ML24215A189
| ML24215A189 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List:
|
| References | |
| LO-169995 | |
| Download: ML24215A189 (1) | |
Text
Response to SDAA Audit Question Question Number: A-16.3.5.3-1 Receipt Date: 09/18/2023 Question:
The third paragraph of the Background section of the generic TS Bases Subsection B 3.5.3, ends with the sentence, Sufficient iodine activity values are reported in FSAR Chapter 15 (Ref.
2). Explain what is meant by sufficient iodine and consider clarifying the sentence consistent with the intended meaning.
Response
NuScale revises the third paragraph of the Background section of Technical Specification Bases B 3.5.3 to replace:
Sufficient iodine activity values are reported in FSAR Chapter 15 (Ref. 2).
with:
"The radiological consequence analysis for the fuel handling accident is provided in FSAR Chapter 15 (Ref. 2)."
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
Ultimate Heat Sink B 3.5.3 NuScale US460 B 3.5.3-1 Draft Revision 2 B 3.5 PASSIVE CORE COOLING SYSTEMS (PCCS)
B 3.5.3 Ultimate Heat Sink BASES BACKGROUND The ultimate heat sink (UHS) consists of three areas identified as the reactor pool (RP), refueling pool (RFP), and spent fuel pool (SFP). The pool areas are open to each other with a weir wall partially separating the SFP from the RP and RFP. The UHS water level indicates the depth of water in the UHS from the reactor pool floor (26 ft building elevation). The UHS supports or provides multiple safety and important functions including:
- a.
Acts as ultimate heat sink during postulated design basis events;
- b.
Provides cooling and shielding of irradiated fuel in the spent fuel storage racks;
- c.
Limits releases from postulated fuel handling accidents;
- d.
Provides a reserve of borated water for filling the containment vessel in MODE 3;
- e.
Limits the temperature of the containment vessel and module during operations; and
- f.
Provides shielding of radiation emitted from the core of an operating module.
The UHS function is performed by providing a sufficient heat sink to receive decay heat from a module via the decay heat removal system (DHRS) heat exchangers and conduction through the containment vessel walls (Ref. 1) after a postulated Emergency Core Cooling System (ECCS) actuation and after transition to long-term shutdown cooling (Ref. 2).
Irradiated fuel is stored in the SFP portion of the UHS that is separated from the balance of the pool by a submerged wall. The submerged wall includes a weir that permits movement of new and irradiated fuel from the storage areas to a reactor during refueling, and also provides a means of inventory communication between the pool areas. The SFP provides cooling and shielding of the irradiated fuel in the storage area, and provides sufficient water level to retain iodine fission product activity in the event of a fuel handling accident. Sufficient iodine activity values are reported in FSAR Chapter 15 (Ref. 2). The radiological consequence analysis for the fuel handling accident is
Ultimate Heat Sink B 3.5.3 NuScale US460 B 3.5.3-2 Draft Revision 2 BASES BACKGROUND (continued) provided in FSAR Chapter 15 (Ref. 2).
During transients and shutdowns which are not associated with design basis events in which DHRS or ECCS is actuated, water from the RP is added to the containment vessel by the Containment Flooding and Drain System (CFDS). After reaching an appropriate level in the containment, the reactor vent valves (RVVs) and reactor recirculation valves (RRVs) are opened to permit improved heat transfer from the reactor coolant system (RCS) to the containment vessel walls.
During normal operations, the RP limits temperatures of the module because the containment vessel is partially immersed in water. The water also provides shielding above and around the region of the core during reactor operations, limiting exposure to personnel and equipment in the area.
In MODE 4, the module is transported from the operating position to the RFP area of the UHS.
APPLICABLE SAFETY ANALYSES During all MODES of operation and storage of irradiated fuel, the UHS supports multiple safety functions.
The UHS level is assumed and credited in a number of transient analyses. A UHS level of 52 ft provides margin above the minimum level required to support DHRS and ECCS operation in response to LOCA and non-LOCA design basis events. The 52 ft level also assures the containment vessel wall temperature initial condition assumed in the peak containment pressure analysis. The upper limit of 54 ft for the maximum pool level is an initial condition that ensures long term cooling analyses assumptions.
The UHS bulk average temperature is assumed and credited, directly or indirectly in design basis accidents including those that require DHRS and ECCS operation such as LOCA and non-LOCA design basis events. The bulk average temperature is also assumed as an initial condition of the peak containment pressure analysis, and the minimum pool temperature is an assumption used in long-term cooling analyses.