05000395/LER-2008-002, Re Control Room Normal and Emergency Air Handling Systems Inoperable Due to Pressure Boundary Breach
| ML081350233 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 05/12/2008 |
| From: | Archie J South Carolina Electric & Gas Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 08-002-00 | |
| Download: ML081350233 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 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)(iv)(A), System Actuation 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), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 3952008002R00 - NRC Website | |
text
Jeffrey B. Archie Vice President, Nuclear Operations 803.345.4214 A SCANA COMPANY May 12, 2008 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555
Dear Sir / Madam:
Subject:
VIRGIL C. SUMMER NUCLEAR STATION (VCSNS)
DOCKET NO. 50-395 OPERATING LICENSE NO. NPF-12 LICENSEE EVENT REPORT (LER 2008-002-00)
CONTROL ROOM NORMAL AND EMERGENCY AIR HANDLING SYSTEMS INOPERABLE DUE TO PRESSURE BOUNDARY BREACH Attached is Licensee Event Report (LER) No. 2008-002-00, for the Virgil C. Summer Nuclear Station (VCSNS). The report describes the sequence of actions that led to South Carolina Electric & Gas Company (SCE&G) determining that the allowed outage time for Technical Specification Limiting Condition for Operation 3.7.6.a.2 had been exceeded. This report is submitted in accordance with 10CFR50.73(a)(2)(i)(B).
Should you have any questions, please call Mr. Bruce Thompson at (803) 931-5042.
Very truly yours, J
B.Arc ie GRAJBAcdr Attachment
.c:
K.B. Marsh S. A. Byrne N. S. Carns J. H. Hamilton R. J. White L. A. Reyes R. E. Martin NRC Resident Inspector M. N. Browne K. M. Sutton D. L. Abstance P. Ledbetter EPIX Coordinator INPO Records Center J&H Marsh & McLennan NSRC RTS (C-08-00944)
File (818.07)
DMS (RC-08-0072)
SCE&G I Virgil C. Summer Nuclear Station - P. 0. Box 88
- Jenkinsville, South Carolina 29065, T (803) 345.5209
- www.sceg.com
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may (See reverse for required number of not conduct or sponsor, and a person is not required to respond to, the diqits/characters for-each block) information collection.
- 3. PAGE Virgil C. Summer Nuclear Station 05000 395 1 OF 4
- 4. TITLE Control Room Normal and Emergency Air Handling Systems Inoperable Due to Pressure Boundary Breach
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MOTHFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR I
NUMBER NO.
05000 0 FACILITY NAME DOCKET NUMBER 03 11 2008 2008 2
0 05 12 20081 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check a// that apply)
Mode 1 fl 20.2201(b)
E 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii)
El 20.2201(d)
[]
20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
C] 50.73(a)(2)(viii)(A) fl 20.2203(a)(1)
[
20.2203(a)(4) 50.73(a)(2)(ii)(B)
E] 50.73(a)(2)(viii)(B)
[]
20.2203(a)(2)()
El 50.36(c)(1)(i)(A) 50.73(a)(2)(iii)
[]
50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
I]
50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A)
E[ 50.73(a)(2)(x) 10%20.2203(a)(2)(iii)
El 50.36(c)(2)
C] 50.73(a)(2)(v)(A)
Ej 73.71 (a)(4) 1060%
[]20.2203(a)(2)(iv)
[]50.46(a)(3)(ii)
- ]50.73(a)(2)(v)(a)
[]73.71 (a)(5)
E] 20.2203(a)(2)(v)
E] 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi)
[]
50.73(a)(2)(i)(B) j 50.73(a)(2)(v)(D)
Specify in Abstract below or in DESCRIPTION OF EVENT (Continued) the duct tape was not restored. Although the post-maintenance test verified that the CRPB had been restored, it only required that the differential pressure be determined with the CR Ventilation System operating in the normal mode. The CRPB differential pressure is normally higher with the CR Ventilation System in the normal mode than in the emergency mode. The breach condition was considered to have existed from February 26, 2008 until the breach was identified and repaired with return to service on March 14, 2008. Since this condition affected both trains of CR Ventilation and existed for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, TS Limiting Condition for Operation (LCO) 3.7.6.a.2 was violated.
CAUSE OF EVENT
Investigation into the test failure determined that a control room pressure boundary (CRPB) breach occurred during normal preventive maintenance performed February 26, 2008 on Instrument and Control (I&C) Area Air Handling Unit XAH0048. The identified breach was sufficient to allow a quantity of air out-leakage that reduced CRPB pressure below TS minimum and resulted in increased outside air flow that exceeded the maximum allowed. Since this condition affected both trains of CR Ventilation and existed for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, TS Limiting Condition for Operation (LCO) 3.7.6.a.2 was violated.
