ML24346A262
| ML24346A262 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/11/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24346A130 | List:
|
| References | |
| LO-175762 | |
| Download: ML24346A262 (1) | |
Text
Response to SDAA Audit Question Question Number: A-15.1.1-3 Receipt Date: 04/01/2024 Question:
Provide calculations supporting the analytical high power trip adjustment that accounts for the downcomer water density increase. FSAR descriptions of overcooling events (e.g. discussion on FSAR pages 15.1-2 and 15.1-7) state that increases in downcomer coolant density can affect power level detection by the excore neutron detectors. In order to account for this effect, the analytical high power trip setpoint is adjusted to account for changes in downcomer coolant temperature. The adjustment is provided in a footnote to Table 15.0-7. Provide the calculation used to determine this adjustment to the eRR for staff audit
Response
Calculation EC-119854, Revision 0, Ex-Core Detector Decalibration Rate Following Cooldown Event, is provided in the Standard Design Approval Application Audit Chapter 15 electronic reading room (eRR) for NRC staff audit. The reactor trip analytical limits in the Final Safety Analysis Report (FSAR) Chapter 15 analyses use a decalibration factor described in Footnote 2 to FSAR Table 15.0-7 that is ((2(a),(c) identified in EC-119854. NRC Feedback On May 8, 2024 the NRC provided the following feedback on NuScales response to this audit item: (( }}2(a),(c NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c NuScale Response to NRC Feedback ((
}}2(a),(c) Footnote 2 of FSAR Table 15.0-7 is revised as shown in the attached markups for clarification.
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Figure 1: (( }}2(a),(c) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
NuScale Response to Additional NRC Feedback On July 26, 2024 the NRC requested that a high-level summary of EC-119854 be added to the response, ((
}}2(a),(c) A high-level summary including this information is provided as follows.
((
}}2(a),(c) The results of EC-119854 are used to support Footnote 2 of FSAR Table 15.0-7 as described previously.
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Figure 2: (( }}2(a),(c) (( }}2(a),(c) Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-49 Draft Revision 2 Audit Question A-15.1.1-3 Table 15.0-7: Analytical Limits and Time Delays Signal(1) Analytical Limit Basis and Event Type Actuation Delay High Power 115%(2) RTP ( 15% RTP) 25% RTP (<15% RTP) This signal is designed to protect against exceeding CHF limits for reactivity and overcooling events. 2.0 sec Source and Intermediate Range Log Power Rate 3 decades/min This signal is designed to protect against exceeding CHF and energy deposition limits during startup power excursions. Variable High Power Rate +/-7.5% RTP/30 sec This signal is designed to protect against exceeding CHF limits for reactivity and overcooling events. 2.0 sec High Source Range Count Rate 5.0 E+05 counts per second(3) This signal is designed to protect against exceeding CHF and energy deposition limits during rapid startup power excursions. 3.0 sec High Subcritical Multiplication 3.2 This signal is designed to detect and mitigate inadvertent subcritical boron dilutions in operating Modes 2 and 3. 150.0 sec High RCS Hot Temperature 620°F This signal is designed to protect against exceeding CHF limits for reactivity and heatup events. 8.0 sec High RCS Average Temperature 555°F This signal is designed to protect against exceeding CHF limits for reactivity events. 8.0 sec High Containment Pressure 9.5 psia This signal is designed to detect and mitigate RCS or secondary leaks above the allowable limits to protect RCS inventory and ECCS function during these events. 2.0 sec High Pressurizer Pressure 2100 psia This signal is designed to protect against exceeding RPV pressure limits for reactivity and heatup events. 2.0 sec High Pressurizer Level 80% This signal is designed to detect and mitigate CVCS malfunctions to protect against overfilling the pressurizer. 3.0 sec Low Pressurizer Pressure 1850 psia(4) This signal is designed to detect and mitigate high-energy line break (HELB) events from the pressurizer vapor space and protect RCS subcooled margin for protection against instability events. 