Non-Destructive Assay of Leached Hulls in a Nuclear Fuel Reprocessing Plant

摘要

The hull monitor at the Barnwell Nuclear Fuels Plant (BNFP) will be a remotely controlled, fully automated system designed to quantitatively assay leached hulls for undissolved U and Pu. The hull monitor will assay the hulls from one metric ton of fuel per dissolver basket with the design goal of detecting 0.1% undissolved fuel and yet remain within the framework of the BNFP materials flow of five hull baskets per day. The non-destructive assay will be accomplished using a computer-based gamma-ray pulse height analysis system employing a 5 x 5 inch NaI(Tl) scintillation detector. The intense radiations from the fission product isotopes and the activation product isotopes produced in the reactor prevent direct assay of the undissolved fuel left in the hulls. The measurement will be made indirectly by demonstrating a correlation between the amount of exp 144 Ce undissolved and the remaining U. The isotope exp 144 Ce is a direct fission product with high cumulative yield. The daughter isotope exp 144 Pr has a gamma ray at 2.18 MeV well above other predominant radiations in the spectrum from the major interferences exp 60 Co, exp 58 Co, exp 95 Zr( exp 95 Nb), exp 137 Cs and exp 106 Ru( exp 106 Rh). Segmented scanning operation of the hull monitor is accomplished by rotation and vertical transversal of the hulls container past the detector station. Proper collimation and absorbers are required to maximize the exp 144 Ce( exp 144 Pr) to background ratio. A basket indexer is provided which monitors the scanning rate and ensures repositioning. The leached hull monitor system will be interfaced to a computer-based multichannel analyzer for ease of operation and data handling. A calibration basket has been fabricated to accomodate radioactive sources and inactive Zircaloy hulls. (ERA citation 03:046873)