ML13330B572
| ML13330B572 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/31/1991 |
| From: | Rosenblum R Southern California Edison Co |
| To: | NRC/IRM |
| Shared Package | |
| ML13329A755 | List: |
| References | |
| TASK-03-05.A, TASK-03-05.B, TASK-3-5.A, TASK-3-5.B, TASK-RR NUDOCS 9111050205 | |
| Download: ML13330B572 (4) | |
Text
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 R. M. ROSENBLUM October 31, 1991 TELEPHONE MANAGER OF (714) 454-4505 NUCLEAR REGULATORY AFFAIRS U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 San Onofre Nuclear Generating Station, Unit 1 SEP Topics: III-5.A, Effects of Pipe Breaks on Structures,
- Systems, and Components Inside Containment; III-5.B, Pipe Break Outside Containment
References:
- 1. Letter, F. R. Nandy, SCE, to NRC, dated April 3, 1990
- 2. Letter, R. M. Rosenblum, SCE, to NRC, dated July 30, 1991 Enclosed are the results of our recent High Energy Line Break (HELB) analysis for San Onofre Nuclear Generating Station Unit 1 (SONGS 1).
The HELB issue is an open item from the Integrated Plant Safety Assessment Systematic Evaluation Program (SEP).
This analysis is being submitted to address SEP Topics III-5.A, "Effects of Pipe Break on Structures, Components, and Systems Inside Containment," and III-5.B, "Pipe Break Outside Containment."
SCOPE The scope of our evaluation encompasses the SONGS 1 potential HELB interactions inside and outside the containment building. The report provides the details of our analysis of the HELB pipe whip and jet impingement effects on systems, structures, and components. The vast majority of the postulated HELB cases were determined to be acceptable. However, in a few cases modifications will be required to eliminate the potential consequences of postulated HELB interactions.
The enclosed HELB report also summarizes our past evaluation of flooding, equipment qualification, and compartment pressurization due to HELB. The structural effects of potential compartment pressurization in the turbine building and fuel storage building are still under evaluation. Further analysis is required to determine the actual pressure exerted on the turbine structure (if any) due to postulated pipe breaks. Because of the openness of those areas, we do not anticipate any modifications resulting from that analysis.
Document Control Desk
-2 BACKGROUND In our efforts to resolve the HELB issue, we have performed three prior studies. The first study, performed in 1973, was superseded by new criteria requiring the analysis of additional lines. The second study, in 1983, left 102 lines unresolved, and was later impacted by changes in the plant configuration due to Appendix R (Fire Protection), and seismic upgrading requirements. A third study was initiated in 1985, however, not all of the lines were resolved. Subsequently, we proposed to resolve this issue using a Probabilistic Risk Assessment (PRA) for HELB interactions related to safe shutdown systems and deterministic methodology for structural interactions.
On April 17, 1991, SCE personnel met with members of the NRC staff to present a general review of this approach.
METHODOLOGY In the enclosed SONGS 1 report, HELB interactions resulting from pipe whip and jet impingement have been characterized as falling into two categories:
- 1) SYSTEMS RELATED--Interactions that affect system piping, equipment, or components required to achieve a safe shutdown, and
- 2) STRUCTURAL--Interactions that affect structural members/components.
Structural interactions were evaluated using deterministic methodology, while system related interactions were evaluated by calculating the increase in risk of core damage associated with the HELB interactions using PRA methodology.
The methodologies and criteria for resolving the system related and structural HELB interactions are described in detail in the enclosed report. Our approach involved the following steps:
Identification of high energy lines Exclusion of lines using SRP criteria, leak-before-break (LBB),
and augmented inservice inspection (ISI)
Break identification Walkdown of lines to identify interactions Post-walkdown design modification review Evaluation of interactions Systems related interactions were evaluated using PRA Structural interactions were evaluated using deterministic methods RESULTS STRUCTURAL EVALUATION The structural evaluation showed that all of the identified structural interactions are acceptable except for two HELB interactions which affect one
Document Control Desk
-3 structural steel member in the turbine building (column K2).
A design change will be implemented to resolve these two unacceptable interactions.
SYSTEMS EVALUATION The total annual risk of core damage due to system related HELB interactions was calculated to be 1.03E-5. This is considered to be a low risk, and represents approximately 5% of the total annual risk of core damage due to internally initiated events (estimated to be 2E-4).
Although 1.03E-5 per year is a low risk, we have elected to implement a design change which will lower the HELB risk by an additional 82%. The design change will protect the recirculation pump motor cables from a potential pipe break, thereby reducing the calculated HELB risk to 1.87E-6 per year. This reduced value constitutes less than 1% of the total annual risk of core damage due to internally initiated events, and is considered to be an insignificant increase in the total core damage risk.
AUGMENTED ISI On July 15, 1975, the NRC issued Amendment 13 to Provisional Operating License DPR-13, which added the Augmented Inservice Inspection Program to the Technical Specifications. The Augmented ISI Program requires periodic volumetric examination of specified welds in the main feedwater, main steam, and first point extraction steam lines. As a result of our recent HELB analysis effort, three branch-line welds on the main feedwater lines were identified that inadvertently were excluded from the Augmented ISI Program.
Although the three welds were not in the Augmented ISI Program, they were inspected in 1980 using volumetric examination as required by the Augmented ISI Program. That inspection was the result of our implementation of an IE Bulletin. These welds are being added to our Augmented ISI Program and will be inspected during the next refueling outage.
We are currently investigating this oversight. Upon completion of our investigation, we will inform the NRC of the results and corrective action.
SCHEDULE As previously indicated in reference 2, these modifications will be implemented during the Cycle 13 refueling outage. We will submit the results
Document Control Desk
-4 of our evaluation of the potential for turbine building/fuel building compartment pressurization prior to commencing the above modifications.
Should you have any questions regarding this issue, or require additional information, please contact me.
Very truly yours,
Enclosure:
High Energy Line Break Analysis, Inside and Outside Containment, dated October 1991 cc:
J. B. Martin, Regional Administrator, NRC Region V George Kalman, NRC Senior Project Manager, San Onofre Unit 1 J. 0. Bradfute, NRC Project Manager, San Onofre Unit 1 C. W. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2&3