Scaling factors for CANDU reactor waste: how reliable are they?

Abstract

Abstract This paper presents the results of a study of the use of the scaling factor method for the determination of the activities of the difficult to measure radionuclides – H-3, C-14, Ni-63, Sr-90, Pu-239/240 and Pu-214 – observed in CANDU radioactive waste. Twenty-six smear samples collected in the vault of Bruce Unit 1 during its refurbishment in the period 2009 to 2012 are used as surrogates for radioactive waste packages generated by the operation, maintenance, refurbishment and decommissioning of a CANDU reactor. A detailed analysis of the data presented in this paper shows that: (i) the activities of H-3 and C-14 cannot be reliably determined by the scaling factor method, and (ii) the activities of Ni-63, Sr-90, Pu-239/240 and Pu-214 estimated by the scaling factor method are typically in agreement with the measured activities to within only an order of magnitude of their true values. It is recommended that activities of CANDU rad-waste samples derived by the scaling factor method should be reported to only one significant figure to better reflect the limited precision and accuracy of this method.