ML111720830

Report of May 24, 2011 Audit of Entergy and General Electric Hitachi Nuclear Energy Americas LLC Calculations Related to Technical Specification Changes and Supporting the Extended Power Uprate

ML111720830
Person / Time
Site:	Grand Gulf
Issue date:	08/10/2011
From:	Wang A Plant Licensing Branch IV
To:	Entergy Operations
Wang, A B, NRR/DORL/LPLIV, 415-1445
References
TAC ME4679
Download: ML111720830 (8)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 August 10, 2011 Vice President, Operations Entergy Operations, Inc.

Grand Gulf Nuclear Station P.O. Box 756 Port Gibson, MS 39150

SUBJECT:

GRAND GULF NUCLEAR STATION, UNIT 1 - AUDIT OF CALCULATIONS RELATED TO EXTENDED POWER UPRATE (TAC NO. ME4679)

Dear Sir or Madam:

By letter dated September 8, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML102660403), as supplemented by letter dated February 23,2011 (ADAMS Accession No. ML110550318), Entergy Operations, Inc. (Entergy, the licensee),

proposed an amendment to increase the maximum reactor power operating limit authorized in the operating license from 3,898 megawatts thermal (MWt) to 4,408 MWt. On May 24, 2011, an audit by the Nuclear Regulatory Commission (NRC) staff of the GE-Hitachi Nuclear Energy Americas, LLC (GEH) calculations, supporting the changes to the instrumentation and controls Technical Specifications, was held at the Nuclear Energy Institute's office in Rockville, Maryland. The audit was needed as GEH stated that the calculations were proprietary and voluminous.

A copy of the NRC staff audit report is enclosed. If you have any questions regarding the audit report, please contact me at (301) 415-1445.

Sincerely, Alan B. Wang, Proje Plant Licensing Branc Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-416

Enclosure:

Audit Report cc w/encls: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 AUDIT REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION AUDIT OF THE INSTRUMENTATION AND CONTROL CALCULATIONS ENTERGY OPERATIONS, INC.

GRAND GULF NUCLEAR STATION. UNIT 1 DOCKET NO. 50-416 By letter dated September 8, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML1002660403), as supplemented by letter dated February 23,2011 (ADAMS Accession No. February 23,2011), Entergy Operations, Inc. (Entergy, the licensee),

proposed an amendment to increase the maximum reactor power operating limit authorized in the operating license for the Grand Gulf Nuclear Station, Unit 1 (GGNS) from 3,898 megawatts thermal (MWt) to 4,408 MWt.

Several Technical Specification (TS) modifications affecting instrumentation and control systems have been proposed in conjunction with the extended power uprate (EPU) license amendment The Main Steam Line (MSL) Flow - High Allowable Value (AV) and Nominal Trip Setpoint (NTSP), Fixed Neutron Flux - High AV and NTSP, and Average Power Range Monitor (APRM) Flow-Biased Thermal Power - High AV and NTSP involve non-trivial calculations. All of the TS changes were reported to use the same Nuclear Regulatory Commission (NRC) approved GE-Hitachi Nuclear Energy Americas, LLC (GEH) setpoint methodology, with the exception of the Oscillation Power Range Monitor (OPRM)-related TS change addressed in the related Power Range Neutron Monitoring System (PRNMS) license amendment request (LAR).

The new values for these TSs were identified in the LAR. On April 5, 2011, the NRC staff transmitted a formal request for additional information (RAI) aimed at further understanding the methodology and values obtained. However, the initial responses to the NRC staff's RAls were insufficient for the NRC staff to reach its safety conclusions. Although none of the proposed values appeared unreasonable, additional understanding of the how the calculations were performed was deemed necessary for the NRC staff to complete its review. GEH stated that the calculations were proprietary and voluminous. The NRC staff and the licensee agreed that an audit of the calculations would help expedite the review process.

On May 24, 2011, the NRC staff and representatives of Entergy and GEH met at the Nuclear Energy Institute (NEI) office in Rockville, Maryland. The purpose of the meeting was: 1) to review proprietary calculations for three TS changes related to the instrumentation and control systems affected by the EPU and 2) to achieve an understanding of how uncertainties were handled, if and how biases were included in the calculations, whether single- or double-sided calculation methods were used, and how as-found tolerances were determined.

Enclosure

-2 The NRC audit participants were:

Timothy Mossman David Rahn Rossnyev Alvarado The Entergy participant was:

Jerry Burford Also participating from GEH were:

Andrew Poulos Larry King Listed below is a summary of the NRC staff's findings and observations from the audit:

• GEH representatives explained their setpoint methodology and presented the figure that indicates the different components they use. Also, they explained how and why they derived multiple NTSPs.