A root cause analysis is currently in progress. Preliminary results indicate that the root cause of the breach was inadequate post-maintenance testing after the normal preventive maintenance was completed on XAH0048. For corrective actions it is expected that station procedures will be revised to specify performance of the surveillance test procedure that verifies the operability of the CRPB when maintenance is performed on XAH0048. A Supplemental Report will be submitted by September 1, 2008, describing the results of the root cause analysis and any additional corrective actions taken.
ANALYSIS OF EVENT
The CRPB is designed and maintained to provide a habitable environment such that occupants within the CRPB can control the reactor safely under normal conditions and maintain it in a safe condition following a radiological event, hazardous chemical release, or a smoke challenge.
The VCSNS Control Room Normal and Emergency Air Handling System consists of two independent, redundant trains that recirculate air in the normal and emergency mode and additionally provide filtration of the air in the emergency mode. It also serves to maintain a positive pressure within the CRPB of greater than 0.125 inch w.g. with a maximum of 1000 SCFM per train of outside air during system operation. Pressurization of the CRPB minimizes infiltration of unfiltered air through the CRPB from all the surrounding areas adjacent to the CRPB.
The subject breach in the suction plenum of Air Handling Unit XAH0048, resulted in the following conditions when the Control Room Normal and Emergency Air Handling System is operating in the emergency mode:
- - The Control Room differential pressure (dp) decreased below the TS limit of 0.125 in w.g., with a measured dp of -0.1 inch w.g.
for Train "A" and a projected dp of greater than 0.1 inch w.g. for Train'"B". This dp loss was attributed to the out-leakage of air due to the breach of XAH0048.
- - To compensate for the out-leakage, OA intake flow increased above the TS limit of 1000 SCFM, with a measured value of -1054 SCFM for Train "A" and a projected value of < 1100 SCFM for Train "B".
Both conditions are adverse as control room personnel could possibly be exposed to a larger dose during a radiological event or to more hazardous conditions during a chemical release.
Outside Air Intake Flow - An increase in outside air intake flow of -100 SCFM (i.e., to 1100 SCFM) is judged to have a small adverse impact on both radiological and chemical event consequences. The impact on control room doses is small because the outside air is filtered before entering the control room in the emergency mode. Significance can be quantified by examining the limiting event for control room doses which, for VCSNS, is the postulated Loss-of-Coolant Accident (LOCA). Current design basis analyses for this accident are performed in accordance with Regulatory Guide 1.4. Thyroid, as opposed to whole body, doses are limiting. Existing studies indicate that an increase in the outside air flow of -100 SCFM would increase the 30-day thyroid dose by
- - 0.85 Rem. This is equivalent to -4.7 SCFM of unfiltered inleakage into the CRPB. Dose impacts on other non-LOCA events
ANALYSIS OF EVENT (Continued) would be significantly less because of the smaller source terms. Hazardous chemical assessments consider a chlorine cylinder release and failure of the Ammonium Hydroxide Tank in accordance with the guidance of Revision 0 and Revision 1 of Regulatory Guide 1.78, respectively. Current analyses are based on the TS limit for outside air flow (1000 SCFM), but have inherent margins to accommodate potential increases in CRPB inleakage in excess of 700 SCFM before the applicable toxicity limit is approached.
Control Room Differential Pressure - A baseline ASTM E741 integrated test was performed in March 2005 to measure leakage into the CRPB. Filtered outside air was found to be within the current TS limits of 1000 SCFM per train and the maximum unfiltered CRPB inleakage recorded was 41 SCFM. This as-found condition was less that the current analysis limit of 55 SCFM, which is based on thyroid doses being less than or equal to 30 Rem during a postulated LOCA. A decrease in the Control Room differential pressure to - 0.1 inch w.g. is adverse since it creates the potential for unfiltered inleakage to increase above the previously measured maximum of 41 SCFM. This is of concern primarily from a LOCA dose standpoint since, based on current methods, margins are small (- 15 SCFM). Increases in unfiltered inleakage (if any) are expected to be small since a positive pressure would have been maintained in the Control Room.
Inleakage margins are small because of the conservatisms inherent to the current licensing basis methods. Substantial increases in the margin (i.e., hundreds of SCFM's) could be made available by crediting the higher thyroid dose limits within Regulatory Guide 1.195 or Alternate Source Term methods. Even though the exact impact on unfiltered inleakage cannot be quantified, these inherent conservatisms provide reasonable assurance that the CR Normal and Emergency Air Handling System would have been able to accomplish its safety function.
CORRECTIVE ACTIONS
Repairs were made to the air handling unit, XAH0048, and the surveillance test was successfully completed on March 14, 2008.
A root cause analysis is currently in progress. Preliminary results indicate that the root cause of the breach was inadequate post-maintenance testing after the normal preventive maintenance was completed on XAH0048. For corrective actions it is expected that station procedures will be revised to specify performance of the surveillance test procedure that verifies the operability of the CRPB when maintenance is performed on XAH0048. A Supplemental Report will be submitted by September 1, 2008 describing the results of the root cause analysis and any additional corrective actions taken.
PRIOR OCCURRENCES There is no historical evidence of a prior occurrence.
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