ML25056A423
| ML25056A423 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 02/25/2025 |
| From: | Shaver M NuScale |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| Shared Package | |
| ML25056A422 | List: |
| References | |
| RAIO-179795 | |
| Download: ML25056A423 (1) | |
Text
RAIO-179795 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com February 25, 2025 Docket No.52-050 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738
SUBJECT:
NuScale Power, LLC Response to NRC Request for Additional Information No. 018 (RAI-10142 R1) on the NuScale Standard Design Approval Application
REFERENCE:
NRC Letter to NuScale, Request for Additional Information No. 018 (RAI-10142 R1), dated March 02, 2024 The purpose of this letter is to provide the NuScale Power, LLC (NuScale) response to the referenced NRC Request for Additional Information (RAI).
The enclosure to this letter contains the NuScale response to the following RAI question from NRC RAI-10142 R1:
15.4.6-1 is the proprietary version of the NuScale Response to NRC RAI No. 018 (RAI-10142 R1, Question 15.4.6-1). NuScale requests that the proprietary version be withheld from public disclosure in accordance with the requirements of 10 CFR § 2.390.
The enclosed affidavit (Enclosure 3) supports this request. Enclosure 2 is the nonproprietary version of the NuScale response.
This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.
If you have any questions, please contact Amanda Bode at 541-452-7971 or at abode@nuscalepower.com.
I declare under penalty of perjury that the foregoing is true and correct. Executed on February 25, 2025.
Sincerely, Mark W. Shaver Director, Regulatory Affairs NuScale Power, LLC
RAIO-179795 Page 2 of 2 02/25/2025 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Distribution:
Mahmoud Jardaneh, Chief New Reactor Licensing Branch, NRC Getachew Tesfaye, Senior Project Manager, NRC Stacy Joseph, Senior Project Manager, NRC
- NuScale Response to NRC Request for Additional Information RAI-10142 R1, Question 15.4.6-1, Proprietary Version : NuScale Response to NRC Request for Additional Information RAI-10142 R1, Question 15.4.6-1, Nonproprietary Version : Affidavit of Mark W. Shaver, AF-179796
RAIO-179795 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com :
NuScale Response to NRC Request for Additional Information RAI-10142 R1, Question 15.4.6-1, Proprietary Version NuScale Confidential, Proprietary Class 2
RAIO-179795 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com NuScale Response to NRC Request for Additional Information RAI-10142 R1, Question 15.4.6-1, Nonproprietary Version
Response to Request for Additional Information Docket: 052000050 RAI No.: 10142 Date of RAI Issue: 03/02/2024 NRC Question No.: 15.4.6-1 Regulatory Basis 10 CFR 52.137(a)(4) states a standard design application must include [a]n analysis and evaluation of the design and performance of SSC with the objective of assessing the risk to public health and safety resulting from operation of the facility and including determination of the margins of safety during normal operations and transient conditions anticipated during the life of the facility, and the adequacy of SSCs provided for the prevention of accidents and the mitigation of the consequences of accidents.
GDC 10, Reactor Design, states that the reactor core and associated coolant, control, and protection systems shall be designed with appropriate margin to assure that specified acceptable fuel design limits are not exceeded during any condition of normal operation, including the effects of anticipated operational occurrences.
GDC 13, Instrumentation and Control, states that instrumentation shall be provided to monitor variables and systems over their anticipated ranges for anticipated operational occurrences as appropriate to assure adequate safety. It further states that appropriate controls shall be provided to maintain these variables and systems within prescribed operating ranges.
GDC 26, Reactivity Control System Redundancy and Capability, states that a reactivity control system shall be provided that is capable of reliably controlling reactivity changes to assure that under conditions of normal operation, including anticipated operational occurrences, and with appropriate margin for malfunctions such as stuck rods, specified acceptable fuel design limits are not exceeded.
Issue NuScale Nonproprietary NuScale Nonproprietary
Malfunction of the NPM-20 chemical and volume control system or operator error could result in inadvertent addition of diluted or unborated water to the reactor coolant system (RCS). Such an addition will dilute boron in the RCS coolant and may result in a loss of shutdown margin, preventing the reactivity control system from performing its safety function and satisfying associated regulatory requirements such as General Design Criteria 10, 13, and 26.
FSAR Section 15.4.6 evaluates these inadvertent boron dilution transients. The at-power evaluation credits automatic isolation of the demineralized water system (DWS) via the module protection system to terminate the dilution. Supporting documents, examined by the staff via audit, indicate that the DWS is isolated by an assumed operator response which terminates inadvertent boron dilution transients initiated later in the cycle, but do not specify whether the module protection system would isolate the DWS to terminate these cases before shutdown margin is lost if the operator response is not assumed consistent with the automatic response of the current US460 design.
Guidance in SRP 15.4.6 describes supporting information and analysis typically provided by active operating reactors if operator action is relied upon to mitigate a boron dilution transient, such as redundant alarms that alert the operator to the unplanned boron dilution and the event sequence that provides operators the shortest time to isolate dilution sources. Additional information is needed to support credit for operator action as NuScales NPM-20 passive design and its approach to design basis event mitigation differs significantly from operating reactors.
Information Requested Provide the analysis of the Mode 1 boron dilution event(s) which demonstrates that the module protection system isolates DWS before shutdown margin is lost without reliance on operator intervention. Operator intervention at any time within the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following the initiating event would constitute a reliance on that operator action to mitigate the event. This analysis should ensure that limiting times-in-cycle are evaluated with consideration of whether loss of shutdown margin occurs before DWS isolation by the module protection system.
Alternately, to enable staff review of the adequacy of the current Mode 1 analysis documented in FSAR 15.4.6 and staff assessment of the use of operator actions, provide the following information in the FSAR: 1) identification and description of redundant instrumentation and control room alarms that alert the operators of an unplanned boron dilution, 2) a listing of the specific operator actions necessary to terminate the event and the total time required (the event duration is considered to include the time from the initiating event through the following 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />), and 3) the event sequence and timing with the smallest elapsed time from the signal NuScale Nonproprietary NuScale Nonproprietary
generated and control room alarm detecting the dilution event to the time a loss of shutdown margin would occur.
The Mode 1 analysis should ensure that limiting (with respect to available time for operator action) times-in-cycle are evaluated. Revise the FSAR with pertinent portions of the analysis and supporting information, including revisions to protection system signals and setpoints, description of control room alarms and indications, and discussions of assumed operator response during the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following the initiating event in FSAR Chapters such as 7, 15, 18, and 19.
NuScale Response:
Executive Summary The Mode 1 boron dilution event analysis is revised to include a new approach to demonstrate that the demineralized water system (DWS) or chemical and volume control system (CVCS) is isolated before shutdown margin (SDM) is lost without reliance upon operator intervention. At beginning of cycle (BOC), reactor trip and DWS isolation are confirmed to occur prior to loss of shutdown margin using NRELAP5 transient results. The letdown system control is modified to preclude automatic letdown when DWS is not isolated. At end of cycle (EOC), the increase in level from the boron dilution with no letdown results in a reactor trip (with DWS isolation) and CVCS isolation on high pressurizer level prior to loss of shutdown margin. Analyses are also performed at the transition from BOC to EOC to show that the different protection schemes overlap to conservatively ensure shutdown margin is maintained throughout the cycle. The Modes 2 and 3 shutdown margin analyses are also revised to credit the CVCS isolation on high pressurizer level. The revised results are provided in the attached markups to Final Safety Analysis Report (FSAR) Section 15.4.6 and confirm that SDM is maintained. The revised approach is also added to TR-0516-49416, Non-Loss-of-Coolant Accident Analysis Methodology, as shown in the attached markups. The change to the control of letdown is identified in attached markups to FSAR Section 9.3.4. In addition, the Bases for Technical Specification (TS) 3.1.9, Boron Dilution Control, is revised as indicated in the attached markups to place a limit on the allowed duration of boron dilution. This limit is not credited in the analysis and so provides additional assurance that a loss of SDM does not occur during a boron dilution. Finally, the Bases for TS 3.3.1, MPS Instrumentation, is revised as indicated in the attached markups to identify that the high pressurizer level signal is credited in the boron dilution event.
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Review of NRC Guidance This request for additional information (RAI) requests that NuScale [p]rovide the analysis of the Mode 1 boron dilution event(s) which demonstrates that the module protection system isolates DWS before shutdown margin is lost without reliance on operator intervention. Review of the NUREG-0800 Standard Review Plan (SRP) Section 15.4.6 identifies in the Requirements subsection of the Acceptance Criteria section that:
5.The general objective of the review of moderator dilution events is to confirm either of the following conditions is met:
A. The consequences of these events are less severe than those of another transient that results in an uncontrolled increase in reactivity and has the same anticipated frequency classification.
B. The plant responds to events such that the criteria regarding fuel damage and system pressure are met and the dilution transient is terminated before the shutdown margin is eliminated.
As indicated, the SRP provides two options to address the boron dilution event. Of the two options, only the second option discusses terminating the transient before the SDM is eliminated. Therefore, the NRC request in this RAI appears to align with the second option (5.B) in the SRP. However, an approach consistent with the first option (5.A) is also identified by the SRP as acceptable even though it is different than the NRC request in this RAI.