The first NTSP is the setpoint with minimum margin to the analytical limit (AL) (NTSP1), and it is based on a 95 percent probability. NTSP1 is the value that should ensure compliance to NRC requirements and guidance.

The second setpoint (NTSP2) provides the margin to the AV for the purpose of avoiding Licensee Event Reports (LERs).

There is a third NTSP, called final adjusted NTSP. This final adjusted NTSP is the margin to the AV to ensure that the NTSP is appropriate relative to the AV when leave-alone tolerance (LAT) values are considered. [Note: the NTSP2 and final adjusted NTSP should be at least as conservative as (and more likely more conservative than)

NTSP1. These alternate NTSPs may be adopted if the licensee believes that the additional margin is beneficial to their operations.]

An additional analysis is performed relative to normal operating conditions to ensure that - if the more conservative NTSP2 or final adjusted NTSP are used - the licensee has not introduced the potential for unnecessary, spurious trips. [In no case, can the NTSP be less conservative than the calculated NTSP1.]

• For those functions that are not derived directly from an AL (because they are not credited in the safety analysis), GEH uses a subset of its methodology to calculate NTSP2 and final adjusted NTSP from AV.

• The three calculations review all used GEH's single-sided methodology.

- 3

• For the calculation of the MSL high flow:

The NRC staff reviewed input data for this calculation as well as the spreadsheet used to perform the computations. Both spreadsheet algorithms and values were available and were reviewed.

GGNS is maintaining the rated steam flow AL value of 140 percent. For operations at the proposed EPU power level, the steam flow in pounds per square inch differential (psid) would be increased. For the calculation performed, the process measurement accuracy is considered as described in Section 2.4.2 of the GGNS EPU LAR dated September 8, 2010, and Attachment 5A 1 to the LAR and appropriately included. The error terms for the Rosemount transmitter had all been normalized to 20' uncertainty estimates (using information supplied by Rosemount). GGNS uses two different model Rosemount transmitters, and although the data for the two models was very similar (if not largely identical), where any differences existed, the setpoint calculation for the MSL high flow used the more conservative data.

Bias terms appeared to be appropriately identified in the calculation including spreadsheet input values and the algorithms. Non-bias uncertainties appeared to be appropriately incorporated and combined.

Surveillance intervals were identified to form a basis for drift values used.

A GE proprietary technique was used to generate drift data that was not specifically identified. Any impact to signal uncertainty from environmental conditions that the instrumentation was expected to experience was identified and incorporated into the calculation. Rounding of the NTSP values was in the direction away from the AL (to ensure a conservative value).

In the MSL high flow calculation, the NTSP selected was more conservative than what would nominally be required to meet NRC requirements and guidance. This extra conservatism was adopted to minimize generation of LERs.

No issues or open items with the MSL high flow calculation were identified.

1 GE-Hitachi Nuclear Energy Americas LLC, "Safety Analysis Report for Grand Gulf Nuclear Station, Constant Pressure Power Uprate," NEDO-33477, Revision 0, August 2010, Non-Proprietary Version (ADAMS Accession No. ML102660399).

-4

• For the APRM calculations related to Fixed Neutron Flux - High and APRM Flow-Biased Thermal Power - High:

The NRC staff reviewed input data for these calculations as well as the spreadsheet used to perform the computations. Both spreadsheet algorithms and values were available and were reviewed.

The Fixed Neutron Flux - High values for AV and NTSP are driven by the AL, which remains at 122 percent. According to the representatives of Entergy and GEH, the APRM Flow-Biased Thermal Power - High scram is not specifically credited in the GGNS safety analyses, as the Fixed Neutron Flux - High is bounding and sufficient to address postulated events. An AV and NTSP have been derived for the APRM Flow-Biased Thermal Power - High.

The uncertainty values for local power range monitor (LPRM) detectors included bias to account for loss of instrument sensitivity between 7-day surveillance intervals.

In the calculation summary provided with the response to the initial Instrumentation and Controls Branch RAls, a number of questions were posed by the NRC staff regarding potentially ambiguous wording in the "comments" attached to certain calculated values. Since that time, GEH has modified comments 6 and 20 (to clarify their intended meaning).

GEH and Entergy indicated that this revision would be available for submission shortly. The NRC staff stated a request for this document would be submitted as a supplemental RAI2.

The Nuclear Measurement Analysis and Control's (NUMAC's) accuracies are provided for both the flow electronics and the power electronics. So the calculation provided presents the values for these two components (in Tables 2.2 and 2.3 of the APRM calculations audited).

The neutron flux scram AL remains at 122 percent. This value is not proposed to change from the current licensed thermal power (CLTP) AL.

