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Home NRC Library Document Collections Advisory Committee on Reactor Safeguards Letter Reports 2001

South Texas Project Nuclear Operating Company Requests for Exemption to Exclude Certain Components from the Scope of Special Treatment Requirements Required by Regulations (Option 2)

July 23, 2001

The Honorable Richard A. Meserve
Chairman
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

SUBJECT: SOUTH TEXAS PROJECT NUCLEAR OPERATING COMPANY REQUESTS FOR EXEMPTION TO EXCLUDE CERTAIN COMPONENTS FROM THE SCOPE OF SPECIAL TREATMENT REQUIREMENTS REQUIRED BY REGULATIONS (OPTION 2)

Dear Chairman Meserve:

During the 482nd, 483rd, 484th meetings of the Advisory Committee on Reactor Safeguards, May 10-11, June 6-8, and July 11-13, 2001, respectively, the Committee met with representatives of the NRC staff, the South Texas Project Nuclear Operating Company (STPNOC), and the Nuclear Energy Institute (NEI) to discuss STPNOC's requests for exemptions from certain Nuclear Regulatory Commission (NRC) regulations, including the adoption of a risk informed approach to the categorization and treatment of structures, systems, and components (SSCs). This matter was also discussed during a February 21, 2001, meeting of the Plant Operations and the Reliability and Probabilistic Risk Assessment Subcommittees. We also had the benefit of the documents referenced.

Recommendation

We concur with the staff that the STPNOC exemption requests should be granted as recommended in the preliminary safety evaluation report dated June 5, 2001.

Discussion

NRC regulations contain special treatment requirements that impose controls to ensure the quality and reliability of SSCs that are safety-related, important to safety, or otherwise within the scope of the regulations. These special treatment requirements include quality assurance (QA), environmental and seismic qualification, inspection and testing, and performance monitoring.

STPNOC has requested exemption from regulatory requirements for some SSCs. STPNOC has categorized SSCs based on risk rather than using the regulatory definition of basic components as found in 10 CFR 21.3.

The staff has determined that some requests for exemption should be granted and some should be denied, as follows:

Exemptions to be Granted

  • 10 CFR 21.3 - Definition of Basic Component
  • 10 CFR 50.34(b)(10) and (11) - Related to 10 CFR Part 100, Appendix A
  • 10 CFR 50.49(b) - Scope of Electrical Equipment Important to Safety
  • 10 CFR 50.55a(f) - ASME Inservice Testing
  • 10 CFR 50.55a(g) - ASME Repair/Replacement & Inspection
  • 10 CFR 50.55a(h) - IEEE 279 Quality & Qualification Requirements
  • 10 CFR 50.59 - Changes, Tests, & Experiments
  • 10 CFR 50.65(b) - Scope of Maintenance Rule
  • 10 CFR Part 50, Appendix B - Quality Assurance Criteria
  • 10 CFR Part 50, Appendix J - Type C Containment Leak Testing
  • 10 CFR Part 100, Appendix A, VI, (a)(1) & (2) - SSE and OBE Design

Exemptions to be Denied

Licensee's Proposed Approach Meets Regulations:

  • GDC 1 - Quality Standards and Records
  • GDC 2 - Protection Against Natural Phenomena
  • GDC 4 - Environmental and Dynamic Effects
  • GDC 18 - Inspect/Test Electrical Power Systems

Update to QA Program Required to Reflect Changes to Commitments:

  • 10 CFR 50.34(b)(6)(ii) - Appendix B Information Included in FSAR
  • 10 CFR 50.54(a)(3) - Changes to QA Program

STPNOC categorized all SSCs in 29 safety systems into four risk categories according to their risk ranking. This ranking was based on a categorization process that used Probabilistic Risk Assessment (PRA) measures and the deliberations of an expert panel. The four risk categories were defined as:

  • RISC-1 - Safety-Related and Risk-Significant
  • RISC-2 - Non-Safety-Related and Risk-Significant
  • RISC-3 - Safety-Related and not Risk-Significant
  • RISC-4 - Non-Safety-Related and not Risk-Significant

No changes in regulatory treatment are proposed for SSCs that fall in categories RISC-1 and RISC-4.

STPNOC has committed to upgrade the 372 SSCs in the RISC-2 category to safety-related to the extent possible. This upgrade will result in an improvement in the safety posture of the facility.

The category that is of immediate interest is RISC-3, which contains the SSCs that are categorized as safety-related under the current system, but are not considered to be risk-significant using the STPNOC methodology. The question is: What treatment should be applied to these components?

