ML21288A528
| ML21288A528 | |
| Person / Time | |
|---|---|
| Site: | 07201032 |
| Issue date: | 10/15/2021 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML21288A521 | List: |
| References | |
| 5018091, CAC 001028, CoC No. 1032, EPID L2021-LLA-0053 HI-2114830 | |
| Download: ML21288A528 (20) | |
Text
To achieve compliance with the above criteria, certain design and operational changes are necessary, as summarized below.
- i. The peak fuel cladding temperature limit (PCT) for long term storage operations and short term operations is generally set at 400ºC (752ºF). However, for MPCs containing all moderate burnup fuel, the fuel cladding temperature limit for short-term operations is set at 570ºC (1058ºF) because the nominal fuel cladding stress is shown to be less than 90 MPa [2.0.2]. Appropriate analyses have been performed as discussed in Chapter 4 and operating restrictions have been added to ensure these limits are met.
ii. A method of drying, such as forced helium dehydration (FHD) is used if the above temperature limits for short-term operations cannot be met.
iii. The off-normal and accident condition PCT limit remains unchanged at 570 ºC (1058ºF).
The MPC cavity is dried, either with FHD or vacuum drying (continuous or cyclic), and then it is backfilled with high purity helium to promote heat transfer and prevent cladding degradation.
The normal condition design temperatures for the stainless steel components in the MPC are provided in Table 2.2.3.
The MPC-37 and MPC-89 models allow for regionalized storage where the basket is segregated into three regions as shown in Figures 1.2.1a and 1.2.2. Decay heat limits for regionalized loading are presented in Tables 1.2.3a and 1.2.4 for MPC-37 and MPC-89, respectively. MPC-37P follows a storage pattern shown in Figure 1.2.9, while MPC-44 is uniformly loaded as specified in Table 1.2.3.e. Specific requirements, such as approved locations for DFCs, DFIs, and non-fuel hardware are given in Section 2.1.
As an alternative to the regionalized storage patterns, The MPC-37 and MPC-89 models allow for the use of the heat load charts shown in Figures 1.2.3 through 1.2.5 (MPC-37) and 1.2.6 through 1.2.7 (MPC-89).
Shielding The dose limits for an ISFSI using the HI-STORM FW System are delineated in 10CFR72.104 and 72.106. Compliance with these regulations for any particular array of casks at an ISFSI is necessarily site-specific and must be demonstrated by the licensee. Dose for a single cask and a representative cask array is illustrated in Chapter 5.
The MPC provides axial shielding at the top and bottom ends to maintain occupational exposures ALARA during canister closure and handling operations. The HI-TRAC VW bottom lid also contains shielding. The occupational doses are controlled in accordance with plant-specific procedures and ALARA requirements (discussed in Chapter 9).
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 10 2-3
Table 2.1.3 (continued)
BWR FUEL ASSEMBLY CHARACTERISTICS (Notes 1, 17)
Fuel Assembly Array 8x8F 8x8G 9x9 A 9x9 B 9x9 C 9x9 D and Class Maximum Planar-Average Initial < 4.5
< 4.8 < 4.8 < 4.8 < 4.8 < 4.8 Enrichment (wt.% 235U) (Note 12)
(Note 14)
No. of Fuel Rod 74/66 64 60 72 80 79 Locations (Note 16) (Note 4)
Fuel Clad O.D. (in.) > 0.4576 > 0.5015 > 0.4400 > 0.4330 > 0.4230 > 0.4240 Fuel Clad I.D. (in.) < 0.3996 < 0.4295 < 0.3840 < 0.3810 < 0.3640 < 0.3640 Fuel Pellet Dia. (in.) < 0.3913 < 0.4195 < 0.3760 < 0.3740 < 0.3565 < 0.3565 Fuel Rod Pitch (in.) < 0.609 < 0.642 < 0.566 < 0.572 < 0.572 < 0.572 Design Active Fuel
< 150 < 150 < 150 < 150 < 150 < 150 Length (in.)
No. of Water Rods N/A 4 2 1 1 2 (Note 10) (Note 2) (Note 15) (Note 5)
Water Rod Thickness
> 0.025315 N/A > 0.00 > 0.00 > 0.020 > 0.0300 (in.)
