Reactor vessel dosimetry, lessons learned

This paper summarizes the experience gained from extensive reviews of reactor dosimetry and describes preferred practices in the estimation of pressure vessel fluence as it relates to licensing actions. The applicable regulations require high confidence in the knowledge of vessel fluence which in turn defines the material properties and the range of temperature and pressure for plant operation. This paper supports the view that a suitable calculated fast neutron (E > 1.0 MeV) vessel fluence value is determined using a benchmarked computer code. The benchmarking should be supported by a qualified data base of measured to calculated fluence ratios. The same data allow the determination of any bias that may exist on the calculated values and the associated uncertainty. Potential fluence adjustments are discussed and it is concluded that fluence values determined in this manner are preferable to plant specific measurements and/or measurement adjustments that are not based on a benchmarked code. (authors)