235U and 239Pu characterization in radioactive waste using neutron-induced fission delayed gamma rays

In view of long-term radioactive waste repository, the Differential Die away Technique (DDT) can be used to determine the amount of fissile materials, mainly 239Pu and 235U, in 225 L bituminized waste drums by detecting prompt and delayed fission neutrons between the pulses of a deuterium-tritium neutron generator. A complementary approach studied in this paper is to detect fission delayed gamma rays. The yields were first measured with bare samples of 235U and 239Pu in REGAIN, a facility dedicated to Prompt Gamma Neutron Activation Analysis (PGNAA) at CEA Cadarache, France. Their detectability in the 225 L bituminized waste drums is then assessed using the MCNPX model of MEDINA, another PGNAA cell dedicated to 220 L drums at FZJ, Germany, because REGAIN was designed only for 118 L drums. The performances in the bituminized drum are limited by a very high gamma emission due to 137Cs but delayed gamma rays could be detected in lower-activity cemented waste drums produced in Germany