Document: NUREG-0800
Document ID: 26aca061-b0de-4983-bbca-3fccb00afc2f
Document Type: srp
Title: PRESSURE-TEMPERATURE LIMITS AND PRESSURIZED THERMAL SHOCK1
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070431.pdf
Revision Date: 2023-06
Chapter: 5
Section ID: 5.3.2
CFR Part: 
CFR Title: 

Content:
e RCPB and specifically the reactor vessel. The Technical Rationale for this rule is established under the Technical Rationale discussion for 10 CFR 50, Appendix G, below. 6. 10 CFR 50.61, establishes fracture toughness requirements for protection against pressurized thermal shock (PTS) events. Pressurized thermal shock events involve transients in pressurized water reactors that cause severe overcooling in conjunction with overpressurization. The thermal stresses in combination with the pressure stresses increase the potential for brittle fracture in the presence of an initiating flaw in low toughness material. This material may be present in the reactor vessel beltline where neutron radiation gradually embrittles the material over the plant lifetime. The PTS rule provides calculational methods and acceptance criteria for determining the effect of embrittlement on the reactor vessel materials and establishing the material reference temperature limits beyond which continued operation of the plant must be justified by corrective actions and plant-specific safety analyses. Establishing, monitoring and maintaining the structural integrity of the reactor vessel materials is essential in protecting against a failure of the RCPB and the subsequent loss of core cooling and fission product containment. Compliance with the requirements of 10 CFR 50.61 provides assurance that the reactor vessel materials will not be subject to failure from PTS during the life of the reactor. 7. 10 CFR 50, Appendix G, establishes that the ferritic pressure-retaining components of the RCPB meet requirements for fracture toughness during system hydrostatic tests and any condition of normal operation, including anticipated operational occurrences. Fracture toughness properties of ferritic materials increase significantly above the point referred to as the nil-ductility transition temperature. This temperature is established for the RCPB material in accordance with Section III of the ASME Code as