ML25014A269
| ML25014A269 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 01/13/2025 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25013A204 | List: |
| References | |
| LO-178078, LO-177590 | |
| Download: ML25014A269 (1) | |
Text
Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-46 Receipt Date: 06/24/2024 Question:
In a number of event specific tables in the Non-LOCA TR (e.g., Turbine Trip, MSIV Closure, Loss of Normal Feedwater Transient Analysis, and Inadvertent Operation of the Decay Heat Removal System) that indicate Initial conditions, biases, and conservatisms, the SG heat transfer and/or DHRS heat transfer is set to nominal, (( 2(a),(c) This treatment is unchanged from the previous revision of the non-LOCA LTR. (( }} 2(a),(c)
Response
The events provided as examples in the audit question (i.e., turbine trip, main steam isolation valve (MSIV) closure, loss of normal feedwater (FW), and inadvertent operation of the decay heat removal system (DHRS)) are examples of heatup events where primary and secondary pressures are the key figures of merit. Section 4.2 of TR-0516-49416-P, Revision 4, Non-Loss-of-Coolant Accident Analysis Methodology, describes how the need to perform sensitivities is related to the available margin. An example is given in Section 4.2 for maximum secondary system pressure, with the conclusion that extensive sensitivity calculations to maximize secondary side pressure are not necessary for the non-LOCA transient analysis calculations. NuScale Nonproprietary NuScale Nonproprietary
In the NuScale Power Module (NPM) design, primary side (reactor coolant system (RCS)) pressure during design-basis events (a DBE) is limited by the lifting of the reactor safety valves (RSVs). The lift setpoint of the RSVs is selected to ensure RCS pressure has adequate margin to acceptance criteria. Therefore, the biases applied to the lift setpoint of the RSVs is ultimately what determines the maximum RCS pressure during a DBE. The biases of other parameters may have minor effects that result in small differences in RCS pressure, but not enough to cause acceptance criteria to be exceeded. A similar discussion is provided in Section 7.2.6.3 of TR-0516-49416-P: The maximum RCS pressure is limited by the RSV lifting and therefore many cases may have similar peak pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases. Consistent with the above discussion, the heatup events appropriately apply a high bias for the RSV lift setpoint. Using a high bias for the RSV lift setpoint delays the opening of the RSV until RCS pressure is higher, resulting in a higher peak RCS pressure. The application of a the high RSV lift setpoint is identified in the tables in TR-0516-49416-P as indicated below:
Turbine trip, loss of external load, and loss of condenser vacuum - Table 7-32
MSIV closure - Table 7-40
Loss of nonemergency alternating current power - Table 7-44
Loss of normal FW - Table 7-48
Inadvertent operation of DHRS - Table 7-52
Feedwater system pipe break - Table 7-56 These events also apply a nominal bias for steam generator (SG) heat transfer as shown in the same identified tables. (( }}2(a),(c) The justification can be further illustrated by a review of the limiting RCS pressures for the heatup events in the Final Safety Analysis Report (FSAR) for the US460 as shown in Table 1. NuScale Nonproprietary NuScale Nonproprietary
Table 1: Limiting Reactor Coolant System Pressure for Heatup Events in FSAR FSAR Section Event Peak RCS Pressure (psia) Margin to Acceptance Criteria (psia) 15.2.1 / 15.2.2 / 15.2.3 Turbine trip, loss of external load, and loss of condenser vacuum 2310 110 15.2.4 MSIV closure 2313 107 15.2.6 Loss of nonemergency AC power 2314 106 15.2.7 Loss of normal FW 2314 106 15.2.8 Feedwater system pipe break 2320 100 15.2.9 Inadvertent operation of DHRS 2317 103 As shown in Table 1, the variation in the peak RCS pressure for the events is less than 10 percent of the margin to the acceptance criteria. Despite the large difference in initiating event and resultant event sequences, there is minimal difference in the calculated peak RCS pressure. This demonstrates that the RSV successfully mitigates the increasing pressure with a similar amount of overshoot, regardless of the specific sequence resulting in the RSV lifting. FSAR Table 5.2-2 identifies the lift pressure and tolerance associated with the RSVs. Based on these values in FSAR Table 5.2-2, and the application of the high bias as previously discussed, the first RSV opens during the events in Table 1 at 2266 psia. Given the margin of at least 100 psia for the events, and considering that the application of the high bias on the RSV is worth 66 psia, two conclusions can be drawn: the margin to acceptance criteria is significant and RSV biasing is the dominant factor to determine peak RCS pressure. ((
}}2(a),(c)
NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c) Table 2: (( }}2(a),(c) (( }}2(a),(c) ((
}}2(a),(c)
NuScale Nonproprietary NuScale Nonproprietary
((
}}2(a),(c)
Regardless of the event or specific biases applied, heatup events produce the same peak RCS pressure that is primarily determined by the capacity and lift pressure of the RSVs. Applying a high bias to RSV lift setpoint is the dominant contributor to margin. For events where the RSV lift setpoint is not reached, the specific biases may have a more significant impact on peak RCS pressure; however, since the RCS pressure remains below the RSV lift setpoint, these events do not challenge acceptance criteria by definition. In summary, regarding RCS pressure, the use of nominal SG heat transfer bias for the heatup events in TR-0516-49416-P Tables 7-32, 7-40, 7-44, 7-48, 7-52, and 7-56 is reasonable. ((
}}2(a),(c) TR-0516-49416-P is revised as shown in the attached markups to add further technical basis consistent with this response.
((
}}2(a),(c) The analyses associated with the methodology in TR-0516-49416-P are run long enough to demonstrate a stable condition, as shown by trends in RCS pressure and temperature. Other aspects of long-term DHRS cooling are addressed in TR-124587-P, Revision 0, Extended Passive Cooling and Reactivity Control Methodology. (( }}2(a),(c) Note that the impact of high SG levels on DHRS performance is explicitly assessed as part of the SG overfill analysis associated with the increase in feedwater flow event. For example, FSAR Figure 15.1-8 shows high SG levels associated with the increase in feedwater flow event (( }}2(a),(c) Audit question NuScale Nonproprietary NuScale Nonproprietary
A-NonLOCA.LTR-60 identifies that TR-0516-49416-P Section 7.2.2 for the increase in feedwater flow event does not identify limiting bias directions for the SG overfill analysis. NuScale will address the impact of SG heat transfer bias on potential SG overfill conditions with the response to audit question A-NonLOCA.LTR-60. Markups of the affected changes, as described in the response, are provided below. NuScale Nonproprietary NuScale Nonproprietary
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 33 DHRS condensers and the energy is transferred to the reactor pool UHS. The maximum pressure in the SG secondary side is limited to the saturation pressure at the temperature of the RCS fluid on the SG primary side. Therefore, the maximum secondary pressure is affected by the secondary side inventory and the primary side conditions at the time of DHRS actuation, and is less sensitive to a specific initiating event. The SG design pressure is significantly higher than pressures expected during DHRS operation. The margin to the SG design pressure is physically limited, based on the primary side conditions. The representative transient results in Section 8.0 demonstrate that significant margin to the maximum SG pressure acceptance criterion is maintained for all types of events. Therefore, extensive sensitivity calculations to maximize secondary side pressure are not necessary for the non-LOCA transient analysis calculations. Audit Question A-NonLOCA.LTR-46 Another example is RCS pressure. In the NPM, operation of an RSV at its lift setpoint is sufficient to mitigate an increasing pressure with minimal overshoot. This design feature ensures that the maximum RCS pressure does not significantly exceed the RSV lift setpoint. With appropriate selection of the RSV lift setpoint, including consideration of uncertainty, the maximum RCS pressure will be well below the acceptance criterion. Modification of other biases can generate many cases with similar maximum RCS pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases.
