CNL-17-108, Response to Request for Additional Information Regarding Request to Modify Technical Specification 3.3.1, Reactor Protection System Instrumentation

Response to Request for Additional Information Regarding Request to Modify Technical Specification 3.3.1, Reactor Protection System Instrumentation

ML17244A033
Person / Time
Site:	Watts Bar
Issue date:	08/31/2017
From:	James Shea Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CAC MF9401, CNL-17-108
Download: ML17244A033 (8)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-17-108 August 31, 2017 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390

Subject:

Response to Request for Additional Information Regarding Request to Modify Technical Specification 3.3.1, Reactor Protection System Instrumentation (CAC No. MF9401)

Reference:

1. TVA Letter to NRC, CNL-17-026, Application to Modify the Watts Bar Nuclear Plant Unit 1 Technical Specification 3.3.1, Reactor Protection System Instrumentation, Turbine Trip Function on Low Fluid Oil Pressure (390-WBN-TS-17-04), dated May 16, 2017 (ML17075A229)

2. NRC Electronic Mail to TVA, Watts Bar, Unit 1 - Final Request for Additional Information Concerning Request to Amend Turbine Trip Low Fluid Oil Pressure Reactor Protection System Trip Setpoint (CAC No.

MF9401), dated August 11, 2017 In Reference 1, Tennessee Valley Authority (TVA) submitted a request for an amendment to the Watts Bar Nuclear Plant (WBN) Unit 1 Technical Specifications (TS) to revise TS 3.3.1, Table 3.3.1-1, Reactor Trip System Instrumentation, Function 14.a. Turbine Trip - Low Fluid Oil Pressure, to:

Increase the nominal trip setpoint (NTSP) from 45 pounds per square inch gauge (psig) to 800 psig, and the allowable value from greater than or equal to () 43 psig to 710 psig.

Add new footnotes (g) and (h) to assess channel performance during testing that verifies instrument channel setting values established by TVAs setpoint methodology.

In Reference 2, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI). Enclosure 1 to this letter provides the TVA response to the RAI.

U.S. Nuclear Regulatory Commission CNL-17-108 Page 2 August 31, 2017 This response does not change the no significant hazards considerations determination contained in Reference 1. There are no new regulatory commitments associated with this submittal. Please address any questions regarding this response to Ed Schrull at 423-7 51-3850.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 31st day of August 2017.

Resp tfull~

. Shea Vi e President, Nuclear Regulatory Affairs and Support Services Enclosure Response to Request for Additional Information Regarding Request to Modify Technical Specification 3.3.1, Reactor Protection System Instrumentation (CAC No. MF9401) cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRR Project Manager - Watts Bar Nuclear Plant

Enclosure CNL-17-108 E1 of 6 Response to Request for Additional Information Regarding Request to Modify Technical Specification 3.3.1, Reactor Protection System Instrumentation (CAC No. MF9401)

Nuclear Regulatory Commission (NRC) Introduction By letter dated March 16, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17075A229), Tennessee Valley Authority (TVA, or the licensee), proposed changes to the Technical Specifications (TSs) for Watts Bar Nuclear Plant (Watts Bar), Unit 1. The proposed changes will revise Watts Bar TS Table 3.3.1-1, Reactor Trip System Instrumentation, to reflect plant modifications to the reactor protection system instrumentation associated with turbine trip on low fluid oil pressure. The proposed changes are due to the replacement and relocation of the pressure switches from the low pressure auto-stop trip fluid oil header that operates at a nominal control pressure of 80 pounds per square inch gauge (psig) to the high pressure turbine electrohydraulic control (EHC) oil header that operates at a nominal control pressure of 2000 psig. The licensee stated that the changes to the nominal trip setpoint (NTSP) and allowable value are needed due to the higher EHC system operating pressure. The proposed change also adds new footnotes (g) and (h) to the turbine trip on low fluid oil pressure trip setpoints to assess channel performance during testing that verifies instrument channel setting values established by TVAs setpoint methodology.

The U.S. Nuclear Regulatory Commission (NRC) staff has determined that additional information, as described in the requests for additional information (RAIs) below, is required for the staff to complete its review of the application.

NRC RAI SBPB-1 Describe if the existing turbine trip system (as described above) and as it related to the proposed changes to TS 3.3.1-1 Tables, is within the scope of Maintenance Rule and described if the proposed turbine trip system is within the scope of Maintenance Rule.

