{"id":30672,"date":"2021-07-21T12:20:29","date_gmt":"2021-07-21T12:20:29","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=30672"},"modified":"2023-09-22T05:12:50","modified_gmt":"2023-09-22T05:12:50","slug":"reactor-vessel-material-surveillance-program","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power-plant\/reactor-and-power-plant-materials\/reactor-vessel-material-surveillance-program\/","title":{"rendered":"Reactor Vessel Material Surveillance Program"},"content":{"rendered":"
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Neutrons with sufficient energy<\/strong> can disrupt materials\u2019 atomic arrangement or crystalline structure. The influence of structural damage is most significant for metals because of their relative immunity to damage by ionizing radiation. Pressurized-water reactors operate with a higher rate of neutron impacts, and their vessels tend to experience greater embrittlement than boiling-water reactor vessels. Many pressurized-water reactors design their cores to reduce the number of neutrons hitting the vessel wall, slowing the vessel\u2019s embrittlement. The NRC\u2019s regulations address embrittlement in 10 CFR Part 50, Appendix G, \u201cFracture Toughness Requirements,\u201d and Appendix H, \u201cReactor Vessel Material Surveillance Program Requirements.\u201d Since the reactor pressure vessel<\/strong> is considered irreplaceable<\/strong>, neutron irradiation embrittlement of pressure vessel steels is a key issue in the long-term assessment of structural integrity for life attainment and extension programs.<\/p>\n

Radiation damage is produced when neutrons of sufficient energy displace atoms (especially in steels at operating temperatures 260 \u2013 300\u00b0C), resulting in displacement cascades<\/strong> that produce large numbers of defects, vacancies, and interstitials. Although the inside surface of the RPV is exposed to neutrons of varying energies, the higher energy neutrons, above about 0.5 MeV<\/strong>, produce the bulk of the damage. To minimize such material degradation type and structure of the steel must be appropriately selected<\/strong>. Today it is known that the susceptibility of reactor pressure vessel steels is strongly affected (negatively) by the presence of copper, nickel, and phosphorus.<\/p>\n

\"ductile\u2013brittleAs was written, the distinction between brittleness and ductility<\/a> isn\u2019t readily apparent, especially because both ductility and brittle behavior are dependent not only on the material in question but also on the temperature<\/strong> (ductile-brittle transition) of the material. The effect of temperature on the nature of the fracture is of considerable importance, and many steels exhibit ductile fracture at elevated temperatures and brittle fracture at low temperatures<\/strong>. The temperature above which material is ductile and below which it is brittle is known as the ductile-brittle transition temperature<\/strong><\/a> (DBTT), nil ductility temperature (NDT), or nil ductility transition temperature. This temperature is not precise but varies according to prior mechanical and heat treatment and the nature and amounts of impurity elements. It can be determined by some form of drop-weight test (for example, the Charpy or Izod tests<\/strong><\/a>).<\/p>\n

To minimize neutron fluence:<\/p>\n