ML19057A619

LLC Supplemental Response to NRC Request for Additional Information No. 259 (Erai No. 9138) on the NuScale Design Certification Application

ML19057A619
Person / Time
Site:	NuScale
Issue date:	02/26/2019
From:	Rad Z NuScale
To:	Document Control Desk, Office of New Reactors
References
RAIO-0219-64688
Download: ML19057A619 (5)

Text

RAIO-0219-64688 February 26, 2019 Docket No.52-048 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738

SUBJECT:

NuScale Power, LLC Supplemental Response to NRC Request for Additional Information No. 259 (eRAI No. 9138) on the NuScale Design Certification Application

REFERENCES:

1. U.S. Nuclear Regulatory Commission, "Request for Additional Information No. 259 (eRAI No. 9138)," dated October 13, 2017

2. NuScale Power, LLC Response to NRC "Request for Additional Information No. 259 (eRAI No.9138)," dated December 12, 2017 The purpose of this letter is to provide the NuScale Power, LLC (NuScale) supplemental response to the referenced NRC Request for Additional Information (RAI).

The Enclosure to this letter contains NuScale's supplemental response to the following RAI Question from NRC eRAI No. 9138:

19-33 This letter and the enclosed response make no new regulatory commitments and no revisions to any existing regulatory commitments.

If you have any questions on this response, please contact Paul Infanger at 541-452-7351 or at pinfanger@nuscalepower.com.

Sincerely, Zackary W. Rad Director, Regulatory Affairs NuScale Power, LLC Distribution: Gregory Cranston, NRC, OWFN-8H12 Samuel Lee, NRC, OWFN-8H12 Rani Franovich, NRC, OWFN-8H12 : NuScale Supplemental Response to NRC Request for Additional Information eRAI No. 9138 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvalis, Oregon 97330, Office: 541.360.0500, Fax: 541.207.3928 www.nuscalepower.com

RAIO-0219-64688 :

NuScale Supplemental Response to NRC Request for Additional Information eRAI No. 9138 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvalis, Oregon 97330, Office: 541.360.0500, Fax: 541.207.3928 www.nuscalepower.com

Response to Request for Additional Information Docket No.52-048 eRAI No.: 9138 Date of RAI Issue: 10/13/2017 NRC Question No.: 19-33 10 CFR 52.47(a)(23) states that a design certification (DC) application must contain a final safety analysis report (FSAR) that includes a description and analysis of design features for the prevention and mitigation of severe accidents (e.g., challenges to containment integrity caused by core-concrete interaction, steam explosion, high-pressure melt ejection, hydrogen combustion, and containment bypass). For staff to make a finding that the applicant has performed an adequate evaluation of the risk from severe accidents in accordance with Standard Review Plan (SRP) 19.0, the applicant is requested to provide the additional information requested below.

a. FSAR Section 19.2.3.3.5 describes a thermodynamic analysis of the energy release from a hypothetical in-vessel steam explosion (i.e., within the reactor pressure vessel (RPV))

which concludes that the energy released is insufficient to challenge RPV integrity. The staff requests additional information to understand how the analysis relates to past Nuclear Regulatory Commission and industry studies of in-vessel steam explosion including An Assessment of Steam-Explosion-Induced Containment Failure. Part 1: Probabilistic Aspects, Theophanous, T. G., Najafi B., and Rumble, E., Nuclear Science and Engineering: 97, 259-281 (1987) and A Reassessment of the Potential for an Alpha-Mode Containment Failure and a Review of the Current Understanding of Broader Fuel-Coolant Interaction Issues; Second Steam Explosion Review Group Workshop, NUREG-1524, August 1996. For example, what did the applicant assume for the conversion ratio versus thermal energy in the mixed melt? What did the applicant assume for the net energy in the head after dissipation in upper internals versus slug energy? Please provide any benchmarking of the applicants analysis against past studies in terms of energy release and mechanical loads, considering the similarities in phenomenology and the design NuScale Nonproprietary

differences (NuScale vs. large light-water reactors)?

b. For in-vessel steam explosion, the applicants analysis addressed different initial reactor coolant system (RCS) hole sizes and emergency core cooling system (ECCS) failure modes by using as input the MELCOR predictions for sequences with different initial RCS hole sizes and ECCS failure modes. However, the NRC staff could not find where the applicants analysis addressed uncertainties in the modeling of physical phenomena in its MELCOR simulations, such as uncertainties in in-vessel melt progression modeling (e.g.,

modeling of core heat-up, collapse, and formation of molten pool). Such uncertainties have the potential to result in a different energy of corium relocating to the water in the RPV lower plenum. An example of consideration of such uncertainties is given in State-of-the-Art Reactor Consequence Analyses (SOARCA) Project: Sequoyah Integrated Deterministic and Uncertainty Analyses, Draft Report, April 2016 (ADAMS Accession Number ML17156A255). The staff requests additional information to understand how the applicants analysis addressed uncertainties in the modeling of physical phenomena.

c. FSAR Section 19.2.3.3.5 states that an ex-vessel steam explosion (i.e., within the containment vessel (CNV)) is judged to be physically unrealistic based on the size of the NuScale core, the physical dimensions of the CNV, the proximity between the RPV and CNV, the associated potential drop height for fuel between the two, and thermal-hydraulic conditions within the CNV in the postulated condition that the RPV were breached. The applicant is requested to provide quantitative justification for this judgment, including addressing the potential for an ex-vessel steam explosion to cause the CNV to move sufficiently to induce a CNV structural failure. For example, AP1000 calculations in NUREG/CR-6849 indicated the potential for large impulse loads on the cavity and the RPV (and subsequently the containment penetrations). The phenomena occurring inside the NuScale CNV with a high water level appears to be similar to the AP1000 analysis.

NuScale Response:

As a result of public discussions held with the NRC on November 13, 2018, January 8, 2019, and January 29, 2019, NuScale is supplementing its response to RAI 9138 (Question 19-33) originally provided in letter RAIO-1217-57631, dated December 12, 2017. In those discussions, NuScale agreed to modify the FSAR by replacing the term physically unrealistic and similar terminology to more directly reflect insights from NuScale phenomenological analyses and to NuScale Nonproprietary

clarify the presence of analysis uncertainty. Other information provided in the original RAI response remains valid.

Impact on DCA:

FSAR Section 19.2 has been revised as described in the response above and as shown in the markup provided with the supplemental response to RAI No. 9108 in NuScale letter RAIO-0219-64684.

NuScale Nonproprietary