05000254/LER-2012-004, Regarding Breech in Secondary Containment
| ML12321A020 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 11/05/2012 |
| From: | Hanley T Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVP-12-109 LER 12-004-00 | |
| Download: ML12321A020 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 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)(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)(i)(B), Prohibited by Technical Specifications |
| 2542012004R00 - NRC Website | |
text
Exelekn Exelon Generation Company, LLC www.exeloncorp.com Nuclear Quad Cities Nuclear Power Station 22710 2o6th Avenue North Cordova, I L 61242-9740 November 5, 2012 10 CFR 50.73 SVP-12-109 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Unit 1 Renewed Facility Operating License No. DPR-29 NRC Docket No. 50-254
Subject:
Licensee Event Report 254/2012-004-00, "Breech in Secondary Containment" Enclosed is Licensee Event Report (LER) 254/2012-004-00, "Breech in Secondary Containment,"
for Quad Cities Nuclear Power Station, Unit 1.
This report is submitted in accordance with 10 CFR 50.73 (a)(2)(v)(C), and (a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: control the release of radioactive material, and mitigate the consequences of an accident.
There are no regulatory commitments contained in this letter.
Should you have any questions concerning this report, please contact Mr. W. J. Beck at (309) 227-2800.
Respectfully, Tim Ha I Site Vice President Quad Cities Nuclear Power Station cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Quad Cities Nuclear Power Station
4RC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 10-20 10)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the digits/characters for each block) information collection.
- 3. PAGE Quad Cities Nuclear Power Station Unit 1 05000254 1 OF 5
- 4. TITLE Breech in Secondary Containment
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED ISEUENTIAL FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER N
EANO. MONTH DAY YEAR Quad Cities Nuclear Power Station Unit 2 05000265 FACILITY NAME DOCKET NUMBER 09 06 2012 2012
- - 004 00 11 05 2012 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[] 20.2201(b)
El 20.2203(a)(3)(i)
[I 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1 [E 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
[E 50.73(a)(2)(viii)(A)
C3 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
[I 50.73(a)(2)(viii)(B)
[__ 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
[I 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[I 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4) 100 El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71 (a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
- 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
U 50.73(a)(2)(v)(D)
Specify in Abstract below or in Since both Units 1 and 2 share a common reactor building, a breech occurred for eight seconds that impacted both Units 1 and 2 secondary containments when the Unit 2 RB 595 Interlock door and the Unit 2 RBI HRSS-Side door were opened at the same time. Given the impact on the secondary containment, this report is submitted (for Units 1 and 2) in accordance with the requirements of 10 CFR 50.73 (a)(2)(v)(C), and (a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: control the release of radioactive material, and mitigate the consequences of an accident.
C.
CAUSE OF EVENT
The apparent cause of the secondary containment breech event was that the Unit 2 RBI HRSS-side door latching mechanism was not fully engaged at the time that the Unit 2 RB 595 Interlock door opened. It is probable that the crash bar was bumped some time after the Security door test and before occurrence of thi~s event.
Troubleshooting performed on September 7, 2012 revealed that the fingers on the Unit 2 RBI HRSS-side door crash bar were not re-engaging consistently after the crash bar was released. It was determined that use of the crash bar on the door will override the secondary containment interlock logic. The Unit 2 RBI HRSS-side door was inspected for any equipment reliability issues with the latching mechanism on the door. No damage to the door or the latching mechanism was found.
Due to the relative position of the strike plate on the door jam to the latching mechanism on the door upon closure, the door could only be latched completely if the door was closed with the aid of the closure device from approximately full open, or if extra pulling force was applied to the crash bar to extend the latch completely outward.
A contributing cause to this event was that the RBV discharge modulating dampers have been "tuned" to slow their response to d/p changes caused by atmospheric conditions outside of the RB. The RB to atmosphere d/p rose above zero (went positive) due to the slow response of the RBV discharge modulating dampers. During normal operations, the pressure that the RBI HRSS-side door in the RB to Turbine Building 595 interlock is exposed to is negative (pulling inward). Regardless of the status of the door latching mechanism, the normal pressure direction and magnitude would be enough to keep the RBI HRSS-side door closed if not acted upon by another force physically pushing it open.
A prior Engineering Change had installed a new control system to reduce or eliminate re-occurring failures of the old d/p control system. During the setup of the new control system, the new controller was tuned to react slower to minimize excessive swinging when the external pressure changes.