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 569 7.2.6.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms presented in Table 7-32 are considered in identifying the bounding transient simulation for primary and steam generator pressure. Audit Question A-NonLOCA.LTR-46 Secondary pressure Peak secondary pressurization is largely a function of DHRS actuation and continued FW operation, in addition to the actual turbine trip or loss of external load. The DHRS heat removal is limited by the DHRS condenser so some pressurization is expected for every actuation of this system. Critical heat flux ratio This criterion is evaluated by downstream subchannel analysis. Maximum fuel centerline temperature This criterion is evaluated by downstream subchannel analysis. Containment integrity Containment integrity is evaluated by a separate analysis methodology. Escalation of an AOO to an accident This criterion is satisfied by demonstrating stable RCS flow rates and constant or downward trending RCS and DHRS pressures and temperatures exist at the end of the transient, all acceptance criteria evaluated in the transient analysis are met, and shutdown margin is maintained at the end of the transient. RCS conditions during extended DHRS cooling are addressed in a separate analysis. Table 7-32 Initial conditions, biases, and conservatisms - turbine trip / loss of external load Parameter Bias / Conservatism Basis (( Initial reactor power RTP biased to the high condition to account for measurement uncertainty. Initial RCS average temperature Varied. }}2(a),(c) Table 7-31 Acceptance criteria - turbine trip / loss of external load (Continued) Acceptance Criteria Discussion
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 570 Initial RCS flow rate Biased to the low condition. Initial PZR pressure Varied. Initial PZR level Biased to the high condition. Initial feedwater temperature Nominal. Initial fuel temperature Biased to the high condition MTC Consistent with BOC conditions. Kinetics Biased to BOC conditions. Decay heat Biased to the high condition. Initial SG pressure(1) Varied. Steam generator heat transfer Nominal. RSV lift setpoint Biased to the high condition. SG tube plugging Biased to the low condition. RCS Temperature Control Automatic rod control Disabled. Boron concentration Not credited. Table 7-32 Initial conditions, biases, and conservatisms - turbine trip / loss of external load (Continued) Parameter Bias / Conservatism Basis (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 571 Audit Question A-NonLOCA.LTR-46 Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event (i.e., system pressures for overheating events, MCHFR for overcooling events). Consequently, sensitivity studies are performed to identify cases with the highest pressure responses for this overheating event. The maximum RCS pressure is limited by the RSV lifting, with its applied lift pressure bias, and therefore many cases may have similar peak pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases. PZR Pressure Control PZR spray Disabled. PZR heaters Nominal. PZR Level Control Charging Not credited. Letdown Disabled. Steam Pressure Control Turbine throttle valves Disabled. Turbine bypass valves Disabled. Feedwater and Turbine Load Control feedwater pump speed Disabled. CNV Pressure Control CNV evacuation system Enabled.
- 1. ((
}}2(a),(c) Table 7-32 Initial conditions, biases, and conservatisms - turbine trip / loss of external load (Continued) Parameter Bias / Conservatism Basis (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 575 7.2.8.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms presented in Table 7-40 are considered in identifying the bounding transient simulation for primary and steam generator pressure. Audit Question A-NonLOCA.LTR-46 Table 7-40 Initial conditions, biases, and conservatisms - main steam isolation valve closure Parameter Bias / Conservatism Basis (( Initial reactor power RTP biased upwards to account for measurement uncertainty. Initial RCS average temperature Varied. Initial RCS flow rate Varied. Initial PZR pressure Varied. Initial PZR level Varied. Initial feedwater temperature Nominal. Initial fuel temperature Biased to the high condition MTC Consistent with BOC kinetics. Kinetics Biased to BOC conditions. Decay heat Biased to the high condition. Initial SG pressure(1) Varied. Steam generator heat transfer Nominal. RSV lift setpoint Biased to the high condition. SG tube plugging Biased to the low condition. RCS Temperature Control Automatic rod control Disabled. Boron concentration Not credited. }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 576 Audit Question A-NonLOCA.LTR-46 Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event (i.e., system pressures for overheating events, MCHFR for overcooling events). Consequently, sensitivity studies are performed to identify cases with the highest pressure responses for this overheating event. The maximum RCS pressure is limited by the RSV lifting, with its applied lift pressure bias, and therefore many cases may PZR Pressure Control PZR spray Disabled. PZR heaters Nominal. PZR Level Control Charging Not credited. Letdown Disabled. Steam Pressure Control Turbine throttle valves Enabled. Turbine bypass valves Disabled. Feedwater and Turbine Load Control feedwater pump speed Enabled. CNV Pressure Control CNV evacuation system Enabled.
