ML24346A258
| ML24346A258 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/11/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24346A130 | List:
|
| References | |
| LO-175762 | |
| Download: ML24346A258 (1) | |
Text
Response to SDAA Audit Question Question Number: A-15.0.5-1 (part a)
Receipt Date:
Question:
SDAA Section 15.0.5 is missing details of the design that are used when applying the Extended Passive Cooling (XPC) and Reactivity Control Methodology topical report in the SDA analyses are missing from the SDA. The following information is missing:
a.
The ranges for the amount of boron in the dissolver basket and boron characteristics used in the analyses.
b.
The boron dissolver basket and collector rail size, location, orientation, key dimensions and resistances used in the analyses.
c.
The containment mixing pipes and collector rail size, location, orientation, key dimensions and resistances used in the analyse.
d.
The riser holes size, location, orientation, key dimensions and resistances used in the analyses.
e.
The application of the XPC methodology (Section 5.2.3) regarding the assessment of lower riser hole flow to justify the use of the rates in SDA boron transport analysis.
Response
The original response was posted on April 20, 2023 and updated on June 8, 2023. NuScale voluntarily supplemented the original response and posted the supplemented response on February 26, 2024. The original and supplemented responses below are unchanged. NuScales response to NRC feedback is added after the original and supplemented responses, starting with the section labeled NuScale Response to NRC Feedback. NuScales response to subsequent NRC feedback is added to the end of the response, starting with the section labeled NuScale Response to Additional NRC Feedback.
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Details of the design that are used when applying the Extended Passive Cooling (XPC) and Reactivity Control Methodology topical report in the SDA analyses are as follows.
a.
The ranges for the amount of boron in the dissolver basket and boron characteristics used in the analyses:
1)
((2(a),(c) b. The boron dissolver basket and collector rail size, location, orientation, key dimensions and resistances used in the analyses: 1) (( }}2(a),(c) 3) Resistance information can be found in the boron transport analysis and methodology (EC-132087, Rev. 1, section 3.3.2; ER-103121, Rev. 0), which are provided in the eRR. c. The containment mixing pipes and collector rail size, location, orientation, key dimensions and resistances used in the analyses: 1) (( }}2(a),(c),ECI NuScale Nonproprietary NuScale Nonproprietary
2) (( }}2(a),(c),ECI 8) Dimensions used in the XPC analyses are provide in EC-132087, Rev. 1, which is provided in the eRR. Sizes, locations, orientations, and key dimensions of the ESB system are designed to accomodate these values as shown in drawing ED-130334 Rev. 0, "ECCS Supplemental Boron System Assembly," which is provided in the eRR. 9) Resistance information can be found in the boron transport analysis and methodology (EC-132087, Rev. 1, section 3.3.2; ER-103121, Rev. 0), which are provided in the eRR. d. The riser holes size, location, orientation, key dimensions and resistances used in the analyses: 1) Riser hole sizes, locations, orientations, and key dimensions: NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c),ECI 2) Riser hole flow area and resistances: Description Forward K Reverse K Flow Area (in2) Lower riser holes 2.8 2.8 7.07(a) Upper riser holes 5.75 4.75 12(b) (a) This value represents the total area of all lower riser holes. (b) This value represents the grouped area of the upper riser holes at each elevation. e. The application of the XPC methodology (Section 5.2.3) regarding the assessment of lower riser hole flow to justify the use of the rates in SDA boron transport analysis is provided in EC-128030 Rev. 0, "Lower Riser Hole Recirculation Flow Calculation," which is provided in the eRR. Response Supplement During an audit meeting held on October 16, 2023 covering the ECCS system and ESB) feature, the NRC staff requested additional information be provided in the SDAA regarding ESB boron oxide pellet parameters. NuScale provides the following supplemental information and NuScale Nonproprietary NuScale Nonproprietary
SDAA markups regarding ESB boron oxide pellet parameters used in the boron transport methodology and analyses. (( }}2(a),(c) Inputs for boron oxide pellet parameters used in the boron transport analyses are added to FSAR Section 15.0.5.3.1 and Table 15.0-22 as shown in the attached markup. Corrections to TR-124587 Section 9.0 and Table 4-11 are also provided in the attached markup. NuScale Response to NRC Feedback On May 9, 2024, NuScale received written feedback from the NRC. The following provides NuScales response to the feedback. NRC feedback is in indented, italic text; NuScales response to the feedback is in normal text. a. The amount of boron, molar mass and pellet diameter has been included in the FSAR markups in the response. However, the boron pellet form was included in the response but not provided in the markups. Please include in the markups that the boron oxide NuScale Nonproprietary NuScale Nonproprietary