If the Standby Gas Treatment System is operating, the amount of negative building pressure seen by the controller will cause the RBV discharge modulating dampers to go closed. When the RBV is started, the RBV discharge modulating dampers consistently react too slowly to prevent the RB d/p from going positive.
D.
SAFETY ANALYSIS
System Design
The function of the secondary containment is to contain, dilute, and hold up fission products that may leak from primary containment following a Design Basis Accident (DBA). In conjunction with operation of the Standby Gas Treatment System (SBGTS) and closure of certain valves [V] whose lines penetrate the secondary containment, the secondary containment is designed to reduce the activity level of the fission products prior to release to the
environment, and to isolate and contain fission products that are released during certain operations that take place inside primary containment, when primary containment is not required to be operable, or that take place outside primary containment.
The SBGTS is designed to maintain the reactor building (reactor building is common to both Units 1 and 2) at a negative pressure and to filter the exhaust of radioactive matter from reactor building spaces to the environment (by particulate filtration and halogen adsorption) in the unlikely event of a DBA, including the Loss of Coolant Accident (LOCA) and the refueling accident. It is also instrumental in maintaining the integrity of secondary containment during a primary to secondary containment instrument line break. Two parallel trains are provided, each of which is capable of producing greater than 0.25 inches water negative pressure required in the reactor building while processing 4000 cubic ft /min of exhaust air.
Safety Impact Since both Units 1 and 2 share a common reactor building, a breech occurred for eight seconds that impacted both Units 1 and 2 secondary containments when the Unit 2 RB 595 Interlock door and the Unit 2 RBI HRSS-side door were opened at the same time.
TS 3.6.4.1, Action A.1, requires restoration of secondary containment to operable status within four hours. This four hour Completion Time provides a period of time to correct the problem that is commensurate with the importance of maintaining secondary containment during Modes 1, 2, and 3, since the probability of an accident occurring during this short period where secondary containment is inoperable is minimal.
Risk Insights The plant Probabilistic Risk Assessment (PRA) model gives no credit to the secondary containment and does not include it in the model, hence the as-found conditions did not contribute to an increase in risk.
Although a secondary containment loss of function occurred momentarily when the Unit 2 RBI HRSS-side door was found open concurrently with the opening of the Unit 2 RB 595 Interlock door, there was no DBA condition in progress, and secondary containment was restored within eight (8) seconds when the Unit 2 RBI HRSS-side door was immediately reclosed.
In conclusion, the overall safety significance and impact on risk of this event were minimal.
E.
CORRECTIVE ACTIONS
Immediate:
- 1. An initial inspection was performed on the latching mechanism for the Unit 2 RBI HRSS-side door.
- 2.
The Unit 2 RBI HRSS-side door (2-0020-153) was closed and confirmed fully latched, which eliminated the immediate secondary containment integrity concerns.
- 3. The RBV was recovered and established to maintain the Reactor Building at a negative d/p compared to the outside atmosphere.
- 4.
A solid robust barrier (block) was placed between the crash bar on the Unit 2 RBI HRSS-side door and the door itself to prevent inadvertent depressing of the crash bar.
- 5.
Operations barricaded and removed the Unit 1 and Unit 2 RBI HRSS-side doors (1-0020-147 and 2-0020-153) from service.
Follow-up:
- 1.
Unit 1 and Unit 2 RBI HRSS-side doors will be inspected and repairs will be made to return the crash bar and door latch assemblies to approved vendor specifications.
- 2.
A determination will be made of the feasibility of installing a secondary latching device on the inside of the Unit 1 and Unit 2 RBI HRSS-side doors, capable of preventing the doors from inadvertent opening in the event the primary latch fails.
- 3.
The Unit 1 and Unit 2 RBI HRSS-side doors will be removed by permanently enclosing the door opening.
- 4. The issue of re-occurring low d/p conditions during Reactor Building ventilation changes will be resolved.
F.
PREVIOUS OCCURRENCES
The station events database, LERs, EPIX, and NPRDS were reviewed for similar events at Quad Cities Nuclear Power Station. This event was a secondary containment loss of function when a latch assembly failed to hold a door closed during a loss of d/p condition in the Reactor Building. No similar events were found.
G.
COMPONENT FAILURE DATA
Door catch - Component Manufacturer: Folger Adam Co., Component Model Number: 310 - 2 3/4.
This event has been reported to ICES as Failure Report No. 300532.