Further review of the SRP in the SRP Requirements subsection of the Acceptance Criteria section identifies that the focus of the review is on event progressions that maximize the reactivity insertion and corresponding power increase. For example, item 5.B identifies that the boron dilution should be assumed to occur at the maximum possible rate, item 5.H identifies that a conservatively high reactivity addition rate should be assumed, and item 5.I identifies that conservative scram characteristics, such as maximum time delay, should be assumed. Item 5.C identifies that the most limiting combination of moderator temperature coefficient, void coefficient, Doppler coefficient, axial power profile, and radial power distribution should be assumed and that the core burnup must be justified by either analysis or evaluation. Item 5.C does not identify the direction associated with most limiting, but the context provided by items 5.B, 5.H, and 5.I indicates that the focus is on maximizing the reactivity insertion and corresponding power increase. Item 5.A also identifies that the licensed core thermal power should be assumed (i.e., 100 percent power). By using a maximum initial power level and then maximizing the reactivity insertion and corresponding power increase, the overall response will NuScale Nonproprietary NuScale Nonproprietary
be limiting with respect to reactor coolant system (RCS) pressure, main steam system pressure, and fuel cladding integrity. This interpretation is consistent with identification of system pressures and fuel cladding integrity as items 1 and 2, respectively, of the SRP Acceptance Criteria. This interpretation is also consistent with the General Design Criteria (GDC) identified as the relevant requirements that are the basis for the acceptance criteria. Specifically, GDC 10 and GDC 26 require that specified acceptable fuel design limits are not exceeded and GDC 15 requires that design conditions of the reactor coolant pressure boundary (RCPB) are not exceeded.
Final Safety Analysis Report Revision 1 Approach In FSAR Revision 1, Section 15.4.6 provided an analysis of the Mode 1 boron dilution event that was consistent with SRP 15.4.6 guidance. Specific examples for comparison to the SRP include:
An initial power level of 100 percent was assumed (SRP 15.4.6 Item 5.A).
A maximum boron dilution rate of 25 gpm at beginning of cycle (BOC) was assumed (SRP 15.4.6 Item 5.B). Note that a higher dilution rate of 50 gpm is possible at later times in cycle as indicated by footnote 2 of FSAR Table 15.4-13, but the reactivity insertion rates with the 50 gpm cases later in cycle are less limiting than the 25 gpm at BOC cases.
A conservatively high reactivity addition rate was assumed (SRP 15.4.6 Item 5.H).
The combination of reactivity coefficients and core burnup from BOC was used to generate the most limiting reactivity insertion and corresponding power increase (SRP 15.4.6 Item 5.I).
The results of this hot full power (HFP) analysis were provided in FSAR Table 15.4-13. The results for the 25 gpm case showed that the maximum reactivity insertion rates calculated with the two specified methods were 17.19 pcm/sec (wave front model) and 0.5908 pcm/sec (complete mixing model). These reactivity insertion rates were then shown to be bounded by the range of reactivity insertion rates assumed in FSAR Section 15.4.2 (0.064 pcm/sec to 24 pcm/sec). The FSAR Section 15.4.6 analysis did not explicitly evaluate specified acceptable fuel design limits but instead relied upon the FSAR Section 15.4.2 evaluations. The confirmation that the FSAR Section 15.4.2 results met acceptance criteria and were bounding of the reactivity insertion rates for the Mode 1 boron dilution analysis were adequate to demonstrate that the Mode 1 boron dilution analysis also met acceptance criteria. This approach was consistent with general objective 5.A of the SRP. Beyond meeting general objective 5.A of the SRP, FSAR Table 15.4-13 also provided the results of an NRELAP5 evaluation of the SDM that showed the NuScale Nonproprietary NuScale Nonproprietary
reactor would trip and DWS would isolate prior to the loss of SDM for this maximum reactivity insertion case. This evaluation confirmed that general objective 5.B of the SRP was also met.
No operator actions were assumed in this analysis. The end state of this transient was that the reactor was no longer in Mode 1 and the dilution flow had ceased.
As described above, the SRP is focused on generating the maximum reactivity insertion rate and does not provide guidance indicating that slower reactivity insertion rates need to be considered. Nevertheless, the NuScale analysis supporting FSAR Section 15.4.6 included a spectrum of Mode 1 cases, varying dilution flow rate, power level, and time in cycle, to determine the most limiting case. The case for 25 gpm at full power at BOC resulted in the maximum reactivity insertion as well as the maximum power. The other cases in FSAR Table 15.4-13 (i.e., 5 gpm and 50 gpm dilution flow rates) were less limiting for power response and had similar SDM remaining at time of trip. The reason these less limiting cases were included in the FSAR for the US460 Standard Design Approval Application (SDAA) is that they were included in the FSAR for the US600 Design Certification Application (DCA) that is approved by the NRC and codified in 10 CFR 52 Appendix G. Where possible, NuScale has maintained the level of detail in Chapter 15 consistent between SDAA and DCA.
FSAR Table 15.4-14 provided results for three cases at hot zero power (HZP) at BOC. The SRP guidance does not describe a need for analysis in Mode 1 at reduced power levels (acceptance criteria Item 5.A). Comparison of the results of FSAR Table 15.4-14 to Table 15.4-13 showed that, in each case, the HZP results had lower reactivity insertion rates. The only difference of note is that the HZP reactivity insertion rates were compared to the range from FSAR Section 15.4.1 (rather than Section 15.4.2), but the ranges were identical. The maximum powers resulting from the reactivity insertions for these HZP cases were well below 100 percent (i.e.,
below the initial power of the cases in FSAR Table 15.4-13). These low power cases were not challenging for the fuel, consistent with the results in FSAR Section 15.4.2 that showed that an initial power of 102 percent resulted in the most limiting minimum critical heat flux ratio (MCHFR) and linear heat generation rate (LHGR) (i.e., confirmed by a comparison of different power levels within FSAR Section 15.4.2 in addition to comparison of Section 15.4.2 to Section 15.4.1). FSAR Table 15.4-14 also provided the results of NRELAP5 evaluations of the SDM that showed the these HZP cases have more SDM remaining than the corresponding HFP cases.
Therefore, the cases in FSAR Table 15.4-14 were less limiting as expected. Similar to above, the reason the table for HZP was included in the FSAR for the SDAA is that it was included for the DCA.
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Additional Results Not Included in Final Safety Analysis Report Revision 1 In addition to the HFP and HZP cases provided in FSAR Tables 15.4-13 and 15.4-14, respectively, the calculation supporting FSAR Section 15.4.6 (referenced in this RAI as having been examined by the staff via audit) also provided analyses at three power levels between full power and HZP. ((2(a),(c) Therefore, these cases were not presented in FSAR Section 15.4.6 for the SDAA (and also were not for the DCA). The calculation supporting FSAR Section 15.4.6 also provided analyses at end of cycle (EOC) for the same power levels and dilution flow rate as performed for BOC. Characteristics typical of EOC conditions include: low boron concentrations, reduced limits on critical boron concentration (CBC), all rods out (ARO), most negative moderator temperature coefficient (MTC), and most negative fuel temperature coefficient (FTC). These characteristics result in the EOC cases behaving differently than BOC cases. When boron concentration is initially lower, it takes a much larger volume of pure water to achieve the same change in concentration as for a higher initial boron concentration. On the other hand, the reactivity effect of a change in boron concentration does not change significantly over the cycle. As a result, EOC conditions are less sensitive to boron dilutions than BOC conditions (i.e., the same dilution flow rate results in a smaller reactivity insertion rate). ((
}}2(a),(c) The guidance in the SRP focuses on identifying the maximum reactivity insertion (and associated highest power). Under this guidance, and given the results described above, the EOC cases were clearly not limiting.
((
}}2(a),(c)
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(( }}2(a),(c) Therefore, as indicated in the RAI, the supporting analyses for FSAR Revision 1 were inconclusive as to whether SDM is maintained for boron dilution events starting from other conditions in Mode 1 (e.g., EOC). The reasons the EOC analyses in FSAR Revision 1 were inconclusive are as follows: (( }}2(a),(c) To address these issues, a revised approach is implemented as described below. Revised Final Safety Analysis Report Approach The approach where a range of conditions is evaluated to determine reactivity insertion rates for various boron dilution scenarios and then compared to the range of reactivity insertion rates evaluated in the uncontrolled CRA withdrawal at power analysis in FSAR Section 15.4.2 and the uncontrolled CRA withdrawal from a subcritical or low power startup condition analysis in FSAR Section 15.4.1 is unchanged. The reactivity insertion rate comparisons are still performed to confirm that the response to the boron dilution event is bounded by these other reactivity insertion events for considerations other than SDM. A revised approach is applied to the boron dilution event for the determination of SDM. The approach is varied based on the time of cycle of interest. For BOC, NRELAP5 results from the events in FSAR Section 15.4.1 and FSAR Section 15.4.2 are first used to determine the total reactivity that can be inserted before a reactor trip occurs. ((
}}2(a),(c)
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((
}}2(a),(c) In this way, the NRELAP5 analyses of these other events are used to bound the maximum total reactivity insertion that can occur for a boron dilution event prior to DWS isolation. The reactivity insertion is then subtracted from the initial shutdown margin to determine the shutdown margin that would remain at the time of DWS isolation to confirm it is greater than zero.
