05000498/LER-2018-001, Main Steam Safety Valve as Left Settings Outside of Required Range Contrary to Technical Specifications Due to Inadequate Procedure
| ML18338A551 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 12/04/2018 |
| From: | Connolly J South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-18003608 LER 2018-001-00 | |
| Download: ML18338A551 (9) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 4982018001R00 - NRC Website | |
text
Nuclear Operating Company South Tenas Protect Electric CrnernlmgStaHon P,O.Bon2S9 Wadswrth, TseK77W December 4, 2018 NOC-AE-18003608 10CFR 50.73 D. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Unit 1 Docket No. STN 50-498 Licensee Event Report 2018-001-00 Unit 1 Main Steam Safety Valve As Left Settings Outside of Required Range Contrary to Technical Specifications Due to Inadequate Procedure Pursuant to reporting requirements 10 CFR 50.73(a)(2)(i)(B), STP Nuclear Operating Company hereby submits the attached South Texas Project Unit 1 Licensee Event Report 2018-001-00 for a condition prohibited by the plant Technical Specifications.
The event did not have an adverse effect on the health and safety of the public.
There are no commitments in this submittal.
If there are any questions, please contact Robyn Savage at 361-972-7438 or me at 361-972-7344.
^%<^
I James Connolly
(/~9vf Executive VP and CNO nb/RS Attachment: Unit 1 LER 2018-001-00, Unit 1 Main Steam Safety Valve As Left Settings Outside of Required Range Contrary to Technical Specifications Due to Inadequate Procedure STI34760243
NOC-AE-18003608 Page 2 of 2 cc:
Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 East Lamar Boulevard Arlington, TX 76011-4511 Lisa M. Regner Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (O9E01) 11555 Rockville Pike Rockville, MD 20852 NRC Resident Inspector U. S. Nuclear Regulatory Commission P. O. Box 289, Mail Code: MN116 Wadsworth, TX 77483
NOC-AE-18003608 Attachment Attachment Unit 1 LER 2018-001-00 Unit 1 Main Steam Safety Valve As Left Settings Outside of Required Range Contrary to Technical Specifications Due to Inadequate Procedure
NRC FORM 366 (04-2018)
NRC FORM 366 (04-2018)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 1. Facility Name South Texas Unit 1
- 2. Docket Number 05000498
- 3. Page 1 OF 6
- 4. Title Unit 1 Main Steam Safety Valve As Left Settings Outside of Required Range Contrary to Technical Specifications Due to Inadequate Procedure.
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Month Day Year Year Sequential Number Rev No.
Month Day Year Facility Name N/A Docket Number 05000 10 02 2018 2018 - 001 - 00 12 04 2018 Facility Name N/A Docket Number 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 1 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
- 10. Power Level 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(v)(A) 73.71(a)(4) 092 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C) 73.77(a)(1) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(ii) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(vii) 73.77(a)(2)(iii) 50.73(a)(2)(i)(C)
Other (Specify in Abstract below or in summary of the event NOTE: all times are Central Standard Time May 22, 2012 The MSSV Inservice test procedure was revised such that the set pressure calculation which accounted for head correction was inadvertently removed from the procedure guidance.
October 2, 2018 [15:46] MSSV N1MSPSV7420C was declared inoperable for surveillance testing and Technical Specification 3.7.1.1 ACTION was entered.
October 2, 2018 [16:05] MSSV N1MSPSV7420C measured an as found set pressure of less than +/- 3% but greater than the +/- 1% as left acceptance criteria requiring adjustment and retesting.
October 2, 2018 [16:23] MSSV N1MSPSV7420C was adjusted and re-tested. The retested set pressure was thought to be within +/- 1% as left acceptance criteria but the head correction factor was not applied. A later re-calculation using the correct formula determined that the as left acceptance criteria was not met.
October 2, 2018 [16:33] MSSV N1MSPSV7420C was incorrectly determined to be OPERABLE and Technical Specification 3.7.1.1 ACTION was exited.
October 2, 2018 [16:34] MSSV N1MSPSV7420D was declared inoperable for surveillance testing and Technical Specification 3.7.1.1 ACTION was entered.
October 2, 2018 [16:59] MSSV N1MSPSV7420D measured an as found set pressure of less than +/- 3% but greater than the +/- 1% as left acceptance criteria.
October 2, 2018 [17:14] MSSV N1MSPSV7420D was adjusted and re-tested. The retested set pressure was thought to be within +/- 1% as left acceptance criteria but the correction factor was not applied. A later re-calculation using the correct formula determined that the as left acceptance criteria was not met.
