ML24326A111
| ML24326A111 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 11/21/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24326A092 | List: |
| References | |
| LO-175900 | |
| Download: ML24326A111 (1) | |
Text
Response to SDAA Audit Question Question Number: A-16.3.3.1-9 Receipt Date: 04/29/2024 Question:
SDAA Part 4, Revision 1 of Bases Subsection B 3.3.1, Background section, first paragraph on page B 3.3.1-8, first sentence states:
The SVM also provide a delayed ECCS actuation signal after an RTS actuation.
Please correct the grammar of this sentence; for example, change the phrase The SVM also provide to The SVMs also provide; or The SVM also provides; or Each divisional SVM also provides; or The SVM in each division also provides; or a similar phrase that is consistent with the SVM design.
Response
NuScale revises the US460 Standard Design Approval Application Part 4, Section B 3.3.1 to correct the grammar.
NuScale revises the markup of the last paragraph on Generic Technical Specification page B 3.3.1-11 to read:
NuScale Nonproprietary NuScale Nonproprietary
The MPS interlocks function automatically. If an MPS interlock fails to function correctly, then each affected corresponding MPS instrumentation function channel is not OPERABLE and the ACTIONS for the affected MPS function(s) are entered. The MPS logic and actuation function OPERABILITY is addressed in LCO 3.3.2 for Reactor Trip System Logic and Actuation and in LCO 3.3.3 for Engineered Safety Features Actuation System Logic and Actuation.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-4 Draft Revision 2 BASES BACKGROUND (continued)
- 8. Pressurizer Heater Trip (PHT) actuation;
- 9. Low Temperature Overpressure Protection (LTOP) actuation; and
- 10. Pressurizer Line Isolation.
Equipment actuated by each of the above signals is identified in the FSAR (Ref. 4). Setpoints are specified in the [owner-controlled requirements manual].
This LCO addresses the equipment from the MPS input sensors to the input to the RTS and Engineered Safety Features Actuation System (ESFAS) Scheduling and Voting Modules (SVM). The MPS RTS and ESFAS equipment from the inputs of the SVMs to the outputs of the equipment interface modules (EIMs) to the actuated devices is addressed in LCO 3.3.2, Reactor Trip System (RTS) Logic and Actuation, and LCO 3.3.3, "Engineered Safety Features Actuation System (ESFAS)
Logic and Actuation", respectively. LCO 3.3.3 also addresses the internally delayed MPS actuation of ECCS after a reactor trip. Manual actuation of the RTS and ESFAS from the actuating switches to the backplane connections of the chassis are addressed in LCO 3.3.4, Manual Actuation Functions.
The roles of each of the MPS functions in the RTS and ESFAS, including the actuation logic of LCO 3.3.2, 3.3.3, and 3.3.4 are discussed below.
Measurement Channels Measurement channels, consisting of field transmitters or process sensors and associated instrumentation, provide a measurable electronic signal based upon the physical characteristics of the process variable being measured. Some measurement channels that are processed by MPS are sent to MCS for control functions (e.g., pressurizer pressure and level).
The excore nuclear instruments are considered components in the measurement channels of the High Power Range Linear Power, High Power Range Positive and Negative Rate, Source Range Count Rate, Source Range Log Power Rate, and High Intermediate Range Log Power Rate Neutron Flux trips.
Four identical measurement channels (also designated separation group-A through D) with electrical and physical separation are provided for each variable used in the generation of trip and actuation signals.
MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-8 Draft Revision 2 BASES BACKGROUND (continued)
The SVMs also provide a delayed ECCS actuation signal after an RTS actuation. The time delay is dependent on reactor fuel and core design so the delay time is an analytical limit subject to the Setpoint Program. The delayed ECCS actuation may be blocked manually if operational conditions warrant.
Logic for Trip or Actuation Initiation The MPS logic, addressed in LCO 3.3.2 and LCO 3.3.3, is implemented in two divisions each of RTS and ESFAS. It employs a scheme that provides a reactor trip or ESFAS actuation when an SFM in any two of the four separation group channels sense and signal the same input variable trip. The three SVMs in the RTS and the three SVMs in the ESFAS evaluate the trip information received from the SFMs from all four separation groups. If two or more of the four redundant channels call for a trip, then a trip request is passed to the associated EIMs.
