NLS2004006, Response to RAI Regarding License Amendment Request to Revise Technical Specifications (TS) Surveillance Requirements and TS Table for Mathematical Symbols and Use of Allowable Values in the Place of Analytical Limits

Response to RAI Regarding License Amendment Request to Revise Technical Specifications (TS) Surveillance Requirements and TS Table for Mathematical Symbols and Use of Allowable Values in the Place of Analytical Limits

ML040720323
Person / Time
Site:	Cooper
Issue date:	03/09/2004
From:	Edington R Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2004006, TAC MC0629
Download: ML040720323 (14)

Text

Nebraska Public Power District Always theme when you need us NLS2004006 March 9, 2004 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Subject:

Response to Request for Additional Information Regarding Licensing Amendment Request to Revise Technical Specifications (TS) Surveillance Requirements and TS Table for Mathematical Symbols and Use of Allowable Values in the Place of Analytical Limits Cooper Nuclear Station, Docket 50-298, DPR-46

References:

1. Letter from M. Honcharik (U.S. Nuclear Regulatory Commission) to C. C.

Warren (Nebraska Public Power District) dated November 26, 2003, "Cooper Nuclear Station - Request for Additional Information Regarding Revision of Technical Specification Surveillance Requirement 3.3.2.1.4 and Table 3.3.2.1 -1 for Mathematical Symbols and Use of Allowable Values in Place of Analytical Limits (TAC No. MC0629)"

2. Letter from C. C. Warren (Nebraska Public Power District) to U.S. Nuclear Regulatory Commission dated October 31, 2003, "Response to Request for Additional Infornation Regarding Licensing Amendment Request to Revise Technical Specifications (TS) Surveillance Requirements and TS Table for Mathematical Symbols and Use of Allowable Values in the Place of Analytical Limits" (NLS20031 11)

3. Letter from C. C. Warren (Nebraska Public Power District) to U. S. Nuclear Regulatory Commission dated August 25, 2003, "License Amendment Request to Revise Technical Specification (TS) Surveillance Requirement (SR) 3.3.2.1.4 and TS Table 3.3.2.1 -I for Mathematical Symbols and Use of Allowable Values" (NLS2003077)

The purpose of this letter is for the Nebraska Public Power District to respond to a Nuclear Regulatory Commission (NRC) Request for Additional Information (RAI) provided in Reference 1. This RAI refers to infornation previously provided in References 2 and 3. Reference 3 was the original amendment request while Reference 2 provided additional materials to facilitate the NRC review of the requested amendment. The response to the RAI is provided in Attachment I to this letter.

COOPER NUCLEAR STATION C)

P.O. Box 98 /Brownville, NE 68321-0098 Telephone: (402) 825-3811/ Fax: (402) 825-5211 www.nppd~com

NLS2004006 Page 2 of 2 This RAI response is limited to supplying information to assist the NRC in completing the review of the license amendment requested in Reference 3 and does not change any part of the original license amendment request and therefore does not change the original no significant hazards consideration.

Should you have any questions concerning this matter, please contact Mr. Paul Fleming at (402) 825-2774.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on C'3/0 I lv Date 44.64 er Randall Edington Vice President Nuclear and Chief Nuclear Officer

/clb Attachment cc: Regional Administrator wv/attachment USNRC - Region IV Senior Project Manager w/attachment USNRC - NRR Project Directorate IV-l Senior Resident Inspector w/attachment USNRC Nebraska Health and Human Services xv/attachment Department of Regulation and Licensure NPG Distribution w/o attachment Records w/attachment

NLS2004006 Attachment I Page I of 11 Response to Request forAdditional Information RegardingLicensingAmendment Request to Revise Technical Specifications (TS) Surveillance Requirements and TS Table for Mathematical Symbols and Use of Allowable Values in the Place of Analytical Limits Cooper Nuclear Station Docket 50-298, DPR46

1. NRC Request The Technical Specification (TS), Table 3.3.2.1-1 and associated TS Bases, define several separate "zones" of percent rated thermal power (%RTP) and minimum critical power ratio (MCPR), in which various trip functions are enabled or suppressed. The functional zones are defined by Conditions a, b, c and d. Condition e overlaps Conditions a, b and c. The associated TS Bases define "no-trip" zones (i.e., zones not requiring any trip function) at power levels below 30 percent for all MCPRs, at all power levels for MCPRs of 1.7 or greater, and at power levels above 90% for MCPR greater than or equal to 1.4. The proposed Allowable Values (AVs) protect against errors in determining which zone is in effect at any given time.

