Year
2008
Abstract
Uranyl fluoride (UO2F2) is the most common form of holdup in uranium enrichment facilities. Quantitative measurement of UO2F2 is necessary for the purposes of safeguards, nuclear criticality safety evaluations and for nuclear material control and accounting. Because UO2F2 is a dense material that severely attenuates gamma rays, neutron measurements are often the method of choice for performing quantitative measurements. UO2F2 produces neutrons via 19F(a,n)22Na reactions and by spontaneous fission, with almost all of the neutrons produced from 234U and 238U. Estimates of thick target yields and 19F(a,n)22Na cross sections have been previously made, and subsequent calculations performed to estimate neutron specific activity for UO2F2. Literature searches revealed no prior studies that involved the direct measurement of neutrons produced by uranium in the form of UO2F2. Neutron specific activity estimates from thick target yields and 19F(a,n)22Na cross sections vary widely, from 257.8 n/s/g 234U to 183.8 n/s/g 234U. An additional complication is that UO2F2 exposed to moist air readily forms hydrates, with the commonly accepted upper bound being UO2F2 ? 2H2O. The presence of H2O affects neutron production via the 19F(a,n)22Na reaction. The purpose of this study was to perform measurements on items containing UO2F2 to determine the neutron specific activity of 234U and 238U in both dry and hydrated UO2F2.