, in the salt (NaCl) in the kitchen of the residents' houses near the JCO plant, the component sodium (Na) had been activated by neutron radiation (i.e. generation of the beta-emitter, sodium-24).

A group of Japanese medical doctors who are the members of Global Health Disaster Net (GHDNet) issued an emergency statement calling the authorities to carry out immediate survey on Na-24 in table salt held by each household within the evacuation zone, and cross check the results with another survey of radioactive copper (Cu-64) in electric lines in the same household. These results would give fairly exact figure how much neutron radiation was dosed on the residents. Remberber they were told to evacuate only after 5 to 6 hours

after the unexpected ignition of the chain reactions.

The GHD doctors also requested that Nuclear Safety Commission (NSC) should disclose all the data they have obtained regarding spacial radiation dose rate, water and soil sampling data, and any other monitoring results.

Yes, the accident is continuing.

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Magpie Country Nukes Headliner
nuclear issues news brief from Japan
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Criticality accident at Tokai uranium processing plant

16th REPORT

TENTATIVE LIFE RISK ASSESSMENT OF WORKERS EXPOSURE

7 October 1999

MagpieNews has worked out a tentative caluculation of collective dose on those 24 JCO Tokai workers who carried out the sacrificial operation which made the nuclear chain reactions (criticality) settle down in the dawn of 1 October (cf. 10th Report). Each worked outside the building for two to three minutes under massive neutron shower.

***These are different from those three hospitalized workers who had been hit by the initial neutron bombard inside the building. The three got the lethal dose (see 12th Report), and they are not included in the following calculation.***

The calculation was done using the dose figures by each worker disclosed by the JCO at its press conference. The 24 workers include 6 car drivers who took the other 18 workers to the site.

The collective dose is estimated at around 0.85 person-sievert (neutron + gamma). Considering additional exposure which still other workers were dosed with during the boron water injection later in the same morning. Then our best guess is that there was well over 1 person-sievert of collective radiation exposure.

Number of additional cancer/leukemia deaths caused by this amount of collective dose will be 0.13 (applying the moderate risk assessment standard worked out by Radiation Effects Research Foundation (RERF), Hiroshima) up to 0.44 (applying the more radical risk assessment claimed by Prof. J.W. Gofman).

This is a very high risk of life. Reportedly, the workers had no sort of "informed consent" to join that operation. Some of them were dosed beyond the ICRP emergency limit of 100mSv.

There will be much radiation-exposed work needed to liquidate and decontaminate the building in which the criticality took place and now filled with radiotoxic fission products. There should be no more brutality of "just go and do it" type operation.

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Sidst opdateret 12. oktober 1999