October 2, 2018 [17:29] MSSV N1MSPSV7420D was incorrectly determined to be OPERABLE and Technical Specification 3.7.1.1 ACTION was exited.
Technical Specification 3.7.1.1 LIMITING CONDITION FOR OPERATION states:
All main steam line Code safety valves associated with each steam generator shall be OPERABLE with lift settings as specified in Table 3.7-2. Table 3.7-2 establishes required lift settings for each MSSV within +/- 3% of the values AND within +/- 1% of the values following testing i.e., as left.
Technical Specification 3.7.1.1 ACTION requirements state:
With four reactor coolant loops and associated steam generators in operation and with one or more main steam line Code safety valves inoperable, operation in Modes 1, 2, and 3 may proceed provided that within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, either the inoperable valve is restored to OPERABLE status or the Power Range Neutron Flux High Trip Setpoint is reduced per Table 3.7-1; otherwise, be in at least 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 />.
Unit 1 did not meet Technical Specification 3.7.1.1 ACTION within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to restore the inoperable MSSVs to operable status (i.e., return the as left lift setpoints to within +/- 1% of the values in Table 3.7-2) OR reduce the Power Range Neutron Flux High Trip Setpoint per Table 3.7-1 within the required outage time. Likewise, Unit 1 did not enter HOT STANDBY or COLD SHUTDOWN within the required shutdown times. This resulted in Unit 1 operating in a condition prohibited by the plants Technical Specifications.
October 5, 2018 [20:00] South Texas Unit 1 commenced shutdown as part of a planned refueling outage 1RE21.
October 6, 2018 [10:34] South Texas Unit 1 entered Mode 4 (HOT SHUTDOWN), shutting down for planned refueling outage 1RE21; Technical Specification 3.7.1.1 is no longer applicable.
October 8, 2018 [14:49] Engineering review of test data identified an error in the set pressure calculation used resulting in the two MSSVs being outside the Technical Specification required as left post test acceptance criteria of
+/- 1%, a condition report was initiated.
October 31, 2018 [15:32] South Texas Unit 1 in Mode 5 (COLD SHUTDOWN), Power Range Neutron Flux High Trip Setpoint reduced to 42.5% of RATED THERMAL POWER to be in compliance with Technical Specification 3.7.1.1 and Technical Specification Table 3.7-1 (43% RATED THERMAL POWER) with two inoperable MSSVs, prior to Mode 3 entry.
November 6, 2018 [17:36] South Texas Unit 1 entered Mode 3 (HOT STANDBY) starting up from planned refueling outage 1RE21 maintaining compliance with Technical Specification 3.7.1.1 LIMITING CONDITION FOR OPERATION with Power Range Neutron Flux High Trip Setpoint reduced below 43% with 2 MSSVs inoperable.
November 7, 2018 [09:23] MSSV Inservice Test performed and found MSSV N1MSPSV7420C setpoint within
+/- 1.5% of Table 3.7-2 value. MSSV N1MSPSV7420C was adjusted and re-tested and left within the +/- 1% as left acceptance criteria of Table 3.7-2.
November 7, 2018 [09:55] MSSV Inservice Test performed and found MSSV N1MSPSV7420D setpoint within
+/- 1.5% of Table 3.7-2 value. MSSV N1MSPSV7420D was adjusted and re-tested and left within the +/- 1% as left acceptance criteria of Table 3.7-2.
November 7, 2018 [10:02] MSSVs N1MSPSV7420C and MSSV N1MSPSV7420D determined to be OPERABLE and Technical Specification 3.7.1.1 ACTION was exited.
F. Method of discovery
This event was discovered during engineering review of the test data where it was determined that an error in the as left calculation resulted in MSSVs N1MSPSV7420C and N1MSPSV7420D not being within +/- 1% as left acceptance criteria.
II. Component failures
A. Failure Mode, mechanism, and effects of failed component Steam generator B MSSVs N1MSPSV7420C and N1MSPSV7420D were operable (i.e., as found setting within
+/- 3%) prior to being adjusted during the calibration on October 2, 2018. MSSVs N1MSPSV7420C and N1MSPSV7420D were rendered inoperable when the valves failed to be adjusted to within the required +/- 1% as left settings. The final lift settings for the two MSSVs obtained on October 2, 2018, which were verified again on November 7, 2018 exceeded the +/-1% acceptance criteria by less than 0.5%. The remaining 3 MSSVs on steam generator B remained OPERABLE throughout this event.
