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A Brief Description of Global Technologies Incorporated (GTI) Detection of Enriched Uranium (DEU) System for Assaying TRIGA Spent Nuclear Fuel
GTI 09-07-00
Spent Nuclear Fuel (SNF) contains a variable amount of fissionable isotopes that are important for economic reasons as well as for non-proliferation, waste storage and transportation issues. One major concern expressed by the U. S. Department of Energy (DOE) regarding the handling and storage of SNF is the verification of the U-235 enrichment declarations, especially where limited fuel irradiation information is available. A technology demonstration project for the Detection of Enrichment of Uranium (DEU), sponsored by the DOE Idaho Operations Office (DOE-ID) to address the above issues, is in progress. The purpose of the DEU measurement system is to verify declarations of U-235 enrichment for the return of the spent nuclear fuel to the U.S. Department of Energy. This project has incorporated detailed numerical modeling to develop a portable experimental measurement system (the apparatus weights about 100 lbs., with approximately 20 lbs. consisting of the neutron-counting electronics). The design was developed using the Monte Carlo N-Particle Transport Code System (MCNP4B2) to optimize the measurement performance. Oak Ridge Isotope Generation and Depletion Code (ORIGEN2) outputs are used to determine TRIGA fuel isotopic inventories that are used within MCNP4B2 to represent the burnup of the TRIGA fuel. The DEU prototype system is portable, yet is constructed to minimize any measurement bias caused by disassembly and re-assembly. The DEU measurement system uses neutron beams with different energy spectra to induce interactions in the SNF material. These neutron beams are produced with neutron filter materials coupled with an external Cf-252 neutron source. In SNF, the detected neutron signals (incorporates He-3 detectors that include a true "cutting edge" technology for performing neutron measurements in high gamma-ray fields) produced with the various neutron beams are directly proportional to the fissionable materials. Thus, SNF with unknown U-235 enrichments can be determined by comparison to calibrated measurements from known materials. The initial fuel-measurement efforts of November 15 through 19 and December 6 through 9, 1999, respectively, at the Texas A&M University (TAMU) Nuclear Science Center (NSC) have shown that the DEU P1 system is capable of performing sensitive measurements that are repeatable. Evaluations reveal an estimated DEU P1 system resolution of 1.9 grams of U-235 for 20%-enriched TRIGA fuel and a 3.9-gram U-235 resolution for 70%-enriched TRIGA fuel. (Resolution is a measure of sensitivity and should not be confused with accuracy.) Both resolutions are based upon composite measurements with a required 95% confidence level (2 standard deviations for a Gaussian distribution) and TAMU-declared U-235 values (grams). DEU measurements conducted July 17-21, 2000 at the KSU Nuclear Reactor Facility have shown that preliminary results are consistent with the TAMU results with regard to the deviation of measured from declared U-235 content. Plans are currently underway to quantify the DEU system accuracy capabilities using certified calibration standards with known U-235 content. |
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Copyright © 1999 Global Technologies Incorporated |