To protect against dilutions at EOC, a design change was implemented to modify the control of letdown. In previous analyses, automatic letdown was enabled so that the increase in RCS inventory due to the addition of the dilution source was offset by letdown and pressurizer level did not increase. As a result, high pressurizer level was not a signal that provided protection for the boron dilution event. The control of letdown is modified to preclude the use of automatic letdown when DWS is not isolated. Without automatic letdown, the RCS inventory addition from a postulated boron dilution causes an increase in pressurizer level and reactor trip eventually occurs on high pressurizer level. The DWS is isolated on the reactor trip and the CVCS is also isolated on high pressurizer level. The addition of high pressurizer level reactor trip as a means to mitigate the event allows for earlier termination of postulated boron dilutions at EOC. To determine the timing of the reactor trip on high pressurizer level, simple hand calculations are performed to determine the volume necessary to raise the pressurizer level from its initial level ((
}}2(a),(c) to the high pressurizer level trip setpoint. Note that the volume is independent of the dilution flow rate. (( }}2(a),(c) The volume is then used to determine the change in boron concentration. The decrease in boron concentration is converted to change in reactivity using the boron worth. Finally, the change in reactivity is subtracted from NuScale Nonproprietary NuScale Nonproprietary
the initial shutdown margin to determine the shutdown margin that would remain at the time of DWS isolation to confirm it is greater than zero. The revised approach above considers two general regions of time in cycle, referred to as BOC and EOC in this discussion. To ensure protection throughout the cycle, an additional evaluation of shutdown margin is performed at the transition between the two regions. Note that the transition point actually occurs near middle of cycle; BOC and EOC designations are used for simplicity. The full power scenario is of interest as it has the limiting shutdown margin result for both BOC and EOC. The transition point is evaluated by comparison to NRELAP5 cases from FSAR Section 15.4.2 using reactivity feedback associated with that time in cycle. The results confirm that shutdown margin is greater than zero at the time of DWS isolation. The evaluation also confirms that the protection provided by the high pressurizer level signal extends beyond the transition point (i.e., into the BOC region). In this manner, the two different protection schemes overlap such that protection against loss of shutdown margin is conservatively ensured throughout the cycle. Although Modes 2 and 3 are not the subject of this RAI, the design change for letdown is also used to revise the Modes 2 and 3 analyses. The Modes 2 and 3 analyses previously credited the isolation of DWS on high subcritical multiplication. The high subcritical multiplication signal detects changes in count rate above a time-averaged background signal. For most dilutions, the high subcritical multiplication signal provides protection because the dilution results in a change in count rate relative to the background signal. For very slow dilutions (e.g., occurring over 24 hours), the time-averaged background signal will increase such that the count rate is not sufficiently above the background to result in the high subcritical multiplication signal being reached. Although such very slow dilutions are unlikely to go unmitigated by operators given the shutdown margin TS surveillance that would occur during the event, the high pressurizer level signal provides automatic protection against such scenarios. The Mode 2 and 3 analyses are revised to credit the high pressurizer level signal for CVCS isolation rather than the high subcritical multiplication signal. The Mode 3 analysis considers the possibility that emergency core cooling system (ECCS) valves are open with containment flooded, such as may occur during the return from refueling. In this scenario, the dilution volume necessary to reach the high pressurizer level signal also considers the containment volume. With consideration of the containment volume and a more limiting boron worth in Mode 3 than in Mode 2, the Mode 2 dilution is bounded by Mode 3. FSAR Section 15.4.6 is revised as shown in the attached markups to describe this method and also provide the results. The revised approach is also incorporated into TR-0516-49416, Non-NuScale Nonproprietary NuScale Nonproprietary
Loss-of-Coolant Accident Analysis Methodology, as shown in the attached markups. FSAR Section 9.3.4 is revised as shown in the attached markup to discuss the restriction on automatic letdown. FSAR Table 15.0-7 and the Bases for TS 3.3.1 are revised as shown in the attached markups to identify the role of the high pressurizer level reactor trip for mitigation of postulated boron dilution events. Conservatism Not Credited in Revised Approach The revised approach retains significant conservatism, as identified below. 1) Operator actions, while not credited, play a role in reasonable assurance. The boron dilution calculation does not credit operator actions. There are no specific, time-critical operator actions to assure that specified acceptable fuel design limits are met. However, operator actions are a likely occurrence during an actual plant response to a boron dilution event. It is not expected that the plant would continue to passively operate indefinitely following a transient because the control systems will respond and be actively working to return conditions to the initial pre-transient conditions. Even with control systems unavailable, the operators may be driven to take actions by alarms, TS surveillances (e.g., channel checks), shift turnover meetings, corrective action program, or other human factor considerations used as part of normal plant operation. These actions are not time-critical nor are they specific to ensure acceptance criteria are met; rather, these actions ensure the plant remains within a defined operating space to limit vulnerability to another initiating event. Plant procedures and controls ensure extended time operating outside the defined operating space, for example up to the full 72 hours discussed in this question, is not allowed because this could challenge the fundamental safety analysis assumption that independent initiating events are analyzed separately. Plant capability to restore the module to its normal operating conditions after a boron dilution event that results in a loss of SDM can be considered. First, it is clarified that loss of SDM is not equivalent to offsetting the minimum negative reactivity insertion provided by the control rods immediately after reactor trip. The SDM is the instantaneous amount of reactivity by which the reactor is subcritical or would be subcritical from its present (normal operating) condition assuming all control rod assemblies except the highest worth assembly are inserted, and while accounting for the power defect. The power defect accounts for the total change in reactivity associated with a change in moderator and fuel temperature accompanying a change in power, including the NuScale Nonproprietary NuScale Nonproprietary
reactivity associated with axial redistribution. In the US460 design, FSAR Table 15.0-6 identifies that the minimum RCS temperature for criticality is 345 degrees F while the nominal RCS average temperature is 540 degrees F for greater than 20 percent power. Therefore, as part of demonstrating that there is adequate SDM in the core design, the negative reactivity worth in the US460 design control rods must account for the change in reactivity associated with moderator and fuel temperature changes from operation at 540 degrees F to 345 degrees F, among other factors. This is a significant amount of negative reactivity inherently accounted for in the SDM. From the condition where power levels are sufficiently low immediately following trip so as to not challenge fuel design limits, additional actions such as increasing RCS boron concentration can be taken as the RCS cools. 2) Boron dilution is performed under manual control and is limited in duration. In the US460 design, boron dilution during Mode 1 is a manual activity. The Bases for TS 3.1.9, Boron Dilution Control, is revised as indicated in the attached markups to add a limit on the allowed duration of boron dilution. The fact that these activities are being performed under operator control in accordance with TS and plant procedures provides further justification that the likelihood of a lengthy manually initiated unintentional boron dilution is remote. The SDM analysis presented above shows that SDM can be limiting when boron concentration is low. Dilution at low boron concentrations takes longer than dilution at high boron concentrations. Therefore, the limiting SDM results are consistent with a long time to the potential loss of SDM. The SDM analysis above takes no credit for the time required for the dilution to occur and the control provided in the Bases for TS 3.1.9. Response to Specific Question Requests Responses to the specific requests in the RAI are provided below based on the rationale and justification provided above. The NRC requests are identified by the indented and italicized text, with the NuScale response following in the non-indented and non-italicized text. Provide the analysis of the Mode 1 boron dilution event(s) which demonstrates that the module protection system isolates DWS before shutdown margin is lost without reliance on operator intervention. Operator intervention at any time within the 72 hours following the initiating event would constitute a reliance on that operator action to mitigate the event. This analysis should ensure that limiting times-in-cycle are evaluated with NuScale Nonproprietary NuScale Nonproprietary
consideration of whether loss of shutdown margin occurs before DWS isolation by the module protection system. NuScale has revised the Mode 1 boron dilution event analysis to demonstrate boron dilution events are terminated before SDM is lost without reliance upon operator intervention. The revised results are incorporated into FSAR Section 15.4.6 as shown in the attached markups. The revised approach is also incorporated into TR-0516-49416, Non-Loss-of-Coolant Accident Analysis Methodology, as shown in the attached markups. Alternately, to enable staff review of the adequacy of the current Mode 1 analysis documented in FSAR 15.4.6 and staff assessment of the use of operator actions, provide the following information in the FSAR: 1) identification and description of redundant instrumentation and control room alarms that alert the operators of an unplanned boron dilution, 2) a listing of the specific operator actions necessary to terminate the event and the total time required (the event duration is considered to include the time from the initiating event through the following 72 hours), and 3) the event sequence and timing with the smallest elapsed time from the signal generated and control room alarm detecting the dilution event to the time a loss of shutdown margin would occur. Not applicable. NuScale is not crediting any specific operator actions. The Mode 1 analysis should ensure that limiting (with respect to available time for operator action) times-in-cycle are evaluated. Revise the FSAR with pertinent portions of the analysis and supporting information, including revisions to protection system signals and setpoints, description of control room alarms and indications, and discussions of assumed operator response during the 72 hours following the initiating event in FSAR Chapters such as 7, 15, 18, and 19. Not applicable. NuScale is not crediting any specific operator actions. Additional Discussion of Markups The markups attached to this response include some changes not strictly related to this RAI response, but identified as part of the overall incorporation of the revised analysis results. These additional markups are described below for information. NuScale Nonproprietary NuScale Nonproprietary
The response to RAI 10142 Question 15.4.6-2 made changes to the FSAR Section 15.4.6 discussion of Mode 5 boron dilution. While incorporating the Mode 1 changes described in this response, it was identified that an outdated statement regarding Mode 5 boron dilution was not deleted from FSAR Section 15.4.6 in the markups included with the response to RAI 10142 Question 15.4.6-2. Specifically, the statement in FSAR Section 15.4.6.3.1 regarding the use of the perfect mixing equation for the pool dilution is no longer accurate. Therefore, the statement is deleted in the attached markups to this RAI response. This change is not related to this RAI response, but is consistent with the other changes made in the RAI 10142 Question 15.4.6-2 response.