The margin applied to the 30 percent limit ensures that an underestimation of thermal power when operating just above 30 percent will tend to result in the application of the Condition a setpoints rather than in the assumption of "low power no-trip" zone and the suppression of all trips. This is clearly conservative. But it is not clear wvhether Condition a setpoints or Condition b setpoints are more conservative for thermal power estimation errors when operating near 65 percent. Similarly, for Condition b and c near 85 percent. The inverse relationship of setpoint to power regime further confuses this matter (the low power trip setpoints are higher than the high power trip setpoints). In addition, the "high power no-trip" zone for power greater than or equal to 90 percent with MCPR greater than or equal to 1.4 seems to indicate, counter intuitively, that operation is safer above 90 percent than below 90 percent.

For all RBM Functions in TS Table 3.3.2.1-1 and for the "no-trip" zones in the TS Bases for the RBM (B3.3.2.1, page B3.3-45), please indicate whether overestimation or underestimation of thermal power is more conservative and provide the reasoning behind each determination.

Show that the proposed margins are on the correct side (i.e., where the margins produce, rather than detract from, conservatism) of each zone boundary. Explain why no margin is needed at the 90 percent power level.

NLS2004006 Attachment I Page 2 of I I NPPD Response:

Please refer to the graph on the following page along with the following explanation. The way that the setpoints for the various regions were determined has not changed from when Cooper Nuclear Station (CNS) converted from flow-biased RBM setpoints to the current three zone method. Instrument uncertainties are deducted from the Analytical Limit (AL) to determine the Allowable Value (AV) and Nominal Trip Setpoint (NTSP), per GE Setpoint Methodology.

Additional tests are then applied to the NTSP (i.e. LER Avoidance, Required Limits Evaluation) and a final operating setpoint determined. In the case for the transition from the

'No Rod Block Required' region less than 30% RTP to the low power (LP) region, the conservative situation is to have the rod block in effect prior to reaching 30%, so the calculated AV is 27.5% and the setpoint is 26%. As mentioned, clearly this is conservative. For the transition from the low power setpoint (LPSP) to the intermediate power setpoint (IPSP) and the IPSP to high power setpoint (HPSP), the same calculational methodology was used, i.e.

deducted instrument uncertainties from the AL to determine the AV and NTSP. In those two cases, it is conservative to have the transition region below the AL (and also below the AV) and use the rod block setpoint of the "higher region." Specifically, when moving from the LP region to the IP region, the rod block setpoint will shift from 1 8% down to 1 3% at 61%

RTP, even though the rod block setpoint could be 118% up to the AV of 62.5% RTP. The same discussion holds for the transition from the IP region to the HP region. Additionally, an underestimation of thermal power when operating just above the AL will still result in a shift to the next higher region's rod block setpoint before reaching the AL, while an overestimation of thermal power will cause a shift to the next higher region at some point below the AL, both of which are more limiting.

The calculation Conclusion Section lists a set of permissible rod block values for AL, AV and Operating Setpoint, based on different MCPR Limits. From USAR Section XIV-7, Table XIV-7-2, the MCPR Limit for Rod Withdrawal Error for the current fuel cycle is 1.32.

Therefore, the setpoints for the various regions were selected based on a MCPR Limit of 1.30, which yields the lower rod block setpoints.

The proposed change to the "algebraic signs" in SR 3.3.2.1.4 and Table 3.3.2.1-1 (Notes) is based on our determination that it is conservative to ensure that the rod block setpoint for the next higher region is in effect prior to the AL because that rod block setpoint is a lower value, and thus more limiting.

Even though the Rod Block Monitor function is not required above 90% when MCPR is greater than 1.4, there is no bypass for this region. The only conditions that will automatically bypass the RBM is operation below the Low Power Setpoint (analytical limit of 30%RTP) or a peripheral control rod selected for movement. Therefore, there is no "high power no-trip" zone and no need to calculate a margin for this value.

