05000251/LER-2016-001, Regarding Technical Specification Action Not Taken for Unrecognized Inoperable Reactor Protection Instrument Channel
| ML16194A341 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 06/30/2016 |
| From: | Summers T Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2016-134 LER 2016-001-00 | |
| Download: ML16194A341 (6) | |
| 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)(A), Loss of Safety Function - Shutdown the Reactor 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)(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), Loss of Safety Function 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 2512016001R00 - NRC Website | |
text
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555-0001 Re:
Turkey Point Unit 4 Docket No. 50-251 Reportable Event: 2016-001-00 Date of Event: May 3, 2016 L-2016-134 10 CFR § 50. 73 June 30, 2016 Technical Specification Action Not Taken for Umecognized Inoperable Reactor Protection Instrument Channel The attached Licensee Event Report 05000251/2016-001-00 is submitted pursuant to 10 CPR ---
50.73(a)(2)(i)(B) as a condition prohibited by the Technical Specifications, and 10 CFR 50.73(a)(2)(v)(A) as a condition that could have prevented the fulfillment of a specified safety function.
If there are any questions, please call Mr. Mitchell Guth at 305-246-6698.
Sincerely,
~~~s~~~~~-
Vice President Turkey Point Nuclear Plant Attachment cc:
Regional Administrator, USNRC, Region II Senior Resident Inspector, USNRC, Turkey Point Nuclear Plant Florida Power & Light Company 9760 SW 344th Street, Homestead, FL 33035
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 1013112018 (11-2015)
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, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Turkey Point Unit 4 05000251 1 OF 5
- 4. TITLE Technical Specification Action Not Taken for Unrecognized Inoperable Reactor Protection Instrument Channel
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.
MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 5
3 2016 2016 - 001
- - 00 6
30 2016 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D 20.2201 <d>
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.. 73(a)(2)(viii)(B)
D 20.2203<a><1>
D 20.2203<a><4>
D 5o.73(a><2><rn>
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203<a><2><n>
D 50.36(c)(1 )(ii)(A)
~
50.73(a)(2)(v)(~)
D 73.11<a><4>
D 20.2203<a><2)(iii)
D 50.36(c><2>
D 50.73(a)(2)(v)(B)
D 73.11(a)(5)
D 20.2203(a)(2)(iv)
D 5o.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 13.11<a><1>
100% RTP D 20.2203(a)(2)(v)
D 50. 73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 13.n<a><2>
D 20.2203(a)(2)(vi)
~ 50. 73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii) 1.?::.. *t ~
- .w,
.~.*.* ~":~ t'.
D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in
ANALYSIS OF THE EVENT
YEAR 2016 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
00 RCS hot leg temperature (Thot) is measured by three RTDs located 120 degrees circumferentially around the RCS pipe in each of the three loops and these indications are averaged. The Thot average is used to determine RCS Delta T and the RCS T avg* The RCS T avg and Delta T calculated values are used in the reactor trip system instrumentation safety functi.ons associated with OTDT and OPDT. The Tavg calculated value is also used in the Engineered Safety Features (ESF) Actuation System associated with Safety Injection, Steani Line Isolation and ESF interlocks. An evaluation concluded that there was no adverse impact on ESF functions.
The OTDT and OPDT reactor trip function consists of three independent channels with one channel in each of the three RCS Loops. Actuation of a trip signal in. two of the three channels is required to trip the reactor. The two-out-of-three trip logic prevents a reactor trip from the spurious actuation of a trip signal from one channel while providing redundancy to accommodate the failure of one channel to generate the required trip signal.
During startup and power ascension from the refueling outage, Engineering personnel noted that the indication from the spare Channel III RTD deviated from the other two RTDs by up to 8 degrees F.
Engineering personnel realized that incorrect coefficients had been entered into Eagle 21 for the spare RTD. RTD cross-cali~rations are performed when RCS temperature reaches 250, 350, 450 and 547 degrees F. The cross-calibrations at 250 and 350 degrees F were satisfactory.