TR-0516-49416, Non-Loss-of-Coolant Accident Analysis Methodology, Section 7.2.16.1 includes discussion of the flow rates associated with various pump configurations. The flow rates are provided to support the demonstration of the method and the example results provided in Section 7.2.16.3. However, the specific flow rates are design-specific information and are not part of the methodology. Therefore, minor editorial changes are made to Section 7.2.16.1 to clarify that the identified flow rates are examples. Impact on US460 SDAA: FSAR Sections 9.3.4 and 15.4.6, FSAR Table 15.0-7, Technical Specification Bases 3.1.9 and 3.3.1, and Topical Report TR-0516-49416, Non-Loss-of-Coolant Accident Analysis Methodology, have been revised as described in the response above and as shown in the markups provided in this response. Note this response references a proprietary version of the topical report that is marked as containing export controlled information (ECI). However, the extracted pages of the topical report that are attached to this response do not contain ECI as submitted herein. Notwithstanding, any proprietary information included in the response and the attachment hereto shall be withheld per 10 CFR 2.390. NuScale Nonproprietary NuScale Nonproprietary
Boron Dilution Control B 3.1.9 NuScale US460 B 3.1.9-2 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES (continued) The demineralized water isolation valves isolate on actuation signals initiated by the low RCS flow, High Subcritical Multiplication or reactor trip system (RTS). The low RCS Flow actuation signal is designed to ensure boron dilution cannot be performed at low RCS flowrates 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. The High Subcritical Multiplication actuation signal is designed to detect and mitigate inadvertent subcritical boron dilution events in MODES 2 and 3. The RTS actuation initiates a signal to isolate the demineralized water isolation valves to support a reactor trip. The demineralized water isolation valves prevent the designed source of dilution water from contributing to events when these conditions exist. The analysis for an inadvertent boron dilution event assumes that the diluting flow is from the demineralized water source, however the boric acid storage tank and boric acid batch tank also supply flow to the CVCS. Controlling the boron concentration in these supplies ensures that they are not a source of dilution water. Thus the boric acid supply boron concentration is an assumption of the boron dilution accident. Another initial assumption of the inadvertent boron dilution event (Ref. 1) is that the maximum CVCS dilution flow rate is limited. at reduced power levels. The CVCS has two makeup pumps that supply the RCS with makeup water. The lowest maximum acceptable demineralized water flow rate is that provided by one CVCS makeup pump. And theNormally one pump is operated at a time and the other is provided for redundancy. The maximum acceptable demineralized water flow rate varies with core design and boron concentration in the RCS. The initial safety analysis assumption limits maximum flow rate to that provided by a single makeup pump, however a regardless of boron concentration, or that provided by two makeup pumps under certain boron concentration conditions. Analyses may also be performed consistent with approved methodologies listed in TS 5.6.3, "Core Operating Limits Report," to permit adjustments to the maximum demineralized water flow limit as a function of core design and boron concentration in the RCS. Dilution of the reactor coolant system is limited to the maximum increments specified in the COLR which are controlled by establishing dilution time durations based on the maximum CVCS makeup pump demineralized water flow rate.
Boron Dilution Control B 3.1.9 NuScale US460 B 3.1.9-3 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES (continued) CVCS flow between units via the module heating system (MHS)MHS headers could result in unplanned changes to the boration of a unit aligned to the MHS. CVCS demineralized water isolation valves satisfy Criterion 3 of 10 CFR 50.36(c)(2)(ii).The boron concentration in the boric acid supply, the CVCS makeup pump demineralized water flow path flowrate, and isolation of MHS flow paths between units satisfy Criterion 2 of 10 CFR 50.36(c)(2)(ii). LCO The requirement that two demineralized water isolation valves be OPERABLE assuresensures that there will be redundant means available to terminate an inadvertent boron dilution event. The requirement that the boron concentration of the boric acid supply be maintained within the limits specified in the COLR ensures that the supply is not a source to the CVCS that could result in an inadvertent boron dilution event. The limits on maximum CVCS makeup pump demineralized water flow path flowrate are established by restricting the flow that can be provided during system operation to within the limits in the COLR. The restrictions may be implemented by use of at least one closed manual or one closed and de-activated automatic valve, or by removing the power supply from one CVCS makeup pump. The requirement that Module heatup system (MHS) flow paths to and from cross-connected systems are isolated by a locked, sealed, or otherwise secured valve or device prevents CVCS flow between units via the module heating system (MHS) headers that could result in unplanned changes to the boration of a unit aligned to the MHS. APPLICABILITY The requirement that two demineralized water isolation valves be OPERABLE, and that the boric acid storage tank boron concentration and maximum CVCS makeup pump demineralized water flow path flowrate is within the limits specified in the COLR is applicable in MODES 1, 2, and 3 with any dilution source flow path in the CVCS makeup line not isolated. In these MODES, a boron dilution event is considered possible, and the automatic closure of these valves is assumed in the safety analysis
NuScale Final Safety Analysis Report Chemical and Volume Control System NuScale US460 SDAA 9.3-31 Draft Revision 2 Volume Control RAI 10142 Question 15.4.6-1 During normal reactor operation, the CVCS maintains the required volume of coolant in the NPM as indicated by the pressurizer liquid level instrumentation. The pressurizer level is maintained in its operating band by operator permissive action or manual operator action to initiate makeup or letdown to the LRWS. Automatic letdown to LRWS is also provided but a Automatic makeup is not provided to avoid the masking of leaks and automatic letdown is not provided when DWS is unisolated to avoid masking a potential inadvertent boron dilution. If letdown flow is higher than a predetermined setpoint, letdown automatically isolates. Pressurizer Spray The CVCS supplies flow to the pressurizer spray nozzles to decrease pressurizer pressure. If pressurizer pressure rises beyond the normal operating band, the spray valve opens to supply the spray nozzles with subcooled coolant. Pressurizer Venting During normal operations, pressurizer venting using the RPV high point degasification line may be performed periodically if noncondensable gas build-up is significant enough to reduce the effectiveness of pressurizer spray or if required for RCS chemistry control. Pressurizer venting is also used during NPM shutdown to remove noncondensable gases and accelerate hydrogen removal from the RCS. Boron Addition System Normal Operations The BAS performs multiple functions during normal operations including batching, mixture transfer, storage, supply, and tank sampling. Batching An operator uses the PCS to place the batch tank in batch mode, which allows the operator to perform the steps necessary to prepare a batch of borated water. Personnel sample contents of the batch tank to ensure boron concentration is acceptable before release for plant usage. Mixture Transfer and Storage An operator uses the PCS to place the batch tank in transfer mode to transfer borated water from the batch tank to the BAST, or supply it to the BAS supply pumps.
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-52 Draft Revision 2 Audit Question A-15.1.1-3, Audit Question A-15.6.5-1 RAI 10357 Question 15.1.1-7, RAI 10142 Question 15.4.6-1 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%(2) 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 and to detect and mitigate inadvertent boron dilutions. 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 Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-17 Draft Revision 2 RAI 10142 Question 15.4.6-1 The MPS is designed to isolate the demineralized water system (DWS) before the loss of a significant portion of the technical specification minimum shutdown margin. The MPS automatically isolates the DWS on high subcritical multiplication, low RCS flow, and any reactor trip system actuation. The MPS also automatically isolates CVCS on high pressurizer level. The CVCS is disconnected from the RCS during Mode 4 (transition) and Mode 5 (refueling), but the refueling mode is evaluated to make sure that it bounds the effects of other possible dilution sources present during the refueling process. An inadvertent decrease in boron concentration in the RCS is classified as an AOO. 15.4.6.2 Sequence of Events and Systems Operation Audit Question A-15.4.6-1 RAI 10142 Question 15.4.6-1 An inadvertent decrease in boron concentration in the RCS is evaluated for Modes 1, 2, 3, and 5. Boron dilution causes an increase in reactivity, and the NPM response to the event is similar to an uncontrolled CRA withdrawal, presented in Section 15.4.1 and Section 15.4.2. The limiting CVCS dilution source considered in this analysis is the DWS supply. To reduce the overall probability of boron dilution events, administrative controls are placed on the boron addition system supply to the CVCS makeup pumps, assuring that it is not a dilution source for the RCS or the Reactor Building pool. Automatic letdown use is also restricted to ensure a potential inadvertent boron dilution is mitigated by the DWS or CVCS automatic isolation from the increase in pressurizer level as described in Section 9.3.4. Unless specified in this section, the RCS boron dilution evaluation assumes the control systems and engineered safety features perform as designed, with allowances for instrument inaccuracy. No operator action is credited to mitigate the effects of an RCS boron dilution event. RAI 10142 Question 15.4.6-1 The CVCS has two makeup pumps that supply the RCS with makeup coolant and change RCS boron concentration by supplying blended makeup water. Each makeup pump has a maximum capacity of 20 gpm as shown in Table 9.3.4-1. Normally one pump is operated at a time and the other is provided for redundancy. Administrative controls prohibit operation with two pumps early in cycle when critical boron concentrations are high. Table 15.4-12 provides the critical boron concentration below which two pump operation is allowed. The analysis uses a maximum makeup flow rate of 25 gpm. A makeup flow rate of 50 gpm (two pumps) is considered when critical boron concentration is below the limit in Table 15.4-12. To prevent reactor trip on low or high pressurizer level, the CVCS letdown mass flow rate is maintained equal to the makeup flow rate for analysis cases where CVCS isolation or reactor trip and DWS isolation on high pressurizer level is not considered. For some analysis cases, the increase in pressurizer level due to the dilution is considered to determine the conditions
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-18 Draft Revision 2 when CVCS isolation or reactor trip and DWS isolation occurs on high pressurizer level. The regulating CRA bank is not credited with mitigating the reactivity insertion associated with a boron dilution of the RCS. Each of the two regulating bank groups is assumed to be at their respective PDIL so that rods do not insert automatically as a result of the reactivity addition of an RCS boron dilution. Technical specifications preclude the possibility of boron dilution when a CRA is stuck out during Modes 2 and 3 by enforcing shutdown margin requirements. A boron dilution event could occur during refueling operation (Mode 5) if unborated water is unexpectedly introduced to the Reactor Building pool, such as due to internal flooding sources. It is assumed that the flooding source immediately enters the pool and mixes perfectly. Audit Question A-15.4.6-1 A loss of normal power is considered. The loss of alternating current (AC) power during Mode 5 results in the loss of the pool cooling and recirculation system. To accommodate the loss of pool cooling circulation, the initial minimum pool mixing volume assumed in the analysis is further reduced for conservatism. In Mode 1 operation, the loss of power scenarios are non-limiting. During Modes 2 and 3, the reactor is subcritical and there is no power produced by the turbine. Therefore, a loss of AC power due to a possible grid disturbance following a turbine trip is not postulated to occur during Modes 2 and 3. The MPS signals to trip the reactor and isolate the CVCS are credited with protecting the NPM in the event of a boron dilution of the RCS. The DWS supply to the CVCS makeup pumps is isolated by two in-series safety-related isolation valves on the following MPS signals: any reactor trip system actuation high subcritical multiplication low RCS flow RAI 10142 Question 15.4.6-1 The MPS signal to isolate CVCS on high pressurizer level is also credited with protecting the NPM in the event of a boron dilution of the RCS. These MPS signals provide protection in Modes 1 through 3. RAI 10142 Question 15.4.6-1 No single failure could occur during a boron dilution of the RCS that results in a more severe outcome for the limiting cases. The diversity, redundancy, and independence of the MPS and DWS and CVCS isolation valves ensure the NPM is protected from a boron dilution of the RCS despite a single failure.
