DOE-HDBK-1017/2-93Brittle FractureMINIMUM PRESSURIZATION-TEMPERATURE CURVESMINIMUM PRESSURIZATION-TEMPERATURE CURVESPlant operations are effected by the minimum pressurization-temperature curves.Personnel need to understand the information that is associated with the curvesto better operate the plant.EO 1.8STATE the two bases used for developing a minimumpressurization-temperature curve.EO 1.9EXPLAIN a typical minimum pressure-temperature curveincluding:a.Location of safe operating regionb.The way the curve will shift due to irradiationEO 1.10LIST the normal actions taken, in sequence, if the minimumpressurization-temperature curve is exceeded during criticaloperations.EO 1.11STATE the precaution for hydrostatic testing.MPTDefinitionand BasisMinimum pressurization-temperature(MPT) curvesspecify the temperature and pressurelimitations for reactor plant operation. They are based on reactor vessel and head stresslimitations and the need to preclude reactor vessel and head brittle fracture. Figure 4 shows somepressure-temperature operating curves for a pressurized water reactor (PWR) Primary CoolantSystem (PCS).Note that the safe operating region is to the right of the reactor vessel MPT curve. The reactorvessel MPT curve ensures adequate operating margin away from the crack arrest curve discussedabove. The curves used by operations also incorporate instrument error to ensure adequate safetymargin. Because of the embrittling effects of neutron irradiation, the MPT curve will shift to theright over core life to account for the increased brittleness or decreased ductility. Figure 4 alsocontains pressurizer and steam generator operating curves. Operating curves may also includesurge line and primary coolant pump operating limitations. The MPT relief valve setting preventsexceeding the NDT limit for pressure when the PCS is cold and is set below the lowest limit ofthe reactor vessel MPT curve.Rev. 0Page 7MS-04
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