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Title: A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation

Abstract

The purpose of this paper is to provide a solution to a decades old safeguards problem in the verification of the fissile concentration in fresh light water reactor (LWR) fuel assemblies. The problem is that the burnable poison (e.g. Gd 2O 3) addition to the fuel rods decreases the active neutron assay for the fuel assemblies. This paper presents a new innovative method for the verification of the 235U linear mass density in fresh LEU fuel assemblies that is insensitive to the burnable poison content. The technique makes use of the 238U atoms in the fuel rods to self-interrogate the 235U mass. The innovation for the new approach is that the 238U spontaneous fission (SF) neutrons from the rods induces fission reactions (IF) in the 235U that are time correlated with the SF source neutrons. Thus, the coincidence gate counting rate benefits from both the nu-bar of the 238U SF (2.07) and the 235U IF (2.44) for a fraction of the IF reactions. Whereas, the 238U SF background has no time-correlation boost. The higher the detection efficiency, the higher the correlated boost because background neutron counts from the SF are being converted to signal doubles. This time-correlation in the IFmore » signal increases signal/background ratio that provides a good precision for the net signal from the 235U mass. The hard neutron energy spectrum makes the technique insensitive to the burnable poison loading where a Cd or Gd liner on the detector walls is used to prevent thermal-neutron reflection back into the fuel assembly from the detector. Here, we have named the system the fast-neutron passive collar (FNPC).« less

Authors:
 [1];  [1]; ORCiD logo [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1402652
Report Number(s):
LA-UR-17-27908
Journal ID: ISSN 0168-9002; TRN: US1703245
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
Additional Journal Information:
Journal Volume: 877; Journal Issue: C; Journal ID: ISSN 0168-9002
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; Fast neutrons; Reactor fuel assemblies; Passive neutron assay; Neutron collar

Citation Formats

Menlove, Howard Olsen, Belian, Anthony P., Geist, William H., and Rael, Carlos D.. A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation. United States: N. p., 2017. Web. doi:10.1016/j.nima.2017.09.038.
Menlove, Howard Olsen, Belian, Anthony P., Geist, William H., & Rael, Carlos D.. A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation. United States. doi:10.1016/j.nima.2017.09.038.
Menlove, Howard Olsen, Belian, Anthony P., Geist, William H., and Rael, Carlos D.. Sat . "A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation". United States. doi:10.1016/j.nima.2017.09.038.
@article{osti_1402652,
title = {A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation},
author = {Menlove, Howard Olsen and Belian, Anthony P. and Geist, William H. and Rael, Carlos D.},
abstractNote = {The purpose of this paper is to provide a solution to a decades old safeguards problem in the verification of the fissile concentration in fresh light water reactor (LWR) fuel assemblies. The problem is that the burnable poison (e.g. Gd2O3) addition to the fuel rods decreases the active neutron assay for the fuel assemblies. This paper presents a new innovative method for the verification of the 235U linear mass density in fresh LEU fuel assemblies that is insensitive to the burnable poison content. The technique makes use of the 238U atoms in the fuel rods to self-interrogate the 235U mass. The innovation for the new approach is that the 238U spontaneous fission (SF) neutrons from the rods induces fission reactions (IF) in the 235U that are time correlated with the SF source neutrons. Thus, the coincidence gate counting rate benefits from both the nu-bar of the 238U SF (2.07) and the 235U IF (2.44) for a fraction of the IF reactions. Whereas, the 238U SF background has no time-correlation boost. The higher the detection efficiency, the higher the correlated boost because background neutron counts from the SF are being converted to signal doubles. This time-correlation in the IF signal increases signal/background ratio that provides a good precision for the net signal from the 235U mass. The hard neutron energy spectrum makes the technique insensitive to the burnable poison loading where a Cd or Gd liner on the detector walls is used to prevent thermal-neutron reflection back into the fuel assembly from the detector. Here, we have named the system the fast-neutron passive collar (FNPC).},
doi = {10.1016/j.nima.2017.09.038},
journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
number = C,
volume = 877,
place = {United States},
year = {Sat Oct 07 00:00:00 EDT 2017},
month = {Sat Oct 07 00:00:00 EDT 2017}
}

Journal Article:
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