ML24215A173
| ML24215A173 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List:
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| References | |
| LO-169995 | |
| Download: ML24215A173 (1) | |
Text
Response to SDAA Audit Question Question Number: A-16.3.4.7-1 Receipt Date: 07/17/2023 Question:
Why have LCO 3.4.7 identified leakage limit if all CES leak detection is assumed to be unidentified RCS leakage? Should GTS Bases explain this?
Response
Original Response The identified leakage limit is included in NuScale GTS Section 3.4.7 to maintain consistency with the industry. Inclusion of the identified leakage limit also allows for new leakage detection technology. The GTS Section 3.4.7 would not require revision should new technology become available that would allow the ability to measure leakage from a specific source.
Follow-Up Discussion During a call with the NRC staff on 10/24/2023, NuScale agreed to provide a supplement to the response to Audit Question A-16.3.4.7-1 to update the TS 3.4.7 bases with discussion of the inability to identify the sources of RCS leakage.
Supplemental Response NuScale revises the bases for GTS Sections 3.4.5 and 3.4.7 to incorporate discussion of the inability to identify the source of RCS leakage in the containment.
NuScale Nonproprietary NuScale Nonproprietary
Follow-Up comments From 1/18/24 NRC Email Supplemental response refers to 3.4.5 in error?; markup should put leakage in all upper case letters.
Supplemental Response The revisions to GTS Bases Section 3.4.5 were inadvertently not included in the previous supplemental response. NuScale revises the previous supplemental response to include markups of GTS Bases Section 3.4.5 and revises GTS Bases Section 3.4.7 to fully capitalize the word leakage.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
RCS Operational LEAKAGE B 3.4.5 NuScale US460 B 3.4.5-1 Draft Revision 2 B 3.4 REACTOR COOLANT SYSTEM (RCS)
B 3.4.5 RCS Operational LEAKAGE BASES BACKGROUND Components that contain or transport the coolant to or from the reactor core comprise the RCS. Component joints are made by welding, bolting, rolling, or pressure loading. Valves isolate connecting systems from the RCS.
During unit life, the joint and valve interfaces can produce varying amounts of reactor coolant LEAKAGE, through either normal operational wear or mechanical deterioration. The purpose of the RCS Operational LEAKAGE LCO is to limit system operation in the presence of LEAKAGE from these sources to amounts that do not compromise safety. This LCO specifies the types and amounts of RCS Operational LEAKAGE.
10 CFR 50, Appendix A, GDC 30 (Ref. 1), requires means for detecting and, to the extent practical, identifying the source of reactor coolant LEAKAGE. Regulatory Guide 1.45 (Ref. 2) describes acceptable methods for selecting leakage detection systems.
The safety significance of RCS Operational LEAKAGE varies widely depending on its source, rate, and duration. Therefore, detecting and monitoring RCS LEAKAGE outside of the reactor coolant pressure boundary (RCPB) is necessary. When possible, separating the identified LEAKAGE from the unidentified LEAKAGE is necessary to provide quantitative information to the operators, allowing them to take corrective action should a leak occur that is detrimental to the safety of the facility and the public.
This LCO deals with protection of the reactor coolant pressure boundary (RCPB) from degradation, in addition to preventing the accident analyses radiation release assumptions from being exceeded. The consequences of violating this LCO include the possibility of a loss of coolant accident (LOCA).
APPLICABLE Except for primary to secondary LEAKAGE, the safety analyses do not SAFETY address RCS Operational LEAKAGE. However, other forms of RCS ANALYSES Operational LEAKAGE are related to the safety analyses for LOCA. The amount of LEAKAGE can affect the probability of such an event.
The safety analysis for an event resulting in steam discharge to the atmosphere assumes a 150 gpd primary to secondary LEAKAGE as the initial condition.
