Measurement and Analysis of Capture Reaction Rate of {sup 237}Np in Various Thermal Neutron Fields by Critical Assembly and Heavy Water Thermal Neutron Facility of Kyoto University

Journal Article · Wed Nov 15 04:00:00 EST 2000 · Nuclear Science and Engineering

OSTI ID:20804673

Iwasaki, Tomohiko ^[1]; Horiuchi, Toshimitu ^[1]; Fujiwara, Daisuke ^[1]; Unesaki, Hironobu ^[2]; Shiroya, Seiji ^[2]; Hayashi, Masatoshi ^[2]; Nakamura, Hiroshi ^[2]; Kitada, Takanori ^[3]; Shinohara, Nobuo ^[4]

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1. Tohoku University (Japan)
2. Kyoto University (Japan)
3. Osaka University (Japan)
4. Japan Atomic Energy Research Institute (Japan)

Capture reaction rate ratios of {sup 237}Np relative to {sup 197}Au were measured in 11 thermal neutron fields provided by the Kyoto University Critical Assembly and the Kyoto University Reactor Heavy Water Neutron Irradiation Facility. In the measurement, both samples of {sup 237}Np and {sup 197}Au were irradiated at the same time, and their gamma activities were measured. The typical experimental error was 3.5%. The analysis was performed by three steps: full-core calculation, self-shielding correction of the sample, and perturbation correction of the sample. Three full-core calculations by a continuous-energy Monte Carlo code (MVP), a transport code (TWOTRAN), and a diffusion code (CITATION) were made with the JENDL-3.2 library. The self-shielding factors were derived by an analytical formula, and the perturbation factors were calculated by another MVP calculation. The reaction rates were derived by multiplying the neutron spectrum, the two correction factors, and the capture cross sections of {sup 237}Np and {sup 197}Au.As a result, the three full-core calculations provided almost the same neutron spectra at the sample position and gave almost the same calculated-to-experimental values (C/Es) for the capture reaction rate ratios of {sup 237}Np relative to {sup 197}Au. Based on the capture cross section of {sup 237}Np taken from the JENDL-3.2 library, the C/Es were between 0.97 and 1.04, and the average C/E among the 11 cores was 1.01. On the other hand, the C/Es using the ENDF/B-VI and the JEF-2.2 were 1.02 to 1.06 for harder spectrum cores, whereas the C/Es for the softer spectrum cores were 1.08 to 1.16. It is concluded that the JENDL-3.2 library has good accuracy for the capture cross section of {sup 237}Np but the ENDF/B-VI and the JEF-2.2 libraries overestimate that of {sup 237}Np >10% in the thermal neutron energy region.

• OSTI ID: 20804673
• Journal Information: Nuclear Science and Engineering, Journal Name: Nuclear Science and Engineering Journal Issue: 3 Vol. 136; ISSN NSENAO; ISSN 0029-5639
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACCURACY
C CODES
CAPTURE
CORRECTIONS
CROSS SECTIONS
DIFFUSION
DISTURBANCES
ERRORS
GOLD 197
HEAVY WATER
KUR REACTOR
MONTE CARLO METHOD
NEPTUNIUM 237
NEUTRON REACTIONS
NEUTRON SPECTRA
NEUTRON TRANSPORT
NUCLEAR DATA COLLECTIONS
NUCLEAR REACTION KINETICS
SELF-SHIELDING
T CODES
THERMAL NEUTRONS
ZERO POWER REACTORS