Decay heat summation calculations using UKFPDD-2

Decay heat summation calculations for 235U, 239Pu and 241Pu have been made with the revised fission product decay data file UKFPDD-2. The results obtained were found to give better agreement with the corresponding experimental results at short cooling times than those obtained with UKFPDD-1. A notable feature of the UKFPDD-2 results is the similarity in 'shape' between them and the corresponding experimental values at short cooling times although there is often a difference in their magnitude. Use of a revised set of fission yield data was also found to produce some improvement in the decay heat estimates. UKFPDD-2 total decay heat estimates for infinite irradiation of 235U, 239Pu and 241Pu were found to differ by only a few per cent, for cooling times of 5-50 seconds, from the corresponding results obtained with UKFPDD-1. However, for cooling times greater than 10 seconds, over 90% of the decay heat calculated with UKFPDD-2 is due to nuclides with known decay schemes. Hence, these results are more complete in terms of the calculated spectral distribution. From the decay heat comparisons discussed, it is implied that some of the reported experimental results may be subject to normalisation errors. (U.K.)