Year
2011
Abstract
There is considerable interest in developing direct measurement methods to determine the plutonium content of spent nuclear fuel within a fuel assembly. One technique that may prove successful is lead slowing--down spectroscopy. Lead Slowing Down Spectroscopy (LSDS) has been used for decades to make cross--section measurements on relatively small isotopic samples of well know masses. For spent fuel assembly measurements, LSDS will be applied in reverse; unknown masses will be determined using well--know cross--sections. In the LSDS, a pulse of neutrons (on the order of 10--100 MeV) is injected into a large lead stack (~ 1m3). The neutrons quickly down--scatter but exhibit little spread in energy about the average, continually--decreasing neutron energy making for a strong correlation between the elapsed time from the initial pulse and the average energy of the neutron. By measuring this elapsed time, it is possible to measure interactions of the neutrons with the fuel in the 0.1 to 1,000 eV range. Many of the actinides have strong resonances in this region, making it possible, through careful measurements and analysis, to extract isotopic masses from LSDS measurements. Pacific Northwest National Laboratory is actively conducting research on both LSDS measurement and data analysis techniques. This paper will present results of the effort to construct and characterize a new lead slowing down spectrometer. The spectrometer was designed to begin testing both experimental measurement and data analysis techniques for determining the plutonium content of spent fuel. To characterize the spectrometer, a series of (n,?) experiments were conducted to measure the correlation between the time after the neutrons enter the lead and the energy of the interaction. Results from these measurements as well as plans for future development of the spectrometer will be discussed.