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-19 Draft Revision 2 15.4.6.3 Boron Mixing, Thermal Hydraulic, and Subchannel Analyses 15.4.6.3.1 Evaluation Models RAI 10142 Question 15.4.6-2 Two calculation techniques are used to analyze the boron dilution event in Modes 1 through 3 that provide conservative boron dilution assumptions for the evaluation of both reactivity insertion and loss of shutdown margin. The first method evaluates the boron dilution by assuming an instantaneous perfect (complete) mixing model. The second method evaluates the boron dilution by assuming a slug flow or dilution front (wave front) mixing model. In the instantaneous perfect mixing model, unborated water injected into the RCS is assumed to mix instantaneously with the effective system volume. The change in core boron concentration with time is continuous and homogeneous, corresponding to the increasing amount of dilution water entering the RCS. In the dilution front model, unborated water injected into the RCS is assumed to mix with a slug of borated water at the injection point. The diluted slug is assumed to move through the RCS (i.e., through the riser, steam generators, downcomer, and finally though the reactor core). The change in core boron concentration with time depends on the location of the diluted slug. Audit Question A-15.4.6-1 RAI 10142 Question 15.4.6-1 The two calculation techniques provide the reactivity insertion rate due to the boron dilution. To ensure that the SRP 15.4.6 acceptance criteria are met, the reactivity insertion rate in Mode 1 operation is compared to the spectrum of reactivity insertion rates evaluated in the uncontrolled CRA withdrawal from a subcritical or low power startup condition and uncontrolled CRA withdrawal at power analyses in Section 15.4.1 and Section 15.4.2, respectively. The reactivity insertion rates are also used as input toSection 15.4.1 and Section 15.4.2 NRELAP5 thermal-hydraulic analyses thatalso provide reactor trip timing to determine when the MPS terminates a reactivity insertion corresponding with the boron dilution event. The NRELAP5 model is based on the design features of the NPM. The non-LOCA NRELAP5 model is discussed in Section 15.0.2. Adequate shutdown margin must remain in the mixing model analyses at the time when the boron dilution event is terminated in the NRELAP5 analyses. For Mode 2 and Mode 3 operation, the boron dilution scenarios are evaluated at the time of CVCS or DWS isolation to ensure that adequate shutdown margin remains at the time of automatic CVCS or DWS isolation. Boron dilution of the pool is estimated using the perfect mixing equation (Equation 15.4-1). RAI 10142 Question 15.4.6-2 In Mode 5, the dilution scenario results in an increase in the Reactor Building pool inventory. The initial boron mass is calculated using the assumed initial pool volume and concentration. The boron concentration at which shutdown margin is lost is determined from the initial shutdown margin and boron worth. The total water volume having the initial boron mass and the boron
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-20 Draft Revision 2 concentration at which shutdown margin is lost is calculated. The assumed initial volume is subtracted from the total water volume to determine the dilution volume that would result in loss of shutdown margin. This dilution volume is then compared to the volumes of possible dilution sources. The boron dilution scenarios in Mode 5 operation are performed with conservative assumptions of water volumes to demonstrate that shutdown margin is maintained. 15.4.6.3.1.1 Boron Dilution Assuming Perfect Mixing The perfect (complete) mixing method evaluates the boron concentration of the RCS with the following equation: Eq. 15.4-1
- where, Qin
= dilution flow rate of unborated water (gpm). The maximum dilution flow rate is used for this parameter based on the ability of the makeup pumps to deliver water to the CVCS injection line. in = dilution water density (lbm/cu.ft). The density value at 14.7 psia, 40 degrees F (minimum temperature value) is used in all cases. The heat addition by the regenerative heat exchangers is not credited, so the analysis assumes that the recirculation pumps are not operational. RAI 10142 Question 15.4.6-1 Vr = effective water volume of the RCS (gal). A conservatively small value is used that removes the volume of the pressurizer. r = density of the water in the RCS (lbm/cu.ft), and C(t) = time dependent concentration of boron in the RCS (ppm). The reactivity insertion rate associated with a given boron dilution rate is calculated with the following equation: Eq. 15.4-2
- where, dR/dt
= reactivity insertion rate (pcm/sec), and dC dt Q inin Vrr
C t( )
= dR dt B dC dt BQinin 60Vrr
C t( )
= =
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-21 Draft Revision 2 B = differential boron worth (pcm/ppm). 15.4.6.3.1.2 Boron Dilution Assuming Dilution Front or Slug Flow Model The dilution front or slug (wave front) model uses the following equation for boron concentration: Eq. 15.4-3 RAI 10142 Question 15.4.6-1 Eq. 15.4-4
- where, C(N)
= the Nth front boron concentration, C0 = initial boron concentration, WD = dilution mass flow rate, RAI 10142 Question 15.4.6-1 WNC = natural circulation mass flow rate, and RAI 10142 Question 15.4.6-1 MRCS = RCS fluid mass minus the pressurizer, RAI 10142 Question 15.4.6-1 MRCSI = initial pass RCS fluid mass (mass between the CVCS injection point to core inlet), and N = number of times the wave front passes through the core. RAI 10142 Question 15.4.6-1 In this model, the boron concentration in the RCS is reduced in discrete steps at each time, t, corresponding to the time the wave front passes through the core. Using these equations, the ratio C0/C(t) is calculated that corresponds to discrete times after dilution begins. The maximum reactivity insertion rate, dR/dt, occurs with the first wave front because initial boron concentration is highest. 15.4.6.3.2 Input Parameters and Initial Conditions The initial conditions and input parameters for the boron dilution of the RCS analysis are selected to ensure a conservative calculation. C N ( ) C0 WNC WD WNC + ( ) N = t MRCSI WD WNC + N 1 ( ) MRCS WD WNC + + =
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-22 Draft Revision 2 The shutdown margin threshold in this analysis for Mode 1 is when keff = 0.995. The shutdown margin threshold for Modes 2 and 3 in this analysis is when keff = 0.93. The shutdown margin threshold in this analysis for Modes 4 and 5 is when keff = 0.90. Therefore, the shutdown margin reactivity credited in this analysis is 503 pcm for Mode 1, 7527 pcm for Modes 2 and 3 and 11,112 pcm for Modes 4 and 5. RAI 10142 Question 15.4.6-1 For Mode 1 operation, the initial power levels considered for a boron dilution of the RCS include: hot zero power (HZP), 25 percent power, 50 percent power, 75 percent power and full (100 percent) power. The BOC and EOC conditions are also considered. The Mode 1 cases of HZP and full power at BOC are provided in this section. RAI 10142 Question 15.4.6-1 For Mode 1 operation, different times in cycle are considered. The cycle is divided in two regions (referred to as BOC and EOC in these analyses) using the boron concentration as identified in Table 15.4-12. RAI 10142 Question 15.4.6-1, RAI 10142 Question 15.4.6-2 Maximum initialcritical boron concentrations and boron coefficients are assumed because the rate of change of concentration and associated reactivity is greater for an initially higher concentration. The initialcritical boron concentrations and boron reactivity coefficients assumed for each mode of operation are provided in Table 15.4-12. For Mode 5, minimum initial pool boron concentration is used to minimize initial boron mass. RAI 10142 Question 15.4.6-1 The makeup flow rates assumed in the analysis are 5 gpm and 25 gpm. A makeup flow rate of 50 gpm is assumed for initialcritical boron concentrations below the limit for two pump operation in Table 15.4-12. The letdown flow rates are assumed to be equal to the makeup flow rates assumed in the analysesis for BOC and at the transition from BOC to EOC. Letdown is disabled in the EOC analyses. A minimum makeup temperature of 40 degrees F is assumed for the analysis of boron dilution of the RCS. The minimum RCS flow rates are assumed to increase loop transit time, which increases the timing for detection and isolation. Audit Question A-15.4.6-1 A conservatively smaller pool volume is used to provide a limiting boron dilution for Mode 5. Allowances for instrument inaccuracy are accounted for in the analytical limits of mitigating systems in accordance with RG 1.105. 15.4.6.3.3 Results RAI 10142 Question 15.4.6-1 The reactivity insertion rate results for a boron dilution of the RCS during Mode 1 operation are presented in Table 15.4-13 for hot full power and Table 15.4-14 for HZP. The tabulated results for the hot full power scenarios demonstrate that the reactivity insertion rates are bounded by the range of the
