74 -
RADIOLOGICAL CLEANUP OF ENEWETAK ATOLL
average exposure rate was defined for each island. When an average Tate
was needed for a group of islands, it was obtained by weighting individu)
island rates according to the area of eachisland in the group. The exposur,
rates were converted to absorbed dose based on assumed duration of
exposure.
Inhalation dose estimates were determined using the Internationa
Commission on Radiological Protection (ICRP) lung model. Intakes tg
this model were derived from concentrations of plutonium in soil and ay
assumed air-mass loading. (Average concentrations for plutonium in Soil
of islands/group of islands were used.) This method was considereg
preferable to using the survey air sample data, which were representative
only of a very short period of time. Had actual air sample data been useg
inhalation dose estimates would have been several orders of magnitude
lower than reported.
Ingestion dose estimates were based on an assumeddiet (including loca
marine andterrestrial food and imported food) and measuredorderived
concentrations of radionuclides in components of the diet. Significant
radionuclides for ingestion dose were determined to be cesium-137 ang
strontium-90. A concentration for these nuclides was determinedfor the
average fish of the atoll, for use in estimating doses via the marine food
pathway. The concentration of the significant radionuclides in terrestrial)
foods was estimated primarily by correlation between concentrations of
radionuclides in soil and in indicator plants or animals.
The survey report included estimates of annual dose rate and
accumulated dose over extended periods of time for the various living
patterns. The effect on possible dose due to cleanup modifications; e.g.,
covering contaminated soil with clean soil, plowing soil to mix
contaminated surface layers with cleaner subsurface layers, was assessed.
The report ranked dose pathways in the following order of decreasing
dose: ingestion of terrestrial food; external gamma exposure;ingestion ofmarine food; and inhalation of contaminated air. The most significant
contribution to dose via the terrestrial food chain was determined to be
strontium-90 in pandanus, breadfruit, and coconut.55
The Enewetak Radiological Survey provided a data base and general
concepts for radiological cleanup. Considerable effort was still required,
however, to evaluate and adapt the data for actual cleanup operations.
AEC TASK GROUP REPORT: JULY 1973-JUNE 1974
In July 1973, an AEC Task Group was appointed by the Director,
Division of Operational Safety of the AEC, to review NVO-140 and to
prepare cleanup and rehabilitation recommendations. Members of the
eeee