ML24215A079

LLC, Response to Sdaa Audit Question Number A-3.11.12-1

ML24215A079
Person / Time
Site:	05200050
Issue date:	08/02/2024
From:	NuScale
To:	Office of Nuclear Reactor Regulation
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Response to SDAA Audit Question Question Number: A-3.11.12-1 Receipt Date: 06/05/2023 Question:

NuScale DCA FSAR Section 3.11.1.2 indicated that a harsh radiation environment is above 1E4 rad for electrical and mechanical equipment and above 1E3 rad for electronic devices and components. These criteria are consistent with NuScale Design Specific Review Standard, Section 3.11. However, the NuScale SDA Section 3.11.1.2 states that a harsh radiation environment is above 1E4 rad for electrical and mechanical equipment and above 1E3 rad for equipment with solid state circuitry. The SDA also now uses the term solid state circuitry instead of electronic equipment, when discussing steam exposure humidity criteria.

Electronics is a broader term than solid state circuitry. Please discuss the reasoning for changing this terminology in the SDA. If the intent of changing the terminology is to exclude certain electronics, please discuss any electronics that will be used that are not considered solid state circuitry and provide justification for why that equipment need not be subject to the 1E3 rad criterion for a harsh radiation environment and the limiting steam exposure criteria used for solid state circuitry.

Response

NuScale agrees that electronic equipment is a broader term than solid state circuitry. NuScale does not use the term solid state circuitry to exclude specific equipment from environmental qualification. SDA Tables 3C-1, 3C-2, and 3C-3 identify the environmental zones within the Reactor Building and Control Building that contain equipment subject to environmental qualification. SDA Table 3C-3 identifies EQ Zone CRB-3 as exceeding the 1.0 E+03 rad threshold for electronics located in the elevation 100 mechanical equipment room (Room 003).

Similarly, EQ Zones RXBG-5 and RXBG-7 are mild environments with the exception of electronics located in the corridors within these zones (Rooms 306, 319, 408, and 421). These NuScale Nonproprietary NuScale Nonproprietary

examples demonstrate that the classifications consider electronic equipment, and are not limited to equipment containing solid state circuitry.

NuScale revises SDA Section 3.11.1.2 to replace the term solid state circuitry with electronic equipment.

Markups of the affected changes, as described in the response, are provided below:

NuScale Nonproprietary NuScale Nonproprietary

NuScale Final Safety Analysis Report Environmental Qualification of Mechanical and Electrical Equipment NuScale US460 SDAA 3.11-3 Draft Revision 2 Equipment required to be environmentally qualified has one or more of the following credited functions: reactor trip, engineered safeguards actuation, PAM, or containment isolation.

For electrical and mechanical devices located in mild environments, compliance with the environmental design provisions of GDC 4 are achieved and demonstrated by proper incorporation of relevant environmental conditions in the design process, including the equipment specification compliance.

Table 3.11-1 provides the list of equipment in harsh environments and requiring environmental qualification. Table 3C-1 shows equipment location zones indicated in Table 3.11-1.

3.11.1.2 Definition of Environmental Conditions The environmental conditions considered in design include normal and AOOs, accident, and post-accident environmental conditions. Appendix 3C specifies the environmental parameters (e.g., radiation, temperature, chemical effects, humidity from steam, pressure, wetting, submergence) applicable to the various environmental conditions in specific plant building and room locations.

Environmental service conditions fall into the following categories.

A harsh environment

is a significant change from normal (including DBE and post-accident conditions) that has the potential to result in environmental or radiation induced common-cause failure mechanisms.

is an environment that is the result of events as cited above that significantly alters the environmental parameters of temperature, humidity, submergence, or radiation such as temperature

>120-degree F and >18-degree F increase above normal operating conditions.

humidity:

steam exposure

>99 percent relative humidity condensing conditions.

Audit Question A-3.11.12-1 85 percent relative humidity with temperatures 120 degree F for electronic equipment with solid state circuitry.

submergence

areas where equipment is subject to submergence that is not subjected to submergence under normal operating conditions.

NuScale Final Safety Analysis Report Environmental Qualification of Mechanical and Electrical Equipment NuScale US460 SDAA 3.11-4 Draft Revision 2 Radiation

total integrated dose of > 1.0E04 rad (60 year normal plus 30 day accident dose) for electrical and mechanical equipment.

Audit Question A-3.11.12-1

total integrated dose of > 1.0E03 rad (60 year normal plus 30 day accident dose) for electronic equipment with solid state circuitry.

A mild environment

areas where the environment at no time is significantly more severe than the environment during normal plant operation, including AOOs.

3.11.1.3 Equipment Post-Accident Operating Time The post-accident operating time is the period of time, beginning with design basis event initiation, during which the equipment must continue to perform its credited function. The post-accident operating time, or operating time, duration can vary, and is based on the credited function of the equipment. Both operating and not failing in a manner detrimental to plant safety are considered in the assignment of post accident operating times.

Table 3.11-1 specifies post accident operating times for the equipment listed. The required post-accident operating time for equipment varies from 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to 720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br />. The conservative bases for the operating times are established for PAM equipment and equipment required for long-term core cooling.

Table 3C-4 defines and documents the four distinct post-accident operating time frames for equipment located in harsh environments listed in Table 3.11-1.

3.11.2 Governing Regulatory and Industry Codes 3.11.2.1 Environmental Qualification of Electrical Equipment Harsh Environments For electrical equipment required to function during or following exposure to a harsh environment, compliance with the environmental provisions of GDC 4 are achieved by demonstrating compliance with 10 CFR 50.49 in accordance with Design Specific Review Standard 3.11, regulatory guidance, and industry standards. Table 3.11-2 lists applicable regulatory guides and industry standards for environmental qualification.

Mild Environments For electrical equipment located in mild environments, compliance with the environmental design provisions of GDC 4 are achieved and demonstrated by proper incorporation of relevant environmental conditions into the design process, including the equipment specification. Regulatory Guide 1.209 endorses IEEE Standard 323-2003 (Reference 3.11-12) for qualification of computer-based I&C systems in mild environments.