|Nyt om atomkraftulykken i Japan
den 30. september 99.
E-mail afsendt fra Japan 25. oktober
Mon Oct 25 12:17:08 1999
Date: Mon, 25 Oct 1999 17:41:24 (lokal tid) +0900
From: email@example.com (Hosokawk)
Subject: MagpieNews #991024 (Tokai accident-22nd report)
Magpie Country Nukes Headliner
nuclear issues news brief from Japan
Criticality accident at Tokai uranium processing plant
URANIUM SOLUTION EXTRACTED, BUT IN A NADEQUATE WAY; MISTERY AS
TO THE QUANTITY OF SOLUTION IN THE TANK; UNRELIABLE FIGURES OF
FISSION PRODUCT RELEASE
24 October 1999
JCO Company plans to shield the accident site (i.e. building) with concrete concrete blocks
30cm thick and 300cm high. The radiation level (mainly gamma) is still abnormally high
around the building and the off-site residents are rightfully worried about it.
On Friday 22 October, JCO and STA (Japanese Government's Science and Technology
Agency) extracted 40cc (or 50cc according to certain insider information) of the uranium
nitrate solution out of the precipitation tank (sediment basin) in which the uncotnrolled
criticality occurred. This would provide crutial data regarding the nature and extent of the
chain reaction that took place in the tank (see 21st Report).
It must be pointed out, however, that 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 malfunctional. 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 ample 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 litters of the uranium solution in the
tank. It had been estimated that there were some 40 litters in there. The JCO workers said
they had poured 7 bucketfuls of the uranium solution into the tank, each bucket containing
6.5 litteres, before unexpectedly triggering the chain reaction. If the volume of the solution in
the tank (i.e. the substance which went into critical) was really less than 20 litters, 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. The responsibility of STA as supervisor is
As to the radioactive iodine-131 concentration that were going out of the accident site (=
reconversion test building), JCO admitted that the data they had previously publicized was
incorrect. On 14 October, JCO stated that they were releasing 0.51x10E-6 Bq/cm^3 of I-131
(which figure is below the STA limit of 10E-6 Bq/cm^3). On 15 October, JCO said that the
figure was actually 1.05x10E-6 (which is above the limit). This figure was based on the
exhaust air they had monitored the previous day. The figure with the air sampled on 14 Oct
was 1.4x10E-6 8 (i.e. increasing leak!)
OOA, Blegdamsvej 4 B - st, 2200 Kbh. N.
Tlf: 35 35 55 07, Fax: 35 35 65 45
Sidst opdateret 25. oktober 1999