Pressurized thermal shock

The pressurized thermal shock (PTS) problem has been for a long time under scrutiny by the safety specialists. In practice, in case of accident (e.g. a LOCA), a quick refrigeration of the primary water (and therefore of the vessel wall) takes place, either because of the depressurization following the accident or because of the emergency cold water injection. Under these conditions, the presence of cracks in some areas of the vessel (e.g. near the inlet nozzles of the vessel itself), combined with inadequate ductility of the material, might create critical situations from the structural point of view (unstable crack propagation). 

The study of this phenomenon has entailed the in-depth examination of thermal-hydraulic aspects (vortices in the vessel and the mixing of injected 

This issue was addressed in the USA with the emission of a specific rule (Fed Reg, 1983) which requires an accurate analysis of the situation and improvement provisions (reduction of the neutron flux, and so on) in cases where it is envisaged to exceed, during the plant life, a specific value of the Reference Temperature (RTPTS) in the material, defined by the rule itself. 

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Selby, D. L. et al Pressurized Thermal Shock Evaluation of Calvert Cliffs Unit 1 Nuclear Plant, September 1985. 

Loss of coolant accidents (LOCAs) as initiators of pressurized thermal shock (PTS). 

Another important project is the pressurized thermal shocks (PTS). Different cases of involving a break of main steam header (MSH) and steamlines, both at nominal power and at zero power were analysed. 

Safety analysis of shutdown states for the Loviisa reactors has been started with analysis of leaks and transient cases during hot and cold shutdown modes. Earlier safety related studies analysed boron dilution events and pressurized thermal shock at low power conditions. 

Pressurized thermal shock analysis for the reactor vessel ... 

Code of Federal Regulations, Title 10, Part 50, Section 50.60, "Acceptance Criteria for Fracture Prevention Measures for Normal Operation" and Section 50.61, "Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock."... 

Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock... 

Fracture toughness requirements for protection against pressurized thermal shock are defined in 10 CFR Part 50,61, These requirements should be reviewed for applicability if applicable, they provide the basis for ensuring the integrity of the reactor vessel for pressurized thermal shock conditions,... 

AR424 1.154 Format and content of plant-spediic pressurized thermal shock safety analysis reports for... 

The heat strengthening process offers improvements in all of the environmental loads that most containers are exposed to loads like internal pressure, thermal shock, vertical load, drop and impact. In addition, we have discovered through cooperation with SSV that the residual compression stress layer also resists scuffing and improves the durability of the surface, which adds further benefit for the use of thermal strengthening in the returnable container markets. 

NRC (2010a), TitlelO Code of Federal Regulations, Part 50.61 (10 CFR 50.61), Eracture toughness requirements for protection against pressurized thermal shock events, US Nuclear Regulatory Commission, Washington, DC. 

Irradiation embrittlement in RPVs mainly results in two consequences. First, it narrows the pressure-temperature operation window for normal operating conditions. Second, it limits RPV lifetime as the transition temperature of RPV materials cannot be higher than that determined from the pressurized thermal shock (PTS) calculations. Several mitigation measures can be applied to decrease radiation embrittlement of RPV beltline materials ... 

IAEA (2010b), Pressurized thermal shock in nuclear power plants good practices for assessment deterministic evaluation for the integrity of reactor pressure vessel, IAEA TECDOC 1627, International Atomic Energy Agency, Vienna. 

The US NRC was developing the Pressurized Thermal Shock (PTS) Rule at the same time that Revision 2 of Regulatory Guide 1.99 was being revised. The original PTS Rule was based on an intermediate embrittlement correlation on a slightly smaller database before Revision 2 of the... 

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