DOE-HDBK-1017/2-93
Brittle Fracture
MINIMUM PRESSURIZATION-TEMPERATURE CURVES
MINIMUM PRESSURIZATION-TEMPERATURE CURVES
Plant operations are effected by the minimum pressurization-temperature curves.
Personnel need to understand the information that is associated with the curves
to better operate the plant.
EO 1.8
STATE the two bases used for developing a minimum
pressurization-temperature curve.
EO 1.9
EXPLAIN a typical minimum pressure-temperature curve
including:
a.
Location of safe operating region
b.
The way the curve will shift due to irradiation
EO 1.10
LIST the normal actions taken, in sequence, if the minimum
pressurization-temperature curve is exceeded during critical
operations.
EO 1.11
STATE the precaution for hydrostatic testing.
M PT Definition and Basis
Minimum pressurization-temperature (MPT) curves specify the temperature and pressure
limitations for reactor plant operation. They are based on reactor vessel and head stress
limitations and the need to preclude reactor vessel and head brittle fracture. Figure 4 shows some
pressure-temperature operating curves for a pressurized water reactor (PWR) Primary Coolant
System (PCS).
Note that the safe operating region is to the right of the reactor vessel MPT curve. The reactor
vessel MPT curve ensures adequate operating margin away from the crack arrest curve discussed
above. The curves used by operations also incorporate instrument error to ensure adequate safety
margin. Because of the embrittling effects of neutron irradiation, the MPT curve will shift to the
right over core life to account for the increased brittleness or decreased ductility. Figure 4 also
contains pressurizer and steam generator operating curves. Operating curves may also include
surge line and primary coolant pump operating limitations. The MPT relief valve setting prevents
exceeding the NDT limit for pressure when the PCS is cold and is set below the lowest limit of
the reactor vessel MPT curve.
Rev. 0
Page 7
MS-04
