Neutron Dosimetry for Reactor Pressure Vessel Surveillance

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Objective for MPD D.4.4

  • Sustain NIST traceable neutron dosimetry protocols for the nuclear power industry.

Background: During power operations of light-water-cooled, pressurized water nuclear power reactors, radiation-induced embrittlement will degrade certain mechanical properties important to maintaining the structural integrity of the reactor pressure vessel (RPV). Specifically, fast-neutron (E > 1 MeV) radiation-induced embrittlement of the RPV steel could lead to a compromise of the vessel integrity, under extreme conditions of temperature and pressure, through a reduction in the steel’s fracture toughness. This so-called fast-neutron embrittlement is a complex function of many factors including the neutron fluence, the neutron energy spectrum, and the chemical composition of the steel. Additional factors may also come into play, such as the neutron fluence-rate, whose effects have not been fully investigated. Because of the obvious safety implications brought about by a potential breech in the pressure vessel’s integrity, the US Nuclear Regulatory Commission (US NRC) has issued requirements designed to help ensure that the structural integrity of the reactor pressure vessel is preserved. In particular, fracture toughness requirements for power reactors, for both normal operating conditions and anticipated operational occurrences, are set forth in Title 10 of the Code of Federal Regulations, Part 50 (10 CFR 50), “Domestic Licensing of Production and Utilization Facilities.” To satisfy the codified fracture toughness requirements, 10 CFR 50 further requires that the operators of all commercial nuclear power stations institute a neutron dosimetry program that provides measurement data for material damage correlations as a function of the fast-neutron fluence. Sustaining such studies is paramount to the US interests in revitalizing the use of nuclear power.

Action Items:

1 – Maintain NIST capabilities for neutron dosimetry.

2 – Enhance NIST’s interaction with the nuclear power industry, which itself allocates substantial manpower resources to conform to NRC regulations.

Resource Requirements:

1 – With facilities and protocols in place, NIST requires a sustained commitment of a minimum of one person-year per year over the next three-year time frame.