Channel Thickness (in.) < 0.055 < 0.120 < 0.120 < 0.120 < 0.100 < 0.100 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 10 2-47
Table 2.1.3 (continued)
BWR FUEL ASSEMBLY CHARACTERISTICS (Notes 1, 17)
Fuel Assembly Array and Class 10x10 C 10x10 F 10x10 G 10x10 I 10x10 J 11x11 A Maximum Planar-Average Initial
< 4.7 < 4.6 Enrichment (wt.% 235U) < 4.8 < 4.8 < 4.8 < 4.8 (Note 13) (Note 12)
(Note 14)
No. of Fuel Rod Locations (Note 16) 92/78 91/79 96/80 112/92 96 96/84 (Note 7) (Note 18) (Note 19) (Note 20)
Fuel Clad O.D. (in.) > 0.3780 > 0.4035 > 0.387 > 0.4047 > 0.3999 > 0.3701 Fuel Clad I.D. (in.) < 0.3294 < 0.3570 < 0.340 < 0.3559 < 0.3603 < 0.3252 Fuel Pellet Dia. (in.) < 0.3224 < 0.3500 < 0.334 < 0.3492 < 0.3501 < 0.3193 Fuel Rod Pitch (in.) < 0.4705
< 0.488 < 0.510 < 0.512 < 0.5100 < 0.5149 (Note 21)
Design Active Fuel Length (in.) < 150 < 150 < 150 < 150 < 150 < 150 No. of Water Rods 5 5 1 1 2 1 (Note 10) (Note 9) (Note 9) (Note 5) (Note 5)
Water Rod Thickness (in.) >
> 0.031 > 0.030 > 0.031 > 0.0315 > 0.0297 0.032040 Channel Thickness (in.) < 0.055 < 0.120 < 0.060 < 0.100 < 0.0938 < 0.100 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 10 2-49
- 16. Any number of fuel rods in an assembly can be replaced by irradiated or unirradiated Steel or Zirconia rods. If the rods are irradiated, the site specific dose and dose rate analyses performed under 10 CFR 72.212 should include considerations for the presence of such rods.
- 17. Any number of fuel rods in an assembly can contain BLEU fuel. If the BLEU fuel rods are present, the site specific dose and dose rate analyses performed under 10 CFR 72.212 should include consideration for the presence of such rods.
- 18. Contains in total 91 fuel rods; 79 full length rods, 12 long partial length rods, and one square water rod replacing 9 fuel rods.
- 19. Contains in total 96 fuel rods; 80 full length rods, 8 long partial length rods, 8 short partial length rods and one water rod replacing 4 or 12 fuel rods.
- 20. Contains in total 112 fuel rods; 92 full length rods, 8 long partial length rods, 12 short partial length rods, and one square water rod replacing 9 fuel rods.
- 21. This is the maximum fixed rod pitch. The assembly may have areas of variable pitch that exceed this value and remains acceptable for storage.
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 10 2-51
Table 4.4.2 RESULTS OF SCREENING CALCULATIONS UNDER NORMAL STORAGE CONDITIONS Storage Scenario Peak Cladding Temperature, oC (oF)
MPC-37 Note 2
- regionalized storage Table 1.2.3a Minimum Height1 353 (667)
Reference Height 342 (648) 316 (601)
Maximum Height MPC-37 (Note 4)
- heat load Figure 1.2.3a 371 (700)
- heat load Figure 1.2.4a 368 (694)
- heat load Figure 1.2.5a 367 (693)
- heat load Figure 1.2.3bNotes 5,6,7 364 (687)
MPC-89 Note 2
- regionalized storage Table 1.2.4a 333 (631)
MPC-89 (Note 4)
- heat load Figure 1.2.6a 366 (691)
- heat load Figure 1.2.6bNote 5, 7 360 (680)
- heat load Figure 1.2.7a 365 (689)
- heat load Figure 1.2.7bNote 5, 7 358 (676)
MPC-37P heat load pattern in Table 1.2.3c 373 (703)
MPC-44, Uniform Heat Load 368 (694)
Notes:
(1) The highest temperature highlighted above is reached under the case of minimum height MPC-37 designed to store the short height Ft. Calhoun 14x14 fuel. This scenario is adopted in Chapter 4 for the licensing basis evaluation of fuel storage in the HI-STORM FW system. See Note 4 (2) All the screening calculations for MPC-37 and MPC-89 were performed using a reference coarse mesh
[4.1.9] and flow resistance based on the calculations in Holtec report [4.4.2].