TVA Response:

The existing turbine generator control system (TGCS) is in the scope of the Maintenance Rule and monitored at the plant level (e.g., unplanned scrams, ESF actuations) as described in Appendix A to TVA procedure 0-TI-119 Maintenance Rule Performance Indicator Monitoring, Trending, and Reporting - 10CFR50.65. The new turbine generator control system and pressure switches that provide a reactor scram function on a turbine trip will be monitored the same way. The referenced letter proposed to modify the output sensors of the TGCS that input to the reactor protection system (RPS). The RPS is also in the scope of the Maintenance Rule and monitored at the specific level (e.g., unavailability, unreliability, condition, or a special plant level criteria) in accordance with 0-TI-119. The Technical Specification (TS) changes in the referenced letter will have no effect on the monitoring of RPS in the Maintenance Rule.

Reference TVA Letter to NRC, CNL-17-026, Application to Modify the Watts Bar Nuclear Plant Unit 1 Technical Specification 3.3.1, Reactor Protection System Instrumentation, Turbine Trip Function on Low Fluid Oil Pressure (390-WBN-TS-17-04), dated May 16, 2017 (ML17075A229)

Enclosure CNL-17-108 E2 of 6 NRC RAI SBPB-2 Confirm whether there is a difference in the time interval from depressurization to trip logic initiation between the current auto-stop oil system configuration and the proposed high pressure turbine EHC oil system configuration. Provide technical justification for any change in the time interval.

TVA Response There is no discernable difference in the time interval from depressurization to trip logic initiation between the current auto-stop oil system configuration and the proposed high pressure turbine EHC oil system configuration. Further justification is provided below.

Section 7.2.1.1.2.6 of the Watts Bar Nuclear Plant (WBN) dual-unit Updated Final Safety Analysis Report (UFSAR) describes the reactor trip on a turbine trip function as follows:

The reactor trip on turbine trip provides additional protection and conservatism beyond that required for the health and safety of the public.

This trip is included as part of good engineering practice and prudent design. No credit is taken in any of the accident analyses (Chapter 15) for this trip.

Consequently, the UFSAR does not contain any response time requirements for the initiation of this trip. The reactor trip on a turbine trip function from the low oil pressure switches response times are not included in the scope of plant surveillance instructions that verify safety system initiation and trip response times.

TVA surveillance instructions 1-SI-99-601-A and 1-SI-99-601-B, that apply to a different part of the plant solid-state protection system (SSPS) circuity (i.e., not associated with the low oil pressure switch function), test the time to depressurize the auto-stop oil system line and the resulting closure of the turbine stop valves. These surveillance instructions require that the desired response time to fully close the stop valves is 0.75 seconds, which includes the time to depressurize the EHC lines.

With the existing EHC configuration, the auto-stop oil system line is depressurized by the actuation of protective devices, solenoid trip valves or an emergency trip valve on a turbine trip condition. The EHC fluid is an incompressible fluid. Therefore, when the solenoid and emergency trip valves are opened, the dump valves at each main steam governor and stop valve are depressurized and the high-pressure EHC fluid to the main steam governor and stop valve actuators is released to drain (approximately zero psig). The governor and stop valves are spring actuated closed so that when the high-pressure EHC fluid is removed from the valve actuators, they close. In 1-SI-99-601-A and 1-SI-99-601-B, a protective relay (K621) is manually actuated that energizes to open the auto-stop oil line solenoid and emergency trip valves and depressurizes the auto-stop oil line. The time interval from the actuation of relay K621 to the closure of the stop valves is recorded and verified to be 0.75 seconds. Because this action includes the time to close the stop valves, the time to depressurize the auto-stop oil line is also 0.75 seconds.