NLS2004006 Attachment I Page 3 of II

'?Rod Block Set'point 108.5% .'

~~~~~.~~n .Vi . -. ,','

, , ': .*e,,o# > -. ;.. .

HPSP Analytical Limit s 85%RTP Proposed IP Range (<82.5%RTP) and HP Range (2 82.5%RTP) TS HPSP Operating Setpoint = 81%RTP Rod Block Setpoint = 113%

IPSP Analytical Limit s 65%RTP Proposed LP Range (<62.5%RTP) and IP Range (2 62.5%RTP) TS IPSP Operating Setpoint = 61%RTP ii,,,  ;,-' -. -. S,.

'^HRod'-Block Set'point=118% -,-

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4,,-t@ ,X 4t>

^it;et s, t S-,fgo tA LPSP Analytical Limit 2 30%RTP Proposed LP Range TS Value 2 27.5%RTP LPSP Operating Setpoint = 26%RTP No Rod Block Required O%RTP Figure 1, Rod Block Monitor operating regions showing associated setpoint values.

NLS2004006 Attachment I Page 4 of II

2. NRC Request If the estimated MCPR were above 1.7, but the actual MCPR were less than 1.7, then Functions I a, I b, Ic and I e would be suppressed when in fact they should be active. This would be a non-conservative condition. A similar situation exists for the MCPR limit of 1.4 for power levels of 90 percent and above, associated with Function Id. Please explain how this condition is to be avoided, given that the proposed TS changes do not include the addition of margin to the MCPR limits.

NPPD Response The question implies that the system is not in-service during periods when the MCPR is above 1.7. However, this is not the case. The system is in service whenever the reference power level is above the Low Power Setpoint, regardless of the calculated MCPR.

3. NRC Request The mark-up for pages B3.3-45 of the TS Bases shows the 30 percent limit changed to 27.5 percent. The description in the TS Bases should show the objectives of the TS settings, not necessarily the TS settings themselves. The TS value is proposed to be changed from 30 percent to 27.5 percent to ensure that the power-related adjustment in trip setpoint does indeed occur at or below 30 percent despite anticipated uncertainty in the power estimation. As far as the bases are concerned, the objective is to establish a limit at 30 percent. It would seem the TS Bases should not be changed here. Please explain the proposed change.

NPPD Response CNS agrees with the comment. The 30 % number will be retained in TS Bases. The bases is discussing the results of an analysis which has a bases value of 30%. We are adjusting the setpoint and allowable value to address instrumentation uncertainty.

4. NRC Request Please show that the margin between each proposed AV and the corresponding Analytical Limit (AL) is adequate to include all uncertainties remaining in the instrument sensor and channel following calibration. Confirm that the AVs are not affected by the "LER Avoidance Evaluation" or by any other setpoint adjustment based upon operational considerations.

NLS2004006 Attachment I Page 5 of 11 NPPD Response By the definition of GE Setpoint Methodology (NEDC-31336P-A, General Electric Instrument Setpoint Methodology), the margin between the AV and AL is a statistical combination of all uncertainties identified except instrument drift. The margin between AL and the NTSP is the statistical combination of all uncertainties identified. The LER Avoidance Evaluation is an adjustment (if necessary) of the trip setpoint (NTSP) away from the AV to assure that there is sufficient margin to avoid violating the AV during surveillance testing. Likewise, any other setpoint adjustments based on operational considerations would be away from the AV to provide additional margin.

5. NRC Request Calculation Section 2.2: The units for the RBM Trip Function AL's are not specified. We presume these to be % RTP. The units for the AL's for the various Trip Setpoints (SP's) are also not specified. Since the Low Trip SP values are higher than the High Trip SP values, these cannot be % RTP. Since they are above 100 percent, they cannot be % Calibrated Span.

Please describe the units and scaling, and provide a brief explanation as to how the associated trip signals are derived. For example: Is there a separate comparator for each of the three neutron monitors, with one of the three comparators enabled on the basis of power level? Is there just one comparator with analog input selected from among the three neutron monitors on the basis of power level?

NPPD Response The preset limits vary with power. The system monitors local thermal power by generating a signal from the Local Power Range Monitors (LPRM) in the detector assemblies which surround the rod selected for movement. The system receives a "rod select" signal from Reactor Manual Control System (RMCS).

