05000298/LER-1999-001, :on 990222,failure to Recognize Set Point Shift Caused Common Mode Failure of HPCI Pressure Switches. Pressure Switches Were Recalibrated & Returned to Svc & Operability Evaluation Performed
| ML20205A694 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 03/22/1999 |
| From: | Radloff R NEBRASKA PUBLIC POWER DISTRICT |
| To: | |
| Shared Package | |
| ML20205A682 | List: |
| References | |
| LER-99-001, LER-99-1, NUDOCS 9903310047 | |
| Download: ML20205A694 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2981999001R00 - NRC Website | |
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s NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION I APPROVED BY OMB NO. 3150-olo4 EXPlRES o6/30/2001 (6-1998)
, the NPc may not mnduct or sponsor, and a person is not required to respond to, the information collection.
FACluTY NAME (1)
DOCKET NUMBER (2)
PAGE (3)
Cooper Nuclear Station 05000298 1 OF 4 TITLE M)
Feilure to Recognize Set Point Shift Causes Common Mode Failure of High Pressure Coolant injection Pressure Switches EVENT DATE 151 LER NUMBER M)
REP 3RT DLTE 171 OTHER FACILITIES INVOLVED (8)
SEQU AL R
t:0 NTH DAY VEAR VIAR MONTH DAY YEAR NM 05000 02 22 1999 1999
-- 001 --
00 03 22 1999 05000 OPERATING THIS REPORT IS SUBM TTFD PURSUANT TO THE REOl'IREMENTS OF to CFR 1: ICheck one or more) fill j
MODE (9) 20.2201(b) 20.2203(aH2)(v) 50.73(a)(2Hi) 50.73(aH2)(viii)
POWER 20.2203(aH1) 20.2203(a)(3)0) 50.73(a)(2Hii) 50.73(a)(2)(x) 100 LEVEL (10) 20m3(ann 20r03(anam 5033mHim 73m 20.2203(a)(2)Dil 20.2203(a)(4) 50.73(aH2)(iv)
OTHER 20.2203(aH2)(iii) 50.36(cH1) 50.73(a)(2)(v) specify in Abstract below 20.2203(a)(2)0v) 50.36(c)(2)
X 50.73(aH2Hvii) r in NRC Form 366A l
LICENSEE CONTACT FOR THIS LEFl(12)
NAME TELEPHONE NUMBER (include Area Codel Roy A. Radioff, Licensing Engineer (402) 825-3811 COMPLETF ONE LINE FOR E ACH COMPONENT FAILURE DEECRIBED IN THIS REPORT L13)
RE RT BLE N
CAUSE
SYSTEM C0lt*0NENT MANUFACTURER
CAUSE
SYSTEM COMPONENT MANUFACTURER T EP D
BJ PS S382 N
SUPPiEMENTAL REPDRT EXPECTED f141 EXPECTED YES SUBMIS$10N X
NO DATE (15)
Uf yes. complete EXPECTED SUBMISSION DATE).
ABSTRACT (Limit to 1400 spaces, Le., approximately 15 single-spaced typewritten lines) (16)
On February 11,1999. during the performance of the Division 11 functional surveillance test for High Pressure j
Coolant injection (HPCi) (Ells:BJ) Steam Line Low Pressure switches (Ells:PS), HPCI-PS-68B and -68D were found out of allowable calibration range and below the Technical Specification (TS) allowable value. The instruments were recalibrated and returned to service. During the subsequent performance of the Division I functional / calibration test, HPCI-PS-68C was also found to be out of allowable calibr:Ilon range and below the TS allowable value.
Action was taken to increase the frequency of the functional / calibration testing to ensure set point accuracy is maintained.
On February 22,1999, during an evaluation of the performance of the pressure switches with the increased surveillance frequency, it was recognized that these failures were due to a single condition. This common mode failure is reportable under the requirements of 10CFR50.73(a)(2)(vii) as an event where a single cause or condition caused two independent trains or channels in a single system designed to control the release of radioactive material to become inoperable.
9903310047 990322 PDR ADOCK 05000298 S
PDR a
NRC FORM 366 (61998)
I-
'.U.S. NUCLEAR REGULATORY COMMISSION (6 1998)
LICENSEE EVENT REPORT (LER)
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TEXT CONTINUATION FACILITY NAME (U DOCKET (21 LER NUMBER (W PAGE(3) 3 E,oE "EuE nan u
Cooper Nuclear Station 05000298 2 OF 4 1999 -- 001 --
00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
PLANT STATUS Cooper /Jucl ear Station (CNS) was in Mode 1 at approximately 100 percent power at the time this condition was identified.
4 BACKGROUND l
The High Pressure Coolant injection (HPCI) (Ells:BJ) pressure switches (Ells:PS) HPCI-PS-68A and C, and
- - 68B and D provide divisionally separate two out of two logic to initiate the steam line low pressure containment isolation function.
HPCI turbine steam line low pressure is used to automatically close the two isolation valves in the HPCI turbine steam line so that steam and radioactive gases will not escape from the HPCI turbine shaft seals into the reactor building after steam pressure has decreased to such a low value that the turbine cannot be operated. The isolation set point is chosen at a pressure below that where the HPCI turbine can operate efficiently.
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EVENT DESCRIPTION
On February 11,1999, during the performance of the Division ll functional surveillance test for HPCI Steam Line Low Pressure switches, HPCI-PS-68B and -68D were found out of allowable calibration range and below i
the Technical Specification (TS) allowable value. The instruments were recalibrated and returned to service.
During the subsequent performance of the Division i functional / calibration test, HPCI-PS-68C was also found to be out of allowable calibration range and below the TS allowable value.
On February 22,1999, during an evaluation of the performance of the pressure switches with the increased surveillance frequency, it was recognized that these failures were due to a single condition. This common
{
mode failure is reportable under the requirements of 10CFR50.73(a)(2)(vii) as an event where a single cause or condition caused two independent trains or channels in a single syster.i designed to control the release of radioactive material to become inoperable.
HPCIlow steam pressure isolation switches HPCI-PS-68A, B, C and D were replaced during Refueling Outage RE18 on or about October 26,1998 to address an Environmental Qualification issue related to Kapton diaphragms in the switches. The replacement switches contained a Stainless S' el diaphragm, but were i
considered to be a like-for-like replacement. New set points, TS allowable values, and extended surveillance frequencies had been established for the implementation of Improved Technical Specifications (ITS) on August 15,1998, and were incorporated into the surveillances. The implementation of ITS raised the TS allowable value and subsequently decreased the margin between the allowable value and leave alone tolerance (LAT) to 0.1 pounds per square inch (psi). In addition, the surveillance frequency in ITS changed i
from monthly to quarterly, which extended the time between start-up and the first calibration check, l
allowing more time for the pressure switches to drift.
The set point for HPCI pressure switches HPCI-PS-68B, C and D had drifted downward approximately 6 psi.
The set point for HPCI pressure switch HPCI PS-68A had drifted downward less that 1 psi, and remained within the LAT.
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4
- U.S. NUCLEAR REGULATORY COMMISSION l
(6 19981 -
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION l
FACILITY NAME (1)
DOCKET (2)
LER NUMBER (61 PAGE (3) sgp guSE Cooper Nuclear Station 05000298 3 OF 4
1999 -- 001 --
00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17l Data compiled by the vendor, Static O Ring (SOR), between early 1997 and 1998 indicated that the replacement switches with the Stainless Steel diaphragms exhibited more set point drift than originally expected. This set point drift was due to the new switches developing a ' set' attributed to hysteresis. This
' set' is believed to develop as the diaphragm conforms to the face of the piston after the switch is subjected to operating pressures and temperatures. Testing confirmed that the set point drift due to hysteresis occurred within the first several weeks of service, and the majority of the drift occurred within the first month. This greater than expected drift, combined with a decreased surveillance frequency and a reduced i
margin to TS allowable values, resulted in the pressure switch as-found value being below the TS allowable i
value but above the analyticallimit. The testing results support the belief that the diaphragm is deforming under pressure, and also indicates that calibration checks within approximately one month of operation will assure set point accuracy is maintained within operating limits.
BASIS OF REPORT i
This condition is reportable under the requirements of 10CFR50.73(a)(2)(vii) as an event where a single cause or condition caused two independent trains or channels in a singte system designed to ccwol the release of radioactive material to become inoperable.
l
CAUSE
l The cause of the HPCI pressure switch as-found set point being below TS limits was that CNS failed to recognize the need to address newly installed pressureawitches developing a ' set' attributed to hysteresis in installation and calibration procedures.
A contributing cause to this event was the implementation of set point and instrument drift calculations l
f ailed to adequately address the margin to Technical Specification Limits.
SAFETY SIGNIFICANCE
The safety significance associated with this condition is low. Although the as-found set point was below the TS limit, the as-found set point was above the CNS accident analysis analytical limit. The HPCI system was capable of performing its safety function and the steam line low pressure containment isolation function would have occurred within the accident analysis analytical limit.
j A Probabilistic Safety Analysis (PSA) Risk Evaluation was performed to determine the impact that a lower than TS Limit isolation of the HPCI steam line on low Reactor Vessel pressure would have on Core Damage Frequency (CDF) and Large Early Release Frequency (LERF). The results of this analysis concluded that the low actuation set point of the HPCI low pressure isolation switch does not impact CDF. The analysis also concluded that there is no impact on LERF from this event, even with the conservative assumption that the isolation function completely f ailed.
CORRECTIVE ACTION
Immediate Actions:
}
The pressuto switches were recalibrated and returned to service.
L
E.
- U.S. NUCLEAR REGULATORY COMMISSION l
16 1996) -
LICENSEE EVENT REPORT (LER) l TEXT CONTINUATION FACILITY MAME (1)
DOCKET (2)
LER Numan*R di)
PAGE (3)
"E W
%%0 w
l' Cooper Nuclear Station 05000298 4 OF 4
l 1999 -- 001 --
00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17}
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An operability evaluation was performed to determine if the pressure switches would remain operable between surveillances performed on an increased frequency.
Actions Completed:
l The frequency of the functional / calibration testing was increased to weekly calibration checks to ensure set point accuracy is maintained. Based on data from the weekly calibration checks which indicated the set point accuracy was being maintained, the weekly calibration checks were discontinued on March 9,1999.
A review of the Problem identification Report data base was performed to determine whether set point drift l
concerns existed for other pressure switches. A specific review of SOR switch performance for switches which were installed during the previous refueling outage was also performed. These SOR switches had been subject to monthly rather that quarterly surveillances immediately following installation, and larger l
margin to TS Limits exists for these switches. Based on the results of these reviews, it was concluded that the HPCI pressure switch set point drift was an isolated case.
l l
On-going Actions:
l A review of the applicable set point calculation will be performed to determine whether set point adjustments can be made to allow additional margin to TS allowable values. The calculation will be revised l
to incorporate the vendor information on set point drift. These actions will be complete by July 25,1999.
Infortnation on the effect of hysteresis on newly installed pressure switches will be evaluated and incoroorated into necessary station documents to assure that newly installed pressure switches are 1
calibrated approximately one month after reaching normal operating pressure by July 25,1999. The replacement of multiple switches in HPCI system was due to a programmatic requirement it is considered to be highly unlikely that multiple switches in a single channel that provides input to a safety function will be required prior to this action being completed. Therefore, there is a low safety significance associated with the time required to complete this action, A program change to ensure HPCI-PS-68A, B, C and D pressure switch functional / calibration surveillance will be scheduled approximately one month after a plant outage will be completed by July 25,1999. This scheduled surveillance will be discontinued after two planned outages, provided trend data supports discontinuing this activity.
Vendor Manual 0769 for Static O Ring pressure switches will be. updated to include newly acquired information from the vendor on the behavior of these pressure switches by June 25,1999.
PREVIOUS EVENTS No previous events related to common mode failure were identified.