TRU Waste Assay Methodology with the Combined Thermal Epithermal Neutron (CTEN) System

The CTEN assay system is designed to measure plutonium bearing 208-L waste drums and make the transuranic versus low-level waste determination. The system was certified for Waste Isolation Pilot Plant operations and the Environmental Protection Agency approved the CTEN in 2002. It is the only system capable of making the transuranic/low-level waste (TRU/LLW) determination since it can routinely assay below 100 nCi/g. The system conducts a measurement by using either (or both) an active 14 MeV neutron pulse to induce fission in 239Pu and 241Pu or measures the spontaneous fission properties of 238Pu, 240Pu and 242Pu. When the coincidence neutron signal is combined with mass fraction data from a gamma system, the result is the total plutonium mass. The system's lower limit of detection is as low as 2 mg of weapons grade plutonium, making it an ideal platform to make the TRU/LLW determination. Analysis of an assay is made with visual basic application driven subroutines and Micros oft Excel spreadsheets. Input values and calculations include: the raw neutron scaler and coincidence counts; mass fraction information; plutonium mass; alpha, total and TRU activity; thermal power, 239Pu Equivalent Curies; fissile gram equivalent mass; decay heat; and uncertainties associated with each parameter. A general diagnostic analysis is performed for each assay to facilitate a technical review of the results. The results of analysis from 372 waste drums are summarized. The results indicate that modifying current operating procedures involving the use of acceptable knowledge isotope data and use of the lower detection limit could increase the number of certifiable assays from 38% to 66%