ML25087A256
| ML25087A256 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 03/28/2025 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25087A254 | List: |
| References | |
| LO-180781 | |
| Download: ML25087A256 (1) | |
Text
Response to SDAA Audit Question Question Number: Containment Response Analysis Updated Results Clarification Receipt Date: 03/18/2025 Question:
Provide a summary of key basemodel differences that result in updated peak containment pressure and peak containment temperature.
Response
The containment response analysis results are updated in FSAR Section 6.2. As previously discussed, the updated results reflect EC-A013-7725, Revision 2, whereas the results previously reflected EC-A013-7725, Revision 0. The updated results reflect the updated NPM-20 NRELAP5 basemodel (Revision 5) and NRELAP version 1.7. The previous results (Revision
- 0) reflected a previous version of the basemodel and NRELAP version 1.6. The updated results (Revision 2) align with the proposed limitation and condition for the Loss-of-Coolant Accident Evaluation Model topical report, TR-0516-49422, to use basemodel Revision 5 and NRELAP version 1.7.
For each of the limiting sensitivity cases, peak containment pressure (PCP) and peak containment temperature (PCT) have decreased from the previous results. For the peak containment pressure case, peak pressure has decreased from approximately 937 psia to approximately 919 psia. The changed results are due to basemodel updates, break model input changes, and the code version changes. This response clarifies the changes that have a significant impact on the changed results (i.e., mass and energy release (M&E), lower peak containment pressure and peak containment temperature results.
The significant basemodel changes that effect containment response analysis (e.g., M&E, PCP, and PCT) are summarized below:
NuScale Nonproprietary NuScale Nonproprietary
1.
Heat transfer:
a.
((2(a),(c) b. (( }}2(a),(c) 2. Mass and energy release: a. (( }}2(a),(c) b. (( }}2(a),(c) Updates 1.a and 1.b result in additional heat transfer to the ultimate heat sink. Notwithstanding, the methodology is still consistent with TR-0516-49422, the initial conditions described in FSAR Table 6.2-2, and application of a DHRS heat transfer penalty as previously described. ((
}}2(a),(c)
Timing in the event sequence has a significant impact on PCP and PCT. In the PCP case, ((
}}2(a),(c) results in earlier emergency core cooling system actuation, as shown in FSAR Table 6.2-7 (133 versus 147 seconds). Coupled with (( }}2(a),(c), the event sequence results in EC-A013-7725, Revision 2 indicate a decreased peak containment pressure and peak containment temperature, compared to the results in EC-A013-7725, Revision 0.
The previous FSAR Section 6.2 containment response analysis results and the updated FSAR Section 6.2 results demonstrate ample margin to the Design-Specific Review Standard criterion of 10 percent margin between peak containment pressure and containment design pressure. Additional discussion of the NPM-20 NRELAP5 basemodel (including changes) is available in request for additional information (RAI) LOCA.LTR-51, 52, 54. NuScale Nonproprietary NuScale Nonproprietary
Supplemental Response Addressing Initial CNV Wall Temperatures The NRC staff observed that EC-A013-7725, Revision 2 includes reduced initial CNV wall temperatures for the cases documented in CP-4170. The staff requests NuScale to revise the summary to explain the reduced initial wall temperatures. Revision 0: ((
}}2(a),(c)
Revision 2: ((
}}2(a),(c)
Figure 1 provides a comparison of initial wall temperatures at respective CNV elevations at event initiation for the limiting peak containment pressure case between EC-A013-7725, Revision 0 (DL-2_Rev0) and EC-A013-7725, Revision 2 (DL-2). NuScale Nonproprietary NuScale Nonproprietary
Figure 1, Comparison of Initial CNV Wall Temperatures (( }}2(a),(c) Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-56 Draft Revision 2 Table 6.2-3: Containment Response Analysis Results Event Description Case Description CNV Pressure (psia) CNV Wall Temperature (°F) RCS Discharge Line Break Base Case 905910 531 RCS Discharge Line Break Limiting Sensitivity Case Results 9199371 5325332 RCS Injection Line Break Base Case 861890 529524 RCS Injection Line Break Limiting Sensitivity Case Results 884909 527531 RPV High Point Vent Degasification Line Break Base Case 786807 515517 RPV High Point Vent Degasification Line Break Limiting Sensitivity Case Results 872877 524525 Inadvertent RVV Actuation Base Case 832822 520519 Inadvertent RVV Actuation Limiting Sensitivity Case Results 871876 524525 Inadvertent RRV Actuation Base Case 883906 527530 Inadvertent RRV Actuation Limiting Sensitivity Case Results 904925 5295332 Inadvertent ECCS Actuation Base Case 867852 524522 Inadvertent ECCS Actuation Limiting Sensitivity Case Results 882889 525527 MSLB Limiting Results 888900 526530 FWLB Limiting Results 874886 524526 1 Limiting NPM primary/secondary release event peak pressure. 2 Limiting NPM primary/secondary release event peak temperature.
