Estimation of plutonium in waste drums containing high amount of beta gamma activity

The allowed limit for disposal of alpha active nuclear waste as specified by I.A.E.A. is 4000 Bq/g. The waste drum may contain plutonium along with high beta-gamma activity due to long lived isotopes such as 137Cs. Hence, it is essential to develop a method for the estimation of Pu in the presence of high beta gamma activity. A segmented gamma ray scanning system has been developed earlier for the assay of Pu in 200 liter waste drums using HPGe detector system. The amounts of 239Pu, 240Pu and 241Pu were estimated using their corresponding gamma rays. A multi gamma ray source of 152Eu was used for the determination of attenuation correction factors. The attenuation corrected count rate of the standard drum and waste drum were used to determine the amount of Pu present in the waste drum. In the present studies, modifications in the counting techniques and spectrum analysis were incorporated for the estimation of ∼1 g of Pu present in the drum in the presence of 137Cs up to an activity level of 20 mCi. As the actual handling of the high dose drums is difficult, the conditions were simulated for very high activity of 137Cs within the drum. The counting was carried out for Pu gamma rays in presence of 137Cs activity varying from 0.4 to 10000 counts per second (CPS). The dead time correction was applied to arrive at the corrected count rate for all the gamma rays