Measurement of neutron and gamma-ray noise in large subcritical condition for criticality safety - 14485

Conference · Tue Sep 15 04:00:00 EDT 2015

OSTI ID:23100907

Misawa, Tsuyoshi; Takahashi, Yoshiyuki ^[1]

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1. Research Reactor Institute, Kyoto University Kumatori, Osaka 590-0494 (Japan)

Various experimental methods have been proposed for subcriticality measurement and neutron noise analysis method is one of important experimental techniques for this purpose. The variance to mean value method, called Feynman-alpha method, is one of well-known noise analysis methods. In this method, variation of neutron count rate distribution from the Poisson distribution caused by fission chain reactions, which is called Y-value, is measured, however, it is difficult to measure the Y-value in large subcritical state such as nuclear fuel facility, because number of emitted neutrons by fission chain reaction is small, which causes large statistical error. We developed new experimental technique based on Feynman-alpha method combined with pulsed neutron source, called Delayed Neutron Noise Analysis (DNNA) method, to monitor the change of subcriticality. In this new method, neutron and gamma-ray counts measured only appeared in the delayed neutron region after injection of pulsed neutron are analyzed, and the prompt neutron region is completely ignored. The advantage of DNNA compared with conventional method is that spatial dependency of detector positions on measured results can be greatly decreased, which result in increase of accuracy of measured subcriticality. The validity of the DNNA method was experimentally investigated in the Kyoto University Critical Assembly (KUCA) at Kyoto University Research Reactor Institute. In the experiments, pulsed neutrons by D-T reactions are injected into the core and we used {sup 3}He detectors to measure neutron noise signals and BGO scintillation detectors to measure gamma-ray noise signals, and all data in the delayed neutron region were analyzed based on Feynman-alpha method. From the experimental results, it was found that the Y-values are clearly larger than zero in the case of existence of fuel assemblies and this method can be applied to detection of hidden special nuclear materials for example in a cargo container. (authors)

• Research Organization: American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
• OSTI ID: 23100907
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACCURACY
CHAIN REACTIONS
COUNTING RATES
CRITICALITY
DELAYED NEUTRONS
DETECTION
FUEL ASSEMBLIES
GAMMA RADIATION
HELIUM 3
NEUTRON SOURCES
NOISE
NUCLEAR FUELS
PROMPT NEUTRONS
RESEARCH REACTORS
SAFETY
SCINTILLATION COUNTERS
SIGNALS
ZERO POWER REACTORS