When the RTD cross-calibration failed at 450 degrees Fon April 25, 2016, it was concluded that it was due to the incorrect coefficients for the spare R TD. It was also assumed that this T hot input would be removed by the Eagle 21 RSA feature. The RCS hot leg RTDs for a particular channel are averaged and the output is compared to the average of the cold leg RTDs for the respective RCS loop. The signals from the RTDs*are checked to see if they deviate from each other by more than a preset amount (DEL T AH). The RSA takes the signal furthest from the average and removes it from the calculation before it is used for Delta 'E. It was assumed that the DELTAH value was set at 4 degrees Fas is normal for steady state power operation, but the setting was not verified. I&C personnel had adjusted the DELTAH value to 12 degrees F during the plant startup via work order instructions. The Eagle 21 RSA did not remove the input from the spare RTD. The change to DELTAH for startup is a temporary configuration change that was not performed in compliance with the temporary configuration change process.
YEAR 2016 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 The correct coefficients for the spare RTD were entered into the Eagle 21 system for Loop C Channel III on May 2, 2016 returning the channel to operable status.
During the approximate five day period of OTDT/OPDT Channel III inoperab.ility, the single failure criterion was not met. During two periods when more than one channel was inoperable (approximate four hours cumulative), the specified safety function was lost.
ANALYSIS OF SAFETY SIGNIFICANCE REV NO.
00 During the period that OTDT and OPDT Channel III was inoperable, OTDT and OPDT Channels I and II were operable except for perioas when testing of the channels occurred. During the testing periods each channel was placed in the tripped condition except during a few hour period when the channels were being returned to service in accordance with TS 3.0.6. During this short period, the TS safety function provided by OTDT and OPDT reactor trips was not available because two of the three channels were inoperable and the reactor trip logic requires two OTDT or OPDT signals. A bounding risk assessment concluded that for the approximate four hour period that the specified safety function was not available, the core damage probability was well below the NRC acceptance criteria for minimal risk impact. As a result, the safety significance of the event is considered low.
CORRECTIVE_ ACTIONS Corrective action is in accordance with condition report AR 2129632 and includes:
- 1. Revise the RCS RTD replacement procedure to require validation of the correct methodology for deriving RCS RTD coefficients.
- 2. Establish a controlled calculation that contains the* basis and methodology for deriving RCS RTD coefficients.
- 3. Update the work order process to ensure any changes to the Eagle 21 RSA complies with the
\\.
temporary configuration change process.
ADDITIONAL INFORMATION
YEAR 2016 -
SEQUENTIAL NUMBER 001 EIIS Codes are shown in the format [IEEE system identifier, component function identifier, second component function identifier (if appropriate)].
FAILED COMPONENTS IDENTIFIED: None.
PREVIOUS SIMILAR EVENTS
None.
DESCRIPTION OF THE EVENT YEAR 2016 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
00 On May 3, 2016 with Unit 4 in Mode 1 at approximately 100% rated thermal ppwer, Engineering personnel identified the potential past inoperability of Reactor Protection System Overtemperature Delta T (OTDT) and Overpressure Delta T (OPDT) Channel III [JC, CHA]. Corrected coefficients were entered into the Eagle 21 Process Protection Upgrade System for a spare Loop C resistance temperature detector (RTD) [AB, TE] that resulted in a significant change to the setpoint. The correct coefficients were input by instrumentation and control (I&C) personnel on May 2, 2016. Evaluation confirmed that the Channel III setpoint had exceeded the Technical Specification (TS) allowable value as specified in TS 2.2.1, Table 2.2-1, Functional Units (FU) 5 and 6, and was inoperable when required for approximately five days. Incorrect Eagle 21 RTD coefficients were entered for the spare RTD on April 20, 2016 during the Unit 4 refueling/maintenance outage. Unit 4 entered Mode 2 and the mode of applicability of TS 3.3.1, Table 3.3-1 for FU 5 and 6 on April 27, 2016 at approximately 2020 hours0.0234 days <br />0.561 hours <br />0.00334 weeks <br />7.6861e-4 months <br />.
Because the inoperable condition was not recognized at the time, TS Required Action to place the channel in the tripped condition within six hours was not take,n. This is a condition prohibited by the TSs and reportable in accordance with 10 CFR 50.73(a)(2)(i)(B).
In addition, during the five day period that OTDT and OPDT Channel III was inoperable another of the three channels was inoperable at times during test/adjustment activities for a cumulative period of approximately four hours. With two channels inoperable, the specified safety function was not met because two operable or operating channels are required to achieve the safety function. This aspect is reportable in accordance with 10 CFR 50.73(a)(2)(v)(A) because of the impact on the reactor trip function to shut down the reactor.
CAUSES OF THE EVENT The root cause is the absence of a controlled engineering document describing the derivation of RTD coefficient data.