It routes the LPRM outputs from the LPRM assemblies adjacent to the selected rod to the averaging circuit. The system adjusts the averaged signal to equal a constant reference signal.

The gain change circuit increases the gain of the averaged signal until its output equals, or exceeds, the constant reference signal. The system then compares this signal to a power-biased trip setpoint. This power biased trip setpoint has three different values. The value used is based on the Average Power Range Monitor (APRM) Reference channel power. A rod withdrawal block is generated if the normalized LPRM signal rises above the power-biased trip setpoint. On the selection of a rod, the control circuitry controls the sequence of events which prepares the RBM system for proper operation. This sequence of events is called the "Nulling Sequence".

NLS2004006 Page 6 of II Low power setpoint (LPSP) provides the reference for the RBM auto bypass (30% of rated power). Below LPSP the RBM is bypassed.

Intermediate power setpoint (IPSP) provides a fixed reference of 65% rated power. Between LPSP and IPSP, the Low Trip Setpoint is in effect.

High power setpoint (HPSP) provides a fixed reference of 85% rated power. Between IPSP and HPSP, the Intermediate Trip Setpoint is in effect. Above HPSP the High Trip Setpoint is in effect.

These setpoints provide a reference for rod block signals. Each time power level increases (on the reference APRMs) the RBM setpoints automatically change to a lower trip setpoint as discussed below.

Low Trip Setpoint (LTSP):

When power level is below 65% (below IPSP), the rod block trip setpoint is < 120%.

Intermediate Trip Setpoint (ITSP):

When power level is above 65% but below 85%, the rod block trip setpoint is automatically changed to < 115%.

High Trip Setpoint (HTSP):

When power level is above 85%, the rod block trip setpoint changes to < I 10.5%.

The units for the "power setpoints" (LPSP, IPSP, HPSP) are a reference input from an APRM channel, and are in units of percent of rated thermal power (%RTP).

The units for the "trip setpoints" (LTSP, ITSP, HTSP) are the indicated value based on a full scale of 125. Therefore, the units are divisions of full scale.

6. NRC Request Calculation Section 2.2 note "**": The TSs show the limit as 90 percent, not 89 percent.

Please explain.

NPPD Response The 90% listed to in TS Table 3.3.2.1-1 notes c, d and e refer to a change in the operating region for the Rod Block Monitor. However, the RBM does not actually change operation at

NLS2004006 Attachment I Page 7 of I I this point, it continues to function as it did below 90%. The note is referring to the Downscale Trip Setpoint (DTSP) with an analytical limit of 89%. The DTSP will generate a control rod block if the selected RBM channel power is too low from its most recent normalized calibration conditions. This assures that the normalization performed at the time of rod selection remains valid before permitting withdrawal of the rod. Therefore, the 90% value listed in the TS table notes is not the same as the 89% DTSP.

7. NRC Request Calculation Section 2.2 note "**": There appears to be missing text between the final two lines.

Please clarify.

NPPD Response The last sentence of the note "The DTSP limit is not utilized in any licensing bases Rod Withdrawal Error (RWE) analysis or that the range is restricted by design to values considered in the RWE analysis." is a combination of statements from two GE documents. Both documents state that the DTSP limit is not used in or affects any of the licensing basis RWE analyses. Therefore, the last half of the sentence does not add to the discussion and will be deleted in a future revision. The following paragraph will replace the current paragraph 2.2, **

note in NEDC 98-024:

"The Downscale Trip Setpoint (DTSP) function is to prevent a rod withdrawal if the selected RBM channel power is too low from its most recent normalized calibration conditions (i.e.

100%). This assures that the calibration (i.e., normalization) performed at the time of rod selection remains valid before permitting withdrawal of the rod. The Analytical Limit was changed from 91% to 89% of reference level per Reference 6. The DTSP limit is not utilized in any licensing bases Rod Withdrawal Error (RWE) analysis."

8. NRC Request Calculation Section 2.2 note "***": TS Table 3.3.2.1-1 Function le, Condition e, indicates that an MCPR limit (less than 1.7) does apply to the Downscale Trip Setpoint. Please resolve this apparent conflict between the calculation and TS.

NPPD Response Condition e associated with function I e refers to the plant operating conditions when the downscale function is required. The MCPR Limits listed in Section 2.2 of the calculation show what the AL should be to protect the fuel during a rod withdrawal accident. Also see the discussion of the DTSP and the 90% value in the response to question 6 above.

