Neutron irradiation embrittlement limits the service life of reactor-pressure vessels (RPV) in nuclear power plants due to the degradation of reactor materials. In order to perform at high efficiency and safely contain coolant water at temperatures around 290°C and pressures of ~7 MPa (for boiling water reactors) to 14 MPa (for pressurized water reactors), the RPV must be heavy-section steel. Due to regulations, RPV failure probabilities must be very low. To achieve sufficient safety, the design of the reactor assumes large cracks and extreme loading conditions. Under such conditions, a probable failure mode is rapid, catastrophic fracture if the vessel steel is brittle. Tough RPV base metals that are typically used are A302B, A533B plates, or A508 forgings; these are quenched and tempered, low-alloy steels with primarily tempered bainitic microstructures. Over the past few decades, RPV embrittlement has been addressed by the use of tougher steels with lower trace impurity contents, the decrease of neutron flux that the vessel is subject to, and the elimination of beltline welds. However, embrittlement remains an issue for older reactors.