Consequence management radiological dose assessors make several
assumptions in dose projections regarding radionuclide depositions
following a radiological release from a nuclear power plant. During
trainings and exercises these coordinators and dose assessors make
assumptions that the radionuclide deposition ratios will remain
constant, only varying in terms of radioactive decay and
weathering. This assumption is sometimes made regardless of large
spatial and terrain variations. Following the Fukushima-Daiichi
accident, the National Nuclear Security Administration's
Consequence Management Response Teams (CMRT) assisted in
consequence management operations in Japan. Part of their work
included taking air samples and in-situ measurements using high
purity germanium detectors throughout certain areas of the country.
The validity of the aforementioned assumption was examined by
analysis of the in-situ measurements that were obtained by the U.S.
response teams and the Japan Atomic Energy Agency (JAEA). Using
isotopic ratios for a LWR core-damage accident, from FRMAC Manual
Volume 3, a comparison was made with the collected in-situ
measurement data to determine how the FRMAC values compare against
actual measured data. The main radionuclides considered in this
evaluation were 134Cs, 136Cs, 137Cs and 131I. The goal of this
comparison was to determine how valid training and exercise
assumptions are pertaining to an actual incident.