Speaker
Description
Fission product yields play an important role for nuclear reactor fuel cycle, nuclear reactor
decay heat, and nuclear reactor waste inventory. Multiple techniques have been used to determine
fission product yields for many decades to support reactor design. For our purposes, we will be
performing $\gamma$-ray spectroscopy on $\beta$-decaying fission products following a prompt fission neutron
spectrum irradiation. Previous work has been performed using the Godiva-IV critical assembly to
determine fission product yields starting 1 hour after irradiation and data was recorded for 7 days.
In order to observe shorter-lived fission products, a new rabbit system and $\gamma$-ray counting setup is
being developed by Lawrence Livermore National Laboratory (LLNL) and Oregon State University
(OSU) for use in a campaign of measurements on $^{238}$U at the OSU TRIGA reactor. The counting
setup will consist of six BGO Compton-suppressed HPGe clover detectors connected to a new
VME-based digital data acquisition system. Data will be recorded in list-mode to analyze time-
dependant behavior of the $\gamma$-spectra. The clover detectors have relative efficiency of 150% (to 3×3
in. NaI(Tl) crystal at 1.33 MeV) and the solid angle coverage of four detectors is approximately
9% for the array. The $^{238}$U samples will be delivered in front of the detectors directly from the
reactor core via the rabbit facility. One complication with rabbit systems is that there may exist trace elements that will undergo neutron capture reactions and introduce extraneous $\gamma$-rays in the
time scale of interest. This prompted a study of different pure polyethylene sample materials from
various suppliers at the OSU TRIGA reactor and the development of a new rabbit. Results from this measurement will be discussed.