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-73 Draft Revision 2 Table 6.2-7: Sequence of Events - Peak Containment Vessel Pressure and Temperature Case Event Time (s) Transient initiated by a RCS discharge line break into the CNV 0 High CNV pressure signal is reached 0.57 Reactor trip DHRS actuation and CNV isolation 2.57 Low RCS level signal is reached 7387 ECCS valve opening 133147 Peak CNV wall temperature is reached (532 °Ffor peak pressure case) 1608 Peak CNV internal pressure is reached (919937 psia) 15670 CNV pressure drops to less than 50% of peak pressure Approximately 3000200
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-77 Draft Revision 2 Audit Question A-6.2-1 Table 6.2-9: Peak Containment Pressure and Temperature Transient Total Mass and Energy Release Rates Time (s) Total Mass Flow Rate (lbm/s) Total Energy Release (BTU/s) 0 0 0 0.01 468.3 217990 0.02 482.3 222964 0.03 494.4 228374 0.04 488.9 226098 0.05 481.2 222681 0.1 476.3 220477 0.5 453.3 210139 1 435.1 201968 1.5 416.2 194140 2 410.3 190915 3 408.0 190139 4 405.0 190135 5 400.0 189769 6 394.9 189231 7 389.6 188413 8 384.7 187526 9 379.9 186476 10 375.3 185452 20 322.3 170820 30 267.4 150580 40 243.4 139783 50 235.5 135123 60 226.0 130024 64 218.7 126577 70 207.7 121334 80 197.2 115806 90 192.6 113019 100 187.1 109834 120 181.6 106041 122 181.4 105814 124 180.8 105433 126 180.4 105088 128 180.1 104862 130 179.7 104535 132 179.2 104219 134 697.8 615249 136 642.7 569068
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-78 Draft Revision 2 138 583.3 522143 140 551.8 494953 142 523.9 474712 144 625.8 476693 146 626.9 456176 148 498.5 424613 150 372.0 294806 152 206.9 170402 154 163.3 115559 156 242.4 146751 158 273.4 160573 160 277.7 160139 162 265.8 152361 164 260.9 148872 166 255.4 144793 168 250.2 141845 170 248.0 140108 172 240.1 134921 174 236.7 132706 176 233.5 130881 178 228.3 127533 180 226.2 126336 190 186.2 105311 200 137.6 80102 202 130.9 76457 204 125.5 73633 206 120.1 70761 208 116.2 68748 210 111.9 66415 212 108.3 64505 214 105.6 63112 216 102.2 61252 218 100.0 60051 220 97.8 58945 222 95.0 57262 224 93.5 56410 226 91.2 55080 228 89.7 54285 230 88.3 53476 Table 6.2-9: Peak Containment Pressure and Temperature Transient Total Mass and Energy Release Rates (Continued) Time (s) Total Mass Flow Rate (lbm/s) Total Energy Release (BTU/s)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-79 Draft Revision 2 232 86.4 52390 234 86.1 52423 236 83.8 50910 238 83.0 50555 240 82.0 49941 242 80.4 48933 244 80.0 48799 246 78.3 47716 248 77.3 47166 250 76.8 46956 300 62.6 38273 330 57.3 35041 350 53.8 32886 400 45.3 27792 450 37.3 23645 500 30.4 19988 550 25.1 17132 600 20.5 14711 650 15.6 12205 700 8.7 8687 730 2.9 5848 750 1.9 5358 800 0.6 4686 850 -0.1 4301 900 -0.1 4275 950 -0.1 4271 1000 -0.3 4163 1500 -1.1 3498 2000 -0.7 3458 2500 -0.1 3596 3000 -0.5 3184 3053.25 0.0 3442 0 0.0 0 0.01 376.1 175886 0.05 366.7 170311 0.1 357.8 166461 0.5 338.5 157780 1 324.4 151852 1.5 303.6 143133 2 297.4 140613 Table 6.2-9: Peak Containment Pressure and Temperature Transient Total Mass and Energy Release Rates (Continued) Time (s) Total Mass Flow Rate (lbm/s) Total Energy Release (BTU/s)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-80 Draft Revision 2 3 294.0 139833 4 292.7 140710 5 291.2 141192 6 290.3 141593 7 289.2 141697 8 288.0 141680 9 286.7 141606 10 285.3 141496 20 270.2 142243 30 253.6 143092 40 241.9 139004 50 233.3 134040 60 227.3 130032 64 225.4 129737 70 214.0 124410 80 193.1 113455 90 179.0 105707 100 172.0 101479 120 165.8 97109 140 164.4 95628 142 164.2 95414 144 163.9 95185 146 163.6 94929 