Applications of the total absorption technique to improve reactor decay heat calculations: study of the beta decay of {sup 102,104,105}Tc

The decay heat of the fission products plays an important role in predicting the heat-up of nuclear fuel after reactor shutdown. This form of energy release is calculated as the sum of the energy-weighted activities of all fission products P(t) = {sigma}E{sub i}{lambda}{sub i}N{sub i}(t), where E{sub i} is the decay energy of nuclide i(gamma and beta component), {lambda}{sub i} is the decay constant of nuclide i and N{sub i}(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 at t{approx}1000 s cooling time for some fuels. A possible explanation for this disagreement can been found in the work of Yoshida et al., who demonstrated that an incomplete knowledge of the {beta}-decay of some Tc isotopes could be the source of the systematic discrepancy. We have recently measured the {beta}-decay process of some Tc isotopes using a total absorption spectrometer at the IGISOL facility in Jyvaeskylae. The results of the measurements are discussed, along with their impact on summation calculations.