A contributing cause is not implementing the temporary design change process when the Eagle 21 Redundant Sensor Algorithm (RSA) value was temporarily increased from 4 degrees F to 12 degrees F for the reactor startup.
ANALYSIS OF THE EVENT
YEAR 2016 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
00 RCS hot leg temperature (Thot) is measured by three RTDs located 120 degrees circumferentially around the RCS pipe in each of the three loops and these indications are averaged. The Thot average is used to determine RCS Delta T and the RCS T avg* The RCS T avg and Delta T calculated values are used in the reactor trip system instrumentation safety functi.ons associated with OTDT and OPDT. The Tavg calculated value is also used in the Engineered Safety Features (ESF) Actuation System associated with Safety Injection, Steani Line Isolation and ESF interlocks. An evaluation concluded that there was no adverse impact on ESF functions.
The OTDT and OPDT reactor trip function consists of three independent channels with one channel in each of the three RCS Loops. Actuation of a trip signal in. two of the three channels is required to trip the reactor. The two-out-of-three trip logic prevents a reactor trip from the spurious actuation of a trip signal from one channel while providing redundancy to accommodate the failure of one channel to generate the required trip signal.
During startup and power ascension from the refueling outage, Engineering personnel noted that the indication from the spare Channel III RTD deviated from the other two RTDs by up to 8 degrees F.
Engineering personnel realized that incorrect coefficients had been entered into Eagle 21 for the spare RTD. RTD cross-cali~rations are performed when RCS temperature reaches 250, 350, 450 and 547 degrees F. The cross-calibrations at 250 and 350 degrees F were satisfactory.
When the RTD cross-calibration failed at 450 degrees Fon April 25, 2016, it was concluded that it was due to the incorrect coefficients for the spare R TD. It was also assumed that this T hot input would be removed by the Eagle 21 RSA feature. The RCS hot leg RTDs for a particular channel are averaged and the output is compared to the average of the cold leg RTDs for the respective RCS loop. The signals from the RTDs*are checked to see if they deviate from each other by more than a preset amount (DEL T AH). The RSA takes the signal furthest from the average and removes it from the calculation before it is used for Delta 'E. It was assumed that the DELTAH value was set at 4 degrees Fas is normal for steady state power operation, but the setting was not verified. I&C personnel had adjusted the DELTAH value to 12 degrees F during the plant startup via work order instructions. The Eagle 21 RSA did not remove the input from the spare RTD. The change to DELTAH for startup is a temporary configuration change that was not performed in compliance with the temporary configuration change process.
YEAR 2016 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 The correct coefficients for the spare RTD were entered into the Eagle 21 system for Loop C Channel III on May 2, 2016 returning the channel to operable status.
During the approximate five day period of OTDT/OPDT Channel III inoperab.ility, the single failure criterion was not met. During two periods when more than one channel was inoperable (approximate four hours cumulative), the specified safety function was lost.
ANALYSIS OF SAFETY SIGNIFICANCE REV NO.
00 During the period that OTDT and OPDT Channel III was inoperable, OTDT and OPDT Channels I and II were operable except for perioas when testing of the channels occurred. During the testing periods each channel was placed in the tripped condition except during a few hour period when the channels were being returned to service in accordance with TS 3.0.6. During this short period, the TS safety function provided by OTDT and OPDT reactor trips was not available because two of the three channels were inoperable and the reactor trip logic requires two OTDT or OPDT signals. A bounding risk assessment concluded that for the approximate four hour period that the specified safety function was not available, the core damage probability was well below the NRC acceptance criteria for minimal risk impact. As a result, the safety significance of the event is considered low.
CORRECTIVE_ ACTIONS Corrective action is in accordance with condition report AR 2129632 and includes:
- 1. Revise the RCS RTD replacement procedure to require validation of the correct methodology for deriving RCS RTD coefficients.
- 2. Establish a controlled calculation that contains the* basis and methodology for deriving RCS RTD coefficients.
- 3. Update the work order process to ensure any changes to the Eagle 21 RSA complies with the
\\.
temporary configuration change process.
ADDITIONAL INFORMATION
YEAR 2016 -
SEQUENTIAL NUMBER 001 EIIS Codes are shown in the format [IEEE system identifier, component function identifier, second component function identifier (if appropriate)].
FAILED COMPONENTS IDENTIFIED: None.
PREVIOUS SIMILAR EVENTS
None. REV NO.
00