05000528/LER-2013-004, Regarding Condition Prohibited by Technical Specification 3.7.2 Due to an Inoperable Main Steam Isolation Valve (MSIV)
| ML14163A529 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 06/09/2014 |
| From: | Mims D Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06889-DCM/SPD LER 13-004-00 | |
| Download: ML14163A529 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| LER closed by | |
| IR 05000528/2000529 (13 August 2014) IR 05000528/2014003 (13 August 2014) | |
| 5282013004R00 - NRC Website | |
text
10 CFR 50.73 Caps DWIGHT C. MIMS Senior Vice President, Nuclear Regulatory & Oversight Palo Verde Nuclear Generating Station P.O. Box 52034 Phoenix, AZ 85072 Mail Station 7605 Tel 623 393 5403 102-06889-DCM/SPD June 9, 2014 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Unit 1 Docket No. STN 50-528/License No. NPF 41 Licensee Event Report (LER) 2013-004-00 Enclosed please find LER 50-528/2013-004-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports a condition prohibited by Technical Specification 3.7.2, Main Steam Isolation Valves.
In accordance with 10 CFR 50.4, copies of this LER are being forwarded to the Nuclear Regulatory Commission (NRC) Regional Office, NRC Region IV, and the Senior Resident Inspector.
Arizona Public Service Company makes no commitments in this letter. If you have questions regarding this submittal, please contact Mark McGhee, Department Leader, Regulatory Affairs, at (623) 393-4972.
Sincerely, DCM/SPD/hsc Enclosure Cc:
M. L. Dapas J. K. Rankin M. M. Waterford M.A. Brown NRC Region IV Regional Administrator NRC NRR Project Manager PVNGS NRC NRR Project Manager PVNGS NRC Senior Resident Inspector PVNGS A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
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Send comments regarding burden estimate to the FOIA, Privacy and Information Collections O
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Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by
.- LICENSEE EVENT REPORT (
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- 3. PAGE Palo Verde Nuclear Generating Station (PVNGS) Unit 1 05000528 1 OF 5
- 4. TITLE Condition Prohibited by Technical Specification 3.7.2 Due to an Inoperable Main Steam Isolation Valve (MSIV)
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
I FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO. I FACILITY NAME DOCKET NUMBER 11 06 2013 2013-004 00 06 09 2014
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[]
20.2201(b)
[]
20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
El 20.2201(d)
E] 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)
[1 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
El 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)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 0% 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
[
50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in 12.__ _ _ _ _ _
The common hydraulic pump provides pressurized hydraulic fluid to both actuator trains on an MSIV and is a pneumatically operated positive displacement pump powered by the instrument air system.
The pump takes suction on a common hydraulic fluid reservoir and discharges to the hydraulic systems for each actuator train to charge the accumulators with hydraulic fluid. The hydraulic pump is also used to provide motive power during normal operations for slow opening and slow closing of the MSIV.
The hydraulic fluid reservoir is used to make up for fluid system losses and is provided with a low fluid level alarm. The annunciation of low hydraulic reservoir fluid level provides indication to control room operators of loss of hydraulic fluid or loss of nitrogen pre-charge pressure in one of the two hydraulic accumulators on the MSIV. Upon receipt of this alarm, operating and alarm response procedures direct the operators to check fluid reservoir level and to perform nitrogen pre-charge checks to verify each accumulator contains an adequate nitrogen volume. To perform a nitrogen pre-charge check the accumulator's pressurized hydraulic fluid is discharged to the reservoir allowing measurement and adjustment of the accumulator nitrogen pressure. During a nitrogen pre-charge check the tested accumulator is inoperable due to its hydraulic fluid pressure being below the required value; however, the associated MSIV can remain operable due to the opposite actuator train remaining fully capable to fast close the MSIV.
The actuation of the MSIV is controlled by the position of two four-way control valves that operate together to direct hydraulic fluid as needed to change valve position. One four-way valve controls the flow of hydraulic fluid from the pressurized accumulator to the MSIV actuator or the fluid reservoir while the other four-way valve controls the flow of hydraulic fluid to either side of the MSIV actuator hydraulic piston (bottom for opening, top for closing). Instrument air provides pilot air to the four-way control valves to position them as needed for opening and closing the MSIV. An air reservoir is provided on each actuator train as a backup control air supply for positioning the hydraulic fluid control valves. The air reservoirs ensure the MSIV can be closed following loss of instrument air system supply pressure.
While all MSIVs are normally fully open during power operations, PVNGS alarm response procedures provide guidance for plant operation following inadvertent closure of one MSIV during power operations. Engineering analysis has shown that plant operation with one MSIV closed is acceptable below 65 percent power for a limited period of time. Following inadvertent closure of one MSIV, procedures direct operators to reduce power to less than 65 percent, stabilize power and monitor power distribution limits until the MSIV can be reopened.
