NLS2020051, Response to Nuclear Regulatory Commission'S Supplemental Request for Additional Information for License Amendment Request for Approval of Emergency Action Level Scheme Change

Response to Nuclear Regulatory Commission'S Supplemental Request for Additional Information for License Amendment Request for Approval of Emergency Action Level Scheme Change

ML20248H493
Person / Time
Site:	Cooper
Issue date:	08/25/2020
From:	Dent J Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2020051
Download: ML20248H493 (9)

Text

H Nebraska Public Power District

.Always there when you need us" NLS2020051 August 25, 2020 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Subject:

Response to Nuclear Regulatory Commission's Supplemental Request for Additional Information for License Amendment Request for Approval of Emergency Action Level Scheme Change Cooper Nuclear Station, Docket No. 50-298, DPR-46

References:

1. Email from Thomas Wengert, U.S. Nuclear Regulatory Commission, to Linda Dewhirst, Nebraska Public Power District, dated August 14, 2020, "Cooper - Supplemental Final RAI RE: License Amendment Request for Approval of EAL Scheme Change (EPID L-LLA-2020-0028)"

2. Letter from Khalil Dia, Nebraska Public Power District, to the U.S.

Nuclear Regulatory Commission, August 6, 2020, "Response to Nuclear Regulatory Commission's Request for Additional Information for License Amendment Request Emergency Action Level Scheme Change"

Dear Sir or Madrun:

The purpose ofthis letter is for the Nebraska Public Power District to respond to the Nuclear Regulatory Commission's supplemental request for additional information (RAI) (Reference 1) related to the Cooper Nuclear Station response to an RAI in Reference 2.

The response to the supplemental RAl question is provided in Attachment 1 to this letter. contains the revised Emergency Action Level (EAL) Technical Basis document pages. Attachment 3 contains the revised EAL Wallchart.

This letter does not contain any new regulatory commitments.

If you have any questions concerning this matter, please contact Linda Dewhirst, Regulatory Affairs and Compliance Manager, at (402) 825-5416.

COOPER NUCLEAR STATION 72676 648A Ave/ P.O. Box 98 / Brownville, NE 68321 http://www.nppd.com

NLS2020051 Page 2 of2 I declare under penalty of perjury that the foregoing is true and correct.

Executed on: I 8' a~ CrJl)

I (Date Jo Dent, Jr.

Vice President and Chief Nuclear Officer

/dv Attachments: 1. Response to Nuclear Regulatory Commission's Supplemental Request for Additional Information (RAI) for License Amendment Request to Adopt Emergency Action Level Scheme Pursuant to NEI 99-01, Revision 6

2. Revised Cooper Nuclear Station EAL Technical Basis

3. Revised EAL Wallchart cc: Regional Administrator w/ attachments USNRC - Region IV Cooper Project Manager w/ attachments USNRC - NRR Plant Licensing Branch IV Senior Resident Inspector w/ attachments USNRC-CNS Nebraska Health and Human Services w/ attachments Department of Regulation and Licensure NPG Distribution w/o attachments CNS Records w/ attachments

NLS2020051 Page 1 of2 Attachment 1 Response to Nuclear Regulatory Commission's Supplemental Request for Additional Information (RAI) for License Amendment Request to Adopt Emergency Action Level Scheme Pursuant to NEI 99-01, Revision 6 Cooper Nuclear Station, Docket No. 50-298, DPR-46 The Nuclear Regulatory Commission (NRC) supplemental request for additional information regarding the request to adopt an emergency action level (EAL) scheme pursuant to Nuclear Energy Institute (NEI) 99-01, Revision 6, is shown in italics. The Nebraska Public Power District (NPPD) response to the request is shown in normal font.

Supplemental RAI-3 Fuel Clad Potential Loss-2 (FC-2) and Reactor Coolant System Loss-I (RC-1) use the condition "Reactor Pressure Vessel (RPV) level cannot be determined" as a threshold value. Considering that CNS emergency operating procedures (EOPs) use the condition "RPV water level cannot be determined" in RC-4 [Reactor Coolant] of RPV Control, the CNP EOPs align well with the guidance provided by NEI 99-01, Revision 6for FC-2 and RCS-I. Based on the NRC staff's initial review of the provided technical bases, the EAL comparison matrix, and CNP EOPs, the addition of the parenthetical "RPV Flooding required" could result in unintended delays in the declaration ofa Site Area Emergency classification. As such, RAI-3 stated:

Please explain how the addition of "RPV Flooding required" to the threshold values for FC-2 and RCS-I will not delay or otherwise impact EAL assessment for conditions where RPV level cannot be determined.

In response to RAI-3, NPPD provided a reiteration of information provided in the technical basis discussion, a discussion on valid instrument readings, and the discussion provided in RAI-3 as justification. As such, the NRC staffremains concerned that the addition of "RPV Flooding required" could result in unintended delays in the declaration of a Site Area Emergency classification.

Please explain how the addition of "RPV Flooding required" to the threshold values for FC-2 and RCS-I will not delay or otherwise impact EAL assessment for conditions where RPV level cannot be determined.

