01-24175. Entergy Operations, Inc. River Bend Station, Unit 1; Exemption

1.0 Background

Entergy Operations, Inc. (the licensee) is the holder of Facility Operating License No. NPF-47 which authorizes operation of the River Bend Station, Unit 1 (RBS). The license provides, among other things, that the facility is subject to all rules, regulations, and orders of the U.S. Nuclear Regulatory Commission (NRC or the Commission) now or hereafter in effect.

The facility consists of a boiling water reactor located in West Felciana Parish in Louisiana.

2.0 Request/Action

Title 10 of the Code of Federal Regulations (10 CFR) part 50, appendix G requires that pressure-temperature (P-T or 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, section IV.2.a states that “* * *[t]he appropriate requirements on both the pressure-temperature limits and the minimum permissible temperature must be met for all conditions.” Pursuant to 10 CFR part 50, appendix G, section IV.2.b, the requirements for these limits are the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code), section XI, appendix G Limits.

To address provisions of amendments to Technical Specification (TS) 3.4.11, “RCS [Reactor Coolant System] Pressure and Temperature (P/T) Limits,” and the RCS P/T limits in TS Figure 3.4-11, “Minimum Temperature Required Vs. RCS Pressure,” in the submittal dated January 24, 2001, as supplemented by letters dated July 2, and August 6 and 20, 2001, the licensee requested that the staff exempt RBS 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. Code Case N-640 permits the use of an alternate reference fracture toughness (K_Ic fracture toughness curve instead of K_Ia fracture toughness curve) for reactor vessel materials in determining the P-T limits. Since the K_Ic fracture toughness curve shown in ASME Code Section XI, appendix A, Figure A-2200-1 provides greater allowable fracture toughness than the corresponding K_Ia fracture toughness curve of ASME Code Section XI, appendix G, Figure G-2210-1, using the K_Ic fracture toughness, as permitted by Code Case N-640, in establishing the P-T limits would be less conservative than the methodology currently endorsed by 10 CFR part 50, appendix G. Considering this, an exemption to apply the Code Case would be required by 10 CFR 50.60.

The licensee has proposed to revise the P-T limits for RBS using the K_Ic fracture toughness curve, in lieu of the K_Ia fracture toughness curve, as the lower bound for fracture toughness.

Use of the K_Ic curve in determining the lower bound fracture toughness in the development of P-T operating limits curve is more technically correct than the K_Ia curve since the rate of loading during a heatup or cooldown is slow and is more representative of a static condition than a dynamic condition. The K_Ic curve 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 K_Ia curve 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 K_Ia curve is well beyond the margin of safety required to protect the public health and safety from potential RPV failure.

In summary, the ASME Code 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 concludes that this increased knowledge permits relaxation of the ASME Code Section XI, appendix G requirements by applying the K_Ic fracture 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.

3.0 Discussion

Pursuant to 10 CFR 50.12, the Commission may, upon application by any interested person or upon its own initiative, grant exemptions from the requirements of 10 CFR part 50, when (1) the exemptions are authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security; and (2) when special circumstances are present. The 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 concluded that the use of the Code Case would meet the underlying purpose of 10 CFR part 50. 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. This is also consistent with the determination that the staff has reached for other licensees under similar conditions based on the same considerations.

The safety evaluation may be examined, and/or copied for a fee, at the NRC's Public Document Room, located at One White Flint North, 11555 Rockville Pike (first floor), Rockville, Maryland. Publicly available records will be accessible electronically from the ADAMS Public Library component on the NRC website, http://www.nrc.gov (the Electronic Reading Room).

Therefore, the staff concludes that requesting 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 RBS, subject to the limitation of 16 EFPYs.

4.0 Conclusion

Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12(a), the exemption is authorized by law, will not endanger life or property or common defense and security, and is, otherwise, in the public interest. Also, special circumstances are present. Therefore, the Commission hereby grants Entergy Operations, Inc., an exemption from the requirements of 10 CFR part 50, Section 50.60(a) and 10 CFR part 50, appendix G, for River Bend Station, Unit 1.

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 (66 FR 48069, published on September 17, 2001).

This exemption is effective upon issuance.

Dated at Rockville, Maryland, this 20th day of September, 2001.

For the Nuclear Regulatory Commission.

John A. Zwolinski,

Director, Division of Licensing Project Management, Office of Nuclear Reactor Regulation.