Simulations of a PSD Plastic Neutron Collar for Assaying Fresh Fuel

Technical Report · Tue Nov 01 00:00:00 EDT 2016

DOI:https://doi.org/10.2172/1339396· OSTI ID:1339396

Hausladen, Paul ^[1]; Newby, Jason ^[1]; McElroy, Robert Dennis ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

The potential performance of a notional active coincidence collar for assaying uranium fuel based on segmented detectors constructed from the new PSD plastic fast organic scintillator with pulse shape discrimination capability was investigated in simulation. Like the International Atomic Energy Agency's present Uranium Neutron Collar for LEU (UNCL), the PSD plastic collar would also function by stimulating fission in the ²³⁵U content of the fuel with a moderated ²⁴¹Am/Li neutron source and detecting instances of induced fission via neutron coincidence counting. In contrast to the moderated detectors of the UNCL, the fast time scale of detection in the scintillator eliminates statistical errors due to accidental coincidences that limit the performance of the UNCL. However, the potential to detect a single neutron multiple times historically has been one of the properties of organic scintillator detectors that has prevented their adoption for international safeguards applications. Consequently, as part of the analysis of simulated data, a method was developed by which true neutron-neutron coincidences can be distinguished from inter-detector scatter that takes advantage of the position and timing resolution of segmented detectors. Then, the performance of the notional simulated coincidence collar was evaluated for assaying a variety of fresh fuels, including some containing burnable poisons and partial defects. In these simulations, particular attention was paid to the analysis of fast mode measurements. In fast mode, a Cd liner is placed inside the collar to shield the fuel from the interrogating source and detector moderators, thereby eliminating the thermal neutron flux that is most sensitive to the presence of burnable poisons that are ubiquitous in modern nuclear fuels. The simulations indicate that the predicted precision of fast mode measurements is similar to what can be achieved by the present UNCL in thermal mode. For example, the statistical accuracy of a ten-minute measurement of fission coincidences collected in fast mode will be approximately 1% for most fuels of interest, yielding a ~1.4% error after subtraction of a five minute measurement of the spontaneous fissions from ²³⁸U in the fuel, a ~2% error in analyzed linear density after accounting for the slope of the calibration curve, and a ~2.9% total error after addition of an assumed systematic error of 2%.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1339396
• Report Number(s): ORNL/TM-2016/680; TRN: US1701468
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION
NUCLEAR FUELS
FAST FISSION
BURNABLE POISONS
SIMULATION
URANIUM
AMERICIUM 241
LITHIUM
PULSE DISCRIMINATION
URANIUM 235
NEUTRON SOURCES
PLASTIC SCINTILLATION DETECTORS
PERFORMANCE
FISSION NEUTRONS
COINCIDENCE METHODS
ACCURACY
CALIBRATION
DEFECTS
LINERS
SAFEGUARDS
SHIELDS
ACTIVATION ANALYSIS