148 668.3 595761 150 609.3 548483 152 525.9 489975 154 487.8 463585 156 478.6 456964 158 540.3 418976 160 583.0 454524 162 606.2 449793 164 355.6 298316 166 224.1 194508 168 135.7 117110 170 51.8 54503 172 43.6 45258 174 41.2 42070 176 38.1 38087 178 36.0 35598 180 33.9 33300 190 31.9 28791 200 37.6 31004 250 44.4 32003 300 47.3 31641 330 50.7 32522 Table 6.2-9: Peak Containment Pressure and Temperature Transient Total Mass and Energy Release Rates (Continued) Time (s) Total Mass Flow Rate (lbm/s) Total Energy Release (BTU/s)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-81 Draft Revision 2 350 47.5 30425 400 41.5 26523 450 34.2 22263 500 28.9 19333 550 25.3 17288 600 21.2 15089 650 16.9 12807 700 12.1 10288 730 8.4 8434 750 3.6 6090 800 1.2 4866 850 0.3 4392 900 -0.1 4162 950 -0.3 4052 1000 -0.5 3931 1500 -0.6 3635 2000 -0.5 3434 2500 -0.5 3228 3000 -0.4 3118 3194 -0.4 3063 Table 6.2-9: Peak Containment Pressure and Temperature Transient Total Mass and Energy Release Rates (Continued) Time (s) Total Mass Flow Rate (lbm/s) Total Energy Release (BTU/s)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-90 Draft Revision 2 Audit Question A-6.2-3 Figure 6.2-7: Maximum Containment Internal Pressure - Peak Containment Vessel Pressure Case 0 100 200 300 400 500 600 700 800 900 1000 0 5 10 15 20 Max CNV Internal Pressure (psia) Time (hr)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-91 Draft Revision 2 Figure 6.2-8: Integrated Break and Emergency Core Cooling System Mass Release Rate - Peak Containment Vessel Pressure Case 0 10000 20000 30000 40000 50000 60000 70000 0 200 400 600 800 1000 1200 1400 Integrated Break and ECCS Mass Release Rate (lbm) Time (sec)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-92 Draft Revision 2 Figure 6.2-9: Integrated Break and Emergency Core Cooling System Energy Release Rate - Peak Containment Vessel Pressure Case 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 0 200 400 600 800 1000 1200 1400 Integrated Break and ECCS Energy Release Rate (MJ) Time (sec)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-93 Draft Revision 2 Figure 6.2-10: Maximum Containment Wall Temperature - Peak Containment Vessel Temperature Case 500 505 510 515 520 525 530 535 540 0 200 400 600 800 1000 1200 1400 Max CNV Wall Temperature (°F) Time (sec)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-94 Draft Revision 2 Figure 6.2-11: Integrated Break and Emergency Core Cooling System Mass Release Rate - Peak Containment Vessel Temperature Case 0 10000 20000 30000 40000 50000 60000 70000 0 200 400 600 800 1000 1200 1400 Integrated Break and ECCS Mass Release Rate (lbm) Time (sec)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-95 Draft Revision 2 Figure 6.2-12: Integrated Break and Emergency Core Cooling System Energy Release Rate - Peak Containment Vessel Temperature Case 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 0 200 400 600 800 1000 1200 1400 Integrated Break and ECCS Energy Release Rate (MJ) Time (sec)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-96 Draft Revision 2 Audit Question A-6.2-1 Figure 6.2-13: Break and ECCS Mass Release Rate - Peak Containment Pressure and Temperature Case 0 100 200 300 400 500 600 700 0 200 400 600 800 1000 1200 1400 Break and ECCS Energy Release Rate (MW) Time (sec)
NuScale Final Safety Analysis Report Containment Systems NuScale US460 SDAA 6.2-97 Draft Revision 2 Audit Question A-6.2-1 Figure 6.2-14: Break and ECCS Energy Release Rate - Peak Containment Pressure and Temperature Case -100 0 100 200 300 400 500 600 700 0 200 400 600 800 1000 1200 1400 Break and ECCS Mass Release Rate (lbm/s) Time (sec)}}