Source: http://thefederalregister.com/2002/02/13/02-3507.html
Timestamp: 2018-09-25 05:16:32
Document Index: 158400381

Matched Legal Cases: ['art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50']

Federal Register | PPL Susquehanna, LLC, Allegheny Electric Cooperative, Inc., S
PPL Susquehanna, LLC, Allegheny Electric Cooperative, Inc., Susquehanna Steam Electric Station, Units 1 and 2; Exemption1.0Background
Title 10 of theCode of Federal Regulations(10 CFR), part 50, Section 50.60(a), requires nuclear power reactors to meet the fracture toughness requirements set forth in 10 CFR part 50, Appendix G. Appendix G of 10 CFR part 50 requires that pressure-temperature (P-T) limits be established for reactor pressure vessels (RPVs) during normal operating and hydrostatic or leak rate testing conditions. Specifically, 10 CFR part 50, Appendix G, states that "[t]he appropriate requirements on * * * the pressure-temperature limits and minimum permissible temperature must be met for all conditions." Appendix G of 10 CFR part 50 specifies that the requirements for these limits are the American Society of Mechanical Engineers (ASME) Code, Section XI, Appendix G, limits.
To address provisions of amendments to the technical specification (TS) P-T limits in the submittal dated July 17, 2001, as supplemented July 26 and October 15, 2001, the licensee requested, pursuant to 10 CFR part 50, section 50.60(b), that the NRC staff exempt SSES-1 and 2, from application of specific requirements of 10 CFR part 50, section 50.60(a), and Appendix G, and substitute use of ASME Code Case N-640 as the basis for establishing the P-T limit curves. Code Case N-640 permits the use of an alternate reference fracture toughness (Klcfracture toughness curve instead of Klafracture toughness curve) for reactor vessel materials in determining the P-T limits. Because use of the Klcfracture toughness curve results in the calculation of less conservative P-T limits than the methodology currently required by 10 CFR part 50, Appendix G, an exemption to apply the Code Case would be required by 10 CFR 50.60.
The licensee proposed to revise the P-T limits for SSES-1 and 2, using the Klcfracture toughness curve, in lieu of the Klafracture toughness curve, as the lower bound for fracture toughness.
Use of the Klccurve in determining the lower bound fracture toughness in the development of P-T operating limit curves is more technically correct than the Klacurve because the rate of loading during a heatup or cooldown is slow and is more representative of a static condition than a dynamic condition. The Klccurve appropriately implements the use of static initiation fracture toughness behavior to evaluate the controlled heatup and cooldown process of a reactor vessel. The staff has required use of the initial conservatism of the Klacurve since 1974 when the curve was codified. This initial conservatism was necessary due to the limited knowledge of RPV materials. Since 1974, additional knowledge has been gained about RPV materials, which demonstrates that the lower bound on fracture toughness provided by the Klacurve is well beyond the margin of safety required to protect the public health and safety from potential RPV failure. Additionally, P-T curves based on the Klccurve will enhance overall plant safety by opening the operating window, with the greatest safety benefit in the region of low-temperature operations.
In summary, the ASME Section XI, Appendix G, procedure was conservatively developed based on the level of knowledge existing in 1974 concerning RPV materials and the estimated effects of operation. Since 1974, the level of knowledge about these topics has been greatly expanded. The NRC staff concurs that this increased knowledge permits relaxation of the ASME Section XI, Appendix G requirements by applying the Klcfracture toughness, as permitted by Code Case N-640, while maintaining, pursuant to 10 CFR 50.12(a)(2)(ii), the underlying purpose of the ASME Code and the NRC regulations to ensure an acceptable margin of safety.
* Pursuant to 10 CFR 50.12(a)(2)(ii), the circumstance that application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule.
The NRC staff accepts the licensee's determination that an exemption would be required to approve the use of Code Case N-640. The staff examined the licensee's rationale to support the exemption request and concurred that the use of the Code Case would meet the underlying intent of these regulations. Based upon a consideration of the conservatism that is explicitly incorporated into the methodologies of 10 CFR part 50, Appendix G; Appendix G of the Code; and Regulatory Guide 1.99, Revision 2, the staff concluded that application of Code Case N-640 as described would provide an adequate margin of safety against brittle failure of the RPV. Since strict compliance with the requirements of 10 CFR 50.60(a) and 10 CFR part 50, Appendix G, is not necessary to serve the overall intent of the regulations, the NRC staff concludes that application of Code Case N-640 to the P-T limit curves meets the special circumstance provision of 10 CFR50.12(a)(2)(ii). This is also consistent with the determination that the staff has reached for other licensees under similar conditions based on the same considerations. Therefore, the NRC staff concludes that requesting the exemption under the special circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate and that the methodology of Code Case N-640 may be used to revise the P-T limits for SSES-1 and 2.
Pursuant to 10 CFR 51.32, the Commission has determined that the granting of this exemption will not have a significant effect on the quality of the human environment(67 FR 5322).
John A. Zwolinski, Director, Division of Licensing Project Management, Office of Nuclear Reactor Regulation.