JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
in the same way as JEFF. This is because the authors of ENDF/B-VII do not introduce any
theoretical correction to their library. They have changed their attitude against the
pandemonium-problem at the time when they moved from ENDF/B-VI to ENDF/B-VII.
Here we propose a list of nuclides to be measured in the future TAGS program focusing our
attention on the U-235 decay heat. It is necessary to revalue the mean - and the -ray
energies against the influence of pandemonium-problem for the better agreement between the
summation calculations and the sample-irradiation measurements without introducing the
theoretical correction.
2. TAGS Activities
The total absorption gamma-ray spectrometer (TAGS) consists of an isotope separator, a
tape transport system, and a large NaI(Tl) scintillation detector. The TAGS system is
expected to be free from the pandemonium-problem. Therefore, TAGS enable us to obtain the
correct mean - and -ray energies (E, E) for the important individual FP nuclides.
In the early 1990’s, R. C. Greenwood et al of Idaho Nuclear Laboratory (INL) started a
series of TAGS measurements and, later, their results were published for 48 FP nuclides
(INL/TAGS) [3]. These data, however, had not been introduced into the decay heat
summation calculations for many years. Anyway, the relation between the failure of the
summation-calculation and the pandemonium-problem were not known. Yoshida et al.
suggested the relation between them [2] and Hagura et al. tried to introduce the INL/TAGS
data into the summation calculations [4]. These studies showed that decay-heat summation
calculations will agree well with the sample-irradiation measurement by introducing TAGS
data appropriately.
In the late 1990’s, INL had completed their TAGS activity. A new series of the TAGS
measurements, however, is now going on by A. Algora et al (Universitat De Valencia of Spain)
at an ion-source of University of Jyväskylä of Finland (UDV/TAGS) [5]. Table.1 shows a
comparison of the UDV/TAGS and ENDF/B-VII where no theoretical correction is applied,
and shows that these nuclides largely suffer from the pandemonium-problem. These
nuclides were selected in order to improve the decay-heat calculation especially for Pu-239 by
Subgroup 25 of WPEC [6]. Fig.1 shows the comparison of decay-heat summation calculation
of Pu-239 before and after introducing the UDV/TAGS. This study shows clearly that TAGS
measurements enable us to solve the pandemonium-problem [1].