STPNOC proposed that SSCs in RISC-3 be treated in accordance with "commercial practice" rather than the special treatment requirements currently applicable to safety-related components. Additional requirements were added to the Final Safety Analysis Report (FSAR) to help ensure the functionality of these components.

STPNOC has developed a methodology that uses PRA importance measures as inputs to the expert panel's structured decision-making process for categorizing SSCs.

STPNOC has developed a state-of-the-art PRA in which the licensee, the regulators, and the public can have confidence. The staff engaged an independent contractor to perform a review of the STPNOC PRA and their report indicates that the STPNOC PRA is of good quality.

Regulatory Guide 1.174 requires that the changes in CDF and LERF be small. There are no models that assess the impact of special treatment requirements on SSC failure probabilities. STPNOC performed a comparative risk analysis by increasing by a factor of 10 the failure rate of the RISC-3 components to be exempted from special treatment. STPNOC justified this choice of increased failure rate through an analysis of component failure data for safety-and non-safety-related components using data from the Nuclear Plant Reliability Data System (NPRDS), the Equipment Performance Information Exchange (EPIX), and the Maintenance Rule and Reliability Information (MRRI) database. The data showed that failure rates of components with commercial treatment were equivalent to failure rates of components with special treatment. The licensee argued that the choice of a factor of 10 was bounding although the failure data only apply to failures under normal operating conditions. Subsequently, the licensee compared the change in CDF and LERF to the original values and concluded the changes were acceptably small. STPNOC has also assessed the potential effect on the probability of late containment failure. It was also acceptably small.

Only about 6 percent of the SSCs currently classified as safety-related (or about 2,400 of the 44,000 SSCs in safety systems of the two units) are categorized based on PRA importance measures. The remaining 94 percent were analyzed and categorized by the expert panel. The deterministic method used by STPNOC's expert panel assured that the necessary instrumentation and controls upon which the operator may rely in emergency and severe accident conditions were categorized as risk-significant.

We have found the application by STPNOC to be adequate. Because plant-specific considerations are so important, the STPNOC application may not be an adequate template for similar applications by other licensees.

Mr. Stephen Rosen did not participate in the Committee's deliberations regarding this matter.

Sincerely,

/RA/

George E. Apostolakis
Chairman

References:

1. Letter dated July 3, 2001, from M. A. McBurnett, STP Nuclear Operating Company, to NRC, Subject: Revised Request for Exemption to Exclude Certain Components from the Scope of Special Treatment Requirements Required by Regulations.
2. Letter dated June 5, 2001, from S. A. Richards, NRC, to W. T. Cottle, STP Nuclear Operating Company, Subject: South Texas Project, Units 1 and 2 - Factual Errors or Omissions in Preliminary Safety Evaluation on Exemptions Requested from Special Treatment Requirements.
3. Letters dated January 15, 18, and 23, March 19, May 8, and 21, 2001, January 29 and August 31, 2000, and October 14 and 22, 1999, from J. J. Sheppard, STP Nuclear Operating Company, to NRC Document Control Desk, Subject: Revised Request for Exemption to Exclude Certain Components from the Scope of Special Treatment Requirements Required by Regulations.
4. Letter dated November 15, 2000, from J. Zwolinski, NRR, to W. Cottle, STP Nuclear Operating Company, Subject: South Texas Project, Units 1 and 2 - Draft Safety Evaluation on Exemption Requests from Special Treatment Requirements of 10 CFR Parts 21, 50, and 100.
5. Letter dated July 19, 2000, from J. A. Zwolinski, NRC, to W. T. Cottle, STP Nuclear Operating Company, Subject: South Texas Project, Units 1 and 2 - Draft Review Guidelines on Risk-Informed Exemptions from Special Treatment Requirements.
6. Safety-Related Versus Non-Safety-Related Equipment Failure Frequency Data Analysis for Nuclear Power Plants in the United States, Final Report, South Texas Project Electric Generating Station, STP Nuclear Operating Company, April 6, 2000.
7. Letter dated January 18, 2000, from R. A. Gramm, NRC, to W. T. Cottle, STP Nuclear Operating Company, Subject: South Texas Project, Units 1 and 2 - Request for Exemption to Exclude Certain Components from the Scope of Special Treatment Requirements Required by Regulations, Request for Additional Information.
8. Letter dated July 13, 1999, from J. J. Sheppard, STP Nuclear Operating Company, to NRC Document Control Desk, Subject: Request for Exemption to Exclude Certain Components from the Scope of Special Treatment Requirements Required by Regulations.

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