The output of the three SVM communication modules is sent via three independent safety data buses to the EIMs. The EIMs receive the information from the three SVMs and performs a two-out-of-three vote. If two or more of the SVMs call for a trip, then a trip is generated and the EIM actuates the component it controls.
RTS Actuation The EIMs for each division of RTS interrupts power to the control rod drive mechanisms (CRDMs) by opening two reactor trip breakers associated with that division.
The RTS EIMs interrupt power to the reactor trip breaker undervoltage trip coils and shunt trip relays, energizing the reactor breaker shunt trip coils.
The reactor trip switchgear, addressed in LCO 3.3.2, consists of four RTBs, which are operated in two sets of two breakers (two divisions).
Power input to the reactor trip switchgear comes from the control rod drive system motor generator (MG) sets. The MG sets are powered from the 480 VAC ELVS and provide 240 VAC to the CRDMs.
Each of the two RTS divisions is capable of producing an automatic reactor trip output signal that opens two of the four reactor trip breakers associated with that division. The four reactor trip breakers are connected in a series-parallel arrangement. Each parallel path contains two trip
MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-10 Draft Revision 2 BASES BACKGROUND (continued) group to be removed from service (channel bypass) for maintenance or testing while still maintaining a minimum two-out-of-three logic.
The failure of one or more components in one of the three safety data paths in any separation group has no impact on the safety function (i.e.,
SBM and SVM). Adequate channel to channel independence includes physical and electrical independence of each channel from the others. This allows operation in two-out-of-three logic with one channel removed from service and bypassed until the next MODE 3 entry since no single failure will either cause or prevent a protective system actuation. This arrangement meets the requirements of IEEE Standard 603-1991 (Ref. 8).
APPLICABLE The MPS is designed to ensure that the following operational criteria are SAFETY met:
ANALYSES, LCO, and APPLICABILITY
- The associated actuation will occur when the variable monitored by each channel reaches its setpoint and the specific coincidence logic is satisfied; and Separation and redundancy are maintained to permit a channel to be out of service for testing or maintenance while still maintaining redundancy within the MPS instrumentation architecture.
Each of the analyzed accidents and transients which require a reactor trip or engineered safety feature (ESF) can be detected by one or more MPS Functions. The MPS Functions that are credited to mitigate specific design basis events are described in FSAR Chapter 15 (Ref. 5). Setpoints are specified in the [owner-controlled requirements manual].
Each MPS setpoint is chosen to be consistent with the function of the respective trip. The basis for each setpoint falls into one of three general categories:
To ensure that the SLs are not exceeded during AOOs; To actuate the RTS and ESFAS during accidents; and To prevent material damage to major components (equipment protection).
The MPS maintains the SLs during AOOs and mitigates the consequences of DBAs in all MODES in which the RTBs are closed.
MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-12 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)
RTS and ESFAS Operating Bypass Interlocks and Permissives Reactor protection permissives and interlocks are provided to ensure reactor trips and ESF actuations are in the correct configuration for the current unit status (Ref. 4). This is to ensure that the protection system functions are not bypassed during unit conditions under which the safety analysis assumes the functions are OPERABLE. Therefore, the permissive and interlock functions do not need to be OPERABLE when the associated reactor trip and ESF functions are outside the applicable MODES. Proper operation of these permissives and interlocks supports OPERABILITY of the associated reactor trip and ESF functions and/or the requirement for actuation logic OPERABILITY. The permissives and interlocks must be in the required state, as appropriate, to support OPERABILITY of the associated functions. The permissives and interlocks associated with each MPS Instrumentation Function channel, each Reactor Trip System (RTS) Logic and Actuation Function division, and each Engineered Safety Features Actuation System (ESFAS) Logic and Actuation Function division, respectively, must be OPERABLE for the associated Function channel or Function division to be OPERABLE. The MPS interlocks function automatically. If an MPS interlock fails to function correctly, then each affected corresponding MPS instrumentation function channel is not OPERABLE and the ACTIONS for the affected MPS function(s) are entered. The MPS logic and actuation function OPERABILITY is addressed in LCO 3.3.2 for Reactor Trip System Logic and Actuation and in LCO 3.3.3 for ESFAS Logic and Actuation. The combination of the continuous self-testing features of the MPS and the CHANNEL CALIBRATION specified by SR 3.3.1.4 verify the OPERABILITY of the interlocks and permissives. Specification 5.5.10, Setpoint Program is used to control interlock and permissive setpoints.
The permissives and interlocks are: