05000389/LER-1998-005, :on 980807,discovered That New MOV Methodology Caused Past PORV Block Valve Operability Problem.Caused by Inadequacies in Original Vendor MOV Methodology.Planned Valve Mods Will Be Implemented During Cycle 11 1998 Outage
| ML17229A930 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 11/25/1998 |
| From: | Frehafer K FLORIDA POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML17229A929 | List:
|
| References | |
| LER-98-005, LER-98-5, NUDOCS 9812020143 | |
| Download: ML17229A930 (9) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(e)(2)(v) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3891998005R00 - NRC Website | |
text
NRC FORM 366 (6-1998)
U.S. NUCLEAR REGUIATORY COMMISSION LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each b(ock)
APPROVED BY OMB NO. 3150-0104 EXPIRES 06/30/2001
, the NRC may not conduct or sponsor, and a person ls not required to respond to, the Informatkxt collection.
FACIUTYNAME (1)
St. Lucie Unit 2 DOCKET NUMBER (2) 05000389 PAGE (3)
Page 1 of 5 TITLE (4)
New MOV Methodology Caused Past PORV Block Valve Operability Problem EVENT DATE 5 LER NUMBER 6 REPORT DATE 7 OTHER FACILITIES INVOLVED 8 MONTH DAY 08 07 1998 1998 - 005
01 11 25 1998 YEAR SEQUENrlAL REVISION MONTH DAY NUMBER NUMBER FACIUTYNAME FACIUTyNAME OOCKETNUM8ER OOCKETNOM8ER OPERATING MODE (9)
POWER LEVEL (10) 100
~ ',yeg"S qPwt'K)'( t+%t~TcCr4$
'HIS REPORT IS SUBMITT 20.2201(b) 20.2203(a)(1) 20,2203(a) (2)(i) 20.2203(a)(2)(ii) 20.2203 (a) (2)(iii) 20.2203(a)(2)(iv)
ED PURSUANT TO THE REQ 20,2203(a)(2) (v) 20.2203(a) (3)(i) 20.2203(a) (3)(ii) 20.2203(a) (4) 50.36(c)(1) 50.36(c)(2)
UIREMENTS OF 10 CFR 5:
(Ghee X 50.73(a) (2)0) k one or inoro) (11) 50.73(a)(2)(viii) 50.73(a) (2)(x) 50.73(a)(2)(ii) 50.73(a)(2)(iii) 50.73(a)(2) (iv) 50.73(e) (2)(v) 73.71 OTHER Specify ln Abstract below or In NAC Form 38SA 50.73(a)(2)(vii)
UCENSEE CONTACT FOR THIS LER 12 TELEPHONE NVM8ER Ondude Arse Code)
K. W. Frehaferr Licensing Engi.neer (561) 467 7748 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13
CAUSE
SYSTEM AB COMPONENT V:MO MANUFACTURER L200 REPORTABLE TO EPIX NO (g
I@I
$rpE,
CAUSE
SYSTEM COMPONENT MANUFAClURER REPORTABLE TO EPIX SUPPLEMENTAL REPORT EXPECTED (14)
YES (If yes, complete EXPECTED SUBMISSION DATE).
X No EXPECTED SUBMISSION DATE (15)
MONTH DAY ABSTRACT lLimitto 1400 spaces, /.e., epproximetely 15 single-spaced typewri(ten lines/ (16)
On August 7, 1998, St. Lucie Unit 2 was in, Mode 1 at 100 percent power.
During a review of NRC Information Notice 96-48, Supplement 1, Engineering discovered that the Unit 2 power operated relief valve b'lock valve (V-1476 and V-1477) margins were insufficient to accommodate the additional conservatism specified in NRC Information Notice 96-48, Supplement 1, and assure valve closure.
Operations entered the one<<hour ACTION statement for Technical Specification 3.4.4.a at 19:59 hours on August 7, 1998.
The ACTION statement was exited at 20:07 hours the same day when both Unit 2 po~er operated relief valve block valves were closed with power removed in accordance with Technical Specification requirements.
The cause of this event was inadequacies in the original vendor motor operated valve methodology as documented in Limitorque Technical Update 98-01 and NRC Information Notice 96-48 Supplement 1.
The new methodology required additional conservatisms when evaluating a Limitorque AC powered motor operator's performance.
Corrective actions
i.nclude the immediate actions taken on August 7,
- 1998, and the implementation of the planned valve actuator modifications during the upcoming fall Unit 2 Cycle 11 1998 refueling outage.
This LER revision changes the safety significance for inoperable PORV block valves based on subsequent safe shutdown analysis re-validation effort findings documented in LER 50-389/1998-007-00.
