Design and performance testing of a novel far field Gamma system to assay radioactive waste in 400 and 200 litre drums - 15339

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

OSTI ID:22822843

Looman, Marc R. ^[1]; Lindburg, Erik; Martin, E. Ray ^[2]; Mason, John A.; Odell, Lawrence V. ^[1]; Piotrowski, Matt ^[2]; Poundall, Adam; Towner, Antony C. N. ^[1]; Wei, Zhang ^[3]

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1. ANTECH, A. N. Technology Ltd., Unit 6, Thames Park, Wallingford, Oxfordshire, OX10 9TA (United Kingdom)
2. ANTECH Corporation, 9050 Marshall Court, Westminster, CO, 80031 (United States)
3. CNNC, China Nuclear Power Engineering CO., LTD., Radiation Monitoring Section, I and C Division, No.117, Xisanhuanbeilu, Haidian District, Beijing, 100840 (China)

A Far Field Gamma ray Measurement system has been developed for measuring and assaying both 400 and 200 litre waste drums with a wide range of activity at nuclear power stations. These include radioactive waste drums with surface dose-rates of less than 2 mSv/h (200 mrem/h) and, at the higher range of activity, 400 litre drums with surface dose-rates of up to 50 mSv/h (5 rem/h). The assay system incorporates an electro-mechanically cooled high purity Germanium profile detector and advanced digital spectroscopic analysis electronics. A novel optimised conical-trapezoidal collimator has been incorporated to reduce the effect of the radioactive background in addition to the conventional detector lead shield with tin and copper graded lining to reduce the effect of lead X-rays. Two features have been incorporated to reduce detector dead time and maintain detector resolution when measuring high activity drums. The first is the inclusion of two automated tungsten filters of different thickness as an integral part of the detector collimator. The filters are used in conjunction with an automated rail system on which the detector platform is mounted. The detector can be positioned at different distances from the drum surface in order to reduce detector dead time. The deployment of the filters and the adjustment of the drum - detector position are automatically controlled based on a user defined dose-rate limit table. The data is provided by two Geiger-Muller dose-rate detectors, which are used to measure the drum surface dose-rate. This data is subsequently used to adjust the detector position and in cases of higher dose-rate deploy one or other of the tungsten filters. The drum rotation platform incorporates a load cell to determine drum weight and hence the drum density. This information is used to calculate an attenuation correction based on the assumption of uniform drum density and uniform distribution of activity within the drum. Where the waste drums have a more complicated and known regular internal structure, such as a small radioactive region surrounded by an annulus of shielding material, the analysis algorithms incorporated into the far field geometry and attenuation correction spectroscopic data analysis code are able to make a more accurate determination of drum activity than would be possible assuming a completely uniform drum. The detector energy and efficiency calibration is achieved using a point source with multiple gamma ray energy peaks. The response of the high purity Germanium detector is also modelled using the Monte Carlo Neutron Photon code and the model is benchmarked using the measured point source calibration data. The performance of the instrument has been determined for a range of uniform density matrix drums containing a set of Eu-152 line or rod sources located in re-entrant tubes positioned on an equal volume basis. When rotated, the test drums with volume distributed line sources simulate waste drums of different density each with a uniformly distributed radioactive source. The measurements have been validated using Monte Carlo simulations. (authors)

• Research Organization: WM Symposia, Inc., PO Box 27646, 85285-7646 Tempe, AZ (United States)
• OSTI ID: 22822843
• Report Number(s): INIS-US-19-WM-15339; TRN: US19V0834067758
• Resource Relation: Conference: WM2015: Annual Waste Management Symposium, Phoenix, AZ (United States), 15-19 Mar 2015; Other Information: Country of input: France; 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
ATTENUATION
BENCHMARKS
COLLIMATORS
COMPUTERIZED SIMULATION
CONTAINERS
COPPER
DATA ANALYSIS
DEAD TIME
DENSITY MATRIX
DOSE RATES
EUROPIUM 152
FILTERS
GAMMA DETECTION
GAMMA RADIATION
GEIGER-MUELLER COUNTERS
HIGH-PURITY GE DETECTORS
LEAD
MONTE CARLO METHOD
NEUTRON TRANSPORT THEORY
NUCLEAR POWER PLANTS
PERFORMANCE TESTING
PHOTON TRANSPORT
POINT SOURCES
RADIATION DOSE UNITS
RADIOACTIVE WASTES
SHIELDING MATERIALS
SPECTROSCOPY
THICKNESS
TIN
TUNGSTEN