05000456/LER-2008-001, Regarding Technical Specification Non-Compliance Due to Inadequate Design of Auxiliary Feedwater (AF) Tunnel Access Covers Causing AF Valves within the Tunnel to Be Inoperable
| ML090480361 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 02/17/2009 |
| From: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BW090018 LER-08-001-00 | |
| Download: ML090480361 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4562008001R00 - NRC Website | |
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10 CFR 50.73 February 17, 2009 6W09001 8 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457
Subject:
Licensee Event Report 2008-001-00, Technical Specification Non-Compliance Due to Inadequate Design of Auxiliary Feedwater (AF) Tunnel Access Covers Causing AF Valves Within the Tunnel to be Inoperable The enclosed Licensee Event Report (LER) is being submitted in accordance with 10 CFR 50.73, Licensee event report system, paragraph (a)(2)(i)(B) as a condition prohibited by the plants Technical Specifications (TS). On December 16, 2008, Braidwood Station determined that certain valves relied upon for a containment isolation function were potentially inoperable from original construction until temporary modifications were installed on Auxiliary Feedwater (AF) tunnel access covers in the summer of 2008, which is longer than allowed by TS 3.6.3 Condition C. 10 CFR 50.73(a) requires an LER to be submitted within 60 days following discovery of the event.
Therefore, this report is being submitted by February 17, 2009.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. David Gullott, Regulatory Assurance Manager, at (815) 417-2800.
Respectfully, Hanson Site Vice President Braidwood Station
Enclosure:
LER Number 2008-001 -00
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the nfnrmatinrr ~nlIerAinn
- 1. FACILITY NAME Braidwood Station, Unit 1
- 2. DOCKETNUMBER 13, PAGE 05000456 1
OF 5
- 4. TITLE lechnical Specification Non-Compliance Due to Inadequate Design of Auxiliary Feedwater (AF) Tunnel Access Covers Causing AF Valves Within the Tunnel to be Inoperable 5, EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SE~J~J~AL R~E~V MONTH DAY YEAR FACILITY NAME DOCKET NUMBER Braidwood Station, Unit 2 05000457 12 16 2008 2008 001 00 02 17 2009 FACILITY NAME DOCKET NUMBER N/A N/A J. OPERATING MODE 1
- 11. THIS REPORT IS SUBMITTED PURSUANTTO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) o 20.2201(b) 0 20.2203(a)(3)(i) 0 50,73(a)(2)O)(C) 0 50.73(a)(2)(vii) 0 20.2201(d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) o 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B)
O 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A) 0 50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A) 0 20.2203(a)(2)(ii) 0 50.36(c)(i)(ii)(A) 0 50.73(a)(2)Ov)(A) 0 50.73(a)(2)(x) o 20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71 (a)(4) 0 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B) 0 73.71 (a)(5) o 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C) 0 OTHER o 20.2203(a)(2)(vi)
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50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)
Specify in Abstract below or in 79-02 and Supplement ito IE 79-02) were determined to be not applicable to this design application. The AFO13 valves in the tunnel were considered operable and actions were initiated to perform permanent modifications to restore the CEAs to the desired design FOS of 4.0 as specified in the design standard.
In June of 2008, two discrepancies were discovered with the 2007 Operability Evaluation. An NRC Inspector discovered the evaluation did not include a Dynamic Loading Factor (DLF) to account forthe energy imparted to the cover as a result of the sudden pressurization of the MS tunnel during a HELB. Additionally, it was self-identified that the MS tunnel ventilation blow-out panels were not installed per design. The existing MS HELB analysis was performed with the assumption that panels in the MS Isolation Valve rooms would blow out during the HELB to relieve room pressure. Inspections of the panels led to a conclusion that theywould not blow out to relieve pressure as expected. This would result in an increase in room pressure. Therefore, the decision was made to install temporary modifications to modify the blow-out panels in order to provide additional pressure relief paths and to install strongbacks on the AF tunnel access covers to regain some margin pending the installation of the permanent modifications to provide a FOS greaterthan 4.0. The temporary modifications were installed by July of 2008.
In this timeframe, a complex analysis was begun to assess operability of the AFO13 valves from a historical perspective. The conclusion was the access covers would perform their functions and protect the operability of the AFO13 valves. This was based on the FOS continuing to be greater than 1.0. This conclusion was also based on an unverified assumption that each access cover had four CEAs. This assumption was to be verified the next time the access covers were removed.
