Impact of USA-Euratom Cooperative Dosimetry Research on NRC Regulation of Light Water Reactors

Abstract

Lifetime predictions of the safe condition of reactors, especially the reactor pressure vessel, are based on trends developed from surveillance program tests of metallurgical specimens representing the vessel steel and by analysis of neutron dosimetry detector materials. Although metallurgical characteristics have been studied in great detail since the late 1950s, only since the mid-1970s has there been a dedicated and effective program to set an accurate basis for light water reactor (LWR) neutron dosimetry. With the startup of the Nuclear Regulatory Commission (NRC) Surveillance Dosimetry Improvement Program, the joining of forces with the Euratom Working Group on Reactor Dosimetry (WGRD), and the founding of the ASTM-Euratom Symposia on Reactor Dosimetry, a significant advance of technology for prediction and measurement of neutron flux, fluence, and spectra in LWR environments was assured. The NRC has been well served by this cooperative program, in that we depend upon the improved dosimetry results as the basis upon which we gain assurance of the accuracy and reliability of submittals involving neutron flux and fluence for a range of issues that include surveillance program analysis, pressurized thermal shock, Regulatory Guide 1.99, “Radiation Embrittlement of Reactor Vessel Materials,” and most recently for core internals. Metrology of the neutron flux in power reactors has come a long way in the last decade in terms of accuracy and reliability; maintenance of that accuracy and reliability will be necessary for the future as utilities begin to apply for license renewal for an additional period of operation. Continued safe operation of nuclear power plants will be dominated by knowledge of vessel embrittlement and that, in turn, will be greatly influenced by the accuracy of neutron dosimetry.