pellets are equilateral cylinders with respect to the pellet diameter to describe the boron oxide pellet form. FSAR Section 15.0.5.3.1 states that the methodology for calculating boron transport is presented in TR-124587-P, Revision 0, Extended Passive Cooling and Reactivity Control Methodology. Table 3-3 of TR-124587 provides design requirements that must be met in order to apply the extended passive cooling (XPC) evaluation method. The table includes an entry stating the current methodology is limited to dissolution of boron oxide pellets that are equilateral cylinders. Additional confirmation of this design requirement is provided in EQ-145418, Revision 0, ECCS Supplemental Boron Oxide Chemistry Specification (previously provided in the eRR). b. The response provided references to the size of the boron basket and other key dimensions (location, orientation, and resistances). However, FSAR markups for the size of the boron basket and other key dimensions (location, orientation, and resistances) has not been provided. Additionally, the boron basket diameter was provided in the response but was not provided in the FSAR mark ups. The boron basket size and key dimensions are requested to ensure that the design values used in the SDAA FSAR analysis supplies sufficient and adequately distributed liquid for dissolution and are consistent with how the methodology was developed and validated (testing). Provide FSAR markups as originally requested. The ESB dissolver basket dimensions, locations, orientations, and resistances are design values determined as part of the design of the ESB feature of ECCS. The boron transport calculations use (( }}2(a),(c) Boron dissolver basket sizing for the ESB dissolver baskets is documented in ER-121191, Revision 0, ECCS Supplemental Boron Dissolver Sizing Report, which was previously provided in the eRR. The response to audit item A-6.3.2.2.1-1 addresses design parameters of the ESB system in the FSAR, including ESB dissolver basket size. NuScale Nonproprietary NuScale Nonproprietary
The response provided references and some values for the size of the collector rail (including capacity) and other key dimensions. However, FSAR markups for the size of the collector rail (including capacity) and other key dimensions have not been provided. The collector rail size and key dimensions are requested to ensure that the design values used in the SDAA FSAR analysis supplies sufficient and adequately distributed liquid for dissolution and are consistent with how the methodology was developed and an appropriate assumed CNV wall condensate collection area is established. The response has added a FSAR markup that states that The ESB is described in Section 6.3. However, FSAR section 6.3 does not describe how the rail system channel supplies condensate into the boron basket and that one of the channels (auxiliary channel) enters below the basket and is not used for diluting the boron in the basket. It is unclear how the CNV wall condensate collection area relates to the condensate that is directed by the rail to the basket that is used for dissolving the boron (vs directed below the basket). FSAR markups are missing that contain this information. Provide FSAR markups as originally requested. (( }}2(a),(c) Collector rail sizing for the ESB dissolver baskets is documented in ER-121191 and collector rail sizing for the ESB mixing tubes is documented in ER-122608, Revision 1, ECCS Supplemental Boron Mixing Tube Sizing Report, both of which were previously provided in the eRR. The response to audit item A-6.3.2.2.1-1 addresses design parameters of the ESB system in the FSAR, including ESB collector rail capacity. The CNV wall area associated with condensate collector rails is addressed in NuScales response to NRC feedback on audit item A-XPC.LTR-2(b). c. The response provided references and some values for the size of the containment mixing pipes and collector rail (including capacity) and other key dimensions (location, NuScale Nonproprietary NuScale Nonproprietary
orientation, and resistances). However, FSAR markups for the size of the containment mixing pipes and collector rail (including capacity) and other key dimensions (location, orientation, and resistances) have not been provided. The mixing pipe and collector rail size and key dimensions are requested to ensure that the design values used in the SDAA FSAR analysis provides sufficient mixing and are consistent with how the methodology was developed and an appropriate assumed CNV wall condensate collection area is established. Provide FSAR markups for this information as originally requested. The response to NRC feedback item b. above addresses ESB collector rails. Similar to the ESB collector rails, ESB mixing tube sizes and key dimensions are also design values determined as part of the design of the ESB feature of ECCS. The boron transport calculations use (( }}2(a),(c) Mixing tube sizing for the ESB is documented in ER-122608, which was previously provided in the eRR. The response to audit item A-6.3.2.2.1-1 addresses design parameters of the ESB system in the FSAR, including ESB mixing tube sizing. The CNV wall area associated with condensate collector rails is addressed in NuScales response to NRC feedback on audit item A-XPC.LTR-2(b). d. The flow area of the riser holes has been included in the response and the FSAR markup. Riser hole losses and flow area uncertainty (min/max) are included in the response but are not included in the FSAR markups. Please include FSAR markups for the riser hole losses and flow area uncertainty (min/max). The riser hole flow areas and resistances are design values determined as part of the design of the reactor vessel internals. The boron transport calculations use ((