- 1. ((
}}2(a),(c) Table 7-40 Initial conditions, biases, and conservatisms - main steam isolation valve closure (Continued) Parameter Bias / Conservatism Basis (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 577 have similar peak pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases. 7.2.9 Loss of Nonemergency AC Power The methodology used to simulate a postulated loss of nonemergency (normal) AC power for an NPM, and an evaluation of the acceptance criteria for an AOO listed in Table 7-4, are presented below. 7.2.9.1 General Event Description The low voltage AC electrical distribution system (ELVS) supplies AC power to plant motors, heaters, packaged equipment, and battery chargers. Loss of normal AC power to the station auxiliaries can result from electrical grid-related failures, failures in plant or switchyard equipment, or external weather events. The nonsafety-related EDNS and EDAS/EDSS may remain available via battery operation; the primary loads for these systems include the module control system (MCS) and the MPS. Loss of the EDNS and/or EDAS/EDSS batteries with the loss of normal AC power is considered as described in Section 7.1.3. A loss of AC power results in a pressurization of the secondary system and overheating of the RCS. Reactor trip and transition to stable DHRS flow terminates the transient with the NPM in a safe, stable condition. Table 7-42 lists the relevant acceptance criteria, SAF, and LOP scenarios. The electrical system design may vary by NPM design. Review of the electrical system is performed to determine the impact on plant equipment from the loss of power. In general, the following typically occur from the loss of power (AC or DC or both):
turbine trip occurs
the feedwater pumps and CVCS pumps stop
the PZR heaters turn off
control rods begin to drop due to loss of power to control rod drive mechanisms (CRDMs)
the MPS actuates reactor trip, DHRS, and various system isolations within 60 seconds after event initiation (if not already actuated during that time), due to loss of AC power to the EDAS/EDSS battery chargers
the MPS actuates ECCS within 24 hours after event initiation, due to loss of AC power to the EDAS/EDSS battery chargers Table 7-41 Not Used
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 579 7.2.9.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms presented in Table 7-44 are considered in identifying the bounding transient simulation for primary and secondary pressure. Audit Question A-NonLOCA.LTR-46 Containment integrity Containment integrity is evaluated by a separate analysis methodology. Escalation of an AOO to an accident This criterion is satisfied by demonstrating stable RCS flow rates and constant or downward trending RCS and DHRS pressures and temperatures exist at the end of the transient, all acceptance criteria evaluated in the transient analysis are met, and shutdown margin is maintained at the end of the transient. RCS conditions during extended DHRS cooling are addressed in a separate analysis. Table 7-44 Initial conditions, biases, and conservatisms - loss of normal AC power Parameter Bias / Conservatism Basis (( Initial reactor power RTP biased upwards to account for measurement uncertainty. Initial RCS average temperature Varied. Initial RCS flow rate Varied. Initial PZR pressure Varied. Initial PZR level Biased to the high condition. Initial feedwater temperature Nominal. Initial fuel temperature Biased to the high condition MTC Consistent with BOC kinetics. Kinetics Biased to BOC conditions. Decay heat Biased to the high condition. Initial SG pressure(1) Varied. SG heat transfer Nominal. }}2(a),(c) Table 7-43 Acceptance criteria - loss of normal AC power (Continued) Acceptance Criteria Discussion
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 581 Audit Question A-NonLOCA.LTR-46 Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event (i.e., system pressures for overheating events, MCHFR for overcooling events). Consequently, sensitivity studies are performed to identify cases with the highest pressure responses for this overheating event. The maximum RCS pressure is limited by the RSV lifting, with its applied lift pressure bias, and therefore many cases may have similar peak pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases. 7.2.10 Loss of Normal Feedwater Flow The methodology used to simulate a postulated loss of normal feedwater flow for an NPM, and an evaluation of the acceptance criteria for an AOO listed in Table 7-4, are presented below. 7.2.10.1 General Event Description A postulated fault results in a partial or complete loss of feedwater flow, and the water in the steam generators boils off. The loss of steam generators as a heat sink leads to a rise in the RCS temperature and pressure until the reactor typically Feedwater and Turbine Load Control feedwater pump speed Enabled. CNV Pressure Control CNV evacuation system Enabled.
- 1. ((
}}2(a),(c)
- 2. Loss of normal AC power initiating event results in a loss of system function by loss of power to the system thereby making the system control not relevant to the event.
