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Brittle  Fracture  Summary
Figure 4   PCS Temperature vs. Pressure for Normal Operation

Material Science Volume 2 of 2
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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







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