}}2(a),(c)
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The response to audit item A-5.4-9 addresses riser hole design information in system-level sections of the FSAR. e. The response did not provide the requested information. A reference to the requested information was provided in the response but the information is not included in the FSAR markups. FSAR markups are requested to describe the riser hole assessment approach that was used for the SDAA specific analysis (and whether the approach is used for justification of use of rates determined from a different source, such as NRELAP5 calculation results) and provide a summary of the assessment and results. This item is addressed by the calculation EC-128030, Revision 0, Lower Riser Hole Recirculation Flow Calculation, and the FSAR markups that were both provided with the original response to this audit item. The following statement is added to FSAR Section 15.0.5.3.1 with the markups in the original response: Lower riser hole flow rates calculated by NRELAP5 are assessed as described in Reference 15.0-8 [Extended Passive Cooling and Reactivity Control Methodology, TR-124587, Revision 0] and determined to be acceptable for use in the boron transport and precipitation analyses. Section 5.2.3 of TR-124587 describes the approach for assessing lower riser hole flow rates determined from sources such as NRELAP5 calculation results. EC-128030 implements this approach described in the topical report, as stated in the FSAR markup. Therefore, the lower riser hole flow assessment used in the standard design approval application-specific analysis is described in the FSAR. NuScale Response to Additional NRC Feedback On July 25, 2024, NuScale received written feedback from the NRC. The following provides NuScales response to the feedback. NRC feedback is in indented, italicized text; NuScales response to the feedback is in normal text. a) The methodology (XPC TR) does not specify the design information for the SDAA. The boron pellet form for the SDAA was requested to be added to the FSAR to appropriately describe the actual design. Unless the SDAA explicitly states that the methodology provides the design information for the SDAA, the methodology applicability requirement would not be actual design information. Provide FSAR markups that the boron oxide pellets are equilateral cylinders with respect to the pellet diameter to NuScale Nonproprietary NuScale Nonproprietary
describe the boron oxide pellet form or explicitly state that the design information for the boron oxide pellet forms for the SDAA are provided in the XPC topical report. The FSAR markup of Section 15.0.5.3.1 provided with this revised response specifies that the boron oxide pellets are modeled as equilateral cylinders. b) Some of the requested information has been provided. Acceptable responses to audit items 6.3-7 and 6.3-8 are needed to resolve this open item. NuScale recommends closing this part of the audit item and tracking resolution of the design and testing related questions through the audit items tracking those questions. c) Some of the requested information has been provided. Acceptable response to audit item 6.3-7 is needed to resolve this open item. NuScale recommends closing this part of the audit item and tracking resolution of the testing related question through the audit item tracking that question. d) The design values for the riser hole losses and flow area uncertainty (min/max) are included in the response but are not included in the FSAR. Please include FSAR markups for the riser hole losses and flow area uncertainty (min/max). The boron transport analysis shows sensitivity to the riser hole flow area and losses. The base design values for these key parameters are needed in the FSAR to adequately describe the design. As described above in NuScales response to the original NRC feedback on this part of the audit item, the response to audit item A-5.4-9 addresses riser hole design information in system-level sections of the FSAR. NuScale recommends closing this part of the audit item as the design related question was resolved in A-5.4-9. e) Please provide an FSAR markup with a summary of the SDAA specific evaluation results that show the riser hole flow rates used in the SDAA specific analyses are adequate in comparison to the evaluation methodology calculated riser hole flow rates. The FSAR markup provided with this revised response adds a summary of the lower riser hole flow rate assessment in Section 15.0.5.3.1. NuScale Nonproprietary NuScale Nonproprietary
Markups of the affected changes, as described in the supplemental response to audit item A-15.0.5-1, are also provided below as markups of SDAA FSAR Draft Revision 2 and TR-124587-P Draft Revision 1. NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-38 Draft Revision 2 Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 ESB parameters used in the boron transport analysis are selected to provide conservative calculations. These parameters include: high-biased mixing tube minor form losses, and nominal inner surface roughness mixing tube length conservatively modeled longer than actual design length mixing tube inlet elevation conservatively modeled lower than actual design elevation mixing tube outlet elevation conservatively modeled higher than actual design elevation Audit Item A-15.0.5-1 boron oxide pellets conservatively modeled as equilateral cylinders with 3/8 in. diameter, which is larger than the actual design diameter, for cases with slow-biased boron dissolution from the ESB Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 The condensate flow into the ESB dissolvers and containment mixing tubes, which is generated by the effective minimum CNV wall condensation area, is modeled in the boron transport and precipitation analyses as described in Reference 15.0-8. The temperature of the ESB condensate is modeled at the saturation temperature of the CNV vapor pressure. Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 Lower riser hole flow rates calculated by NRELAP5 are assessed as described in Reference 15.0-8 and. The flow rates are determined to be acceptable for use in the boron transport and precipitation analyses because the use of the average riser hole flow from NRELAP5 increases the difference between the calculated core and downcomer boron concentrations during ECCS cooling. This bias is used to demonstrate conservative boron transport analysis results. The parameters used for modeling riser holes in the extended passive cooling analyses include: total lower riser hole flow area of 7.07 sq in. grouped upper riser hole flow area of 12 sq in. at each of the four upper riser hole elevations elevation of riser holes groups are distributed to match the design within constraints of model nodalization forward and reverse losses are considered Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 The result for the limiting cases for the boron transport analysis are given in Table 15.0-18. Results for beginning of cycle (BOC) and middle of cycle (MOC) are also given for the injection line break for comparison. Figures 15.0-5 through Figure 15.0-10 show the boron concentrations and boron masses in the RPV and CNV for the limiting cases. The methodology
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-72 Draft Revision 2 Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 Table 15.0-22: Input Parameters for Emergency Core Cooling System Extended Passive Cooling Analysis - Limiting Boron Cases Parameter Boron Precipitation Boron Transport Single failure one RVV fails to open one RVV fails to open Power availablity AC and DC power available AC and DC power available Decay heat 80% of ORIGEN 80% of ORIGEN Core power 100% RTP 100% RTP Reactor pool level 54 ft 54 ft Reactor pool temp 65°F 65°F Noncondensable gas zero negligible(1) ECCS valve flow capacity biased low biased low Initial boron concentration 1900 ppm 5 ppm ESB dissolution biasing fast fast ESB mass per dissolver 30 kg boron oxide 25 kg boron oxide ESB boron oxide pellet molar mass 69.6 g/mol 69.6 g/mol CNV wall condensate collection area - ESB dissolver 35 sq ft 35 sq ft CNV wall condensate collection area - ESB mixing tube N/A 140 sq ft Notes: (1) A negligible amount of noncondensable gas is included for calculational stability.
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 106 Audit Question A-15.0.5-1 Audit Question A-15.0.5-1 Table 4-9 Boron Oxide Dissolution Test Data Summary (( }}2(a),(b),(c),ECI Table 4-10 Pellet Batch Weight Summary Table (( }}2(a),(b),(c),ECI Table 4-11 Pellet Batch Dimension Summary Table (( }}2(a),(b),(c),ECI
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 294 representative results demonstrate that the collapsed liquid level remains above the TAF, showing the DHRS and ECCS provide adequate core cooling for an extended period. In addition, boron precipitation is evaluated and representative results show boron precipitation does not occur for the conditions evaluated for extended passive cooling, thereby demonstrating the core remains in a coolable geometry. Potential criticality during cooldown was evaluated and representative results indicate acceptable reactivity margin is available for design basis cooldown scenarios. The XPC EM is applicable to NPM plant designs if the following criteria are met:
- 1. The plant design is as described generally in Section 3.2.
- 2. The plant design has the specific features or requirements identified in Table 3-3.
- 3. The conclusions of supporting evaluations identified in Section 3.2.3 are met.
- 4. The range of conditions for extended ECCS cooling are within the range identified in Table 4-11.
- 5. The range of conditions for extended DHRS cooling are within the ranges identified in Table 4-8 and Table 4-9.
- 6. Any changes to the LOCA EM or non-LOCA EM applicability ranges identified in Table 4-11, Table 4-8, or Table 4-9 are identified for impact on the XPC EM.
Audit Question A-15.0.5-1
- 7. Boron oxide pellet diameter is less than or equal to 0.25 in, or applicability of the slow-biased boron dissolution method is specifically justified and approved.
After application of the methodology is approved for a plant design, cycle-specific evaluations are required to confirm the analysis of record remains applicable. Comprehensive identification of required cycle-specific evaluations is outside scope of this report.}}