Use of gamma spectroscopy for neutronic analysis of LMFBR Blankets

Abstract

It was the purpose of the present investigation to extend and apply Ge(Li) gamma-ray spectroscopy to the study of fast reactor blankets. The focal point for this research was the Blanket Test Facility at the MITR and Blanket No. 2, a realistic mockup of the blanket reflector region of a large liquid metal cooled fast breeder reactor. It was found that Ge(Li) detectors can be simultaneously used as both high energy neutron spectrometers and continuous gamma-ray spectrometers. The broadened internal conversion spectral line at 691.4 KeV has been analyzed for the former purpose, and the Compton recoil continuum has been analyzed and unfolded for the latter. This development makes the Ge(Li) spectrometer an extremely valuable shield analysis tool. The moisture content of the sodium chromate used in the blanket mockup has been confirmed to be less than 0.1 w/o by prompt activation analysis. Prompt capture and inelastic gamma, and decay gamma spectra emitted by the blanket were also analyzed to perform a neutron balance with mixed results. The inability to resolve U-238 prompt capture gammas made it necessary to use the low energy Np-239 decay gammas, with the attendant uncertainties due to large self-shielding corrections. Lack of data on the variation of prompt gamma yield with neutron energy for all blanket constituents also contributed to the uncertainties, which together made it impossible to develop this method to the point where reliable practical application can be recommended.