(3) Not Used.
(4) Screening evaluation used the same mesh as licensing basis mesh adopted in Section 4.4.1.6. The computed temperatures are bounded by the licensing basis minimum height temperatures tabulated in Table 4.4.3.
(5) PCT of intact fuel assemblies in the loading patterns with fuel debris in the DFCs is bounded by that with damaged fuel in the DFCs as justified next. It is conservatively assumed that the damaged fuel assemblies inside DFCs/DFIs have the same axial heat distribution as the intact fuel assemblies to maximize the PCT of intact fuel assemblies. Fuel debris consistent with its physical condition is modeled as packed towards bottom of the DFCs. This yields less impact on the PCT of intact fuel assemblies.
(6) The computed temperature under short length Damaged Fuel Storage is bounded by undamaged fuel temperatures computed above in heat load Figure 1.2.3a. This reasonably supports the conclusion that Damaged Fuel Storage under standard and long fuel storage in Figures 1.2.4b/c, 1.2.5b/c is bounded by undamaged fuel heat load scenarios evaluated in Figure 1.2.4a and 1.2.5a above.
1 Bounding scenario adopted in this Chapter for all thermal evaluations.
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-48
Table 4.4.5 (continued)
SUMMARY
OF MPC INTERNAL PRESSURES UNDER LONG-TERM STORAGE*
Condition MPC-32ML MPC-44 MPC-37P (psig) (psig) (psig)
Initial maximum backfill** (at 45.5 44.0 47.0 70F)
Normal:
intact rods 91.8 91.8 96.4 1% rods rupture 91.1 92.9 97.2 Off-Normal (10% rods rupture) 98.7 102.3 104.5 Accident 167.5 183.6193.4 177.5 (100% rods rupture)
- Per NUREG-1536, pressure analyses with ruptured fuel rods (including BPRA rods for PWR fuel) is performed with release of 100% of the ruptured fuel rod fill gas and 30% of the significant radioactive gaseous fission products.
- Conservatively assumed at the Tech. Spec. maximum value (see Table 4.4.8).
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-52
4.5.7 HI-DRIP The design function of HI-DRIP is to protect the water in the MPC contained in the transfer cask from boiling during the interval after it has been lifted out of the fuel pool and is subject to surface decontamination, lid welding, and related operations which precede the evacuation of water from the MPC followed by drying. As such, HI-DRIP is essentially a device to prevent boiling of the MPC water during the period it is full of water due to the decay heat produced by the MPC contents extending its time-to-boil (TTB) indefinitely. The HI-DRIP is system has been approved for use with HI-STORM 100 system The HI-DRIP is system has been approved for use with HI-STORM 100 system [AM2][$][4.1.8].
[
PROPRIETARY INFORMATION WITHHELD PER 10 CFR 2.390
]The operations needed to package the fuel in an MPC (hereafter called MPC packaging operations) can be divided into three intervals; namely, (1) When the MPC is full of water and in the pool, (2) When the MPC, full of water, is out of the pool in an ambient environment, and (3) The bulk water from the MPC is pumped out and its contents are dried by the FGD eliminating the risk of uncontrolled pressure rise from rising water vapor pressure even if the MPC were to be sealed shut. Interval 1 is not of concern because submergence in the pools large inventory of water (typically maintained at below 120oF through the fuel pool cooling system) precluded the potential of boiling. Interval 3 is likewise immune to boiling because in this interval, water has been removed from the system. Interval 2, however, is vulnerable to uncontrolled boiling of water because the heat rejection rate to the ambient air is quite low. If the canisters heat generation rate, Q, is sufficiently high (typically over 20kW) then the heat dissipation rate from the cask to the ambient environment cannot keep pace with the decay heat generation rate causing the canister to heat up monotonically, eventually leading its contained water to reach the boiling point. Boiling of water in the canister should be avoided to prevent excessive water vapor in the vicinity of the lid-to-shell weld puddle (which may degrade the weld quality) and to prevent uncontrolled loss of shielding water. Because the MPC internal space is vented to the environment throughout the duration of Interval 2, there is no risk of vapor over-pressure. It serves a valuable ALARA function by eliminating TTB limitations and the associated human activities that accrete dose to the crew.
