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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


23rd REPORT

STA ADMITS GENERAL PUBLIC EXPOSURE TO NEUTRON RADIATION;
DOSE ESTIMATION PUBLICIZED;
REGISTRATION OF THE EXPOSED RESIDENTS FOR LONG-TERM HEALTH MONITORING COMMENCES

4 November 1999

The Tokai Criticality Accident Investigation Committee today presented the results of the analysis of the uranium solution samples obtained from the accident site (see 22nd report). According to the calculation by the Japan Atomic Energy Research Institute (JAERI), the first 25 minute of the criticality, which eventually lasted nearly 18 hours, yielded a total 75mSv exposure at the distance of 80m from the ground zero. (This is the minimam distance from the precipipitation tank where the uranium went critical to the JCO site boundary).

It is estimated that as much as 48% of the total energy emmission took place during the first 25 minutes of the criticality.

The cumulative doses for the first 5 hours (i.e. before the residents evacuated) are estimated by STA at 110mSv at 80m point, and 1.4mSv at 350m point (neutron plus gamma, roughly at 10:1 proportion). This can mean that almost all the members of the general public around the plant had got the dose over annual limit (1mSv) before they escaped.

STA (the Science and Technology Agency of the Japanese Government) says that the doses are of harmful levels in a long term, and admits that there is a high possibility that the members of the general public around the site were exposed to considerable doses.

Oh, what a decent expression!

Also publicized today are the doses suffered by the JCO workers (other than those of the rush platoon) on site on the day of the accident: between 64mSv (max) and 0.6mSv (min). As reported earlier, the rush platoon members were dosed with the maximum of 120mSv.

The seven construction workers, who had been working outdoors on a ground adjacent to the JCO plant (not "golf course" as incorrectly reported earlier), were dosed with between 15mSv (max) and 6.4mSv (min).

From the data newly disclosed by JAERI/STA, Dr Jinzaburo Takagi estimates the number of the fission at around 2.5E+18, and the weight of U235 that went into chain reaction at around 1mg. He reserves a possibility that the figure s may be larger if we consider the problems in the method of taking samples (see 22nd report).

Earlier on 29th of October, the local governments (namely Tokai-mura and Naka-machi, with the supervison of Ibaraki Prefecture) started to register the affected people. Initially 120 evacuees were registered, and a hundred more people are expected to register, not only the residents, but also the passers-by who happened to be in the neutron radiated areas on the day of the accident. The prefecture administration say that those registered will be monitored over 10 years period for their health conditions.

The residents of the radiated zone are expressing fear and anxiety over the state of affairs. Media reports also oscilate between "no worries" and "cancer in ten years". Discriminations not only against the farm and sea products of Tokai region, but also against the people are already being reported, as it happened very badly against the surviving victims of Hiroshima and Nagasaki.

One big question is what lessons we ever had in the last 54 years of nuclear age...

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