Calculation of gamma-ray dose rate from storage cask with radioactive sludge

Sludge contaminated by 137 Cs and 60 Co collected from bottom of the spent fuel storage pool of the RA research reactor is conditioned and stored as low-level radioactive waste in specially designed casks. This paper describes an attempt to estimate the ambient dose equivalent rate of gamma-rays at the cask surfaces filled with the conditioned sludge by using the MCNP code and compare the result to the measuring data. Various data exist for measured activities of 137 Cs and 60 Co in sludge, depending on water content. Precise data for materials compositions and their fraction, used during sludge conditioning process, does not exist. Consequently, obtained calculation results show wide discrepancies compared to measured ambient equivalent dose rate of gamma-rays at surfaces of the storage cask. This indicates that better knowledge of composition of wet sludge and its mixture with cement, together with precise data for activity measurement conditions, is necessary to obtain more reliable calculation results. (author)