- 3.
INITIAL PLANT CONDITIONS
On November 6, 2013, at 1307, PVNGS Unit 1 was in Mode 1 (Power Operation) operating steady state at 100 percent power and normal operating temperature and pressure. There were no other major structures, systems, or components out of service that contributed to the event.
- 4.
EVENT DESCRIPTION
On November 6, 2013, at 0945, the Unit 1 control room received an alarm for MSIV-1 70 hydraulic reservoir low fluid level. An operator was sent to respond to the alarm and reported to the control room that there was no evidence of hydraulic fluid leakage, and reservoir level was confirmed to be low. In
accordance with alarm response and operating procedures operators initiated the performance of MSIV accumulator pre-charge checks for MSIV-170. On November 6, 2013, at 1307, during performance of the train A accumulator pre-charge check, while discharging hydraulic fluid from the pressurized accumulator to the vented reservoir, operators in the main steam support structure reported a major failure of the hydraulic reservoir and ejection of approximately 15 gallons of hydraulic fluid from the reservoir to the surrounding area.
Following the event, the MSIV-1 70 train A accumulator was inoperable due to the nitrogen pre-charge check and the train B accumulator became inoperable when its hydraulic fluid pressure dropped below 5000 psig due to hydraulic fluid leakage from a mechanical union on the accumulator outlet pipe which was displaced from the failure of the hydraulic reservoir.
At 1307, the control room operators declared MSIV-170 inoperable and entered the following Conditions of LCO 3.7.2:
Condition A - One MSIV with a single actuator train inoperable Condition D - Two actuator trains for one MSIV inoperable Condition F - One MSIV inoperable in MODE 1 At 1707, the completion time for LCO 3.7.2 Condition F was exceeded and LCO 3.7.2 Condition G was entered, which requires the Unit be in Mode 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. At 1952, Unit 1 commenced a power reduction to comply with the shutdown requirement of Condition G. Activities were also initiated to prepare for closure of MSIV-170 during the power reduction.
At 2247, MSIV-1 70 was closed, deactivated, and declared operable and LCO 3.7.2, Conditions A, D, F, and G were exited. An operability determination was performed that concluded the MSIV was operable because the valve safety function was met with the valve closed and deactivated. Plant power was stabilized at 60 percent.
On November 9, 2013, MSIV-1 70 was opened at 0028 following completion of corrective maintenance and successful retesting. Following power ascension Unit 1 returned to 100 percent power on November 9, 2013, at approximately 0900.
On April 10, 2014, a post-event review conducted in response to a proposed NRC non-cited violation concluded the actions to close and deactivate MSIV-1 70 on November 6, 2013, did not meet the operability requirements of LCO 3.7.2. As a result, the requirement of LCO 3.7.2 Condition G to place the unit in Mode 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> was not completed and a condition prohibited by technical specifications occurred.
- 5.
ASSESSMENT OF SAFETY CONSEQUENCES
This event did not result in a potential transient more severe than those analyzed in the Updated Final Safety Analysis Report (UFSAR) or result in the release of radioactive materials to the environment. There were no actual safety consequences as a result of this event and the event did not adversely affect the health and safety of the public.
The safety function of the MSIVs is to isolate the steam generators in the event of a high energy line break (HELB), the most limiting of which is a HELB upstream of the MSIVs inside the containment
building. The safety analysis for the event assumes the MSIV on the faulted line fails to close upon receipt of an MSIS.
During the period while MSIV-1 70 was inoperable and open while the reactor was in Mode 1, the three remaining operable MSIVs were capable of actuation and closure to perform the required isolation function to ensure the analyzed safety function would have been met. When MSIV-170 was closed to facilitate repair the safety function was met by all four MSIVs. Therefore, the event did not result in potential safety consequences beyond those analyzed in the UFSAR.
The event would not have prevented the fulfillment of a safety function; and, the condition did not result in a safety system functional failure as defined by 10 CFR 50.73 (a)(2)(v).
- 6.
CAUSE OF THE EVENT
An investigation determined the cause of the condition prohibited by TSs was the operability determination was overly focused on the ability of the MSIV to perform its specified safety function and did not adequately consider the definition of operability and compliance with the TS.
- 7.
CORRECTIVE ACTIONS
To prevent recurrence, PVNGS operability determination (OD) guidance will be revised to explicitly require evaluation of applicable LCOs to ensure the OD technical conclusions support compliance with the LCOs.
- 8.
PREVIOUS SIMILAR EVENTS
No similar conditions have been reported by PVNGS.