9812020i43 98ii25 PDR ADOCK 05000389 PDR
NRC FORhll 366A I8.1998)
LICENSEE EVENT REPORT (LER)
TfXT CONTINUATION U.S. NUCLEAR REGULATORY COMMISSION FACILITYNAME I1)
St. Lucie Unit 2 DOCKET NUMBER 2) 05000389 LER NUMBER {6)
~
3EQUEITNL REVISION NUMBER NUMBER 1998 005 01 PAGE (3)
Page 2 of 5 TEXT Iifmore space is required, use eddidonal copies ofIVRCForm 3MAI (17]
Description of Event
On August 7, 1998, St. Lucie Unit 2 was in Mode 1 at 100 percent power. During review of NRC Information Notice (IN) 96-48, Supplement 1, Engineering discovered that the Unit 2 power operated relief valve (PORV) block valve (V-1476 and V-1477)
[EIIS:AB:V:MO) margins were insufficient to assure valve closure.
In light of recent tests and studies of motor actuator output, Limitorque retracted its relaxation of the sizing criteria for AC powered motor actuators through issuance of Limitorque Technical Update (TU) 98-01.
The Limitorque'TU revised requirements such that an additional factor of conservatism'eeds to be added to evaluate motor operator performance.
NRC IN 96-48, Supplement 1, titled "Motor Operated Valve Performance Issues,"
disseminated this information to the industry.
Operations entered the one-hour ACTION statement for Technical Specification 3.4.4.a at 19:59 hours on August 7, 1998.
The ACTION statement was exited at 20:07 hours the same day when both Unit 2 PORV block valves were closed with power removed in accordance with Technical Specification requirements.
Cause of the Event
The cause of this event'as inadequacies in the original vendor motor operated valve (MOV) methodology as documented in Limitorque TU 98-01 and NRC 1N 96-48, Supplement 1.
Analysis of the Event
Technical Specification 3.4.4. requires that each PORV block valve be operable in Modes 1, 2, and 3, with no more than one block valve open.
ACTION a. states that:
"With one or more block valve(s) inoperable, within I hour either restore the block valve(s), to OPERABLE status or close the block valve(s) and remove power from the block valve(s); otherwise, be in at'east HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. "
The past inoperability of the PORV block valves constitutes a condition for which firm evidence exists that the condition existed in the past.
It is concluded that the past inoperability time exceeded the allowed outage time (i.e., greater than 1
hour) of Technical Specification 3.4.4.a and therefore constitutes operation prohibited by the plant's Technical Specifications.
Accordingly this condition is reportable under 10 CFR 50.73(a)(2) (i) (B), that states "Licensees shall report: 'any operation or condition prohibited by the plant's Technical Specifications.'"
The purpose of the Limitorque Technical Update (TU) was to provide new guidance to determine the output torque capability of a Limitorque valve actuator with an AC motor.
The motor operated valve (MOV) output torque capability is determined by using the following factors:
- 1. Motor Rated Torque
- 2. Pullout Efficiency NRC FORM 300A (0 1998)
0(8-1998)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION U.S. NUCLEAR REGULATORY COMMISSION FAGILITYNAME(1)
St. Lucie Unit 2 DOCKET NUMBER 2 05000389 LER NUMBER (6)
SEQUENTIAL REVISION NUMBER NUMBER 1998 005 01 PAGE I3)
Page 3 of 5 TEXT itfmore spaceis required, use additional copies offVRC Form 366AJ (17)
I
- 3. Overall Actuator Gear Ratio
- 4. Motor Terminal Voltage
- 5. Motor Rated Voltage
- 6. Application Factor (AF) selected in accordance with Limitorque SEL-4 Engineering reviewed the current NRC Generic Letter (GL) 89-10 MOV program calculations and determined that the Motor Rated Torque, Overall Actuator Gear Ratio, and the Motor Terminal and Rated Voltage factors were consistent with the TU requirements.
I However, for some MOVs, calculations utilized motor running efficiency (versus pullout efficiency) and the relaxed AF criteria previously provided by Limitorque in TU 93-03.
TU 93-03 allowed the assumption of an AF of 1.0 (rather than 0.9) when the motor voltage was less than 90 percent of the motor's rated voltage.
Engineering reviewed applicable MOVs, and determined that several valves did not have sufficient margin to account for the additional conservatism introduced by Limitorque TU 98-01.
However, only the Unit 2 PORV block valves, V-1476 and V-1477, were determined to be a Technical Specification OPERABILITY concern.
Using the new methodology for the Unit 2 PORV block valves, the calculated closing thrust was 10,464 lbs.,
and the required closing thrust is 17,440 lbs.
Therefore, there is a possibility that the PORV block valves would not close if required.
Analysis of the Effect on Safety The past inoperability of the PORV block valves did not constitute operation outside the design basis of the plant and would not have prevented the fulfillment of a safety function.
The Technical Specifications require that one block valve be closed during power operation.
In the event of an inadvertent PORV opening, the safety analysis does not credit closing of the associated block valve to prevent exceeding safety limits.
The PORVs are discussed in Emergency Operating Procedure EOP-15 for initiation of once through cooling.
However, this is a beyond design basis scenario that'equires multiple safety related system failures.
