ML24346A339

LLC - Response to SDAA Audit Question Number A-19.2-34

ML24346A339
Person / Time
Site:	05200050
Issue date:	12/11/2024
From:	NuScale
To:	Office of Nuclear Reactor Regulation
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Download: ML24346A339 (1)

Text

Response to SDAA Audit Question Question Number: A-19.2-34 Receipt Date: 06/10/2024 Question:

DCA FSER Section 19.2.4.2.7, Severe Accident-Induced Steam Generator Tube Failure, describes the staffs review of DCA FSAR Section 19.2.3.3.6, Containment Bypass. This FSER section contains the following statements:

1.

For tube flaws, the applicant assumed a flaw distribution based on foreign object wear by adapting steam generator operating experience and placing the highest percentage of flaws at the top of the tube bundle coincident with the location of highest temperature during a severe accident.

2.

For flaw depth, the model predicted that very high stress magnification factors (flaws more than 80 percent through-wall) were necessary for any reduction in life.

The staff reviewed the SDAA FSAR, the DCA FSAR, the response to DCA eRAI 8889, and documents available in the portal and is unable to confirm these statements.

NuScale is requested to:

1.

Confirm the validity of these statements for the SDAA.

2.

If these statements are valid for the SDAA, provide documentation to support these statements.

If these statements are not valid for the SDAA, discuss how tube flaws are considered in the evaluation of thermally induced tube failure.

Response

1. NuScale confirms that the statements from the Final Safety Evaluation Report of the US600 Design Certification Application cited in this audit issues question also apply to the US460 Standard Design Approval Application.

2. ER-116288, Thermally Induced Steam Generator Tube Failure Probabilistic Assessment, Revision 1, describes the analysis performed for the US460 design. The US460 analysis is the NuScale Nonproprietary NuScale Nonproprietary

same as the US600 analysis, except the US460 analysis uses steam generator (SG) tube temperatures and stresses that are derived from MELCOR simulations corresponding to the US460 design.

((2(a),(c) Figure 1, Critical Stress Magnification Factor Cumulative Density Function, ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

Figure 1: Critical Stress Magnification Factor Cumulative Density Function (( }}2(a),(c) No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}