JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
34.
Improvements of FP Decay Heat Summation Calculations by Introducing TAGS Data
II. Priority Proposal for Future Measurements
Takayuki ARAI and Tadashi YOSHIDA
Tokyo City University, Tamazutsumi 1-28-1, Setagaya-ku, 158-8557 Tokyo, Japan
E-mail: g1181002@tcu.ac.jp
Summation calculations of fission-product (FP) decay heat for U-235, which do not agree
well with sample-irradiation measurements, suffer from the pandemonium-problem. Decay
data taken by a total absorption gamma-ray spectrometer (TAGS) is expected to be free from
this problem. Therefore TAGS is, at least at present, an ideal source of the FP decay data to
be used for calculating the mean-ray and -ray energies of individual FP nuclides, and it can
solve the discrepancy between calculations and measurements in the FP decay heat
calculations. Here we propose a list of nuclides to be measured in the future TAGS program
focusing our attention on the improvement of the decay heat summation calculation for
U-235.
1. Introduction
The FP decay-heat summation calculations without any theoretical correction do not
reproduce well the sample-irradiation measurements for U-235 [1]. This is because the
decay-data of the individual FP nuclides contributing much to the U-235 decay-heat suffer
from the pandemonium-problem. The pandemonium-problem is caused by missing
-feedings to the high energy regions of the daughter nuclides in the current decay schemes.
As a result, the mean -ray energy per decay (E) is overvalued and the mean -ray energy
(E) is undervalued. This leads to the failure of the summation calculations [2]. In the case
of JENDL of Japan and ENDF/B-VI of America, the gross theory of beta decay was introduced
for supplementing the calculation of E and E in order to cope with the
pandemonium-problem and, then, they lead to a good agreement between the calculations
and the measurements. On the other hand, JEFF of Europe dose not introduce any
theoretical correction for the decay data for the summation calculations. Therefore, the
overvaluation of E and the undervaluation of E are clearly identified in JEFF, which
explicitly demonstrate the presence of the pandemonium-problem as a result. The latest
calculation based on ENDF/B-VII does not agree with the sample-irradiation measurements