The past inoperability of the PORV block valves would not have adversely affected the operation of the PORVs for low temperature over pressure protection (LTOP).
Zn the LTOP mode the PORV block valves only need to be open and are not required to be operated.
The PORV system is a high/low pressure interface with the primary system.
To preclude a fire-induced LOCA, the safe shutdown analysis protects the PORVs from possible spurious operation.
The PORVs'ontrol and power cables are protected or manual action is taken to isolate the PORVs'ower by use of isolate switches in the electrical penetration room in case of a fire in the control room or cable spread room.
No credit is taken for operation of the Unit 2 PORV block. valves as far as the 10 CFR 50, Appendix R safe shutdown analysis is concerned.
NRC FORM 388A I8-1998)(0-1998)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION U.S. NUCLEAR REGULATORY COMMISSION FACILITYNAME(1)
St. Lucie Unit 2 DocKET NUMBER (2 05000389 LER NUMBER (6)
SEQUENTIAL REVISION NUMBER NUMBER 1998 005 01 PAGE (3)
Page 4 of 5 TEXTllfmore speceis required, use edditionel copies of NRC Form 3684) (17)
Analysis of the Effect on Safety (cont'd)
A subsequent St. Lucie Unit 2 LER (50-389/1998-007-00) documents a concern pertaining to inadequate protection of the St. Lucie Unit 2 pORVs from hot shorts resulting from a fire within the control room,reactor turbine generator (RTG) boards.
This could result in a spurious operation of a PORV during a control rocm fire.
Although operation of the PORV block valves are not credited for a fire, this new discovery may require operation of the pORV block valves to terminate a fire induced LOCA.
The fire must occur inside of the control room RTG boards at the correct location to
cause
the insulation to burn off two or more cables of the coriect polarity and cause hot shorts to occur before the control room operators have any chance of responding.
Because the control room is,continuously occupied and fire detection exists inside of the control room RTG boards, the existence of a fire of this magnitude would have a low probability of occurrence.
Zn the unlikely event a pORV spuriously opened as a result of a fire, the event could be mitigated by opening the pORV DC feeder breaker.
Although this'ction was not proceduralized, it is a readily apparent action that the operators could take to mitigate the transient.
As an interim compensatory
- measure, a procedure change was issued for procedure 2-ONP-110.02, Appendix A, "Control Room Inaccessibility," which de-energizes the 125 volt PORV DC feeder breakers as the first step when evacuating the control room.
This action removes both the motive and control power from the PORVs and eliminates the potential for spurious PORV operation during a fire.
Based on the preceding discussion, past PORV block valve inoperability had no adverse affect on the health and safety of the public.
However, in order to provide operational flexibilityto the operators during postulated beyond design bases
- events, St. Lucie implemented temporary system alterations (TSAS) on the Unit 2 PORV block valves to restore these valves to operable status.
The TSA for V-1476 was implemented on August 14,
- 1998, and the TSA for V-1477 was implemented on August 19, 1998.
The TSAs will be removed after the permanent plant modifications are implemented next outage.
NRC FOAM 300A (8.1898)(8 1998)
LlCENSEE EVENT REPORT (LER)
TEXT CONTINUATION U.S. NUCLEAR REGULATORY COMMISSION FACILITYNAME(1)
St. Lucie Unit 2 DOCKET NUMBER (2) 05000389 LER NUMBER (6)
SEQUENTIAL REVISION NUMBER NUMBER 1998 005 01 PAGE (3)
Page 5 of 5 TEXT (ifmore spaceis required, use additional copies ofNRC Form 366AJ (17)
Corrective Action
1.
Zmmediate action was taken on August 8, 1998 to close the PORV block valves and remove power in accordance with the requirements of Technical Specification 3.4.4.a.
- 2. St. Lucie implemented temporary system alterations (TSAs) on the Unit 2 PORV block valves to restore these valves to operable status on August 14, 1998, for V-1476, and August 19, 1998, for V-1477.
- 3. Both PORV block valves will be modified during the upcoming fall 1998 Unit 2 Cycle 11 refueling outage under PC/M 98013.
- 4. The St. Lucie GL 89-10 program requires review of industry operating experience and the incorporation of new information into the program documentation.
The information and issues identified in NRC ZN 98-48 Supplement 1 will be incorporated into the GL 89-10 program documentation by January 31, 1999.
- 5. Corrective actions for the Unit 2 PORV SSA fire protection deficiencies are document'ed in LBR 50-389/1998-007-00, "Fire Protection SSA Re-Verification Zdentified Potential PORV and 2A BDG Cable Failure Modes."
Similar Events
LBR 50-335/97-009, dated September 17, 1997, reported MOV calculation deficiencies associated with the St. Lucie Unit 1 PORV block valve V-1403.
Failed Components Zdentified Component:
V-1476 and V-1477, PORV block Valve Motor/Actuator Manufacturer:
Limitorque Model Number:
SB-00 (3G0861A)
P~