HI-DRIP consists of a ring that girdles the transfer cask around its main cylindrical body. The ring is equipped with small spray nozzles uniformly spaced around its circumference such that the entire circumference of the transfer cask shell can be drenched by the spray from them. The ring is connected to the plants water supply with a gate valve serving to regulate the flow of water to the ring. The amount of water sprayed should be set such that the entire surface of the cask is wetted by gravity. As discussed below, as long as the external surface of the transfer cask HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-91
remains wet, the water in the canister will remain below boiling. It is noted that the operation of HI-DRIP does not require any pump or electric power; the motive pressure is provided entirely by the plant's water supply system. (In PWR pools, draining un-borated water into the pool would reduce its boric acid concentration. This fact must be considered in setting up HI-DRIP if the pool is used as the recipient of the drain).
The difference between the MPC water and the surface temperature of a HI-TRAC class of transfer casks containing MPC and its annulus filled with water arrayed vertically in an ambient environment can be obtained by simply calculating the total thermal resistance between the HI-TRAC surface and MPC water. However, a more detailed CFD analysis was performed and found to have this temperature difference less than 45oF less than the temperature of the boiling water (i.e., 212oF). It can be readily deduced by intuitive reasoning that at a lower MPC water temperature, the difference will be smaller. Thus, the temperature of the HI-TRAC surface (say, approximately at its mid-height) will be greater than 165oF when the MPC water is boiling. A scoping calculation to illustrate that HI-DRIP will not permit the MPC water to boil is provided below for a typical application:
Assuming that the cask surface temp is 165oF, the ambient air is at 110oF, the heat rejection rate from the shortest and smallest HI-TRAC i.e. 7.5 feet dia by 14 feet high cask surface wetted by water, is conservatively estimated to be, Z = (15)(55)(3.14)(7.5)(15)=291431 BTU/hr or 85kW, where the heat transfer coefficient from the vaporization-aided cask surface is conservatively assumed to be 15 BTU/ft2-hr-oF. Therefore, when the MPC water is boiling, the external surface of the cask will reject approximately 85 kW, in excess of a typical maximum cask heat load of approximately 43 kW. Therefore, it follows that a cask kept wet by HI-DRIP will never retain sufficient quantity of heat to cause boiling of canister water. In other words, the TTB will be infinity if HI-DRIP is used.
Application:
- 1) The following preparatory calculations shall be performed during the design phase of this ancillary:
- a. Using the NRC reviewed FLUENT model, compute the average surface temperature (T) at the mid-height of the cask for applicable heat load, ambient temperature and cooling water temperature assuming continuous wetting.
- b. Compute the mid-height surface temperature as in (a) above, except assume that the cask is dry surrounded by ambient air (T).
- c. Use the FLUENT solution to refine the estimate of cooling water flow rate required.
- d. Use the simplified adiabatic heat up method described in the FSAR to compute the very conservative time to boil (t).
- 2) HI-DRIP should be mounted in the neck region of the transfer cask and connected to the plant's water supply. The gate valve should be adjusted such that the spray nozzles keep the cask cylindrical surface wet continuously all around its cylindrical surface.
- 3) The cooling water drip should be initiated no later than 50% of t into Interval 2.
In an event the plants water supply system were to fail, the time-to-boil (TTB) limits shall be HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-92
calculated by measuring the water temperature inside the MPC similar to that described in Section 4.5.3.1. The measured MPC water temperature shall be used as the initial temperature (Tinitial) to re-evaluate the maximum allowable time duration for fuel to be submerged in water (tmax). The re-calculated maximum allowable time may be used as an updated time-to-boil clock.
Alternately, a forced water circulation can be initiated and maintained to remove the decay heat from the MPC cavity as described in Section 4.5.3.3. At the conclusion of forced water circulation, the measured temperature of water in the MPC shall be used to re-calculate the maximum allowable time duration for fuel to be submerged in water (tmax) and update the time-to-boil clock.
