05000265/LER-2014-004, Regarding HPCI Inlet Drain Pot Level Switch Failure
| ML15008A027 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 12/30/2014 |
| From: | Darin S Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVP-14-094 LER 14-004-00 | |
| Download: ML15008A027 (5) | |
| 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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2652014004R00 - NRC Website | |
text
Aw-Exe!on Generation.
December 30, 2014 10 CFR 50.73 SVP-14-094 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20585 Quad Cities Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-30 NRC Docket No. 5M265
Subject:
Licensee Event Report 265/2014-004-00, "Unit 2 HPCI Inlet Drain Pot Level Switch Failure" Enclosed Is Licensee Event Report (LER) 265/2014-004-00, "Unit 2 HPCI Inlet Drain Pot Level Switch Failure," for Quad Cities Nuclear Power Station, Unit 2.
This report Is submitted in accordance with 10 CFR 50.73 (a)(2)(v)(O) which requires the reporting of any event or condition that could have prevented fulfillment of a safety function.
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.
Re~
Ito Vice President Quad Cities Nuclear Power Station cc:
Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - Quad Cities Nuclear Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 (02-2014)
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Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
.LICENSEE EVENT REPORT (LER)
Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. It a means used to impose an information collection does not display a currently valid OMB digits/characters for each block) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Quad Cities Nuclear Power Station Unit 2 05000265 1 OF 4
- 4. TITLE Unit 2 HPCI Inlet Drain Pot Level Switch Failure
- 5. EVENT DATE
- 6. LER NUMBER T 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR EAR SEQUENTIAL REV FACITY NAME DOCKET NUMBER NUMBER NOI N/A l
iz lz lFACILITY NAME DOCKET NUMBER 11 04 2014 2014
- - 004 0
12 30 2014 N/A I
N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
[1 50.73(a)(2)(i)(C)
E] 50.73(a)(2)(vii)
U 20.2201(d)
LI 20.2203(a)(3)(ii)
LI 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
U 20.2203(a)(1)
U 20.2203(a)(4)
U 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
U 20.2203(a)(2)(i)
[: 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
[:
50.73(a)(2)(ix)(A)
- 10. POWER LEVEL LI 20.2203(a)(2)(ii)
LI 50.36(c)(1)(ii)(A)
LI 50.73(a)(2)(iv)(A)
LI 50.73(a)(2)(x)
LI 20.2203(a)(2)(iii)
LI 50.36(c)(2)
LI 50.73(a)(2)(v)(A)
LI 73.71 (a)(4) 10 20.2203(a)(2)(iv)
[
50.46(a)(3)(ii)
U 50,73(a)(2)(v)(B)
LI 73.71 (a)(5) 100 LI 20.2203(a)(2)(v)
LI 50.73(a)(2)(i)(A)
LI 50.73(a)(2)(v)(C)
LI OTHER El 20.2203(a)(2)(vi)
LI 50.73(a)(2)(i)(B)
[
50.73(a)(2)(v)(D)
Specify in Abstract below or in I_
particular level switch is designed to actuate on a slow rate of change in process fluid. Vendor data has shown that rapid pressure surges can cause degradation to the drain pot assembly.
For the reasons outlined above, it was concluded that current system restoration practices may cause a premature failure of the level switch components. When restoring HPCI, the inlet drain pot should be isolated from the main steam line until the system is fully pressurized and then placed into service in a controlled manner utilizing the inlet drain pot manual isolation valves. Isolating the inlet drain pot from the steam supply line is not a requirement, but considered a good practice by the vendor.
D. SAFETY ANALYSIS
System Design
The HPCI system is designed to inject water into the Reactor Vessel under loss-of-coolant conditions which do not result in a rapid depressurization of the Reactor Vessel (small break LOCA). Steam condensate inside the turbine or steam lines can cause turbine blade erosion, high thrust bearing loads or a significant hydraulic system pressure transient. The HPCI system is equipped with turbine drain lines that maintain the HPCI turbine in a standby condition by removing condensed steam from upstream of the steam supply isolation valve, the steam chest, the turbine case and the turbine exhaust line upstream of the exhaust check valve. On an automatic or manual pushbutton start, the drain system valves will realign to meet injection demands.