In the Fall 2008 Byron Unit 2 refuel outage, the access covers were removed and it was determined that some of the access covers had only three CEAs. During installation of the permanent modifications, the same configuration was found to exist at Braidwood for a single access cover. A subsequent evaluation recommended not performing a re-analysis given the already low margin condition that existed, assuming the absence of the temporary modifications. This recommendation came after it was determined that use of a FOS of 1.0 to demonstrate operability was not supported. Consequently, on December 16, 2008, it was determined that it was possible that one or more of the AF tunnel covers may have been insufficiently designed to withstand a design basis HELB outside of containment for a time period covering date of original construction until temporary modifications were installed in the summer of 2008. This would have impacted the AFO13 valves ability to perform their containment isolation function (i.e., to close), and would therefore render them inoperable during the applicable design basis event (MS Line Break outside of containment).
This potential historical condition is reportable to the NRC in accordance with 10 CFR 50.73(a)(2)(i)(B), as a condition prohibited by Technical Specifications 3.6.3 Condition C.
Cause of Event
The cause of this condition was an inadequately designed component during original construction.
An investigation could not determine whythe 1987 calculation did not consider HELB forces nor identify the FOS less than 4.0 non-compliance into the Corrective Action Program.
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Safety Consequences
There were no actual consequences from the condition since an HELB did not occur while the AF tunnel access covers had minimal structural margin.
To assess the potential consequences of AF tunnel access cover failures, the function of the equipment protected by the access covers (i.e., AFO13s) must be considered. From a review of the Updated Final Safety Analysis Report (UFSAR) and Technical Specifications, the AFO13s have the following design functions:
1.
Containment Isolation valves, 2.
Maintain an AF flowpath to the SGs for heat removal, 3.
Isolation of AF to the SGs during a SG Tube Rupture, and 4.
Isolation of AF for secondary side piping breaks on the SGs.
For the first three functions the AFO13s would not be affected because the initiating events are inside containment and do not result in pressurization of the AF tunnel access covers. Therefore, there was no challenge to the ability of the AFO13 valves from performing these design functions.
Isolation of AF for secondary side breaks is desired primarily to limit mass and energy releases from the SGs and minimize reactivity effects of excessive RCS cooldown. For secondary side breaks inside containment, the rationale for the first three functions also applies (i.e., a secondary side break in containment will not result in pressurization of the AF tunnel covers).
For secondary side breaks outside containment, continued release of energy could damage safety related components in the MS Isolation and Safety Valve room. However these components have either already performed their safety function (MS Isolation Valve closure, detection of low steam line pressure) or are not needed for accident diagnosis or mitigation in conjunction with a steam line break outside containment (MS line radiation monitors).
Isolation of AF flow is not credited in the UFSAR for steam line breaks. Essentially, the event is terminated when boron reaches the core within the firstfew minutes of the accident. For Main Feedwater (FW) [SJ] line breaks, the UFSAR does assume isolation of AF flow at 20 minutes after the event; however, the energy release from an FW line break is substantially less than that from an MS line break.
Therefore, the AF tunnel covers are designed not to fail and the AFO13s will remain available for their isolation function.
Based on the above, the low structural margin of the AF tunnel access covers on the AFO13s did not have adverse actual or potential consequences on the AFO13 valves ability to perform their containment isolation valve function.
There were no safety system functional failures as a resultof this event.
Corrective Actions
Corrective actions include:
1.
Completed installation of temporary modifications in the summer of 2008 to regain some design margin.
2.
Completed installation of permanent modifications (final Braidwood modification, for both Units 1 and 2, completed on 1/2/09) to restore compliance with design standards (i.e., FOS greater than or equal to 4.0).
3.
Communications of the event to selected personnel.
4.
Completed training request for engineering personnel for the lessons learned from this event.
5.
Enhancements to the Operational and Technical Decision Making (OTDM) process. Specifically, utilize the OTDM process to document issues like low margin (operational risk exposure) that are beyond the scope of an Operability Evaluation.
6.
Review existing station practices associated with recurring review of open Operability Evaluations to identify opportunities to incorporate lessons learned from this event, including confirmation of appropriate prioritization of corrective actions.
Previous Occurrences
There have been no similar Licensee Event Report events at Braidwood Station in the last three years.
~. Component Failure Data:
Manufacturer Nomenclature Model Mfa. Part Number N/A N/A N/A N/APRINTED ON RECYCLED PAPER