ML24215A093
Text
Response to SDAA Audit Question Question Number: A-4.6-3 Receipt Date: 12/26/2023 Question:
DCA Table 3.111, List of Environmentally Qualified Electrical/I&C and Mechanical Equipment Located in Harsh Environments, included information related to the control rod drive system (CRDM) drive and position coils, and associated control cabinets. These items were removed in SDAA FSAR Table 3.11-1.
This information is needed for the staff to make a safety finding and ensure these components will be designed to perform their design basis function(s) in the environmental conditions expected during normal operating, anticipated operational occurrence, and accident conditions.
The staff requests NuScale to reinsert these components in FSAR Table 3.11-1, or identify where in the FSAR the environmental qualification information is specifed for these compoents.
Response
The control rod drive system (CRDS) components that are not in FSAR table 3.11-1 are not required to be environmentally qualified. The following excerpt is from FSAR Section 3.11.1.1, with emphasis in bold.
Equipment identification includes electrical and mechanical equipment that perform a credited function for a design basis event (DBE) that results in a significant change in environmental conditions within the plant that has the potential to result in environmentally induced common cause failures.
NuScale Nonproprietary NuScale Nonproprietary
Equipment required to be environmentally qualified has one or more of the following credited functions: reactor trip, engineered safeguards actuation, PAM (post accident monitoring), or containment isolation.
The identification of mechanical and electrical equipment as being subject to environmental qualification includes any equipment whose functionality is directly or indirectly related to one or more of the following:
Active, passive or fail-safe mechanical equipment that is relied upon to remain functional (or not fail) during and following exposure to design basis conditions, including functional requirements related to:
o preventing or mitigating the consequences of a design basis event (DBA) or infrequent event (lE) o maintaining the post-accident environmental conditions within analyzed limits o
maintaining the capability to achieve and maintain a safe shutdown condition
Active, passive or fail-safe electrical equipment that is relied upon to remain functional (or not fail) during or following a design basis accident, including functional requirements related to:
o detecting the occurrence of a DBA or lE o
mitigating the consequences of a DBA or lE o
maintaining the post-accident environmental conditions within analyzed limits o
achieving and maintaining a safe shutdown condition o
providing or supporting PAM functions The CRDS drive and position coils, and associated control cabinets are not relied upon to remain functional during or following a DBE. The CRDS equipment that environmental qualification applies to are the following:
The pressure boundary (to retain the reactor coolant pressure boundary)
The magnetic jack assembly (to not fail in a manner that prevents control rod assembly insertion)
The control rod drive shaft assembly (to not fail in a manner that prevents control rod assembly insertion)
The most recent FSAR Table 3.11-1 markup can be found in the Chapter 3 portion of the eRR posted on December 21, 2023.
NuScale Nonproprietary NuScale Nonproprietary
Updated Response While the CRDS performs safety-related, non-risk-significant functions, the specific electrical components of the CRDM drive and position coils and associated control cabinets do not perform safety-related functions post-DBE because these components are downstream of the reactor trip breakers as shown in FSAR Figure 7.0-6. Reactor trip breakers are located in a mild environment in their respective module protection system division room as described in FSAR Section 7.2.2.1. The scope of FSAR Section 3.11 and FSAR Table 3.11-1 is for equipment that falls within the scope of 10 CFR 50.49. The CRDM drive and position coils and associated control cabinets are not subject to 10 CFR 50.49; thus, the CRDM drive and position coils and associated control cabinets are not subject to GDC 4 harsh environmental qualification in FSAR Table 3.11-1.
For functional performance during normal operating conditions, the CRDM drive and position coils are located in the containment environment that is normally at near-vacuum conditions.
The CRDM coils generate heat during normal operation and are water-cooled to maintain temperature below the design temperature of the CRDM coil windings as described in FSAR Section 4.6.1. The CRDM control and rod position indication cabinets are located in separate rooms in the Reactor Building that are held at a normal temperature of 105 degrees Fahrenheit, ambient pressure, and relative humidity less than 85 percent.
Additionally, the CRDS is subject to an Operability Assurance Program, described in FSAR Section 3.9.4.4, that verifies the performance capabilities of the CRDM drive and position coils and associated control and indication cabinets to remain functional during normal operation.
FSAR Section 4.6.2 and Section 3.6 describes CRDS compliance with GDC 4. FSAR Section 4.6.2 and Section 4.3 describe CRDS compliance with GDC 26. Below is an excerpt from FSAR Section 4.3 with emphasis in bold.
There are two independent reactivity control systems based on different design principles to satisfy GDC 26. The control rod drive system uses control rod assemblies (CRAs) to provide reactivity control, and the chemical and volume control system (CVCS) uses soluble boron from the boron addition system for reactivity control. The CRAs and associated rod control system are designed with a positive means for inserting the rods and reliably controlling reactivity changes during normal operation. The control rod design ensures the SAFDLs are not exceeded during an AOO assuming a single stuck CRA. The CVCS provides reactivity control associated NuScale Nonproprietary NuScale Nonproprietary
with planned normal power changes including the effects of fuel burnup and is capable of holding the reactor subcritical during cold conditions, in accordance with GDC 26.
If the CRDM drive and position coils or associated control cabinets fail, the CRDS remains capable to reliably control reactivity to ensure specified acceptable fuel design limits are not exceeded. The CRDS passively inserts the control rods and safely trips the reactor even if there is a failure of these non-safety related CRDM components.
No changes to the SDAA are necessary.
NuScale Nonproprietary NuScale Nonproprietary