ML14168A018

Xcel Energy Responses to NRC Questions Regarding Flood Hazard Reevaluation Report Extension Requests

ML14168A018
Person / Time
Site:	Monticello, Prairie Island
Issue date:	05/16/2014
From:	Xcel Energy
To:	Office of Nuclear Reactor Regulation
Beltz T
Shared Package
ML14153A026	List: ML14153A024 ML14153A025 ML14168A018
References
TAC MF3629, TAC MF3630, TAC MF3651
Download: ML14168A018 (2)

Text

414 Nicollet Mall - MP4 Minneapolis, MN 55401 INTRODUCTION On May 16, 2014, the NRC held a public meeting regarding NSPMs Flood Hazard Reevaluation Report (FHRR) extension requests for Prairie Island and Monticello Nuclear Generating Plants. NSPM requested to complete the FHRRs within 10 months after receiving the USACE information. The purpose of the public meeting was for the NRC to gain a better understanding of the acceptability/basis of the timeframe for the proposed schedule extension to ensure that the safety aspects were considered.

During this meeting, NSPM agreed to follow-up with the NRC on the following two items:

1) NSPM will review the schedule to see if the task related to evaluating the USACE data should be changed based on the NRCs indication that the USACE will not be providing hydrographs per dam.

2) NSPM will provide the NRC a plan for developing interim actions.

This document provides NSPMs responses to the actions from the May 16th public meeting. The actions are noted below in italics and then followed by the NSPM response.

RESPONSE TO ACTIONS FROM PUBLIC MEETING ACTION 1: Review the schedule to see if the task related to evaluating the USACE data should be changed based on the NRCs indication that the USACE will not be providing hydrographs per dam.

RESPONSE: The task Evaluate Revised Hydrology from the USACE Information includes receiving information from USACE and determining how best to utilize it in the hydrologic model. Then the team will combine the USACE hydrographs with site specific PMP values and incorporate failure data known for important dams not operated by USACE.

The 3 to 4 months duration includes time to review the response information from the USACE and time to seek additional clarification, adjust the model and refine the subbasin modeling if necessary. Benchmarking and calibration of the model will also take place during this time and several iterations are expected in order to get the hydrologic model to accurately reflect the behavior of the watershed during floods and dam failures. At this time, based on the scope of work planned and the uncertainty of what information NSPM will receive from the USACE, NSPM continues to estimate the task will take 3 to 4 months to complete.

Enclosure 2

To the extent possible, all non-USACE related work will be completed prior receiving the USACE information to expedite the process once the USACE information is received.

ACTION 2: Provide a plan for developing interim actions for external flooding.

RESPONSE: The interim actions will occur in four steps and will be developed in parallel with the refined flood hazard analysis.

Step 1: Preparation. This includes assembling and briefing the team, reviewing the flood coping concepts that have been developed to date, and benchmarking another plant that faces similar flood hazards. The assumed flood height and timing will be developed at this stage to guide development of interim actions. These inputs will be validated in step 3.

Step 2: Strategies. The second step is the development of strategies to fulfill each of the key safety functions in the event of a flood. The components and site areas that are needed to perform the safety functions will either be located above the assumed flood height or protected from flood water intrusion. The strategies will be assessed by developing an implementation flowchart, and performing walkthroughs. Drafts of implementation procedures will also be developed.

Step 3: Validation. The strategies developed in step 2 will be validated when the final flood height and timing results are completed for each flooding mechanism. The validation will check that the flood height and timing that were used to develop the strategies remain bounding. If not, then the strategies will be adjusted as needed. This step will also serve as the trigger to determine whether interim actions are required.

Step 4: Implementation. This step will be performed if any flood hazard reevaluation analysis determines that the flood hazard is not fully bounded by the design basis flood.

This involves creating formal procedures, requesting and budgeting for plant modifications (if needed) and training personnel on how to manage a beyond design basis flood. The exact schedule will be determined by the number and type (outage or non-outage) of modifications needed to effect the interim actions and training required for the new procedures.

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