Design and testing of a combined neutron and gamma assay system for measuring fissile material in fuel and waste items - 15340

Conference · Wed Jul 01 00:00:00 EDT 2015

OSTI ID:22822844

Burke, Kevin J. ^[1]; Ancius, Darius ^[2]; Chaudry, Asam ^[1]; Gunn, Richard D. ^[3]; Looman, Marc R.; Maina, David J.; Mason, John A. ^[1]; Paton, Douglas ^[3]; Towner, Antony C. N.; Wood, Graeme H. ^[1]

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1. ANTECH, A. N. Technology Ltd., Unit 6, Thames Park, Wallingford, Oxfordshire, OX10 9TA (United Kingdom)
2. Nuclear Safeguards Directorate, DG ENER, European Commission, L-2920 Luxembourg (European Commission (EC))
3. Dounreay Site Restoration Ltd., Dounreay, by Thurso, Caithness, KW14 7TZ (United Kingdom)

A combined neutron and gamma ray assay system for the measurement of fissile material in both fuel and waste items has been designed, modelled, developed and tested. The purpose of the system is to measure and characterize a wide range of fissile materials including uranium, plutonium, americium and mixed oxide fuel arising from a variety of processes and facilities across the United Kingdom. Dounreay Site Restoration Limited at Dounreay currently stores these items form the United Kingdom Nuclear Decommissioning Authority's un-irradiated fuel inventory. This inventory comprises historic materials from ex-United Kingdom Atomic Energy Authority nuclear fuel projects and experiments together with fast reactor fuel materials and some commercial fuel items as delivered to Dounreay for recovery. The combined assay system has been designed and constructed to support the operation of a fuel processing facility, which will be operated at Dounreay to treat these historic legacy fuel materials, making them suitable for long term storage. Appropriate characterization of the fissile material is required for safety, criticality control and nuclear materials safeguards purposes prior to final disposition. The system consists of both gamma ray and neutron measurement components. The results of a neutron measurement are combined with the gamma ray isotopic ratio measurement results to generate the assay result for the fissile material being characterized. The gamma ray component of the system employs a safeguards quality high purity Germanium detector with electro-mechanical cooling and the measurements of fissile material containers are made in a shielded chamber with a tin and copper graded lining. Containers of fissile material are rotated during the gamma ray measurement and a variable automatic steel collimator aperture mechanism is employed to adjust the measured count rate to control detector dead time. Gamma ray spectra are analysed using the plutonium and uranium isotopic ratio code PC/FRAM. The gamma ray system can also be configured to perform a direct assay of small quantities of uranium bearing material. For this assay measurement a series of cadmium filters can be positioned in front of the detector to reduce the contribution from 59 keV gamma rays from Am-241. In addition to gamma ray isotopic measurements, both active and passive neutron assay is performed by the system. The neutron-measuring component consists of a thick walled cylindrical polyethylene chamber, which provides neutron moderation for 30 one-inch diameter He-3 detector tubes located in re-entrant channels in the polyethylene moderator. Two removable polyethylene-inserts incorporating lower plug assemblies are provided, one with and one without a cadmium lining. Also two top plug units are provided, again one with cadmium and one without a cadmium liner. The Neutron Subsystem can be operated both as a passive and as an active neutron coincidence counter. In both fast and thermal active neutron mode, the neutron component employs two americium-beryllium (Am-Be) alpha-n neutron sources, one positioned in the top and the other in the bottom plug unit. The neutron sources are removed when the counter is operated in passive mode. Passive neutron detection efficiency and active neutron performance has been modelled using the MCNP Monte Carlo computer simulation code as part of the design process. In the absence of fissile samples, operation of the gamma ray component of the system has been tested initially using calibrated Eu-152 and Ba-133 gamma ray sources and the use of archived spectra from fissile material measurements. Initial testing of the neutron system has employed a calibrated Cf-252 spontaneous fission neutron source. Neutron testing has been confirmed using further MCNP simulations. The results of test measurements with the system are presented and compared with the results of MCNP measurement simulations. (authors)

• Research Organization: WM Symposia, Inc., PO Box 27646, 85285-7646 Tempe, AZ (United States)
• OSTI ID: 22822844
• Report Number(s): INIS-US-19-WM-15340; TRN: US19V0835067759
• Resource Relation: Conference: WM2015: Annual Waste Management Symposium, Phoenix, AZ (United States), 15-19 Mar 2015; Other Information: Country of input: France; 9 refs.; Available online at: http://archive.wmsym.org/2015/index.html
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
AMERICIUM
AMERICIUM 241
BARIUM 133
BERYLLIUM
CADMIUM
CALIFORNIUM 252
COMPUTERIZED SIMULATION
COPPER
EUROPIUM 152
FAST REACTORS
FISSILE MATERIALS
FISSION NEUTRONS
GAMMA DETECTION
HIGH-PURITY GE DETECTORS
ISOTOPE RATIO
MATERIALS RECOVERY
MIXED OXIDE FUELS
MONTE CARLO METHOD
NEUTRON DETECTION
NEUTRON SOURCES
PLUTONIUM
POLYETHYLENES
RADIOACTIVE WASTES
REMEDIAL ACTION
SAFEGUARDS
SPONTANEOUS FISSION
UNITED KINGDOM
URANIUM