Enclosure CNL-17-108 E3 of 6 With the new EHC configuration, a solenoid valve trip block assembly is connected to the high-pressure EHC emergency trip header. On a trip condition, the solenoid valves are de-energized and open to depressurize the dump valves that release the high-pressure EHC fluid to the main steam governor and stop valves actuators to drain (approximately zero psig). By removal of the low-pressure auto-stop line, the time to directly depressurize the high-pressure EHC emergency trip header is expected to be the same or better than the existing configuration. The time response of the new trip block assembly to depressurize the EHC lines and close the stop valves is confirmed during post installation testing by the performance of plant surveillance instructions 1-SI-99-601-A and 1-SI-99-601-B. With the modified EHC system, protective relay K621 is manually actuated which energizes interposing control relays that open normally closed contacts to de-energize the new EHC solenoid trip block assembly, which depressurizes the high-pressure EHC Emergency Trip header. The time interval from the actuation of relay K621 to the closure of the stop valves will be recorded and verified to be 0.75 seconds.

Therefore, the time to depressurize the EHC header to less than the low oil pressure switch actuation setpoint is 0.75 seconds for both the existing and new configuration.

The response times of both the existing United Electric model J402/270 pressure switches and the new Barksdale TC9622-3-V pressure switches are not provided in the vendor datasheets. However, as both are the same type of piston-actuated pressure switches, there is not expected to be any discernable delay in actuation at the low-pressure setpoints.

NRC RAI SBPB-3 Describe the electrical power design to the new pressure switches and describe given a loss of power to these new pressure switches if the low fluid oil pressure logic would fail in a safe position.

TVA Response The new Barksdale TC9622-3-V pressure switch has a hydraulically-actuated piston that closes the electrical contacts on the switch. The only electrical connections to the pressure switch are to the two sets of contacts on each switch. The wiring to the existing pressure switches will be lifted and re-landed on the new pressure switches so that the electrical connections to the SSPS are the same as the existing pressure switches. Power to one set of the contacts on each pressure switch is from the SSPS Train A. Power to the second set of contacts on each pressure switch is from the SSPS Train B. The SSPS system is configured as a fail safe system so that a scram is initiated on a loss of SSPS power to one train of the SSPS system.

NRC RAI EICB-1 The licensee proposed to increase the allowable value from 43 psig to 710 psig for turbine trip on low fuel oil pressure. On page E1-9 of 16 of the license amendment request, the licensee stated that, The allowable value is derived from the NTSP in accordance with BTI-EEB-TI-28. Provide technical justification in the form of a calculation summary for the BTI-EEB-TI-28 methodology detailing how the 710 psig value was established. The calculation summary should include, but not be limited to, total loop uncertainty (TLU),

as-left tolerance (ALT), as-found tolerance (AFT), basis for selection, and limitations pertaining to the proposed NTSP of 800 psig.

Enclosure CNL-17-108 E4 of 6 TVA Response Table 3.3.1-1, item 16.a of NUREG-1431, Revision 4, Standard Technical Specifications Westinghouse Plants, provides the referenced NTSP for turbine trip on low fluid oil pressure as 800 psig. This value is consistent with the EHC operating system pressure range associated with this parameter for the WBN Unit 1. The setpoint value of 800 psig is based on the minimum required EHC fluid oil pressure, the expected calibration tolerance and frequency of the switches, and the expected time-based drift of the pressure switches.

The safety analyses in Chapter 15 of the WBN dual-unit UFSAR do not credit the operation of the reactor trip on turbine trip function of the low fluid oil pressure switches. Therefore, an Analytical Limit (AL) or Limiting Trip Setpoint (LTSP) is not defined for the low oil pressure trip function.

The allowable value (AV) is derived from the NTSP based on performance data and not on an evaluation of TLUs applied to an AL or LTSP. The Acceptance Band (Ab) and AV were calculated in accordance with TVA Branch Technical Instruction BTI-EEB-TI-28, Setpoint Calculations, as described below. A summary of the calculations is provided at the end of this RAI response.

Acceptance Band or As-Left Tolerance The Ab, which is sometimes referred to as the "As-Left Value" or "Setting tolerance," is the acceptable parameter variation limits above or below the desired output for a given input standard associated with the calibration of the instrument channel. The Ab is calculated in accordance with BTI-EEB-TI-28 section 5.5.6, as the square root sum of the squares combination of reference accuracy (Re), measuring and test equipment (M&TE) error (ICTe and OCTe), and M&TE readability (ICRe and OCRe)

= ()2+()2 + ()2+()2 + ()2 Where:

RePS = Reference Accuracy ICTe = Reference accuracy of the input M&TE ICTePS = Input Test Instrument Calibration Inaccuracy ICRePS = Input Test Instrument Reading Inaccuracy OCTe = Reference accuracy of the output of M&TE OCTePS = Output Test Instrument Calibration Inaccuracy OCRePS = Output Test Instrument Reading Inaccuracy The TVA calculation in support of the turbine high pressure EHC trip header pressure switches states, as part of the design input, that:

For ICTePS, the accuracy of the calibrating test equipment is as accurate as or better than the component reference accuracy (ICTePS = RePS).

