ML22089A116

Comments and Questions on Constellations March 31st Presentation

ML22089A116
Person / Time
Site:	Limerick
Issue date:	03/28/2022
From:	Marshall M Plant Licensing Branch 1
To:	David Helker Exelon Nuclear, Exelon Generation Co
Marshall, M.
References
EPID L-2020-LRM-0041
Download: ML22089A116 (2)

Text

From: Marshall, Michael To: Helker, David P:(Constellation Nuclear); Golub, Pareez E Cc: Jain, Bhagwat

Subject:

Heads-Up: Comments and Questions on Constellations March 31st Presentation (L-2020-LRM-0041)

Date: Monday, March 28, 2022 8:35:00 AM

Hello Dave and Pareez,

For your awareness, the NRC staff plans on asking the following question during the March 31st meeting between the NRC and Constellation concerning the planned Limerick digital instrumentation and controls license amendment request.

1. Section 4, BTP 7-19 Position 4 Displays and Controls, of the Limerick D3 analysis examines the five critical safety functions from SECY-93-0087 and defines the diverse controls to achieve each critical safety function and displays to monitor the performance of these functions from the control room. The NRC staff notes that the Limerick PRA results are only referenced in the analysis of the containment isolation critical safety function. It is unclear to the NRC staff why PRA results are included only for this analysis. Please discuss the rationale and basis for including PRA results in the analysis of the containment isolation critical safety function.

2. Clarify the screening process used for containment penetrations and what is meant by RAW of approximately 2 in Section 4.4.1 of the Limerick D3 analysis. Please discuss the rationale for using RAW alone and not both RAW and FV in the process for screening containment penetrations with the PRA.

3. Section 4.4.1 of the Limerick D3 Analysis states that for those containment penetrations not screened by the PRA, screening is applied to any containment isolation valves determined to be risk insignificant based on the pipe size. Slide 21 for the pre-submittal meeting states For penetrations not screened, additional screening is applied to containment isolation valves determined to be risk significant based on pipe diameter, where small leak failures of containment were risk insignificant. The NRC staff is unable to reconcile the two sentences because one uses risk insignificant and the other uses risk significant for the size based screening. In addition, the NRC staff is unclear about the purpose and mechanics of this screening. Please (i) reconcile and clarify the two sentence quoted in this question, (ii) discuss the need, rationale, and basis for using pipe size for the screening, (iii) discuss how the size based screening was performed, and (iv) why the LERF model includes penetrations sizes that would not contribute to LERF.

4. The presubmittal meeting slides (i.e., March 31st presentation) state that not all containment penetrations or isolation valves are modeled for isolation function.

Please discuss how the Limerick D3 analysis was performed for containment penetrations and isolation valves not modeled in the PRA or justify that excluding these penetrations and valves does not impact this application.

This list is not a complete list of questions that the NRC staff will have on the information contained in the March 31st presentation. If we develop any other comments or questions prior to the March 31st meeting, they will be sent in a separate email.

Best Regards, Michael L. Marshall, Jr.

Senior Project Manager

Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

301-415-2871