2.0 sec Low-Low Pressurizer Pressure 1200 psia(5) This signal is designed to protect RCS subcooled margin for protection against instability events. 2.0 sec Low Pressurizer Level 35% This signal is designed to detect and mitigate pipe breaks to protect RCS inventory and ECCS functionality during LOCAs, primary HELB outside containment events, or SGTF, and to protect the pressurizer heaters from uncovering and overheating during decrease in RCS inventory events. 3.0 sec Low-Low Pressurizer Level 15% This signal is designed to detect and mitigate pipe breaks to protect RCS inventory and ECCS functionality during LOCAs, primary HELB outside containment events, or SGTF. 3.0 sec
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-50 Draft Revision 2 Low-Low Main Steam Pressure 20 psia This signal is designed to detect and mitigate secondary HELB outside containment to protect steam generator inventory and DHRS functionality. 2.0 sec Low Main Steam Pressure 300 psia(6) This signal is designed to detect and mitigate secondary HELB outside containment to protect steam generator inventory and DHRS functionality. 2.0 sec High Main Steam Pressure 1200 psia This signal is designed to detect and mitigate loss of main steam demand to protect primary and secondary pressure limits during heatup events. 2.0 sec High Main Steam Superheat 150°F This signal is designed to detect and mitigate steam generator boil off to protect DHRS functionality during at power and post trip conditions. 8.0 sec Low Main Steam Superheat 0.0°F This signal is designed to detect and mitigate steam generator overfilling to protect DHRS functionality during at power and post trip conditions. 8.0 sec Low RCS Flow 1.0 ft3/s This signal is designed to ensure boron dilution cannot be performed at low RCS flow rates where the loop time is too long to be able to detect the reactivity change in the core within sufficient time to mitigate the event. 6.0 sec Low-Low RCS Flow 0.0 ft3/s This signal is designed to ensure flow remains measureable and positive during low power startup conditions. 6.0 sec Low RPV Riser Level Range 540-552 in.(7) This signal is designed to actuate ECCS upon riser uncovery for LOCA events. 60.0 sec Low-Low RPV Riser Level Range 460-472 in.(7) This signal is designed to actuate ECCS before the upper riser holes uncover. 60.0 sec Low AC Voltage Note 8 This signal is designed to ensure appropriate load shedding occurs to EDAS in the event of extended loss of normal AC power to the EDAS battery chargers. 60.0 sec High Under-the-Bioshield Temperature 250°F This signal is designed to detect high energy leaks or breaks at the top of the NPM under the bioshield to reduce the consequences of HELBs on the safety-related equipment located on top of the module. 8.0 sec Notes:
- 1. Interlocks, permissives, and overrides for these signals are described in Table 7.1-5.
- 2. The overcooling event analyses account for decreased power detectionuncertainty due to decreasing downcomer temperature. The reductionuncertainty is 7%
for downcomer temperature decreases up to 10°F and is scaled upwards from 7% by 0.7%/°F for downcomer temperature decreases beyond 10°F.
- 3. The high count rate trip is treated as a source range over power trip that occurs at a core power analytical limit of 500 kW, which functionally equates neutron monitoring system counts per second to core power in watts. This trip is bypassed once the intermediate range signal is established.
- 4. If RCS hot temperature is above 500°F as shown in Figure 4.4-2.
- 5. If RCS hot temperature is below 500°F as shown in Figure 4.4-2.
- 6. If RCS hot temperature is above 500°F.
- 7. The RPV water level is presented in terms of elevation where reference zero is the bottom of the module assembly (at the bottom of the reactor pool). The range accommodates instrumentation uncertainty.
- 8. Normal AC voltage is monitored at the battery chargers for the EDAS. The analytical limit is based on an average voltage below 80% of normal.
Table 15.0-7: Analytical Limits and Time Delays (Continued) Signal(1) Analytical Limit Basis and Event Type Actuation Delay}}