JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
Minoru GOTO 1 , Satoshi SHIMAKAWA 1 and Takashi YASUMOTO 2
1. Japan Atomic Energy Agency, 4002, Oarai-machi, Higashi-ibaraki-gun, Ibaraki 311-1393, Japan
2. Kyushu University, 744, Motooka, Nishi-ku, Fukuoka-city 819-0395, Japan
e-mail: goto.minoru@jaea.go.jp
In the past, benchmark calculations of criticality approach for the HTTR, which is a Japanese HTGR,
were performed by research institutes in several countries, and almost all of the calculations overestimated the
excess reactivity. In Japan, the benchmark calculations performed by JAEA also resulted in overestimation.
JAEA improved the calculations by revising the geometric model and replacing the nuclear data library with
JENDL-3.3, which was the latest JENDL at that time. However, the overestimation remained and this problem
has not been resolved until today. We performed calculations of the HTTR criticality approach with several
nuclear data libraries, and found that slight difference in the capture cross section of carbon at thermal energy
among the libraries causes significant difference in the keff values. The cross section value of carbon was not
concerned in reactor neutronics calculation because of its small value of the order of 10 -3 burn, and
consequently the cross section value was not revised for a long time even in the major nuclear data libraries:
JENDL, ENDF and JEFF. We thought that the cross section value should be revised based on the latest
measurement data in order to improve the accuracy of the neutronics calculations of the HTTR. In May 2010,
the latest JENDL: JENDL-4.0 was released by JAEA, and the capture cross section of carbon was revised.
Consequently, JENDL-4.0 yielded 0.4-0.9%k smaller keff values than JENDL-3.3 in the calculation of the
HTTR critical approach, and then the problem of the overestimation of the excess reactivity in the HTTR
benchmark calculation was resolved.
1. Introduction
In the past, the neutronics calculations for the HTTR critical approach were performed
with the three major nuclear data libraries, which are JENDL-3.3 (Japan), ENDF/B-VI.8
(U.S.A) and JEFF-3.0 (Europe)[1]. As a result, JENDL-3.3 yielded the keff values which were in
better agreement with the experimental results than the other libraries. Additionally, it was
found that the discrepancies of the keff values between JENDL-3.3 and the other libraries are
mainly caused by the slight difference of the neutron capture cross section of carbon at
0.0253eV among the libraries, and we had been focusing on the accuracy of this cross section as
one of the important subjects for the improvement of the neutronics calculations for the
HTGRs.