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Figure 2 Heatup Stress Profile |
PRESSURIZED THERMAL SHOCK
DOE-HDBK-1017/2-93
Thermal Shock
PRESSURIZED THERMAL SHOCK
Personnel need to be aware how pressure combined with thermal stress can cause
failure of plant materials. This chapter addresses thermal shock (stress) with
pressure excursions.
EO 1.6
DEFINE the term pressurized thermal shock.
EO 1.7
STATE how the pressure in a closed system effects the severity
of thermal shock.
EO 1.8
LIST the four plant transients that have the greatest potential
for causing thermal shock.
EO 1.9
STATE the three locations in a reactor system that are of
primary concern for thermal shock.
Definition
One safety issue that is a long-term problem brought on by the aging of nuclear facilities is
pressurized thermal shock (PTS). PTS is the shock experienced by a thick-walled vessel due to
the combined stresses from a rapid temperature and/or pressure change. Nonuniform temperature
distribution and subsequent differential expansion and contraction are the causes of the stresses
involved. As the facilities get older in terms of full power operating years, the neutron radiation
causes a change in the ductility of the vessel material, making it more susceptible to
embrittlement. Thus, if an older reactor vessel is cooled rapidly at high pressure, the potential
for failure by cracking increases greatly.
Evaluating Effects of PTS
Changes from one steady-state temperature or pressure to another are of interest for evaluating
the effects of PTS on the reactor vessel integrity. This is especially true with the changes
involved in a rapid cooldown of the reactor system, which causes thermal shock to the reactor
vessel. These changes are called transients. Pressure in the reactor system raises the severity
of the thermal shock due to the addition of stress from pressure. Transients, which combine high
system pressure and a severe thermal shock, are potentially more dangerous due to the added
effect of the tensile stresses on the inside of the reactor vessel wall. In addition, the material
toughness of the reactor vessel is reduced as the temperature rapidly decreases.
MS-03
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