Methods for Verification of the Hydrogen and Boron Content of the RCSB for Storage of HEU at the HEUMF

Abstract

BoroBond{trademark}, which is a ceramic material containing natural boron carbide (B{sub 4}C, a neutron absorber) and water (a neutron attenuator), is the filler material of the Rackable Can Storage Boxes (RCSBs) that will store highly enriched uranium in cans at the Highly Enriched Uranium Materials Facility (HEUMF). Both attenuation and absorption are essential for criticality safety of the fissile material stored in RCSBs. This BoroBond{trademark} material has not yet been used for storage of highly enriched uranium (HEU). To characterize the neutron attenuation and neutron absorption properties of this material, ORNL has performed an extensive series of measurements (over 900) which included: fast neutron and gamma time-of-flight transmission utilizing the Nuclear Materials Identification System (NMIS), thermal and epithermal neutron counting with {sup 3}He proportional counters, and activation analysis with gamma ray spectrometry using a high purity germanium (HPGe) detector. These measurements were performed for a series of 12 x 12-inch square blocks of thickness varying from 2 to 12 inches, with natural B{sub 4}C contents of approximately 0, 2.3, 4.6, and 9 wt%, and varying water contents achieved by baking the blocks to remove approximately 5/6 of the water. These measurements were also performed with a special mockup of the RCSB of BoroBond. material with {approx} 4.6% natural B{sub 4}C. All three methods used Cf-252 sources. This report does not describe these measurements in any detail, but presents a method of verifying and quantifying the B{sub 4}C and hydrogen content of the RCSBs at the factory, upon receipt at Y-12, and at any time later while in use at the HEUMF. The data from these measurements can be used to assess the uniformity of the BoroBond in the RCSB and be stored for future comparisons. The details of these measurements are given in ORNL/TM-2002/254.