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-93
TABLE 4.5.1 THRESHOLD HEAT LOADS UNDER VACUUM DRYING OF HIGH BURNUP FUEL (See Figures 1.2.1a and 1.2.2) Notes 1, 2 MPC-37 Number of Regions: 3 Number of Storage Cells: 37 Maximum Heat Load: 34.36 Region No. Decay Heat Limit per Number of Cells Decay Heat Limit per Cell, kW per Region Region, kW 1 0.80 9 7.2 2 0.97 12 11.64 3 0.97 16 15.52 MPC-44 Number of Regions:1 Number of Storage Cells: 44 Maximum Heat Load: 30kW Region No. Decay Heat Limit per Number of Cells Decay Heat Limit per Cell, kW per Region Region, kW 1 0.681 44 30.0 MPC-89 Number of Regions: 3 Number of Storage Cells: 89 Maximum Heat Load: 34.75 Region No. Decay Heat Limit per Number of Cells Decay Heat Limit per Cell, kW per Region Region, kW 1 0.35 9 3.15 2 0.35 40 14.00 3 0.44 40 17.60 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-94
Table 4.5.19 MPC DRYING OPERATIONS MPC Type Fuel Heat Load Limit (kW) Method of Drying FHD/Vacuum Drying without MBF 44.16 (Note 1)
Time Limit FHD/Vacuum Drying with Time MPC-32ML 44.16 (Note 1)
Limit (Note 2)
HBF FHD/Vacuum Drying without 28.704 Time Limit 44.09 (Pattern A) 45.0 (Pattern B) 37.4/39.95/44.85 (Figures 1.2.3a, 1.2.4a, FHD/Vacuum Drying without MBF 1.2.5a)
Time Limit 34.4 (Figures 1.2.3b/c) 36.65 (Figures 1.2.4b/c)
MPC-37 40.95 (Figures 1.2.5b/c)
(Note 1) 44.09 (Pattern A)
FHD/Vacuum Drying with Time 45.0 (Pattern B)
Limit (Note 2)
HBF (Note 1)
FHD/Vacuum Drying without 29.6 Time Limit 46.36 (Table 1.2.4a) 46.2 (Figure 1.2.6a) 44.92 (Figure 1.2.6b) FHD/Vacuum Drying without MBF 46.14 (Figure 1.2.7a) Time Limit 44.98 (Figure 1.2.7b)
MPC-89 (Note 1)
FHD/Vacuum Drying with Time 46.36 (Note 1)
Limit (Note 2)
HBF FHD/Vacuum Drying without 30 Time Limit 45.0 (Table 1.2.3c)$
44.09 (Pattern A) FHD/Vacuum Drying without MBFMBF 45.0 (Pattern B) Time Limit$
(Note 1) 45.0 (Table 1.2.3c)
MPC-37P 44.09 (Pattern A) FHD/Vacuum Drying with Time 45.0 (Pattern B) Limit (Note 2)$
HBFHBF (Note 1)$
FHD/Vacuum Drying without 33.3 Time Limit HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-111
44.0 (Table 1.2.3e) FHD/Vacuum Drying without MBFMBF (Note 1)44.0 (Table Time LimitFHD/Vacuum Drying 1.2.3e) (Note 1) without Time Limit FHD/Vacuum Drying with Time MPC-44 44.0 (Table 1.2.3e)
Limit (Note 2)FHD/Vacuum (Note 1)30.0 HBFHBF Drying without Time Limit FHD/Vacuum Drying without 30.0 Time Limit HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 89 4-112
Table 4.I.6.4 PRINCIPAL SITE-SPECIFIC HI-STORM UVH FIRE ACCIDENT MODELING STEPS PROPRIETARY INFORMATION WITHHELD PER 10 CFR 2.390 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev 9 4.I-21
TABLE 6.1.2 BOUNDING MAXIMUM keff VALUES FOR EACH ASSEMBLY CLASS IN THE MPC-89 (HI-TRAC VW)
Fuel Assembly Class Maximum Allowable Maximum keff Planar-Average Enrichment (wt% 235U) 7x7B 4.8 0.9317 7x7C 4.8 0.9318 8x8B 4.8 0.9369 8x8C 4.8 0.9399 8x8D 4.8 0.9380 8x8E 4.8 0.9281 8x8F 4.5 0.93500.9328 8x8G 4.8 0.9301 9x9A 4.8 0.9421 9x9B 4.8 0.9410 9x9C 4.8 0.9338 9x9D 4.8 0.9342 9x9E/F 4.5 0.9346 9x9G 4.8 0.9307 10x10A 4.8 0.9435 10x10B 4.8 0.9417 10x10C 4.8 0.9389 10x10F 4.7 0.9440 10x10G 4.6 0.9466 10x10I 4.8 0.9422 10x10J 4.8 0.9477 11x11A 4.8 0.94550.9457 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 6-11 Proposed Rev. 9
