Reconstruction of Two Victim’ Posturing Based on the Induced Radioactivities in Their Bones in the Criticality Accident in Tokai-Mura, Japan

Abstract

On 30 September 1999, three workers were severely exposed to neutrons and gamma rays in a criticality accident that occurred at a uranium conversion facility in Tokai-mura, Ibaraki Prefecture, Japan. Radiochemical analyses of 32P and 45Ca induced by neutrons in bone matrix were carried out after the deaths of two of the victims. It was found that more than several million becquerels of both nuclides had been produced in their body skeletons. Results showed non-homogeneous distributions of neutron fluence in the bodies, from which it could be deduced how both workers were positioned relative to the fission source during exposure, i.e., at the moment of the first nuclear excursion. For the victim who died first, the activities in the central part of his body were more than those of his extremities. Also, in the central part of his body, the right side showed more activities than the left side. As for the second man, the activities indicated rather uniform exposure to neutrons to the whole body although the geometrical distribution of the activity varied enough to assume his orientation. Such information on the geometrical distribution of neutron-induced radioactivities in the skeleton can be used to reconstruct the posturing of the victims, which is necessary to estimate their apparent absorbed doses.

Review of retrospective dosimetry techniques for external ionising radiation exposures

“…In the case of the Tokai-mura accident, for example, post-mortem analysis of activation in bones was also performed to estimate the neutron dose distribution by measuring 32 P and 45 Ca activities (103) .…”

Chromosome condensation outside of mitosis: Mechanisms and new tools

“…The drug‐induced PCC has been indeed applied after the 1999 criticality accident at the uranium fuel conversion test facility of JCO in Tokai‐mura, Japan. Three workers were exposed to very high doses (two of them died within a few months), and 24 Na and 32 P radioactivity measurements by whole‐body counters suggested soon that two of them were exposed to lethal doses (Miyamoto et al, 2002). However, cytogenetic analysis by drug‐induced PCC provided the best estimate of the absorbed dose (Kanda et al, 2002).…”

Dose assessment in the criticality accident at Tokai-mura

“…Mathematical human models with movable arms and legs (Yamaguchi, 1992) were used to recreate the posture of the workers at the moment of exposure. The posture of the 2 workers was reconstructed by (1) asking the workers themselves, (2) conducting an experiment using a mock-up life-sized facility, and (3) analyzing skin lesions and induced activity in bone samples taken from the workers (Miyamoto et al, 2002). Using the model, the generation and transport of neutrons and g-rays from the critical system and their interactions in the human body were simulated by the Monte Carlo method.…”