This explanation should provide a justification for adding an extra condition to FC-2 and RCS-I, as well as providing a clear definition ofwhat is specifically meant by "RPV Flooding required. "

NLS2020051 Page2 of2 NPPD Response:

The phrase, "RPV Flooding Required," was not intended to be an extra condition nor expected/intended to delay or otherwise impact EAL assessment conditions where RPV water level cannot be determined. Upon further review and to avoid any potential for confusion, NPPD has elected to remove the phrase thereby negating the need to explain how it will not result in an unintended delay in declaration of a Site Area Emergency and the need to provide a clear definition of what is specifically meant by "RPV Flooding Required." Revised pages of the EAL Technical Basis Document are included in Attachment 2 and the revised Hot Condition Wallchart is included in Attachment 3.

NLS2020051 Attachment 2 Revised Cooper Nuclear Station EAL Technical Basis Cooper Nuclear Station, Docket No. 50-298, DPR-46 (Attachment 2 contains two pages)

COOPER EAL Technical Bases Document NUCLEAR Revision XX STATION Attachment 1 - Emergency Action Level Technical Bases Barrier: Fuel Clad Category: A. RPV Water Level Degradation Threat: Potential Loss Threshold:

FC2 RPV water level cannot be restored and maintained> -158 in. {TAF) or cannot be determined (RPV Flooding required)

Definition(s):

None Basis:

This water level (-158 in.) corresponds to the top of the active fuel and is used in the EOPs to indicate a challenge to core cooling (ref. 1). When RPV level is at or above the TAF, the core is completely submerged. Core submergence is the most desirable means of core cooling. When RPV level is below TAF, the uncovered portion of the core must be cooled by less reliable means (i.e., steam cooling or spray cooling). If core uncovery is threatened, the EOPs specify alternate, more extreme, RPV water level control measures in order to restore and maintain adequate core cooling. Since core uncovery begins if RPV level drops to TAF, the level is indicative of a challenge to core cooling and the Fuel Clad barrier.

When RPV water level cannot be determined, EOPs require entry to RPV Flooding procedures. RPV water level indication provides the primary means of knowing if adequate core cooling is being maintained. When all means of determining RPV water level are unavailable, the Fuel Clad barrier is threatened and reliance on alternate means of assuring adequate core cooling must be attempted. The instructions in the RPV Flooding procedures specify these means, which include emergency depressurization of the RPV and injection into the RPV at a rate needed to flood to the elevation of the main steam lines (ref. 2, 4). If RPV water level cannot be determined with respect to the top of active fuel, a potential loss of the Fuel Clad barrier exists.

In high-power ATWS/failure to scram events, EOPs may direct the operator to deliberately lower RPV water level to the top of active fuel in order to reduce reactor power. RPV water level is then controlled between the top of active fuel and the Minimum Steam Cooling RPV Water Level (MSCRWL). Although such action is a challenge to core cooling and the Fuel Clad barrier, the immediate need to reduce reactor power is the higher priority. For such events, EALs SA6.1 or SS6.1 will dictate the need for emergency classification (ref. 3).

Page 122 of 258

COOPER EAL Technical Bases Document NUCLEAR Revision XX STATION Attachment 1 - Emergency Action Level Technical Bases Barrier: Reactor Coolant System Category: A. RPV Water Level Degradation Threat: Loss Threshold:

RCS1 RPV water level cannot be restored and maintained> -158 in. (TAF) or cannot be determined (RPV Flooding required)

Definition(s):

None.

Basis:

In high-power ATWS/failure to scram events, EOPs may direct the operator to deliberately lower RPV water level to the top of active fuel in order to reduce reactor power. RPV water level is then controlled between the top of active fuel and the Minimum Steam Cooling RPV Water Level (MSCRWL). Although such action is a challenge to core cooling and the Fuel Clad barrier, the immediate need to reduce reactor power is the higher priority. For such events, EALs SA6.1 or SS6.1 will dictate the need for emergency classification (ref. 3).

This water level (-158 in.) corresponds to the top of active fuel and is used in the EOPs to indicate a challenge to core cooling (ref. 1). When RPV level is at or above the TAF, the core is completely submerged. Core submergence is the most desirable means of core cooling. When RPV level is below TAF, the uncovered portion of the core must be cooled by less reliable means (i.e., steam cooling or spray cooling). If core uncovery is threatened, the EOPs specify alternate, more extreme, RPV water level control measures in order to restore and maintain adequate core cooling. Since core uncovery begins if RPV level drops to TAF, the level is indicative of a challenge to core cooling and the Fuel Clad barrier.

When RPV water level cannot be determined, EOPs require entry to RPV Flooding procedures. RPV water level indication provides the primary means of knowing if adequate core cooling is being maintained. When all means of determining RPV water level are unavailable, the Fuel Clad barrier is threatened and reliance on alternate means of assuring adequate core cooling must be attempted. The instructions in the RPV Flooding procedures specify these means, which include emergency depressurization of the RPV and injection into the RPV at a rate needed to flood to the elevation of the main steam lines (ref. 2, 4). If RPV water level cannot be determined with respect to the top of active fuel, a potential loss of the Fuel Clad barrier exists.

Page 135 of 258

NLS2020051 Attachment 3 Revised EAL Wallchart Cooper Nuclear Station, Docket No. 50-298, DPR-46 (Attachment 3 contains one page)

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