Exploring the reactor heat problem: Study of the beta decay of 104,105Tc using the TAS technique

The decay heat of fission products plays an important role in predictions of the heat up of nuclear fuel in reactors. The released energy is calculated as the summation of the activities of all fission products $P(t) =\sum E_i\lambda_iN_i(t)$ , where Ei is the decay energy of nuclide i, λi is the decay constant of nuclide i and Ni(t) is the number of nuclide i at cooling time t. Even though the reproduction of the measured decay heat has improved in recent years, there is still a long standing discrepancy in the t ∼1000 s cooling time for some fuels. A possible explanation to this improper description has been found in the work of Yoshida et al [1], where it has been shown that the incomplete knowledge of the β-decay of some Tc isotopes can be the source of the systematic discrepancy. Motivated by [1], we have recently measured the β-decay process of some Tc isotopes using a total absorption spectrometer at the IGISOL facility in Jyvaskyla. The results of the measurements as well as the their consequences on summation calculations are discussed.