JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
33. Improvement of FP Decay Heat Calculation by Introducing TAGS Data
. Gamma-Ray Energy Spectra.
Hideo TAJIMA , Tadashi YOSHIDA
Tokyo City University
Tamazutumi 1-28-1, Setagaya-ku, Tokyo 158-8557, Japan
e-mail: g1081008@tcu.ac.jp
Sample-irradiation measurements and summation calculations of FP decay-heat still
disagree each other without a theoretical correction which was introduced in the JNDC FP
Decay Data Library long before. This disagreement is caused by the pandemonium problem
in the FP decay-data, on which the calculations are based. The pandemonium problem
comes from the limitation of the current method of constructing the decay schemes of
short-lived nuclides. Recently a series of new TAGS measurements was initiated by a
European group. In the mean time, we plan to include these new TAGS data into JENDL to
exclude the pandemonium problem without the theoretical correction. This procedure needs
not only the average energies but also the energy spectra of the -rays and the-particles.
The TAGS data, however, provides us only with the -feedings into energy-bins. So we
have to estimate the energy spectra with the aid of theoretical consideration along with the
TAGS results. For this purpose, we calculate the energy spectrum of the -ray on the basis
of the -feedings obtained by TAGS.
1. Introduction
Currently summation calculations are used widely for predicting the fission product (FP)
decay heat from a reactor core or a spent fuel. This method is based on summing up all the
recoverable energy contributions from all the individual FPs undergoing -decay and the
subsequent -transitions. This method, then, requires the average -ray and the -ray
energies (E and E) per -decay. Neutrino plays no role in this context because of its
absolute insensibility to the surrounding materials. The total absorption gamma-ray
spectrometer (TAGS) method is one of the best ways to know these average energies. This
method enables us to obtain the average energies of the-ray and the -particles per decay
without any bias and to solve the pandemonium problem. The pandemonium problem is
essentially the absence of our knowledge about the -feedings to the highly excited states of
the daughter nuclides. This problem is caused by the limitation of the current method for