performed for cross sections where all full-length and part-length, or only all full-length rods are present. For each case, two conditions are analyzed that places the different enrichment in areas with different local fuel-to-water ratios. Specifically, one condition places the higher enriched rods in locations where they are more surrounded by other rods, whereas the other condition places them in locations where they are more surrounded by water, such as near the water-rods or the periphery of the assembly. The results are also included in table 6.2.2 and show that in all cases, the maximum keff calculated for the distributed enrichments are statistically equivalent to or below those for the uniform enrichments. Therefore, modeling BWR assemblies with distributed enrichments using a uniform enrichment equal to the planar-average value is acceptable and conservative. The assumed enrichment distributions analyzed are shown in Appendix 6.B.
Note that for some BWR fuel assembly classes, the Zircaloy water rod tubes are artificially replaced by water in the bounding cases to remove the requirement for water rod thickness from the specification of the authorized contents. For these cases, the bounding water rod thickness is listed as zero.
Two BWR classes (8x8B and 8x8D) are specified with slight variation in the number of fuel and/or water rods (see Section 6.B.4). The results listed in Section 6.1 utilize the minimum number of fuel rods, i.e. maximizing the water-to-fuel ratio. To show that this is appropriate and bounding, calculations were also performed with the alternative configurations, and are presented in Table 6.2.5. The results show that the reference conditions used for the calculations documented in Section 6.1 are in fact bounding.
For BWR assembly class 9x9E/F, two patterns of water rods were analyzed (see Section 6.B.4).
The comparison is also presented in Table 6.2.5 and shows that the condition with the larger water rod spacing is bounding.
For BWR assembly class 10x10J, a water rod may have a variable diameter that occupies 4 or 12 Formatte fuel rod cells (See Section 6.B.4). But in all the calculations of this analysis, a water rod segment Formatte that displaces 4 fuel rods is assumed along the entire active fuel length. This is conservative Formatte since smaller water rod contains less material thus displaces less moderator, while the amount of Formatte fissile material remains the same (the 8 short partial length rods facing the water rod that would Formatte be displaced by the larger water rod have been completely removed in the design basis Formatte calculations).
For BWR assembly class 11x11A, rod pitch may be fixed in the middle and top zones while various rod pitches may present in the bottom zone of the fuel assembly, and the maximum rod pitch in the bottom zone may be larger than the fixed rod pitch in the middle and top zones.
Calculations are performed for the case where the fixed rod pitch shown in the middle and top zone was also applied to the bottom zone, and for the case where the various rod pitches shown in the bottom zone were assumed in the whole fuel assembly. The results listed in Table 6.2.10 confirm that using the fixed rod pitch in the middle and top zones along the entire active fuel length is bounding. This case is therefore used for 11x11A assembly class to determine the bounding BWR fuel assembly (See Table 6.1.2) of this analysis.
