05000529/LER-2003-001, Regarding Reactor Trip with Loss of Forced Circulation Due to Failed Pressurizer Main Spray Valve
| ML032810233 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 09/29/2003 |
| From: | Overbeck G Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 192-01125-GRO/RAS LER 03-001-00 | |
| Download: ML032810233 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 5292003001R00 - NRC Website | |
text
1 OCFR50.73 Gregg R Overbeck Mail Station 7602 Palo Verde Nuclear Senior Vice President TEL (623) 393-5148 P.O. Box 52034 Generating Station Nuclear FAX (623) 393-6077 Phoenix, AZ 85072-2034 192-011 25-GRO/RAS September 29, 2003 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-37 Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS) Unit 2 Docket No. STN 50-529 License No. NPF-51 Licensee Event Report 2003-001-00 Attached please find Licensee Event Report (LER) 50-529/2003-001-00 prepared and submitted pursuant to 10 CFR 50.73. This LER reports the Unit 2 manual reactor trip and related events which occurred on July 29, 2003.
The corrective actions described in this LER are not necessary to maintain compliance with regulations and therefore, Arizona Public Service Company makes no NRC commitments in this correspondence. In accordance with 10 CFR 50.4, a copy of this LER is being forwarded to the NRC Region IV Office and the Senior Resident Inspector.
If you have questions regarding this submittal, please contact Daniel G. Marks, Section Leader, Regulatory Affairs, at (623) 393-6492.
Sincerely, GRO/RAS Attachment cc:
B. S. Mallet, Region IV Administrator (all with attachment)
N. L. Salgado, Sr. Resident Inspector M. B. Fields, PVNGS Project Manager A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon Palo Verde South Texas Project
- Wolf Creek
i APPROVED BYOMB NO. 3150-0104 EXPIRES 7-31-2004
Abstract
On July 29, 2003, at 1500 Mountain Standard Time (MST), Unit 2 was at approximately 98% power when pressurizer main spray valve RCE-IOOF failed in the full open position. Attempts to close the valve per the alarm response procedure were unsuccessful. At 1515 MST, control room personnel manually tripped the reactor. In accordance with the applicable alarm response procedure, control room personnel secured the reactor coolant pumps (RCPs) to stop the reactor coolant system (RCS) depressurization. Control element assemblies fully inserted into the reactor core. Safety related buses remained energized during and following the reactor trip.
Automatic safety injection and containment isolation actuation system (SIAS/CIAS) actuations occurred following the reactor trip, as RCS pressure continued to lower to the reactor protection system setpoint. The RCS was cooled on natural circulation with secondary heat removal via the main condenser. By 1616 MST, a containment entry was made and RCE-10OF was manually isolated. At 1715 MST, RCP 1A was restarted restoring forced circulation to the reactor core. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event There were no previous events that involved the same underlying cause within the last three years.
NRC FORM 380 (7-2001)
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Subsequent to the reactor trip the plant responded as designed. The reactor trip was uncomplicated, no safety limits were exceeded, and the event was bounded by current
safety analyses
Primary and secondary pressure boundary limits were not exceeded as a result of the reactor trip. The transient did not cause any violation of the safety limits.
Therefore, there were no adverse safety consequences or implications as a result of this event This event did not adversely affect the safe operation of the plant or health and safety of the public.
The condition (RCE-100F full open) did not prevent the fulfillment of any safety function and did not result in a safety system functional failure as defined by 1 OCFR50.73(a)(2)(v).
- 6.
CAUSE OF THE EVENT
RCE-1 OF's positioner balance beam was found disengaged from its pivot point and came to rest in a position that obstructed the positioner air vent. This obstruction prevented the venting of the positioner air relay, which then caused the maximum amount of air to be delivered to open the spray valve, overriding the close demand signal from the control room. At the time of submittal, APS had not conclusively determined the root cause of the balance beam disengagement from its pivot point.
No unusual characteristics of the work location (e.g., noise, heat, poor lighting) directly contributed to this event.
- 7.
CORRECTIVE ACTIONS
Control room personnel took immediate action to place the reactor in a stable condition in accordance with the applicable procedures.
Unit 1, 2 and 3 Fisher air operated valve positioners for the RCE-100 E and F main pressurizer spray valves were replaced with new positioners.
Applicable procedures were revised to require the monitoring of the main pressurizer spray valve operation prior to fully aligning these valves for RCS pressure control.
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- 8.
PREVIOUS SIMILAR EVENTS
In the past three years there have been no similar events where a Palo Verde Generating Unit experienced a reactor trip with LOFC due to a failed pressurizer main spray valve.
- 9.
ADDITIONAL INFORMATION
Subsequent to the event, the shift technical advisor (STA) group did not promptly notify the System Engineering department that a safety injection had occurred as a result of the reactor trip (this delay was also noted by the resident NRC inspector).
During the post-trip plant performance evaluation, the initiation of the SIAS signal and RCS pressures were reviewed and it was noted that RCS pressure had lowered to 1792 psia (below the 1837 psia SIAS/CIAS setpoint). The STA group was initially not certain that an actual injection had occurred due to the lack of confirmatory flow indication and unknown piping head losses present at the time of the event. The subsequent review confirmed a safety injection had occurred and the initial NRC event notification was supplemented to reflect this finding.
Procedural enchantments were made to ensure that the total number of HPSI nozzle thermal cycles does not exceed the UFSAR limit without prior engineering evaluation.
The current Unit 2 HPSI thermal cycle count was seven, with a procedural limit of 112 (70% of the UFSAR allowable cycles) before an Engineering evaluation is necessary.
The HPSI cycle (injection) that occurred during this event has been taken into account by the System Engineering department through the corrective action program.