NLS2004006 Attachment I Page 8 of II

9. NRC Request Assumption 3.2: Please justify the claim that seismic effects are insignificant. Note that the zero period acceleration (ZPA) is a property of the mounting location, not of the device itself; and must be at least equal to the floor ZPA, which is likely greater than the ground ZPA. It is not clear that this is an inconsequential value.

NPPD Response GE document NEDC-31336P-A, General Electric Instrument Setpoint Methodology, sections 3.19 and 3.20 provide guidance for assumptions for the RBM and APRM. Neither section discusses seismic effect. Additionally, the prior setpoint calculation for the APRM and RBM was performed by GE, and included an assumption that stated "GE APRM/RBM equipment accuracy specification includes the uncertainties due to seismic effect on the equipment located in the relay room panels. The panels are qualified as a unit." Therefore, seismic effect is not included as a separate item in the setpoint calculation.

10. NRC Request Calculation Assumption 3.3: Uncertainties are usually two-sigma values. The assumption that the standard deviation is only 1/3 - rather than /2 - of the uncertainty seems non-conservative.

This is especially true since the accuracy of the calibration standard is assumed to be only as good as the test equipment that it is used to calibrate. In addition, it is not clear how the fact that "100 percent testing" is implemented relates to the question of whether the associated uncertainties are two-sigma or three-sigma values. Please clarify and justify Assumption 3.3.

NPPD Response The assumption that individual calibration accuracy terms are three-sigma values is from a CNS specific, GE setpoint guidance document This document also uses the term "controlled by 100% testing" to signify that the calibration tests performed on both the instrument itself and all of the calibration standards are actual performance results and not sample results that are statistically applied to a batch of instruments or standards. Additionally, by assuming that the calibration standard's uncertainty is equal to the calibration tool's uncertainty, NPPD is adding additional conservatism to the determination of the Allowable Value.

11. NRC Request Calculation Assumption 3.9: The important quantity is the expected variation in current with the design basis variation in voltage, not necessarily just a I percent variation in voltage. Is this effect not already addressed in the overall accuracy specification for the detection system?

NLS2004006 Page 9 of II NPPD Response: This assumption is associated with determination of the Primary Element Accuracy (PEA) for the LPRM detectors. Section 4.5 of GeneralElectriclulstlulment Setpoint MethodoloDg (NEDC-31336P-A) provides guidance for determining uncertainties associated with the detectors, specifically sensor sensitivity, sensor non-linearity and other sensor non-linearities. Section 4.15 of the calculation (pages 32 and 33) address the sensor sensitivity and sensor non-linearity based on the setpoint methodology document. Both of the "other sensor non-linearities" mentioned in the setpoint methodology document (cable leakage currents and variation in ion chamber output current with changes in ion chamber supply voltage) are assumed to be negligible. Assumption 3.9 is included to address the variation in ion chamber output current, and the value referenced (+/- I % change in ion chamber voltage) is a design specification for the regulated Ion Chamber Power Supply.

12. NRC Request Calculation Assumption 3.11: This addresses a fundamental design issue that seems too important to be covered in an assumption, and it begs the question of why such an assumption should be required. Is the installed equipment the same as that originally provided by General Electric or not? If it is not actually the same equipment, in what sense is it "the same?" Why is the calculation not simply based explicitly upon the actually-installed equipment?

NPPD Response The equipment installed is the same as originally provided by General Electric.

13. NRC Request Calculation Assumption 3.14: Please show that the temperature and humidity effects are negligible, based upon the design conditions at the equipment locations and upon the anticipated limiting effects of temperature and humidity upon the equipment.

NPPD Response GE document NEDC-31336P-A, GeneralElectric hnstninientSetpoint Methodolog,,

