05000528/LER-2007-005

LER-2007-005, Inadequate Surveillance Test Procedure Resulted in Failure to Meet Surveillance Requirement

Palo Verde Nuclear Generating Station (Pvngs)
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function
5282007005R01 - NRC Website

Note: All times listed in this event report are approximate and Mountain Standard Time (MST) unless otherwise indicated.

1. REPORTING REQUIREMENT(S):

This LER (50-528/2007-005-01) is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) to report operation in a condition prohibited by Technical Specifications (TS). Specifically, TS Surveillance Requirement (SR) 3.3.5.4 requires verification every 18 months that Engineered Safety Features (ESF) response times are within limits. Contrary to this requirement, the existing surveillance test proCedures (STP) did not verify that the TS SR for response time testing was met for certain Auxiliary Feedwater (AF) System valves (EDS Code: BA), the Main Steam Isolation Valves (MSIV) (ElIS Code: SB), the Feedwater Isolation Valves (FWIV) (EllS Code: SJ), and the AF pump steam admission valves.

Equipment Description:

Valves identified within the scope of this condition are as follows:

• Eight AF System flow regulating and isolation valves for all three units: AFAHVO032, AFCHVO033, AFCUV0036, AFAUV0037, AFBHVO030, AFBHVO031, AFBUV0034, and AFBUV0035

• Four MSIVs for all three units: SGEUV0170, SGEUV0171, SGEUV0180, and SGEUV0181

• Four FWIVs for all three units: SGBUVO132, SGBUV0137, SGAUV0174, and SGAUV0177

• Four AF pump steam admission valves for all three units: SGAUV134, SGAUV138, SGAUV134A, and SGAUV138A The AF regulating and isolation valves provide water to the Steam Generators (SG) upon receipt of an Auxiliary Feedwater Actuation System (AFAS) signal, and serve to isolate the AF system upon receipt of a SG differential pressure signal indicative of a ruptured SG.

The AF valves also automatically cycle open and closed based on SG water levels after AFAS is initiated.

The AF system steam admission valves supply steam to the turbine driven AF pump, which supplies feedwater to the SG.

The AF system provides an independent means of supplying feedwater to the SG during normal shutdown, startup, and emergency or accident conditions. The AF system functions to maintain water inventory for reactor decay heat removal during those phases of plant operation when the Main FW system is unavailable.

The control circuitry for the AF valves and the steam admission valves uses relays AX and AY to control automatic valve operation (open and closed) during events that require an auxiliary feedwater actuation.

The MSIVs isolate the Main Steam (MS) System (ElIS Code: SB) upon receipt of an actuation signal in response to a High Energy iLine Break (HELB) inside containment, a MS line break, a SG tube rupture, or a feedwater line break.

The FWIVs isolate the Feedwater (FW) System (EllS Code: SJ) upon receipt of an actuation signal in response to a HELB inside containment, a MS line break, a SG tube rupture, or a feedwater line break.

The control circuitry for the MSIVs and the FWIVs uses an isolation relay, commonly referred to as a buffer relay, to provide isolation from transient noise which could otherwise cause a spurious actuation.

3. INITIAL PLANT CONDITIONS:

On August 21, 2007, Palo Verde Units 1, 2 and 3 were in Operating Mode 1 (Power Operations), at approximately 100 percent power. No other components were inoperable that contributed to this condition.

4. EVENT DESCRIPTION:

On August 21, 2007, during performance of a Component Design Basis Review (CDBR) of the AF system motor operated valves (MOV), station personnel determined that the existing STPs for the AF regulating and isolation valves did not ensure compliance with TS SR 3.3.5.4, verification of ESF response time. The TS definition of ESF response time is:

"The ENGINEERED SAFETY FEATURES RESPONSE TIME shall be that time interval from when the monitored parameter exceeds its ESF actuation setpoint at the channel sensor until the ESF equipment is capable of performing its safety function (i.e., the valves travel to their required positions, pump discharge pressures reach their required values, etc.).

There were two separate issues identified which impacted the existing test program's ability to meet SR 3.3.5.4 as follows:

• The complete circuit was not being properly time tested in that not all relays in the valve circuitry were included in the response time testing.

• The stroke time measurement used a test method that measured the time from hand switch initiation to receipt of valve position indication, either in the closed or open direction. Depending on the position limit switch setting, the measured time can end prior to full travel of the valve.

On August 21, 2007, Control Room personnel were notified of the conditions noted above for the AF regulating and isolation valves. At this time, station personnel had identified that the AX relay was not included in the STPs for response time testing for these valves. Control Room personnel entered the Operability Determination process.

The Shift Managers for all three units concluded that there was a reasonable assurance of operability for the identified valves, and entered TS SR 3.0.3 to allow a delay for compliance with the requirement to declare the limiting condition for operation (LCO) not met.

As part of the extent of condition analysis, a review of components in each unit which require ESF response time testing was completed. The analysis revealed the following additional components that were impacted by the two conditions identified above as follows:

• On September 7, 2007, Control Room personnel were notified that the AY relays were not tested for the AF regulating and isolation valves, and that the scope of valves impacted by the two conditions identified above had increased to include the steam admission valves to the steam driven AF pump. The Shift Managers for all three units again concluded that there was a reasonable assurance of operability for these additional components.

• On September 18, 2007, Control Room personnel were notified that the scope of valves impacted by the two conditions identified above had increased to include the MSIVs and the FWIVs. The buffer relays in the actuation circuitry for the MSIVs and FWIVs were not response time tested'as part of any STP. The Shift Managers for all three units again concluded that there was reasonable assurance of operability for these additional valves.