For ICRePS, the input calibration reading error cannot exceed the accuracy of the calibrating test equipment. Therefore, either a digital gauge or an analog gauge with a minor division less than or equal to 48 psi (ICRePS = RePS) is used.

OCTePS and OCRePS are both insignificant when determining contact status because the contact is either open or closed.

Enclosure CNL-17-108 E5 of 6 Where:

Calibrated Span (CS)minPS = 250 psi (Input - Minimum)

RePS = 2.0% CSPS CSmaxPS = 2650 psi (Input - Maximum)

CSPS = CSmaxPS - CSminPS CSPS = 2650 psi - 250 psi = 2400 psi RePS = (0.02)(2400 psi) = 48 psi ICTePS = RePS = ICRePS = 48 psi Therefore,

= (48)2+(48)2 + (48)2+02 + 02 AbPS = 83.14 psi.

However, BTI-EEB-TI-28 sections 5.5.3.A and 5.5.6.B.6 state that Ab should always be equal to or greater than the device's reference accuracy. The Ab should not be so large that it could prevent or mask detection of instrument degradation or failure. As-left tolerances should never dominate the as-found tolerance. Therefore, AbPS was conservatively set to equal Reference Accuracy (i.e., AbPS = RePS = 48 psi).

Normal Measurable Accuracy or As-Found Tolerance Normal measurable accuracy (Anf) is calculated in accordance with BTI-EEB-TI-28 Sections 5.5.5 and 5.5.6. For instrument calculations where a bias error is only applied in either the positive or negative direction, it is convenient to separate the calculation into a positive as-found tolerance (Anfpos) calculation and a negative as-found tolerance (Anfneg) calculation.

For the Barksdale pressure switches used in the low oil pressure trip application, the drift error is a negative bias and is only applied to the Anfps_neg term to determine the total negative as-found tolerance as follows.

_= ()2+()2 + ()2

_= ()2+()2 + ()2 +

Where:

DePS = Drift Error ICTePS = Input Test Instrument Calibration Inaccuracy ICRePS = Input Test Instrument Reading Inaccuracy Drift and repeatability was calculated by a statistical analysis performed using historical drift data for the same type of pressure switches in a similar EHC application. No credit was taken for temperature effect in the Anf calculation, which results in a more conservative AV.

Enclosure CNL-17-108 E6 of 6 Where:

Drift error = -0.1% URL bias1(DePSbias), +/-2.1% URL random (DePSrandom)

DePSbias = 0.1% CSmaxPS (Input - Maximum)

DePSbias = (0.001)(2650 psi)

DePSbias = 2.65 psi (to be applied to only the negative as-found tolerance calculation)

DePSrandom = 2.1% CSmaxPS (Input - Maximum)

DePSrandom = (0.021)(2650 psi)

DePSrandom = 55.65 psi Therefore:

_= (55.65 )2+(48 )2 + (48 )2

_= (55.65 )2+(48 )2 + (48 )2 + 2.65 AnfPSpos = 87.78 psi AnfPSneg = 87.78 psi + 2.65 psi = 90.43 psi Allowable Value AVPS = SPPS - AnfPSneg AVPS = 800 psi - 90.43 psi AVPS = 709.57 (approximately 710 psi)

Where: SPPS = Setpoint value Summary Instrument Setpoint (SPPS) (psi)

Range (psi)

(CSminPS to CSmaxPS)

Output As-Left Value (AbPS)

(psi)

Allowable Value (AVPS)

(psi) 1-PS-047-0073 800 250 to 2650 (OP DECR) 48 710 1-PS-047-0074 800 250 to 2650 (OP DECR) 48 710 1-PS-047-0075 800 250 to 2650 (OP DECR) 48 710 1 Because this is a negative bias, it is only applied to the Anfps_neg term by adding it to the SRSS of the random drift error, instrument calibration and reading inaccuracy to determine the total negative as-found tolerance.