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-23 Draft Revision 2 reactivity insertion rates that are evaluated in the uncontrolled CRA withdrawal at power analysis, presented in Section 15.4.2. Boron dilution reactivity insertion rates at 25 percent power, 50 percent power, and 75 percent power are the same as for hot full power and so are also bounded. The tabulated results for the HZP scenarios demonstrate that the reactivity insertion rates are bounded by the range of the reactivity insertion rates that are evaluated in the uncontrolled CRA withdrawal from a subcritical or low power startup condition analysis, presented in Section 15.4.1. The tabulated results for the Mode 1 scenarios also demonstrate that shutdown margin is maintained at the time of reactor trip and DWS isolation. RAI 10142 Question A-15.4.6-1 The shutdown margin results for a boron dilution of the RCS during Mode 1 operation are presented in Table 15.4-14 for hot full power. The results show that shutdown margin is maintained at the time of DWS isolation throughout the cycle. The shutdown margin remaining at the time of DWS isolation for the other power scenarios (75 percent, 50 percent, 25 percent, and HZP) is evaluated and confirmed to be bounded by the hot full power results in Table 15.4-14. RAI 10142 Question A-15.4.6-1 The results for a boron dilution of the RCS during Mode 2 operation and Mode 3 operation isare presented in Table 15.4-15 and Table 15.4-16, respectively. The tabulated results for the Mode 2 and Mode 3 scenarios demonstrates that shutdown margin is maintained at the time of CVCSDWS isolation. Results for Mode 2 are not provided because the results of the Mode 3 scenario in Table 15.4-16 is bounding of Mode 2 scenarios. The Mode 3 results are bounding due to the use of a larger dilution volume than is possible in Mode 2 and the more negative boron worth than Mode 2 as indicated in Table 15.4-12. Audit Question A-15.4.6-1 RAI 10142 Question 15.4.6-2 The results for a boron dilution of the RCS during Mode 5 operation are presented in Table 15.4-17 for the limiting case with power unavailable. The total dilution volume necessary to achieve criticality is greater than the largest volume of water that could be unexpectedly introduced to the Reactor Building pool from internal flooding sources. The tabulated results demonstrate that shutdown margin is maintained during Mode 5 operation. Although operator actions are not necessary to ensure shutdown margin is maintained in the limiting case, Table 15.4-17 shows that operator actions prompted by the technical specifications or associated with the Reactor Building flooding evaluation in Section 3.4.1 limit the dilution volume and preserve more shutdown margin. 15.4.6.4 Radiological Consequences The NPM conditions after the limiting decrease in boron concentration cases during Mode 1 operation are bounded by the uncontrolled CRA withdrawal from a subcritical or low power startup condition and uncontrolled CRA withdrawal at
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-46 Draft Revision 2 RAI 10142 Question 15.4.6-1, RAI 10142 Question 15.4.6-2 Table 15.4-12: Bounding InitialCritical Boron Concentrations and Boron Reactivity Coefficients (15.4.6 Inadvertent Decrease in Boron Concentration in the Reactor Coolant System) Operation Mode InitialCritical Boron Concentration1,2,3 (ppm) Boron Reactivity Coefficient (pcm/ppm) Mode 1, 25% power 1600 / 600 -10 Mode 1, hot zero power 1900 / 1000 -10 Mode 2 2200600 -11 Mode 3 2200650 -12.5 Modes 4 and 5 1900 -11.5 Mode 5 1900 -11.5 1Where two values are provided for initialcritical boron concentration, the two values correspond to the evaluation regions referred to in this event as BOC and EOC, respectively. 2Operation with two makeup pumps is prohibited when critical boron concentration is above 600 ppm. 3The values reflect the maximum initial concentration assumed. For Mode 5, the concentration is the minimum pool concentration.
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-47 Draft Revision 2 RAI 10142 Question 15.4.6-1 Table 15.4-13: Mode 1, Comparison of Boron Dilution Reactivity Insertion Rates to Other Reactivity EventsHot Full Power Results, Beginning of Cycle2 (15.4.6 Inadvertent Decrease in Boron Concentration in the Reactor Coolant System) Parameter Value Power level 100, 75, 50, and 25 Percent Power Hot Zero Power Time in cycle BOC EOC BOC EOC Dilution rate (gpm) 5 25 525 2550 502 5 25 5 25 502 Reactivity insertion rate - complete mixing model (pcm/sec) 0.12182 0.60 0.0430. 5908 0.220.4 310 0.45 0.14 0.71 0.07 0.37 0.45 Initial reactivity insertion rate - wave front model (pcm/sec) 3.644 18.15 1.3617. 19 6.8112. 89 13.58 4.26 20.11 2.24 10.58 11.88 Range of reactivity insertion rates assumed in Section 15.4.1 and Section 15.4.2 (pcm/sec)1 0.064 to 24 Time to loss of shutdown margin - complete mixing model (minutes) 70.9 14.1 19.4 Time to reactor trip/DWS isolation actuation signal - complete mixing model (minutes) 20.8 3.9 6.3 Shutdown margin remaining at time of reactor trip/DWS isolation actuation signal - complete mixing model (pcm) 352.5 359.6 330.0 1Reactivity insertion rates from all dilution rates are bounded by the range of reactivity insertion rates assumed in the uncontrolled control rod assembly withdrawal from a subcritical or low power startup condition (Section 15.4.1) and the uncontrolled control rod assembly withdrawal at power condition (Section 15.4.2) are converted from $/sec to pcm/sec conservatively using the Table 4.3-2 maximum eff for the lower end of the range and minimum eff for the upper end of the range to cover both BOC and EOC. 2The dilution flow rate of 50 gpm is associated with low critical boron concentrations associated with EOC (Table 15.4-12)instead of a time in cycle. 3Although this value is less than the minimum of the range of reactivity insertion rates assumed in Section 15.4.2, the Section 15.4.2 analyses show that reactivity insertion rates at the lower end of the range are less limiting than higher reactivity insertion rates. Therefore, this case is also bounded by the Section 15.4.2 results. In the same manner, smaller boron dilution reactivity insertion rates (e.g., due to smaller dilution rates) are bounded by the Section 15.4.1 and Section 15.4.2 results.
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-48 Draft Revision 2 RAI 10142 Question 15.4.6-1 Table 15.4-14: Mode 1, Hot ZeroFull Power Results, Shutdown Margin, Beginning of Cycle2 (15.4.6 Inadvertent Decrease in Boron Concentration in the Reactor Coolant System) Parameter Value Time in cycle BOC BOC to EOC transition EOC Limiting boron dilution reactivity insertion rate for hot full power - complete mixing model (pcm/s)1 0.60 0.45 N/A3 Bounding reactivity insertion rate from Section 15.4.2 hot full power cases (pcm/s)2 1.43 6.46 Signal for reactor trip and DWS isolation High RCS hot temperature High RCS hot temperature High pressurizer level Bounding total reactivity insertion before DWS isolation (pcm) 145 475 456 Dilution rate (gpm) 5 25 50 Initial reactivity step - wave front model (pcm) 234.91 1119.19 667.53 Initial reactivity insertion rate - wave front model (pcm/sec) 3.43 17.15 10.83 Reactivity insertion rate - complete mixing model (pcm/sec) 0.1131 0.5653 0.3076 Duration of the reactivity insertion rate for each wave - wave front model (seconds) 68.5 65.3 61.6 Range of reactivity insertion rates assumed in Section 15.4.1 (pcm/sec)1 0.064 to 24 Time to loss of shutdown margin - wave front model (minutes) 321.0 57.0 112.5 Time to reactor trip/DWS isolation actuation signal - wave front model (minutes) 27.2 25.7 24.4 Shutdown margin remaining at time of reactor trip/DWS isolation actuation signal - wave front model (pcm) 3581889.3 281147.7 1541.3 47 1Reactivity insertion rates from all dilution rates are bounded by the range of reactivity insertion rates assumed in uncontrolled control rod assembly withdrawal from a subcritical or low power startup condition (Section 15.4.1).In the range of reactivity insertion rates possible by boron dilution, the Section 15.4.2 results show that higher reactivity insertion rates are more limiting for total reactivity insertion prior to reactor trip. The reactivity insertion rate value corresponds to the maximum boron dilution rate from Table 15.4-13 for the time in cycle with the complete mixing model. The complete mixing model is applicable for hot full power. 2The dilution flow rate of 50 gpm is associated with low critical boron concentrations instead of a time in cycle.The Section 15.4.2 case is selected as the case with the nearest reactivity insertion rate to the boron dilution reactivity insertion rate, biased in the direction of larger total reactivity insertion. 3The EOC case determines total reactivity insertion associated with the dilution volume causing a high pressurizer level reactor trip and is independent of reactivity insertion rate.
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-49 Draft Revision 2 RAI 10142 Question 15.4.6-1 Table 15.4-15: Not UsedMode 2 Results (15.4.6 Inadvertent Decrease in Boron Concentration in the Reactor Coolant System) Parameter Value Value Dilution rate (gpm) 5 25 Initial wave reactivity step (pcm) 207.37 979.34 Time to loss of shutdown margin (minutes) 1690 334 Time of DWS isolation (minutes) 1592 241 Shutdown margin remaining at DWS isolation (pcm) 245 1351
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-50 Draft Revision 2 RAI 10142 Question 15.4.6-1 Table 15.4-16: Mode 3 Results (15.4.6 Inadvertent Decrease in Boron Concentration in the Reactor Coolant System) Parameter Value Value Dilution rate (gpm)Initial RCS volume (ft3), corresponding to pressurizer level of 42% 22285 25 Initial wave reactivity step (pcm)Pressurizer dilution volume (ft3), corresponding to pressurizer level of 80% 255203.34 966.48 Time to loss of shutdown margin (minutes)Containment dilution volume (ft3) 3411660 336 Time of DWS isolation (minutes)Boron concentration (ppm) at time of CVCS isolation on high pressurizer level 16731562 243 Total reactivity inserted (pcm) 6590 Shutdown margin remaining (pcm) at time of CVCS isolation on high pressurizer levelDWS isolation (pcm) 937231 1275
NuScale Final Safety Analysis Report Reactivity and Power Distribution Anomalies NuScale US460 SDAA 15.4-51 Draft Revision 2 Audit Question A-15.4.6-1 RAI 10142 Question 15.4.6-2 Table 15.4-17: Mode 5 Results, Limiting Power Unavailable Scenario (15.4.6 Inadvertent Decrease in Boron Concentration in the Reactor Coolant System) Parameter Value Assumed initial mixing volume (ft3gallons) 124,412935,282 Total dDilution volume required to reduce shutdown margin to zero (gallons) 366,686967,700 Maximum dilution volume causing violation of pool level technical specification limits (gallons) 117,609 TotalMaximum dilution volume offrom largest internal flooding source1 (gallons) 363,000 Maximum dilution volume from largest assumed internal flooding source2 (gallons) 600,000 1 Internal flooding of the Reactor Building is evaluated as described in Section 3.4.1. 2 The maximum flooding source in this scenario is the combined volume of the firewater storage tanks described in Section 9.5.1.