TS SR 3.0.3 was entered for AF steam admission valves, MSIVs and FWIVs. In addition, at this time it was identified that entry into TS SR 3.0.3 should have been made on September 7, 2007, for the steam admission valves to the steam driven AF pump.

The operability determinations were based on the following information:

• For the AF regulating and isolation valves, licensing basis documents establish that the most limiting consideration for valve actuation is to close within 15 seconds of receipt of the actuation signal. The worst case for the latest response time testing for any of these valves was 13.13 seconds which, when added to the expected response time of the AY relay (180 milliseconds) and the additional travel time estimated to achieve closure following receipt of the closed indication (660 milliseconds), yields a revised response time of 13.97 seconds, which is within the limit of 15 seconds.

• For the MSIVs, licensing basis documents establish the most limiting consideration is to close within 4.6 seconds from receipt of an actuation signal.

The worst case for the latest response time testing for any of the MSIVs was 3.78 seconds which, when added to the expected response time of the buffering relay (25 milliseconds), yields a revised response time of 3.8 seconds, which is within the limit of 4.6 seconds.

• For the FWIVs, licensing basis documents establish the most limiting consideration is to close within 9.6 seconds from receipt of an actuation signal.

The worst case for the latest response time testing for any of the FWIVs was 6.94 seconds which, when added to the expected response time of the buffering relay (25 milliseconds), yields a revised response time of 6.97 seconds, which is within the TS limit of 9.6 seconds.

• For the steam admission valves to the steam driven AF pump, licensing documents establish the most limiting consideration is for the valves to open within 10 seconds from receipt of an actuation signal. The worst case for the latest response time testing for any of the valves was 7.62 seconds which, when added to the expected response time of the AX relay (180 milliseconds) and the additional travel time estimated to complete opening following receipt of the open indication (1.91 seconds), yields a revised response time of 9.71 seconds, which is within the limit of 10 seconds.

5. ASSESSMENT OF SAFETY CONSEQUENCES:

Risk assessments were performed to determine potential adverse impact of the conditions as required by TS SR 3.0.3. These assessments considered the design safety functions of the components, the previous test data for performance, and the timing requirements for actuation signals. The summation of this assessment is as follows:

• For the AX and AY relays, data indicates an expected response time of 180 milliseconds. These relays are functionally tested, but not time tested, in the STP "ESFAS Train A (/B) Subgroup Relay Functional Test.

• For the buffering relays in the MSIV and FWIV actuation circuitry, commercial data indicates an expected response time of 25 milliseconds. These relays are functionally tested, but not time tested, in the STP "Class 1 E Diesel Generator and Integrated Safeguards Test Train A (IB)".

• The additional time required for the valves to travel to their required position, after the position indication indicates the valve is at that position, was determined to be 660 milliseconds for the AF regulating and isolation valves, 1.91 seconds for the steam admission valves and negligible for the MSIVs and FWIVs.

• When adding the additional time for relay response time and the additional valve travel time to the latest response time testing for the valves affected by this condition, the revised overall response time for each of the valves is within limits.

• The risk assessments concluded that there was no increased risk from the failure to include the relays and additional valve travel time in response time testing.

This conclusion was based on two considerations:

1. The valves passed their most recent functional SR tests to demonstrate the relays were functional.

2. The maximum time that the relay response and additional valve travel could possibly add to the response time was not significant compared to the required design response time. Additionally, the risk critical timing is significantly longer than design response time; therefore risk was not adversely impacted since the additional time would not result in exceeding the design response time.

The event did not result in any challenges to the fission product barriers or result in the release of radioactive materials. There were no adverse safety consequences or implications as a result of this event and the event did not adversely affect the safe operation of the plant or health and safety of the public.

The event did not result in a transient more severe than those analyzed in the updated Final Safety Evaluation Report Chapters 6 and 15. The event did not have any nuclear safety consequences or personnel safety impact.

The condition would not have prevented the fulfillment of any safety function of structures or systems as defined by 10 CFR 50.73(a)(2)(v).

6.�CAUSE OF THE CONDITION:

The direct cause of the failure to perform the required testing of the AX, AY and buffer relays in the affected MOV actuation circuitry was inadequate STPs which did not contain steps to test the AX, AY and buffer relay response times as part of the overall component actuation response time testing.

The root cause of the failure to adequately perform the required testing of the subject components was inadequate oversight of the TS required testing, where testing requirements were satisfied by sequential or overlapping tests. Prior to initial plant startup, adequate hot functional testing was performed to meet the TS SRs for the subject components. However, in the transition to operational testing, not all TS SRs were captured in the sequential or overlapping tests.

7. CORRECTIVE ACTIONS:

STPs have been revised to test the AX, AY, and buffer relays for the affected valves.

A review of TS SRs that are met through the performance of sequential or overlapping STPs did not identify any other issues with meeting the TS SRs.

The Component Engineering Group was assigned the responsibility to act as the program owner for all required surveillance tests as defined in procedure 73DP-OAP05, Engineering Programs Management and Health Reporting.

Study 13-MS-0003 was conducted to evaluate available stroke time test data, design data and provide an adjustment factor, if required, for static stroke time testing using control room indicating lights. An evaluation of the study results is being performed on each valve to determine if test changes are required.

8. PREVIOUS SIMILAR CONDITIONS:

TS SR to ensure the Containment Spray system headers were full of water. The corrective actions from the 004 LER could not have prevented the condition in the current LER due to the length of time the condition described in the current LER has existed.

removal of required testing of Shutdown Cooling isolation valve interlocks. The cause of this event was personnel error during performance of the 10CFR 50.59 review for the STP revision. The corrective actions for that event would not have prevented this event due to the different nature of the cause.