PRESSURIZED THERMAL SHOCKDOE-HDBK-1017/2-93Thermal ShockPRESSURIZED THERMAL SHOCKPersonnel need to be aware how pressure combined with thermal stress can causefailure of plant materials. This chapter addresses thermal shock (stress) withpressure excursions.EO 1.6DEFINE the term pressurized thermal shock.EO 1.7STATE how the pressure in a closed system effects the severityof thermal shock.EO 1.8LIST the four plant transients that have the greatest potentialfor causing thermal shock.EO 1.9STATE the three locations in a reactor system that are ofprimary concern for thermal shock.DefinitionOne safety issue that is a long-term problem brought on by the aging of nuclear facilities ispressurized thermal shock(PTS). PTS is the shock experienced by a thick-walled vessel due tothe combined stresses from a rapid temperature and/or pressure change. Nonuniform temperaturedistribution and subsequent differential expansion and contraction are the causes of the stressesinvolved. As the facilities get older in terms of full power operating years, the neutron radiationcauses a change in the ductility of the vessel material, making it more susceptible toembrittlement. Thus, if an older reactor vessel is cooled rapidly at high pressure, the potentialfor failure by cracking increases greatly.EvaluatingEffectsof PTSChanges from one steady-state temperature or pressure to another are of interest for evaluatingthe effects of PTS on the reactor vessel integrity. This is especially true with the changesinvolved in a rapid cooldown of the reactor system, which causes thermal shock to the reactorvessel. These changes are called transients. Pressure in the reactor system raises the severityof the thermal shock due to the addition of stress from pressure. Transients, which combine highsystem pressure and a severe thermal shock, are potentially more dangerous due to the addedeffect of the tensile stresses on the inside of the reactor vessel wall. In addition, the materialtoughness of the reactor vessel is reduced as the temperature rapidly decreases.MS-03Page 6Rev. 0
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business