NOC-AE-11002779, Status of the Risk-Informed (Ri) Approach to Resolve Generic Safety Issue (GSI)-191

Status of the Risk-Informed (Ri) Approach to Resolve Generic Safety Issue (GSI)-191

ML11354A386
Person / Time
Site:	South Texas
Issue date:	12/14/2011
From:	Crenshaw J South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-11002779, G25, GSI-191, STI: 3317049
Download: ML11354A386 (3)

Text

Nuclear Operating Company South Texas ProjectElectric GencratingStation P.. Box 289 Wadworth. rexas 77483 - - J vv-December 14, 2011 NOC-AE-11002779 STI: 33171049 File: G25 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Status of the South Texas Project Risk-Informed (RI)

Approach to Resolve Generic Safety Issue (GSI)-191

Reference:

STPNOC Letter dated December 9, 2010, from Ed Halpin to Chairman Jaczko, "Letter to NRC Commissioners Regarding GSI-191 Status" (NOC-AE-10002625)

(ML103481027)

A summary of South Texas Project's progress during 2011 towards a risk-informed resolution of GSI 191, "Assessment of Debris Accumulation on PWR Sump Performance" is provided in the Enclosure.

There are no regulatory commitments in this letter.

Should you have any questions regarding this letter, please contact either Jamie Paul, Licensing, (361) 972-7344, or me at (361) 972-7074.

J.W. Crenshaw VP New Plant Deployment / Special Projects JLP

Enclosure:

Risk-Informed Closure of GSI-191 at the South Texas Project, Executive Summary 2011

NOC-AE- 11002779 Page 2 cc:

(paper copy) (electronic copy)

Regional Administrator, Region IV A. H. Gutterman, Esquire U. S. Nuclear Regulatory Commission Kathryn M. Sutton, Esquire 612 East Lamar Blvd, Suite 400 Morgan, Lewis & Bockius, LLP Arlington, Texas 76011-4125 Balwant K. Singal John Ragan Senior Project Manager Chris O'Hara U.S. Nuclear Regulatory Commission Jim von Suskil One White Flint North (MS 8B13) NRG South Texas LP 11555 Rockville Pike Rockville, MD 20852 Kevin Polio Senior Resident Inspector Richard Pena U. S. Nuclear Regulatory Commission City Public Service P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 C. M. Canady Peter Nemeth City of Austin Crain Caton & James, P.C.

Electric Utility Department 721 Barton Springs Road C. Mele Austin, TX 78704 City of Austin Bill Ruland Richard A. Ratliff Director, Division of Safety Systems (DSS) Alice Rogers U.S. Nuclear Regulatory Commission Texas Department of State Health Services One White Flint North (MS 011-Fl) 11555 Rockville Pike Rockville, MD 20852 Balwant K. Singal Stewart Bailey Bill Ruland Branch Chief, Safety Issues Resolution Stewart Bailey U. S. Nuclear Regulatory Commission Donnie Harrison One White Flint North (MS 011 F01) U. S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852 Donnie Harrison Branch Chief, PRA U. S. Nuclear Regulatory Commission One White Flint North (MS 011 F01) 11555 Rockville Pike Rockville, MD 20852

Enclosure NOC-AE-11002779 Page 1 of I RISK-INFORMED CLOSURE OF GSI-191 AT THE SOUTH TEXAS PROJECT Executive Summary for 2011 The main objective of the Risk-Informed GSI-191 Closure Project is, "Through a risk-informed approach, establish a technical basis that demonstrates that the current design is sufficient to gain NRC approval to close the safety issues related to GSI-191 by the end of 2013." The results presented in this summary are the joint work of STP Nuclear Operating Company (STPNOC) Risk Management, Los Alamos National Laboratories, the University of Texas at Austin, Texas A&M University, Alion Science and Technology, ABS Consulting, ScandPower, Dr. Mike Golay, the University of New Mexico, and KnF Consulting Services, LLC.

In the risk-informed approach, STPNOC intends to seek exemption from certain requirements of 10 CFR 50.46 based on a determination that the risk associated with the fibrous insulation in STPNOC's containment buildings is low enough to meet the requirements of Regulatory Guide (RG) 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions On Plant-Specific Changes to the Licensing Basis."

The 2011 preliminary results show that the change in risk for fibrous insulation in containment is 4.96E-07 in delta core damage frequency (CDF) and 3.10E-10 for delta large early release frequency (LERF) and is thus non-risk significant per RG 1.174.

This result represents the uncertainties of more than 20 input parameters and the complementary execution of the physics-based (CASA Grande) model, thermal-hydraulics model, and Probabilistic Risk Assessment (PRA) models. Although previous realistic testing has shown that chemicals are unlikely to affect the head loss in STPNOC debris beds (sump strainers and fuel assemblies), STPNOC has used an initial methodology that adds pessimistic head-loss estimates from chemicals. Including these conservative chemical effects estimates is believed to fully address NRC concerns raised in pre-licensing meetings related to sump chemistry.

This preliminary assessment of CDF and LERF provides confidence that the issues associated with fibrous insulation in the STPNOC reactor containment buildings will be further shown to be non-risk significant with adequate defense-in-depth and safety margins.

STPNOC plans to submit a License Amendment Request (LAR) for the exemption by the end of 2012.

During 2012, STPNOC will expand upon the project's technical contributions by including the uncertainties of more than 50 input parameters and the seamless integration of CASA Grande, new jet formation model, uncertainty propagation in the thermal-hydraulics models, and PRA analysis that takes into account detailed operational conditions. The resulting framework will provide STPNOC the ability to assess future issues on a risk-informed basis as they may arise. These analysis and testing activities will serve only to lower the above listed bounding risk numbers for delta CDF and LERF.