05000298/LER-2015-002, Regarding Failure of Main Steam Differential Pressure Indicating Switches Results in a Condition Prohibited by Technical Failure of Main Steam Differential Pressure Indicating Switches Results in a Condition
| ML15111A448 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 04/16/2015 |
| From: | Limpias O Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2015047 LER 15-002-00 | |
| Download: ML15111A448 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2982015002R00 - NRC Website | |
text
H Nebraska Public Power District Always there when you need us NLS2015047 April 16, 2015 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2015-002-00 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2015-002-00.
There are no new commitments contained in this letter.
Vic President Nu lear-Chief Nuclear Officer
'jo Attachment: Licensee Event Report 2015-002-00 cc:
Regional Administrator w/attachment USNRC - Region IV Cooper Project Manager w/attachment USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/attachment USNRC - CNS SRAB Administrator w/attachment NPG Distribution w/attachment INPO Records Center w/attachment via ICES entry SORC Chairman w/attachment CNS Records w/attachment COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 www.nppd.com
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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01131/2017 02-20 14) 02-2014)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REV NUMBER NO Cooper Nuclear Station 05000298 2015
- - 002
- - 00 3 of 4 was revised to add a new section, T 5.14, "Setpoint Control Program (SCP)." A table exists in this section identifying Nominal Trip Setpoints (NTSP) for automatic protective instrumentation channels that have Limiting Safety System Settings in the Technical Specifications (TS). The SCP ensures the NTSP values and As-Left Tolerance and As-Found Tolerance methodologies are listed for the applicable Functions in the following TS: "Reactor Protection System (RPS) Instrumentation," "Control Rod Block Instrumentation,"
"Emergency Core Cooling System (ECCS) Instrumentation," and "Reactor Core Isolation Cooling (RCIC)
System Instrumentation."
When the 24-month refueling cycle License Amendment was implemented in 2012, all setpoint calculations and their related setpoint change requests were revised to make reference to TRM T 5.14. However, the Main Steam DPIS setpoint was inappropriately changed as the Main Steam DPIS Function is not in the TRM.
Investigation revealed that prior to implementation of TSTF-493, the switches had an As-Left Tolerance of
+/- 3.0". Review of the calibration/functional log sheets illustrate that the switches had been reliable and very rarely required an adjustment with the As-Left Tolerance of +/- 3.0". When TSTF-493 was inappropriately applied, the As-Left tolerance was tightened to +/- 1.12", causing additional switch adjustments that normally would have been in tolerance in 2012 and 2014. On August 21, 2014, all of the switches had drifted low, with seven of the eight switches requiring adjustment up.
As part of the resolution, the calculations that did not require a setpoint change as part of TSTF-493 implementation were revised, new setpoint changes were generated, and surveillance procedures were revised back to the pre-TSTF-493 values.
BASIS FOR REPORT CNS is reporting this event as an operation or condition prohibited by plant TS per 10 CFR 50.73(a)(2)(i)(B), and also as a common cause inoperability of independent trains or channels as defined under 10 CFR 50.73(a)(2)(vii).
SAFETY SIGNIFICANCE
Actual and potential safety consequences are minimal in that an adequate number of high MSL flow DPIS remained within tolerance to provide needed high flow isolation of the MSLs. Although three of the eight Division 2 main steam high flow DPIS did not trip prior to reaching their TS limit, the other five Division 2 switches were within tolerance, and would have provided the needed isolation signal prior to exceeding TS setpoint limits. The design of the main steam high flow isolation function represents a "one out of two taken twice" logic. By this design, the five in tolerance switches would have provided the main steam isolation regardless of the out of tolerance actuation of the three failed switches. Because the in tolerance switches preserved the isolation function as part of the "one out of two taken twice" main steam high flow logic, the associated safety function was available for a main steam line break event.
NRC U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/3112017 FORM 366
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REV NUMBER NO Cooper Nuclear Station 05000298 2015
- - 002
- - 00 4 of 4 Based on the fact that the safety function associated with the main steam high flow isolation signal being preserved through successful testing of five of the eight Division 2 switches, safety significance is negligible with regard to an increase in core damage probability.
CAUSE
Two apparent causes were identified:
- 1.
TSTF-493 requirements were inappropriately applied to the Main Steam DPIS instruments during the original 24-month cycle project for changing the TS, causing a much smaller As-Left tolerance which forced unnecessary equipment adjustments.
- 2.
Inappropriately applied TSTF-493 requirements were not removed in a timely manner as they were viewed as administrative only (no change in setpoint and viewed as conservatively tightening the As-Left Tolerance).
CORRECTIVE ACTIONS
The applicable surveillance procedures have been revised to remove the TSTF-493 As-Found Tolerance.
In addition, the As-Left Tolerance was returned to +/- 3.0 psid.
PREVIOUS EVENTS There have been no reportable events in the past three years related to setpoint calculations.