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Report No.

Measurement of $$^{237}$$Np Fission Cross Section at YAYOI

Oki, Shigeo ; Takashima, Hideki ; Wakabayashi, Toshio; Yamaguchi, Kenji*; Yamawaki, Michio*

In the framework of the study on transmutation of minor actinide (MA) nuclides with fast reactors, the fission cross section ratio of 237Np relative to 235U has been measured by using a back-to-back (BTB) fission chamber at YAYOI fast neutron source reactor. The compact BTB fission chamber was prepared for the measurements in the experimental holes called Glory hole and Grazing hole passing though the core center and the side blanket of YAYOI, respectively. Dependence of fission cross section ratios on neutron spectrum was investigated by changing the measurement position in these experimental holes.The measured values of fission cross section ratios were compared with those calculated with the following nuclear data libraries: JENDL-3.2, ENDF/B-VI, JEF-2.2, and JENDL-2. It was found that the calculated values in the center of the core systematically overestimated the measurements by about 30%. Dispersion of the calculated values among the nuclear data libraries was smaller than the above difference from the measured value. We also see the dependence of C/E value on the measurement position. It is hardly said that uncertainty of nuclear data brings about the above overestimation of 30%.The present result remained some issues in terms of the measurement accuracy. If we can get rid of those causes, for example, by means of the unfolding technique on pulse height distribution, the result could be utilized as expletive information in nuclear data validation not only for 237Np, but also for 235U and 238U which characterize the neutron spectrum.



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