The MSSVs are used in Modes 1, 2, and 3 to ensure the secondary system pressure will be limited to within 110% of its design pressure during a postulated turbine trip from 100% RATED THERMAL POWER coincident with an assumed loss of condenser heat sink (i.e., no steam bypass to the condenser). Both valves were initially adjusted to within +/-1.5% set pressure. When both valves were retested in November they were found to still be within +/-1.5%
set pressure. The as found acceptance criteria is +/-3% set pressure. Had the MSSVs been challenged they would have performed their intended design function to protect the steam generator B and associated steam lines from overpressure while in Modes 1, 2, and 3.
B. Cause of component failure
There was no material condition associated with MSSVs N1MSPSV7420C and N1MSPSV7420D; the valves became inoperable when the set pressure correction factor, required due to the difference in elevation between the main steam line and the pressure gauge, was not applied during the test and the as left lift settings were not within Technical Specification limits.
C. Systems or secondary functions that were affected by failure of components with multiple functions The MSSVs do not have several functions. No secondary functions were affected.
D. Failed component information
There was no component failure.
System: Main Steam System (Main/Reheat Steam System) {SB}
Component Type: Valve, Relief {RV}
Component Manufacturer: Consol / Dresser Model No: 6-3707RAX-RT-25-XNC1012
III. Analysis of the event
A. Safety system responses that occurred No safety systems were required to respond as a result of this event.
B. Duration of safety system inoperability
While South Texas Unit 1 was in the applicable Modes 1, 2, and 3 Technical Specification 3.7.1.1 applied:
MSSV N1MSPSV7420C was inoperable from October 2, 2018 [15:46] until October 6, 2018 [10:34] when South Texas Unit 1 entered Mode 4 (HOT SHUTDOWN) where Technical Specification 3.7.1.1 was no longer applicable (3 days 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> and 48 minutes).
MSSV N1MSPSV7420D was inoperable from October 2, 2018 [16:34] until October 6, 2018 [10:34] when South Texas Unit 1 entered Mode 4 (HOT SHUTDOWN) where Technical Specification 3.7.1.1 was no longer applicable (3 days 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> and 0 minutes).
During startup from the refueling outage South Texas Unit 1 restored compliance with Technical Specification 3.7.1.1 prior to Mode 3 (HOT STANDBY) entry where Technical Specification 3.7.1.1 was applicable.
Compliance with the Limiting Condition for Operation was established when the Power Range Neutron Flux High Trip Setpoint was reduced below 43% with MSSVs N1MSPSV7420C and N1MSPSV7420D inoperable.
MSSVs N1MSPSV7420C and N1MSPSV7420D were declared operable on November 7, 2018 [10:02].
C. Safety consequences and implications
Safety consequences were determined by quantifying the risk accumulated during the period of time when Technical Specification 3.7.1.1 was exited for the first valve (post-test), October 2, 2018 [16:33], until Mode 4 entry on October 6, 2018 [10:34].
The approved Probabilistic Risk Assessment (PRA) model incorporated the pressure relief function of the MSSVs.
There were five MSSVs on each steam generator and the model treated them all equivalently (setpoints are not modeled). As the design setpoint of the valves allows for a +/- 3% range and all Unit 1 MSSVs were within this range, and relieving capacity and capability were not impacted, the MSSVs were considered capable of fulfilling the functions described in the PRA model.
Because there is no impact on modeled functions, the Incremental Core Damage Probability (ICDP) and Incremental Large Early Release Probability (ILERP) are zero. A zero ICDP and ILERP concludes that this event accrued zero cumulative risk impact from October 2, 2018 [16:33] until October 6, 2018 [10:34].
Therefore, there was no adverse effect on the health and safety of the public.
IV. Cause of the event
The cause of the event was an inadvertent deletion of a critical head correction equation in the MSSV Inservice test procedure in 2012. The formula adjusted the steam line pressure input to account for the difference in elevation between the main steam line and the pressure gauge. The Test Coordinator is an STP engineer who oversees contractors performing the actual testing of the MSSVs. The Test Coordinator who performed these tests was not aware of the need to include the correction factor. However, the previous Test Coordinator had performed this test for a number of years and was aware of the required adjustment.
V. Corrective actions
- 1. MSSVs N1MSPSV7420C and N1MSPSV7420D setpoints were adjusted and left within the Technical Specification requirements.
- 2. A review of the last South Texas Unit 2 MSSV test data confirmed the correction factor was applied as required.
- 3. The MSSV Inservice test procedure was revised to incorporate steps to account for the head correction adjustment.
VI. Previous similar events
An operating experience review over the past five years was conducted for similar events regarding MSSVs.
No similar events were found at South Texas Unit 1 or Unit 2.