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 634 RAI 10297 Question NonLOCA.LTR-31, 32, 46, 56, 65 7.2.16 Inadvertent Decrease in Boron Concentration The methodology used to simulate an inadvertent decrease in boron concentration for an NPM, and an evaluation of the acceptance criteria for an AOO listed in Table 7-4, are presented below. 7.2.16.1 General Event Description and Methodology The boric acid blend system incorporated into the NuScale plant design permits the operator to control the boron concentration of the reactor coolant via the charging fluid chemistry. While the NuScale plant design incorporates both automatic and manual controls, strict administrative procedures govern the process for adjusting the boron concentration of the reactor coolant. These administrative procedures establish limits on the rate and duration of the dilution. RAI 10142 Question 15.4.6-1 The primary means of causing an inadvertent decrease in boron concentration is failure of the blend system, either by controller or mechanical failure, or operator error. The event is terminated by isolating the source for the diluted water, i.e., by closing the demineralized water system (DWS) isolation valves or closing the CVCS isolation valves. RAI 10142 Question 15.4.6-2 For Mode 1 plant operating conditions, the perfect mixing model and the wave front model are both evaluated. The perfect mixing model is evaluated for Mode 1 operating conditions because it provides a slower reactivity insertion rate, delaying detection, potentially allowing further loss of shutdown margin. The wave front model is physically conservative because it assumes the maximum amount of reactivity as the diluted slug of water sweeps through the core. This model does not assume any axial blending to ensure that this reactivity insertion rate is Table 7-71 Representative sensitivity studies - control rod misoperation, dropped control rod assembliesNot Used (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 636 the RCS flow rate, therefore the ratio of total reactivity step change and core transport time makes the initial reactivity insertion rate independent of the RCS flow rate. Equation 7-2 Equation 7-3 where: = the Nth front boron concentration, ppm = initial boron concentration, ppm = dilution mass flow rate, lbm/s = natural circulation mass flow rate, lbm/s = RCS fluid mass minus the pressurizer, lbm =initial pass RCS fluid mass (mass between the CVCS injection point to core inlet), lbm = number of times the wave front passes through the core Mode 1 (Operations) HFP to 25 percent RTP RAI 10142 Question 15.4.6-1 In this mode of plant operation, an inadvertent decrease in boron concentration causes a reactivity insertion that increases reactor power, which leads to a rise in coolant temperature, pressurizer level, and RCS pressure. A loss of shutdown margin would occur quickest for theThe highest reactivity insertion rate, i.e., will occur with the maximum dilution flow rate of 50 gpm ((e.g., 50 gpm for 2 CVCS pumps) with unborated water. However, operation with two CVCS pumps is typically limited to certain conditions by administrative controls. For example, two pump operation may only be allowed at certain power levels or when critical boron concentration is below a certain threshold. As a result, the single pump dilution flow rate of(e.g., 25 gpm) is also evaluated. Similarly, the operation of letdown in an automatic mode could prevent detection and mitigation of an inadvertent CN Ci WNC WD WNC + ( ) N = t MRCSI WD WNC + ( ) N 1 ( ) MRCS WD WNC + ( ) + = CN Ci WD WNC MRCS MRCSI N
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 637 dilution event by high pressurizer level. Therefore, automatic letdown is also typically limited to certain conditions by administrative controls. RAI 10142 Question 15.4.6-1 The reactivity insertion rates associated with these configurations are determined using both the perfect mixing model (Equation 7-1) and the wave front model (Equation 7-2 and Equation 7-3). The times of reactor trip and isolation of the dilution source via closure of the DWS isolation valves are obtained from the NRELAP5 results for these reactivity insertion rates. The calculations performed with the perfect mixing model are also used to determine the shutdown margin available after isolation of the DWS, and the time at which the shutdown margin would be lost if the dilution source is not terminated. The system responses for all other acceptance criteria, such as MCHFR and peak RCS pressure, are comparable to the uncontrolled control rod bank withdrawal at power event (Section 7.2.14) by comparison of the reactivity insertion rates. The spectrum of NRELAP5 analyses for the uncontrolled control rod bank withdrawal at power event (Section 7.2.14) can also be used to determine the limiting total reactivity insertion prior to reactor trip and DWS isolation to determine remaining shutdown margin as an alternative to performing NRELAP5 analysis for specific boron dilution reactivity insertion rates to determine shutdown margin. For cases where automatic letdown is disabled and high pressurizer level trip is credited, the shutdown margin remaining at the time of reactor trip and DWS isolation can be determined from the volume change without NRELAP analysis. Mode 1 (Operations) HZP RAI 10142 Question 15.4.6-1 In this mode of plant operation, an inadvertent decrease in boron concentration causes a reactivity insertion that increases reactor power, but does not lead to a rise in coolant temperature, pressurizer level, or RCS pressure. A loss of shutdown margin would occur quickest for the highest reactivity insertion rate, considering the maximum dilution flow rate scenarios discussed above. The reactivity insertion rates associated with these configurations are determined using both the perfect mixing model (Equation 7-1) and the wave front model (Equation 7-2 and Equation 7-3). The time of reactor trip and isolation of the dilution source via closure of DWS isolation valves is obtained from the NRELAP5 results for these reactivity insertion rates. The calculations performed with the wave front model are also used to determine the shutdown margin available after isolation of the DWS, and the time at which the shutdown margin would be lost if the dilution source is not terminated. The system responses for all other acceptance criteria, such as MCHFR and peak RCS pressure, are comparable to the uncontrolled CRA bank withdrawal from subcritical or low power startup conditions event (Section 7.2.13) by comparison of the reactivity insertion rates. The spectrum of NRELAP5 analyses for the uncontrolled control rod bank withdrawal from subcritical or low power startup conditions event (Section 7.2.13) can also be used to determine the limiting total reactivity insertion prior to reactor trip and DWS isolation to determine remaining shutdown margin as an alternative to performing NRELAP5 analysis for specific boron dilution reactivity insertion rates to determine shutdown margin. For cases where automatic letdown is
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 638 disabled and high pressurizer level trip is credited, the shutdown margin remaining at the time of reactor trip and DWS isolation can be determined from the volume change without NRELAP analysis. Mode 2 (Hot Shutdown) and Mode 3 (Safe Shutdown) In these modes of plant operation, the MPS protection logic ensures the DWS is isolated when the RCS flow rate is less than the low flow setpoint (1.7 ft3/s in the example Table 7-3). This protection scheme precludes the possibility for an inadvertent decrease in boron concentration. RAI 10142 Question 15.4.6-1 When the RCS flow rate is greater than or equal to the low flow setpoint (1.7 ft3/s in the example Table 7-3), the reactivity insertion from the maximum dilution flow rate of(e.g., 25 gpm (for 1 CVCS pump) with unborated water causes an increase in reactor power (neutron population). The increase in neutron flux is detected by the MPS count rate protection signal and used to close the DWS isolation valves. The calculations performed with the wave front model (Equation 7-2 and Equation 7-3) determine the shutdown margin available after isolation of the DWS, and the time at which the shutdown margin would be lost if the dilution source is not terminated. For cases where automatic letdown is disabled and high pressurizer level isolation is credited, the shutdown margin remaining at the time of DWS or CVCS isolation can be determined from the volume change. Mode 4 (Transition) In this mode of plant operation, all CVCS connections to an NPM are disconnected, isolated, or locked out. Thus, the possibility of a design-basis inadvertent decrease in boron concentration is precluded. Mode 5 (Refueling) Audit Question A-NonLOCA.LTR-43 RAI 10142 Question 15.4.6-2 In this mode of plant operation, the Technical Specifications require the pool boron concentration to be sufficient to have appropriate shutdown margin. For some NPM designs, the Technical Specifications also require the pool level to be maintained within a narrow range. Surveillance of the boron concentration, and level if applicable, of the refueling pool is performed at appropriate intervals and is expected to prompt operator actions in accordance with Technical Specifications during an inadvertent dilution of the pool; such operator actions are not credited.to prevent significant inadvertent dilution from flow paths to the reactor pool, or proximate water sources such as fire mains or feedwater piping. RAI 10142 Question 15.4.6-2 Two methods can be used for assessing the dilution volume that, if allowed to enter the pool, could cause a loss of shutdown margin in Mode 5. If the pool volume is treated as constant, then the perfect mixing model described above for Mode 1 can be used to calculate the time to dilution for an arbitrary flow rate. The
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 640 7.2.16.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms presented in Table 7-74 are considered in order to identify the bounding conditions for loss of shutdown margin. Audit Question A-NonLOCA.LTR-56 RAI 10142 Question 15.4.6-1 Maximum fuel centerline temperature This criterion is not evaluated because the reactivity insertion rates are insufficient to challenge the temperature limit. 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 (if actuated) 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 7-74 Initial conditions, biases, and conservatisms - inadvertent decrease in boron concentration Parameter Bias / Conservatism Basis Initial reactor power ExcludedVaried. (( }}2(a),(c) Initial RCS average temperature Biased to the high condition. (( }}2(a),(c) Initial RCS flow rate Biased to the low condition. (( }}2(a),(c) Initial PZR pressure Nominal. (( }}2(a),(c) Table 7-73 Acceptance criteria - inadvertent decrease in boron concentration (Continued) Acceptance Criteria Discussion
