Verification of plutonium content in spent fuel assemblies using neutron self-interrogation
- Los Alamos National Laboratory
The large amounts of plutonium in reactor spent fuel assemblies has led to increased research directed toward the measurement of the plutonium for safeguards verification. The high levels of fission product gamma-ray activity and curium neutron backgrounds have made the plutonium measurement difficult. We have developed a new technique that can directly measure both the {sup 235}U concentration and the plutonium fissile concentration using the intrinsic neutron emission fronl the curium in the fuel assembly. The passive neutron albedo reactivity (PNAR) method has been described previously where the curium neutrons are moderated in the surrounding water and reflect back into the fuel assembly to induce fissions in the fissile material in the assembly. The cadmium (Cd) ratio is used to separate the spontaneous fission source neutrons from the reflected thermal neutron fission reactions. This method can measure the sum of the {sup 235}U and the plutonium fissile mass, but not the separate components. Our new differential die-away self-interrogation method (DDSI) can be used to separate the {sup 235}U from the {sup 239}Pu. The method has been applied to both fuel rods and full assemblies. For fuel rods the epi-thermal neutron reflection method filters the reflected neutrons through thin Cd filters so that the reflected neutrons are from the epi-cadmium energy region. The neutron fission energy response in the epi-cadmium region is distinctly different for {sup 235}U and {sup 239}Pu. We are able to measure the difference between {sup 235}U and {sup 239}Pu by sampling the neutron induced fission rate as a function of time and multiplicity after the initial fission neutron is detected. We measure the neutron fission rate using list-mode data collection that stores the time correlations between all of the counts. The computer software can select from the data base the time correlations that include singles, doubles, and triples. The die-away time for the doubles distribution is distinctly different for {sup 235}U and {sup 239}Pu. The {sup 239}Pu has a higher fission cross-section in the epi-cadmium neutron region and larger induced fission moments than {sup 235}U, so the measured die-away time can provide the relative amounts of {sup 239}Pu and {sup 235}U. This paper will present the Monte Carlo simulations for the detector and sample configurations for both fuel pins and full fuel assemblies.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC52-06NA25396
- OSTI ID:
- 989835
- Report Number(s):
- LA-UR-09-03715; LA-UR-09-3715; TRN: US1007166
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION
ALBEDO
CADMIUM
CURIUM
FISSILE MATERIALS
FISSION
FISSION NEUTRONS
FISSION PRODUCTS
FUEL ASSEMBLIES
FUEL PINS
FUEL RODS
NEUTRON EMISSION
NEUTRONS
PLUTONIUM
REFLECTION
SAFEGUARDS
SAMPLING
SPENT FUELS
SPONTANEOUS FISSION
THERMAL NEUTRONS
VERIFICATION