Any condensed steam in the HPCI steam supply line upstream of the turbine inlet valve is drained through a steam trap/orifice and two normally open air-operated isolation valves [ISV] to the main condenser [SG]. During a HPCI system actuation, the open air-operated valves automatically close and the steam line drain valve to the exhaust drain pot opens. The exhaust drain pot is then drained via turbine exhaust pressure to the Torus.
A float-type level switch is provided to detect a failure of the steam trap/orifice during standby conditions. On high level in the inlet drain pot, the level switch actuates to provide an alarm in the Control Room and automatically opens the steam trap bypass valve to drain the collected condensate. If the HPCI system is started in this condition, a water slug could be accelerated through the turbine and cause equipment damage.
Safety Impact The primary condensate removal pathway for the HPCI system in a standby condition is through a steam trap/orifice and two normally open air-operated isolation valves to the main condenser. The identified condition did not impact the primary condensate removal pathway. The Unit 2 HPCI Inlet Drain Pot High Level Alarm is a means to identify any potential issues with the primary pathway. In the event the primary pathway becomes unavailable due to a blocked steam trap/orifice or a potential stem/disk separation of a manual isolation valve, the drain pot level switch will actuate on a high level, and open the steam trap bypass valve to drain the collected condensate within the HPCI steam supply line. After the identification of the level switch failure on November 4, the primary pathway was validated via thermography to be functional at the first available opportunity. The opportunity to validate the primary pathway was not available until the HPCI system was unisolated and the steam supply line was repressurized. This occurred on November 5, 2014, as part of the system restoration.
The verification that the primary pathway was functional provides reasonable assurance that the HPCI steam supply was always clear of condensate to support the operability of HPCI during prior operation. The steam trap/orifice and the two associated manual isolation valves [ISV] for the steam trap/orifice, which are passive by design, were not manipulated as part of the HPCI surveillance activities. No extra water was passed through this drain line as part of the HPCI surveillance activities. The clean water used in the surveillance is added/removed via manual valves located on the drain pot, and the drain pot remained isolated from the steam line drains during this surveillance until drained. The only water that passed through the drain lines would have been the condensate that was normally formed as a result of isolating and restoring the HPCI steam supply system. This provides
reasonable assurance that the conditions of the primary pathway immediately following the restoration of HPCI were as close as possible to the conditions of the primary pathway before HPCI was removed from service for planned surveillances.
This condition does not constitute a Safety System Functional Failure (SSFF) as the condition did not affect the function of HPCI to respond to a design basis event. As noted above, while the Unit 2 HPCI Inlet Drain Pot Level Switch was degraded, the ability of the HPCI to complete its specified safety function was not compromised. It is reasonable based on the above discussion that the operability of the Unit 2 HPCI system was maintained given there was no adverse impact on the ability to remove condensate from the HPCI steam supply line.
The engineering analysis that was performed demonstrated this event did not constitute a SSFF. (Reference NEI 99-02, Revision 7, Regulatory Assessment Performance Indicator Guideline, Section 2.2, Mitigating Systems Cornerstone, Safety System Functional Failures, Clarifying Notes, Engineering analyses.) As such, this event will not be reported in the NRC Performance Indicator (PI) for safety system functional failures since an engineering analysis was performed which determined that the system was capable of performing its safety function with the identified degraded condition.
Risk Insights Since the operability of HPCI was maintained at all times, there was no impact on safety or risk.
E. CORRECTIVE ACTIONS
Immediate:
Temporary procedures have been implemented to verify periodically that the HPCI inlet drain pot is clear of condensate and the steam trap bypass valve remains open.
Follow-up:
Incorporate procedure changes to isolate the HPCI Inlet Drain Pot before system restoration.
F. PREVIOUS OCCURRENCES
The station events database, LERs, and INPO Consolidated Event System (ICES) were reviewed for similar events at Quad Cities Nuclear Power Station. This event was caused by excessive/repeated level switch cycling due to system restoration practices.
No previous occurrences were identified in this search applicable to the outlined apparent cause.
G. COMPONENT FAILURE DATA
Failed Equipment: Level Switch Component Manufacturer: Magnetrol Component Model Number: XB40 Component Part Number: 1403923 This event has been reported to ICES as Failure Report No. 313737