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 641 Initial PZR level Varied.Excluded. (( }}2(a),(c) Initial feedwater temperature Excluded. Not part of mixing model. Initial fuel temperature Excluded. Not part of mixing model. MTC Excluded. Not part of mixing model. Kinetics Biased to BOC conditions. (( }}2(a),(c) Decay heat Excluded. Not part of mixing model. Initial SG pressure Excluded. Not part of mixing model. SG heat transfer Excluded. Not part of mixing model. RSV lift setpoint Excluded. Not part of mixing model. SG tube plugging Excluded. Does not alter active RCS volume. Shutdown margin Biased to the low condition. (( }}2(a),(c) Initial boron concentration Biased to the high condition (( }}2(a),(c) Boron worth Biased to the high condition. (( }}2(a),(c) Active RCS volume Biased to the low condition. (( }}2(a),(c) Makeup flow rate Biased to the high conditionVaried. (( }}2(a),(c) Makeup temperature Biased to the low condition. (( }}2(a),(c) RCS Temperature Control Automatic rod control Excluded. Not part of mixing model. Boron concentration Not credited. (( }}2(a),(c) Table 7-74 Initial conditions, biases, and conservatisms - inadvertent decrease in boron concentration (Continued) Parameter Bias / Conservatism Basis
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 642 RAI 10297 Question NonLOCA.LTR-31, 32, 46, 56, 65 (( }}2(a),(c) RAI 10297 Question NonLOCA.LTR-31, 32, 46, 56, 65 PZR Pressure Control PZR spray (normal) Excluded. Not part of mixing model. (bypass) Excluded. Not part of mixing model. PZR heaters (non-prop.) Excluded. Not part of mixing model. (prop.) Excluded. Not part of mixing model. PZR Level Control Charging Enabled. (( }}2(a),(c) Letdown Enabled.Varied. (( }}2(a),(c) Steam Pressure Control Turbine throttle valves Excluded. Not part of mixing model. Turbine bypass valves Excluded. Not part of mixing model. Feedwater and Turbine Load Control feedwater pump speed Excluded. Not part of mixing model. CNV Pressure Control CNV evacuation system Excluded. Not part of mixing model. Table 7-75 Representative results - inadvertent decrease in boron concentration in Mode 1 at hot full powerNot Used Mode 1 (HFP) 1 CVCS Pump 2 CVCS Pumps Dilution Flow Rate (gpm) 25 50 Initial boron concentration (ppm) 1400 1400 Final boron concentration (ppm) 1196 1196 Table 7-74 Initial conditions, biases, and conservatisms - inadvertent decrease in boron concentration (Continued) Parameter Bias / Conservatism Basis
MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-31 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)
- 3. Reactor Coolant System Level RCS Level is measured by four (one per separation group) detectors to detect the water level in the RCS vessel. The sensors are located such that they can monitor water level from above the reactor core to the top of the pressurizer.
- a. High Pressurizer Level - Reactor Trip, CVCS Isolation, and Demineralized Water System Isolation (Table 3.3.1-1 Functions 10.a, b, c)
The High Pressurizer Level trip provides protection for system malfunctions that increase the reactor coolant system inventory including inadvertent decrease in boron concentration in the RCS. Four High Pressurizer Level reactor trip channels are required to be OPERABLE when operating in MODE 1 and in MODES 2 and 3 when capable of withdrawing more than a single CRA. In MODES 2 and 3 with no capability of withdrawing more than a single CRA, and in MODES 4 and 5 the reactor will remain subcritical. Four High Pressurizer Level DWSI channels are required to be OPERABLE when operating in MODES 1, 2, and MODE 3 above the RCS temperature T-3 interlock. In MODE 3 below the RCS temperature T-3 interlock actuation the reactor is shutdown. The high subcritical multiplication signal and the low RCS flow signal provide the required protective functions below the RCS T-3 interlock temperature. In MODES 4 and 5 the demineralized water system is isolated from the reactor module. Four High Pressurizer Level CVCSI channels are required to be OPERABLE when operating in MODES 1, 2, and 3. In MODES 4 and 5 the reactor will remain subcritical. Four channels are provided to permit one channel in trip or bypass indefinitely and still ensure no single random failure will disable this trip Function.
- b. Low Pressurizer Level - Reactor Trip, Containment Isolation, Decay Heat Removal System Actuation, Secondary System Isolation, Demineralized Water System Isolation, Chemical and Volume Control System Isolation, and Pressurizer Heater Trip (Table 3.3.1-1 Functions 11.a, b, c, d, e, f, g)
RAIO-179795 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Affidavit of Mark W. Shaver, AF-179796
AF-179796 Page 1 of 2
NuScale Power, LLC AFFIDAVIT of Mark W. Shaver I, Mark W. Shaver, state as follows: (1) I am the Director of Regulatory Affairs of NuScale Power, LLC (NuScale), and as such, I have been specifically delegated the function of reviewing the information described in this Affidavit that NuScale seeks to have withheld from public disclosure, and am authorized to apply for its withholding on behalf of NuScale. (2) I am knowledgeable of the criteria and procedures used by NuScale in designating information as a trade secret, privileged, or as confidential commercial or financial information. This request to withhold information from public disclosure is driven by one or more of the following: (a) The information requested to be withheld reveals distinguishing aspects of a process (or component, structure, tool, method, etc.) whose use by NuScale competitors, without a license from NuScale, would constitute a competitive economic disadvantage to NuScale. (b) The information requested to be withheld consists of supporting data, including test data, relative to a process (or component, structure, tool, method, etc.), and the application of the data secures a competitive economic advantage, as described more fully in paragraph 3 of this Affidavit. (c) Use by a competitor of the information requested to be withheld would reduce the competitors expenditure of resources, or improve its competitive position, in the design, manufacture, shipment, installation, assurance of quality, or licensing of a similar product. (d) The information requested to be withheld reveals cost or price information, production capabilities, budget levels, or commercial strategies of NuScale. (e) The information requested to be withheld consists of patentable ideas. (3) Public disclosure of the information sought to be withheld is likely to cause substantial harm to NuScales competitive position and foreclose or reduce the availability of profit-making opportunities. The accompanying Request for Additional Information response reveals distinguishing aspects about the response by which NuScale develops its NuScale Power, LLC Response to NRC Request for Additional Information (RAI No. 10142 R1, Question 15.4.6-1) on the NuScale Standard Design Approval Application. NuScale has performed significant research and evaluation to develop a basis for this response and has invested significant resources, including the expenditure of a considerable sum of money. The precise financial value of the information is difficult to quantify, but it is a key element of the design basis for a NuScale plant and, therefore, has substantial value to NuScale. If the information were disclosed to the public, NuScales competitors would have access to the information without purchasing the right to use it or having been required to undertake a similar expenditure of resources. Such disclosure would constitute a misappropriation of NuScales intellectual property, and would deprive NuScale of the opportunity to exercise its competitive advantage to seek an adequate return on its investment. (4) The information sought to be withheld is in the enclosed response to NRC Request for Additional Information RAI 10142 R1, Question 15.4.6-1. The enclosure contains the designation Proprietary at the top of each page containing proprietary information. The information considered by NuScale to be proprietary is identified within double braces, (( }} in the document.
AF-179796 Page 2 of 2 (5) The basis for proposing that the information be withheld is that NuScale treats the information as a trade secret, privileged, or as confidential commercial or financial information. NuScale relies upon the exemption from disclosure set forth in the Freedom of Information Act (FOIA), 5 USC § 552(b)(4), as well as exemptions applicable to the NRC under 10 CFR §§ 2.390(a)(4) and 9.17(a)(4). (6) Pursuant to the provisions set forth in 10 CFR § 2.390(b)(4), the following is provided for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld: (a) The information sought to be withheld is owned and has been held in confidence by NuScale. (b) The information is of a sort customarily held in confidence by NuScale and, to the best of my knowledge and belief, consistently has been held in confidence by NuScale. The procedure for approval of external release of such information typically requires review by the staff manager, project manager, chief technology officer or other equivalent authority, or the manager of the cognizant marketing function (or his delegate), for technical content, competitive effect, and determination of the accuracy of the proprietary designation. Disclosures outside NuScale are limited to regulatory bodies, customers and potential customers and their agents, suppliers, licensees, and others with a legitimate need for the information, and then only in accordance with appropriate regulatory provisions or contractual agreements to maintain confidentiality. (c) The information is being transmitted to and received by the NRC in confidence. (d) No public disclosure of the information has been made, and it is not available in public sources. All disclosures to third parties, including any required transmittals to NRC, have been made, or must be made, pursuant to regulatory provisions or contractual agreements that provide for maintenance of the information in confidence. (e) Public disclosure of the information is likely to cause substantial harm to the competitive position of NuScale, taking into account the value of the information to NuScale, the amount of effort and money expended by NuScale in developing the information, and the difficulty others would have in acquiring or duplicating the information. The information sought to be withheld is part of NuScales technology that provides NuScale with a competitive advantage over other firms in the industry. NuScale has invested significant human and financial capital in developing this technology and NuScale believes it would be difficult for others to duplicate the technology without access to the information sought to be withheld. I declare under penalty of perjury that the foregoing is true and correct. Executed on February 25, 2025. Mark W. Shaver}}