Table 7-45 Not Used Table 7-44 Initial conditions, biases, and conservatisms - loss of normal AC power (Continued) Parameter Bias / Conservatism Basis (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 583 7.2.10.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms indicated in Table 7-48 are considered in identifying a bounding transient simulation for primary and steam generator pressure. Audit Question A-NonLOCA.LTR-46 Escalation of an AOO to an accident This criterion is satisfied by demonstrating stable RCS flow rates and constant or downward trending RCS and DHRS pressures and temperatures exist at the end of the transient, all acceptance criteria evaluated in the transient analysis are met, and shutdown margin is maintained at the end of the transient. RCS conditions during extended DHRS cooling are addressed in a separate analysis. Table 7-48 Initial conditions, biases, and conservatisms - loss of normal feedwater flow Parameter Bias / Conservatism Basis (( Initial reactor power RTP biased upwards to account for measurement uncertainty. Initial RCS average temperature Varied. Initial RCS flow rate Varied. Initial PZR pressure Varied. Initial PZR level Varied. Initial feedwater temperature Varied. Initial fuel temperature Biased to the high condition. MTC Consistent with BOC kinetics. Kinetics Biased to BOC conditions. Decay heat Biased to the high condition. Initial SG pressure(1) Varied. SG heat transfer Nominal. RSV lift setpoint Biased to the high condition. }}2(a),(c) Table 7-47 Acceptance criteria - loss of normal feedwater flow (Continued) Acceptance Criteria Discussion
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 585 Audit Question A-NonLOCA.LTR-46 Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. Consequently, sensitivity studies are performed to identify cases with the highest primary and secondary pressures, varying the magnitude of the feedwater flow rate decrease (other parameters are biased as indicated in Table 7-48). The maximum RCS pressure is limited by the RSV lifting, with its applied lift pressure bias, and therefore many cases may have similar peak pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases. 7.2.11 Inadvertent Decay Heat Removal System Actuation The methodology used to simulate a postulated inadvertent DHRS actuation for an NPM, and an evaluation of the acceptance criteria for an AOO listed in Table 7-4, are presented below. This event is unique to the NPM designs. 7.2.11.1 General Event Description Inadvertent actuation of the DHRS may result from either an unexpected DHRS valve actuation or a spurious DHRS actuation signal. Due to the DHRS design and configuration, several scenarios exist for consideration. The specific scenarios considered are discussed below. The sequence of events and the MPS signals that are reached first depend on the scenario. Reactor trip and transition to stable DHRS flow terminates the transients with the NPM in a safe, stable condition. The relevant acceptance criteria, SAF, and LOP scenarios are listed in Table 7-50. Scenario 1: The unexpected opening of a single DHRS valve can occur at full power or reduced power conditions. At low power conditions, a portion of the DHRS liquid inventory drains into the feedwater line, which momentarily increases feedwater flow and causes overcooling. This overcooling event is not considered further because it is bounded by other, more limiting overcooling events (i.e., increase in feedwater flow). The most challenging conditions for this heatup scenario occur at full power with initial conditions biased in the conservative directions. Since feedwater flow tends to increase in response to the reduced steam enthalpy and turbine load, limiting the feedwater response maximizes the heatup.
