Document: NRC Regulatory Guide
Document ID: e16da529-b6b4-4fdf-bc3f-7490180363f3
Document Type: regulatory_guide
Title: Environmental Qualification of Certain Electric Equipment Important to Safety for Nuclear Power Plants (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2018/ML20183A423.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.89
CFR Part: 
CFR Title: 

Content:
the AP1000 Standard Design,” issued September 2004 (Ref. 35), the staff considers a mild radiation environment for electronic equipment to be a total integrated dose less than 10 gray (Gy) (103 rad) and a mild radiation environment for other equipment to be less than 100 Gy (104 rad), to be acceptable.) An additional stressor to be considered in the qualification of digital systems is smoke exposure from an electrical fire. For smoke exposure, important failure mechanisms are not only long-term effects such as corrosion, but also short-term and perhaps intermittent malfunctions, such as leakage current. Smoke can cause circuit bridging and thus affect the operation of digital equipment. Because the edge connections and interfaces are typically uncoated, the most likely effect of the smoke is to impede communication and data transfer between subsystems. RG 1.209 provides several references that detail the effects of smoke exposure. d. In 10 CFR 50.49(e)(5), the NRC calls for equipment qualified by test to be preconditioned by natural or artificial (accelerated) aging to its end-of-installed-life condition and further specifies that consideration must be given to all significant types of degradation that can affect the functional capability of the equipment. There are considerable uncertainties with regard to the processes and environmental factors that could result in such degradation. Diffusion-limited oxidation, synergisms, dose-rate effects, and inverse temperature are examples of such effects. Because of these uncertainties, state-of-the-art aging techniques are not capable of simulating all significant types of degradation, and natural pre-aging is not practical for producing timely results. As the state-of-the-art advances and uncertainties are resolved, techniques to simulate aging may become more effective. Experience suggests that consideration should be given, for example, to a combination of the following: (1) preconditioning of test samples employing