Magpie Country Nukes Headliner

nuclear issues news brief from Japan

Criticality accident at Tokai uranium processing plant



18 October 1999

**** correction ****

In the 19th Report of MagpieNews on Tokai criticality accident, the indication of the volume/number of the British scientific journal was inadequate.

"Nature Number 401" should read as follows:
Nature, volume 401, number 6753, dated 7 October 1999.

Magpie apologizes for any inconveniences our readers may have had.


The union of the employees of JAERI (Japan Atomic Energy Research Institute, see ##th Report) 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 16 and 17 October nationwide. It unequivocally shows that evacuation of at least 600m radius zone (rather than the actual evacuation of 350m zone) should have been encour aged, as it was revealed that the anual 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 1 Oct) 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.

According to NHK (national TV/radio network) news on 18 October, STA (Science and Technology Agency of the Japanese Government) plans to extract the uranyl nitrate solution that remains in the precipitation tank in which the fissile uranium elements went criticial. However, the dosage rate in the reconversion test building in which the tank in question is installed is still as high as over 10mSv/h (gamma, or gamma + neutron?). Anybody who approaches the tank will be dosed with unacceptably high amount of radiation. STA says they will sort out an operational procedure with certain time limit so that rad-exposure can be minimized, and hopes to carry out the operation before the end of this week. They declines to say how.

Radiochemically speaking, retrieving the solution is of crutial 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).

How many people must be exposed how much to the very dangerous level of radiation just in order to obtain several decilitters of the solution, which is a sufficient amount for the analysis, is a hard question, both in terms of science and of justice.

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