RCS Operational LEAKAGE B 3.4.5 NuScale US460 B 3.4.5-2 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES (continued)
Primary to secondary LEAKAGE is a factor in the dose releases outside containment resulting from a steam line break (SLB) accident. To a lesser extent, other accidents or transients involve secondary steam release to the atmosphere, such as a steam generator tube failure (SGTF). The leak contaminates the secondary fluid.
The FSAR Chapter 15 (Ref. 3) analyses for the accidents involving secondary side releases assume 150 gpd primary to secondary LEAKAGE as an initial condition. The design basis radiological consequences resulting from a postulated SLB accident and SGTF are provided in Sections 15.1.5 and 15.6.3 of FSAR Chapter 15, respectively.
The RCS Operational LEAKAGE satisfies Criterion 2 of 10 CFR 50.36(c)(2)(ii).
LCO RCS operational LEAKAGE shall be limited to:
- a. Pressure Boundary LEAKAGE Pressure boundary LEAKAGE is prohibited as the leak itself could cause further RCPB deterioration, resulting in higher LEAKAGE.
- b. Unidentified LEAKAGE 0.5 gpm of unidentified LEAKAGE is allowed as a reasonable amount that the Containment Evacuation System (CES), condensate monitoring equipment required by LCO 3.4.7, "RCS Leakage Detection Instrumentation," can detect within a reasonable time period. Separating the sources of leakage (i.e., leakage from an identified source versus leakage from an unidentified source)
Detecting and monitoring RCS LEAKAGE outside of the reactor coolant pressure boundary (RCPB) is necessary for prompt identification of potentially adverse conditions, assessment of the safety significance, and corrective action.
- c. Identified LEAKAGE Up to 2 gpm of identified LEAKAGE is considered allowable because LEAKAGE is from known sources that do not interfere with detection of unidentified LEAKAGE and is well within the capability of the RCS Makeup System. Identified LEAKAGE includes LEAKAGE to the containment from specifically known and located sources. The existing containment leak detection system is unable to differentiate between identified and unidentified LEAKAGE.
RCS Leakage Detection Instrumentation B 3.4.7 NuScale US460 B 3.4.7-2 Draft Revision 2 BASES BACKGROUND (continued)
Reactor coolant radioactivity can therefore be used for leak detection.
The CES system has a gaseous effluent monitor to detect isotopes that provide indication of LEAKAGE.
In addition to meeting the OPERABILITY requirements, the monitoring instrumentation is typically set to provide the most sensitive response without causing an excessive number of spurious alarms.
APPLICABLE The need to evaluate the severity of an alarm or an indication is SAFETY important to the operators, and the ability to compare and verify ANALYSES with indications from other systems is necessary. The system response times and sensitivities are described in FSAR Sections 5.2, 3.6, and 11.5 (Refs. 3, 4, and 5).
The safety significance of RCS LEAKAGE varies widely depending on its source, rate, and duration. Therefore, While it is not possible to identify the specific source of RCS LEAKAGE into the containment, detecting and monitoring RCS LEAKAGE into the containment area is necessary to provide quantitative information to the operators, allowing them to take corrective action should a leak occur that is detrimental to the safety of the facility and the public. Separating the identified LEAKAGE from the unidentified LEAKAGE provides quantitative information to the operators, to take corrective action should a leak occur.
RCS LEAKAGE detection instrumentation satisfies Criterion 1 of 10 CFR 50.36(c)(2)(ii).
LCO One method of protecting against large RCS LEAKAGE derives from the ability of instruments to rapidly detect extremely small leaks that indicate a possible RCPB degradation. This LCO requires instruments of diverse monitoring principles to be OPERABLE to provide a high degree of confidence that small leaks are detected in time to allow actions to place the unit in a safe condition.
The LCO is satisfied when monitors of diverse measurement means are available. Thus, the CES sample vessel level monitors, in combination with CES inlet pressure channels and a CES gas discharge radioactivity monitor, provides five channels of leakage detection using three diverse methods. The specification requires two of the three diverse methods to be OPERABLE. CES inlet pressure monitoring is performed by two redundant, seismically qualified pressure instruments.