Document: NUREG-0800
Document ID: 0e5dd9d7-fef0-46ca-ba6d-f3d06f5c7801
Document Type: srp
Title: REACTOR SYSTEMS (Tier 1)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070662.pdf
Revision Date: 2023-06
Chapter: 14
Section ID: 14.3.4
CFR Part: 
CFR Title: 

Content:
ated transient without scram (ATWS), are adequately addressed. Applicants should provide tables in DCD Tier 2 Section 14.3 to show how the important input parameters used in the transient and accident analyses for the design are verified by the ITAAC. SRXB should also receive inputs from PRA, including shutdown safety evaluations, and severe accident analyses to ensure important insights and design features from these analyses are incorporated into Tier 1. For the severe accident analyses in particular, the basis for the staff's review for the evolutionary standard designs was the Commission guidance related to SECYs 90-016 and 93-087, later included in the design certification rules for these designs. For both PRA and severe accident analyses, although large uncertainties and unknowns may be associated with the event phenomena, design features important for severe accident prevention and mitigation resulting from these analyses should be selected for treatment in Tier 1. The supporting information regarding the detailed design and analyses should remain in Tier 2. For many of the design features, it may be impractical to test their functionality because of the absence of simulated severe accident conditions. An example might be the ability of the reactor cavity to absorb the heat and radiation effects of a molten core. Consequently, the existence of the feature on a figure, subject to a basic configuration walkdown, may be considered sufficient Tier 1 treatment. The specific fuel, control rod, and core designs presented in Tier 2 will constitute an approved design that may be used for the COL first cycle core loading, without further NRC staff review. If any other core design is requested for the first cycle, the COL applicant or licensee will be required to submit for staff review that specific fuel, control rod, and core design analyses as described in DCD Tier 2 Chapters 4, 6 and 15. Much of the detailed supporting information in Tier 2 for the nuclear fuel,