ML25027A215

GL 04-02 RAIs to Licensee

ML25027A215
Person / Time
Site:	Seabrook
Issue date:	01/14/2025
From:	Shivani Mehta NRC/NRR/DSS/STSB
To:	Hipolito Gonzalez NRC/NRR/DORL/LPL1
References
EPID L-2017-LRC-0000
Download: ML25027A215 (2)

Text

Seabrook GL 04-02 Summary RAIs Regulatory Basis By letter dated June 24, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML21208A054 (package)), NextEra Energy, Seabrook, LLC, the licensee, submitted an updated response to Generic Letter (GL) 2004-02, dated September 13, 2004 (ADAMS Accession No. ML042360586), Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors, for the Seabrook Station.

10 CFR 50.46 requires that plants are able maintain adequate long-term core cooling (LTCC) to ensure that the fuel in the core can be cooled and maintained in a safe and stable configuration following a postulated accident. GL 2004-02 requested that licensees provide information confirming that their plants are in compliance with the regulation. During its review of the licensees submittal the NRC staff identified that it required additional information to confirm the licensees evaluation. The questions in this RAI identify the information required by the NRC to confirm the plant compliance with 10 CFR 50.46.

Requests for Additional Information

1) On page E1-20 of the submittal dated June 24, 2021, the licensee credited the reactor cavity seal ring for protection of insulation on the reactor head. Provide details that justify that the seal ring is a robust structure capable of shielding insulation on the reactor head from breaks in the reactor cavity.

2) Tables 3.e.6-6 through 8 provide overall transport fractions including those where CBS is not operating. The NRC staff noted that these cases result in less transport to the strainer for fine fibrous and qualified coating debris than the cases where CBS is operating. What are the transport cases for CBS not operating used for in the analysis?

Why is there a significant reduction in the transport of fine fiber and qualified coatings debris for these cases? Alternately confirm that only the CBS running cases were used to determine the transported debris amounts for the strainer evaluation.

3) Page E1-82 states that no voids will form at the mid-height of the strainer and concludes that there will be zero void fraction. The NRC staff concluded that evaluating void fraction at the midpoint of the strainer and using that value to estimate void fraction over the height of the strainer is valid only if voiding occurs over the full height of the strainer.

If no voiding occurs at the top of the strainer than it is apparent that voids will not occur at lower elevations. If it has not been demonstrated that voids do not occur at the top of the strainer using the midpoint to estimate void fraction can result in non-conservative void fraction calculations. Justify the use of the mid-height of the strainer or re-evaluate the void fraction.

4) On page E1-85, and in other locations in the submittal, it was stated that a modification was planned to ensure that excessive water will not be held up in the refueling canal due to blockage of the drains. The modification included adding a drain line, enlarging the existing drain line, and installing strainers on each drain. Confirm that this modification has been completed or provide the estimated completion date.

5) On page E1-119, the submittal provides the equations used to calculate the structural acceptability of the strainers. Provide the Crush Pressure and the Debris Mass assumed in the structural evaluation.

6) On page E1-145, the chemical precipitation time for in-vessel effects is discussed., The chemical effects evaluation relies on the precipitation boundary equation contained in WCAP-17788-P, Volume 5, to determine precipitation timing. Although the evaluation methodology used all NaOH group autoclave tests with pH less than 10, confirm that the WCAP-17788 Volume 5 autoclave testing that directly applies to Seabrook is Test Group

9.

7) In the section for in-vessel fiber loads (starting page E1-148 of the submittal), many margins have been removed decreasing confidence in the availability of long-term core cooling. The use of a longer sump switchover (SSO) time to set the decay heat value removes margin in the decay heat used. The Seabrook SSO time is increased not only to its maximum conservative value of 26 minutes, but a realistic value of 28.5 minutes is used to determine decay heat. This also reduces margin compared to the WCAP.

Also, the use of the WCAP RAI model timing removes significant margin in PCT that results from the use of a fast debris buildup assumption in the base model. The NRC staff closure guidance and acceptance of use of the methods described in WCAP-17788-P were based on the significant margins resulting from the WCAP methodologies.

Describe any margins that remain in the in-vessel fiber load analyses and justify that they are adequate to assure that core blockage will not inhibit long-term core cooling.

8) Figure 3.n.1-14 references a case similar to Seabrook. Provide specific similarities and differences between this case and Seabrook and justify the use of this figure for modeling peak cladding temperature at Seabrook.