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Nuclear News
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introduction
Pressure-Temperature (P-T) operating curves are required to ensure safe
operation of pressure vessels. The regulations governing the
calculation of P-T curves for nuclear power plants are found in the Code of
Federal Regulations (CFR), the ASME Boiler and Pressure Vessel Code, and Nuclear
Regulatory Commission (NRC) Regulatory Guides. The fracture toughness
requirements for the pressure vessel for testing and operational conditions are
specified in Section IV of 10 CFR 50, Appendix G. This appendix requires
implementation of the acceptance and performance criteria of Appendix G to
Section III of the Code. Appendix G to 10 CFR 50 requires that the effects
of neutron irradiation on the nil ductility reference temperature of the vessel
beltline materials must be included in the P-T curve calculations.
Surveillance capsules are periodically pulled and analyzed to monitor neutron
damage to the vessel. In most cases, the P-T curves must be updated after
the capsule analysis has been completed.
P-T Curve Software
MPM has developed PT Curve™ v2.0 to perform the
calculations required to determine the allowable loadings on the reactor
pressure vessel during heat up, cool down, and leak/hydro testing. PT
Curve™ v2.0 has been Quality Assurance (QA) verified in accordance with 10 CFR
50, Appendix B under the MPM Nuclear Quality Assurance Program. The
calculations and models of PT Curve™ v2.0 are based on years of experience obtained
by MPM and the result is accurate and conservative P-T curves which have been
approved by the Nuclear Regulatory Commission (NRC) in numerous submittals.
The key features of the model are summarized below:
- Limiting adjusted nil-ductility reference
temperature in accordance with NRC Regulatory Guide 1.99
- Thermal transient heat transfer analysis to
determine thermal loads
- Instrument errors are accounted for in a
conservative manner
- If it is beneficial, Code Case N-640
(approved by ASME in 1997), which allows KIc to be used in place
of KIa as the reference fracture toughness, can be implemented
- If applicable, Code Case N-588 can be used.
This code case allows for the assumption of circumferential cracks if
considering weld metal in a circumferential weld. This code case is
beneficial to the final P-T curves primarily if the limiting material is in
a circumferential weld.
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