Nuclear-accident dosimetry: measurements at the Los Alamos SHEBA critical assembly

Abstract

Criticality dosimeters were exposed to different degraded neutron and g arm a-ray energy spectra from the Los Alamos Solution High Energy Burst Assembly (SHEBA). The liquid critical test assembly was operated in the continuous mode to provide a mixed source of neutron and gamma-ray radiation for the evaluation of Los Alamos criticality detector systems.Different neutron and gamma-ray spectra were generated by operating the reactor (a) shielded by 12 cm of Lucite, (b) unshielded, (c) shielded by 20 cm of concrete, and (d) shielded by 15 cm of steel. This report summarizes the dosimetry measurements conducted f r these different configurations.In-air measurement, were conduc .ed with shielded and unshielded area and personnel dosimeters. Phantom measurements were made using personnel dos meters. Combined blood-sodiun and hair sulfur activation measurements of absorbed dose were also maH°. in addition, indiun foils placed on phantoms were evaluated fo*-the purpose of screening personnel for radiation expo? I.

Determination of Gamma-Ray Exposure Rate from Short-Lived Fission Products under Criticality Accident Conditions.

“…1) To clarify neutron and γ -ray doses under such accidental conditions, several experimental studies have been conducted using solution-fueled supercritical facilities, SHEBA (Solution High Energy Burst Assembly) at the Los Alamos National Laboratory in the United States of America, 2,3) SILENE (Source d'Irradiationà Libre Evolution Neutronique) at the Institut de Protection et de Sûreté Nucléaire in France, 4,5) and TRACY (Transient Experiment Critical Facility) at the Japan Atomic Energy Research Institute (JAERI) in Japan. 6) In these studies, experimental data were mainly obtained as integrated dose rates during experiments by using activation matters, thermo-luminescent dosimeters and alanine dosimeters, and dose rates, which varied with time, were not sufficiently evaluated.…”

“…On the other hand, time histories of γ -ray dose rates will become different from those of power and fission rates, because γ rays from short-lived fission products (FPs) yielded in an initial power burst may contribute to the dose rates after the initial burst. The contribution of short-lived FPs to γ -ray doses was not, however, experimentally comprehended in the aforementioned studies [2][3][4][5][6] because it is difficult to evaluate separately the contribution of γ -ray doses from short-lived FPs from data on integrated γ -ray doses during experiments. It is, therefore, important to determine γ -ray dose rates varying with time under criticality accident conditions, and evaluate the contribution of γ rays from FPs by experiments.…”