Estimates of decay heat can only be calculated with confidence if the neutron cross sections, fission yields and radionuclidic decay data are known with confidence, and extensive data libraries have been assembled at both the national and international levels in an agreed format (ENDF-6) to achieve this objective. All data in these libraries are subjected to comprehensive checking procedures and some form of validation before they are released for general use. Their adoption in decay-heat calculations has shown measurement-based files to be inadequate, and therefore efforts continue to improve and extend their contents (particularly isomeric fission yields and the decay data of short-lived fission products), as requested by users.

Systematic fitting procedures, gross energy measurements and theoretical data have played important roles in addressing the problem of non-existent (unmeasured) fission-yield and decay data. Along with evaluations of measured discrete data, these approaches will continue to be used in order to extend the contents of the data libraries, and so improve decay-heat calculations and increase operational confidence in the results.

Acknowledgments

The author wishes to thank the following for their assistance in formulating specific features of this article:

C. J. Dean (AEA Technology, Winfrith),

M. A. Kellett (NEA Data Bank),

M. Lammer (IAEA Nuclear Data Section),

F. Storrer (CEN Cadarache),

E. B. Webster (AEA Technology, Winfrith).

cooling time t (s)

References