- 1. ((
}}2(a),(c) Table 7-49 Not Used
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 587 7.2.11.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms presented in Table 7-52 are considered in identifying the bounding transient simulation for primary and steam generator pressure. Audit Question A-NonLOCA.LTR-46 Table 7-51 Acceptance criteria - inadvertent decay heat removal system actuation Acceptance Criteria Discussion Primary pressure Primary pressure quickly rises to the peak value, then drops as the lowest setpoint RSV lifts to reduce pressure. Secondary pressure Peak secondary pressurization is largely a function of DHRS actuation. The DHRS heat removal is limited by the DHR condenser so some pressurization is expected for every actuation of this system. Critical heat flux ratio This criterion is evaluated by downstream subchannel analysis. Maximum fuel centerline temperature This criterion is evaluated by downstream subchannel analysis. Containment integrity Containment integrity is evaluated by a separate analysis methodology. Escalation of an AOO to an accident This criterion is satisfied by demonstrating stable RCS flow rates and constant or downward trending RCS and DHRS pressures and temperatures exist at the end of the transient, all acceptance criteria evaluated in the transient analysis are met, and shutdown margin is maintained at the end of the transient. RCS conditions during extended DHRS cooling are addressed in a separate analysis. Table 7-52 Initial conditions, biases, and conservatisms - inadvertent decay heat removal system actuation Parameter Bias / Conservatism Basis (( Initial reactor power RTP biased upwards to account for measurement uncertainty. Initial RCS average temperature Varied. }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 588 Initial RCS flow rate Biased to the low condition. Initial PZR pressure Varied. Initial PZR level Varied. Initial feedwater temperature Nominal. Initial fuel temperature Biased to the high condition MTC Consistent with BOC kinetics. Kinetics Biased to BOC conditions. Decay heat Biased to the high condition. Initial SG pressure(1) Varied. Steam generator heat transfer Nominal. RSV lift setpoint Biased to the high condition. SG tube plugging Biased to the low condition. RCS Temperature Control Automatic rod control Disabled. Boron concentration Not credited. PZR Pressure Control PZR spray Varied. Table 7-52 Initial conditions, biases, and conservatisms - inadvertent decay heat removal system actuation (Continued) Parameter Bias / Conservatism Basis (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 589 Audit Question A-NonLOCA.LTR-46 Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. Consequently, sensitivity studies are performed to identify cases with the highest pressure responses for this event. The maximum RCS pressure is limited by the RSV lifting, with its applied lift pressure bias, and therefore many cases may have similar peak pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases. PZR heaters Nominal. PZR Level Control Charging Not credited. Letdown Disabled. Steam Pressure Control Turbine throttle valves Enabled. Turbine bypass valves Disabled. Feedwater and Turbine Load Control feedwater pump speed Disabled. CNV Pressure Control CNV evacuation system Enabled.
- 1. ((
}}2(a),(c) Table 7-52 Initial conditions, biases, and conservatisms - inadvertent decay heat removal system actuation (Continued) Parameter Bias / Conservatism Basis (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 592 7.2.12.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms presented in Table 7-56 are considered in identifying the bounding transient simulation for primary and steam generator pressure. Audit Question A-NonLOCA.LTR-46 Table 7-56 Initial conditions, biases, and conservatisms - feedwater line break Parameter Bias / Conservatism Basis (( Initial reactor power RTP biased upwards to account for measurement uncertainty. Initial RCS average temperature Biased to the high condition. Initial RCS flow rate Biased to the low condition. Initial PZR pressure Varied. Initial PZR level Varied. Initial feedwater temperature Varied. Initial fuel temperature Biased to the high condition. MTC Consistent with BOC kinetics. Kinetics Biased to BOC conditions. Decay heat Biased to the high condition. Initial SG pressure(1) Varied. SG heat transfer Nominal. RSV lift setpoint Biased to the high condition. }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 594 Audit Question A-NonLOCA.LTR-46 Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event (i.e., system pressures for overheating events, MCHFR for overcooling events). Consequently, sensitivity studies are performed to identify cases with the highest pressure responses for this overheating event. The maximum RCS pressure is limited by the RSV lifting, with its applied lift pressure bias, and therefore many cases may have similar peak pressures. Extensive sensitivity studies are not required to investigate the small differences between those cases. 7.2.13 Uncontrolled Control Rod Assembly Bank Withdrawal from Subcritical or Low Power Startup Conditions The methodology used to simulate a postulated uncontrolled CRA bank withdrawal from subcritical or low power startup conditions for an NPM, and an evaluation of the acceptance criteria listed for an AOO in Table 7-4, are presented below. The range of initial power levels associated with low power startup conditions for an NPM is based on the low setting for the high power signal (below 15 percent RTP for the example in Table 7-3). When core power reaches the low setting level, a hold point is established to alter the high power setting. Thus, low power startup conditions exist until reactor power reaches the low setting level. 7.2.13.1 General Event Description and Methodology The limiting event consequences to an uncontrolled CRA bank withdrawal from subcritical or low power startup conditions typically (for most PWR designs) occur for cases with very low initial power levels (~1 Watt). The primary reason for this CNV Pressure Control CNV evacuation system Enabled.
- 1. ((
}}2(a),(c) Table 7-57 Not Used Table 7-56 Initial conditions, biases, and conservatisms - feedwater line break (Continued) Parameter Bias / Conservatism Basis (( }}2(a),(c)}}