However, the AV and NTSP have changed (to be more conservative in terms of percent rated thermal power (%RTP) for the EPU. Since the "old" calculation for the CLTP was not readily available, it was not clear what drove the AV and NTSP to be set more conservatively. The licensee indicated that it would provide an informal answer.

2 Subsequent to the audit on May 24, 2011, the NRC's supplemental RAI was transmitted to the licensee via e-mail onJune29,2011 (ADAMSAccessionNo.ML111801362).

- 5 To determine the APRM flow biased scram and rod block, GEH determined the slope and coordinate (or interception). This is done using the errors and accuracy of the loop components. These functions use a single-loop operation (SLO) setting adjustment to calculate the single loop NTSP from the two-loop operation (TLO) NTSP value. Note that the SLO setting adjustment only applies to NTSP because it is only related to the instrument settings. Comment 12 in the material to be docketed explains how this is performed.

Bias terms appeared to be appropriately identified in the calculation, including spreadsheet input values and the algorithms. Non-bias uncertainties appeared to be appropriately incorporated and combined.

Surveillance intervals were identified to form a basis for drift values used.

A GEH proprietary technique was used to generate drift data that was not specifically identified. Any impact to signal uncertainty from environmental conditions that the instrumentation was expected to experience was identified and incorporated into the calculation. Rounding of the NTSP values was in the direction away from the AL (to ensure a conservative value).

No issues or open items with the Fixed Neutron Flux - High and APRM Flow-Biased Thermal Power - High calculations were identified.

The NRC staff noted that although the spreadsheet and calculation summary documents showed that the temperature effect and humidity effect errors for the NUMAC equipment were "included within the NUMAC accuracy performance specification," upon review of a copy of a design calculation for the NUMAC performance, and its reference specifications, it was noted that a calculation had been performed to demonstrate the negligible magnitude of the temperature effect specification, but no calculation had been performed for the humidity effect specification. Yet, the calculation summary merely stated that the humidity effect was enveloped without providing a calculation to demonstrate that it was, just as it had for the temperature effect. The staff noted that this appeared to be an unverified assumption, which would need further evaluation or a statement as to why it is considered negligible. The NUMAC performance specification for humidity performance was listed as 20-50 percent relative humidity, which is suitable for a typical nuclear plant controlled environment such as would exist in a control room or auxiliary electrical equipment room.

- 6

• GEH performed the setpoint calculations assuming that GGNS will move to 24-month fuel cycle, instead of the current 18 months. In this manner, the licensee would not have to revise its setpoint calculation if/when it submits an amendment for this modification to its license. However, the NRC staff was concerned whether this would affect the as-found value for these functions in the interim. In particular, if the PRNM NUMAC modification is implemented but the EPU is not implemented, the estimate of as-found tolerance will likely be too large to appropriately be used to detect degraded operation. GEH and the licensee understood the question and will provide a response on this issue. The NRC staff stated that this item would be submitted as a supplemental RA13.

Principal Contributor: Timothy Mossman Date: August 10, 2011 3 Subsequent to the audit on May 24, 2011, the NRC's supplemental RAI was transmitted to the licensee via e-mail onJune29,2011 (ADAMSAccessionNo.ML111801362).

August 10, 2011 Vice President, Operations Entergy Operations, Inc.

Grand Gulf Nuclear Station P.O. Box 756 Port Gibson, MS 39150 SUB.JECT: GRAND GULF NUCLEAR STATION. UNIT 1 - AUDIT OF CALCULATIONS RELATED TO EXTENDED POWER UPRATE (TAC NO. ME4679)

Dear Sir or Madam:

By letter dated September 8, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML102660403), as supplemented by letter dated February 23, 2011 (ADAMS Accession 1\10. ML110550318), Entergy Operations, Inc. (Entergy, the licensee),

proposed an amendment to increase the maximum reactor power operating limit authorized in the operating license from 3,898 megawatts thermal (MWt) to 4,408 MWt. On May 24, 2011, an audit by the Nuclear Regulatory Commission (NRC) staff of the GE-Hitachi Nuclear Energy Americas, LLC (GEH) calculations, supporting the changes to the instrumentation and controls Technical Specifications, was held at the Nuclear Energy Institute's office in Rockville, Maryland. The audit was needed as GEH stated that the calculations were proprietary and voluminous.

A copy of the NRC staff audit report is enclosed. If you have any questions regarding the audit report, please contact me at (301) 415-1445.

Sincerely, IRA!

Alan B. Wang, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-416

Enclosure:

Audit Report cc w/encl: Distribution via Listserv DISTRIBUTION:

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