Neutron Dosimetry Overview for WWERs

Abstract

Neutron dosimetry is a mandatory part of the monitoring of irradiation conditions within the reactor pressure vessels (RPVs) of all type of reactors, including water-water energetic reactors (WWERs). The main experimental part is connected with the surveillance specimen programs because the determination of neutron fluence in each of the surveillance specimens is required for the evaluation of radiation damage in RPV materials. Ex-vessel (cavity) neutron dosimetry is practically mandatory for all WWERs because it serves as the basis for fitting results from calculations of neutron fluence in the RPV wall. In addition, retrospective neutron dosimetry in WWER RPVs is supported by a high content (approximately 1 wt.%) of niobium in the upper layer of the austenitic cladding on the inner RPV surface. This paper describes the main principles of experimental neutron dosimetry in WWER RPVs and some specific results for different types of their units and different surveillance specimen programs. Some discussion is also held regarding different approaches for neutron fluence determination, i.e., for a differential threshold energy equal to 0.5 MeV in WWER studies.