sections 3.19 and 3.20 provide guidance for the environmental effects assumptions for the RBM and APRM. For the RBM, "There will not be an environmental effect during the RWE (Rod Withdrawal Error) transient before the rod block function is completed." Similar wording is provided for the APRM in section 3.20, "There will not be an environmental effect during the Design Basis Events before the scram function is complete. Therefore, the harsh environment effect is not applicable." The GE design and performance specification for the APRM Page, Local Power Range Monitor, and design specification for Neutron Monitoring System (RBM-ARTS) specifies the uncertainty to be used based on environmental conditions (temperature and humidity), either in the "restricted" case or the "full" case. For the 'restricted case'

NLS2004006 Attachment I Page 10 of II accuracy (which is used in the calculation), the temperature range is 60-90'F and humidity range of 25-75%RH. If the Control Room ambient temperature should increase above 90'F, station procedures direct the operator to commence a normal plant shutdown, and if temperature exceeds 950 F, to scram the reactor. Therefore, temperature and humidity effects would be included in the accuracy term and do not need to be considered separately.

14. NRC Request Calculation Assumption 3.16: Flow element uncertainty would normally be expressed in terms of the uncertainty in the differential pressure produced for a given flow rate. The actual flow measurement uncertainty includes uncertainty in the measurement of that differential pressure as well as in the behavior of the venturi itself. Please confirm that the assumed 2 percent uncertainty is the composite flow measurement channel uncertainty, not just the element uncertainty. Please explain how the uncertainty in this specific application is known to be bounded by the analyses in the referenced documents.

NPPD Response The venturi uncertainty is 2% of flow based on the design specification. However, the overall flow loop uncertainty is 2.965% of flow as determined in the first half of Step 4 on page 15 of

64. This value is then 'converted' in the second half of Step 4 to an equivalent power level of 1.957%. Additionally, the factory test report results for the flow venturi's states "the average flow rate for each run should be within +/- 0.25% of the true value" which indicates that the flow uncertainty assumed in the calculation is conservative.

15. NRC Request Calculation Assumption 3.18: Please clarify. The uncertainty in the output of the summer would be equal to the combination of the uncertainties in the input signals combined with the additional uncertainty introduced by the summer itself. It is not clear that the summer uncertainty is included here.

NPPD Response The uncertainty of the flow loop is a combination of the uncertainties of the 2 flow elements, 2 flow transmitters, and the flow unit (which includes the summer) and is calculated in step 4.1.3.3.4.. lb on pages 14 and 15 of 64, and in Appendix B. The assumption simply assumes that the As Left Tolerance (ALT) on the output of the summer is equal to twice the ALT of the two summer input values. Refer to diagram on page 23 and the values for ALTIO and ALT,1 on page 21 of the calculation.

NLS2004006 Attachment I Page 11 of II

16. NRC Request Calculation Assumption 3.20: Show that the design basis limits on control room temperature are bounded by the temperature variation assumed in the derivation of the accuracy specification.

NPPD Response The GE design and performance specification for the APRM Page, Local Power Range Monitor, and design specification for Neutron Monitoring System (RBM-ARTS) specifies the uncertainty to be used based on environmental conditions (temperature and humidity), either in the "restricted" case or the "full" case. For the 'restricted case' accuracy (which is used in the calculation), the temperature range is 60-90'F and humidity range of 25 -75%RH. If the Control Room ambient temperature should increase above 90WF, station procedures direct the operator to commence a normal plant shutdown, and if temperature exceeds 957, to scram the reactor.

ATTACHMENT 3 LIST OF REGULATORY COMMITMENTSl Correspondence Number: NLS2004006 The following table identifies those actions committed to by Nebraska Public Power District (NPPD) in this document. Any other actions discussed in the submittal represent intended or planned actions by NPPD. They are described for information only and are not regulatory commitments. Please notify the Licensing & Regulatory Affairs Manager at Cooper Nuclear Station of any questions regarding this document or any associated regulatory commitments.

COMMITTED DATE COMMITMENT OR OUTAGE None 4

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