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 6-25 Proposed Rev. 9
TABLE 6.2.3 (continued)
EFFECT OF THE FLOODING OF THE PELLET-TO-CLAD GAP Fuel Assembly Maximum keff Class Flooded Empty Difference Pellet-to-Clad Pellet-to-Clad Gap Gap MPC-89 7x7B 0.9317 0.9261 -0.0056 7x7C 0.9318 0.9263 -0.0055 8x8B 0.9369 0.9318 -0.0051 8x8C 0.9399 0.9331 -0.0068 8x8D 0.9380 0.9334 -0.0046 8x8E 0.9281 0.9230 -0.0051
-0.0047-8x8F 0.93500.9328 0.93030.9275 Formatte 0.0053 8x8G 0.9301 0.9240 -0.0061 9x9A 0.9421 0.9370 -0.0051 9x9B 0.9410 0.9292 -0.0118 9x9C 0.9338 0.9290 -0.0048 9x9D 0.9342 0.9294 -0.0048 9x9E/F 0.9346 0.9261 -0.0085 9x9G 0.9307 0.9250 -0.0057 10x10A 0.9435 0.9391 -0.0044 10x10B 0.9417 0.9317 -0.0100 10x10C 0.9389 0.9333 -0.0056 10x10F 0.9440 0.9395 -0.0045 10x10G 0.9466 0.9408 -0.0058 10x10I 0.9422 0.9383 -0.0039 10x10J 0.9477 0.9419 -0.0058 11x11A 0.94550.9457 0.94270.9421 -0.0028-0.0036 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 6-30 Proposed Rev. 9
Table 6.2.8 EFFECT OF PARTIAL LENGTH RODS FOR ASSEMBLY CLASSES 10x10I, 10x10J AND 11x11A Parameter Variation reactivity Maximum standard effect keff deviation Assembly Class 10x10I full-length rods only Reference 0.9422 0.0006 full-length and part-length rods -0.0041 0.9381 0.0006 (real assembly) part-length rods extended to full-length -0.0117 0.9305 0.0005 Assembly Class 11x11A full-length rods only Reference 0.94550.945 0.00030.0006 7
full-length and part-length rods -0.0033- 0.94220.941 0.00030.0005 Formatte (real assembly) 0.0040 7 part-length rods extended to full-length -0.0046- 0.94090.939 0.00030.0006 0.0062 5 Assembly Class 10x10J full-length rods only -0.0151 0.9298 0.0003 full-length and part-length rods Reference 0.9449 0.0003 Formatte (real assembly) part-length rods extended to full-length -0.0015 0.9434 0.0003 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 6-37 Proposed Rev. 9
Table 6.2.10 EFFECT OF VARIATIONS IN ROD PITCH IN THE 11x11A FUEL ASSEMBLY CLASS Description Maximum keff Difference 11x11A (4.8 wt% 235U)
Fixed Rod Pitch present in Middle 0.9455 Reference and Top Zones (Reference)
Various Rod Pitches present in 0.9453 -0.0002 Bottom Zone HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 6-39 Proposed Rev. 9
conditions is that the permanent deflection of the basket panels is limited to a fraction of 0.005 (0.5%) of the panel width (see Chapter 3). The analyses in Chapter 3 demonstrate that permanent deformations of the basket walls during accident conditions are far below this limit. In fact, the analyses show that the vast majority of the basket panels remain elastic during and after an accident, and therefore show no permanent deflection whatsoever, and that any deformation is limited to small localized areas. Nevertheless, it is conservatively assumed that 2 adjacent cell walls in each cell are deflected to the maximum extent possible over their entire length and width, i.e. that the cell ID is reduced by 0.5% of the cell width, or 0.045 for the MPC-37 cells, 0.048 for the MPC-32ML cells, 0.0405 for the MPC-44 cells and 0.030 for the MPC-89 cells.
Stated differently, the minimum cell ID based on tolerances was further reduced by the amounts stated above for all cells in each basket to account for the potential deflections of basket walls during accident conditions. Assuming that all cell sizes are reduced is a simplifying, but very conservative assumption, since cell walls are shared between neighboring cells, so while the deflection of a basket wall would reduce the cell size on one side, it necessarily increases that on the other side of the wall. MCNP5 was used to determine the manufacturing tolerances and deflections that produced the most adverse effect on criticality. After the reactivity effect (positive effect with an increase in reactivity; or negative effect with a decrease in reactivity) of the manufacturing tolerances was determined, the criticality analyses were performed using the worst case conditions in the direction which would increase reactivity. For simplification, the same worst case conditions are used for both normal and accident conditions. For all calculations, fuel assemblies were assumed to be eccentrically located in the cells, since this results in higher reactivities (see Section 6.3.3). Maximum keff results (including the bias, uncertainties, or calculational statistics), along with the selected dimensions, for a number of dimensional combinations are shown in Table 6.3.2 for various baskets. The cell ID is evaluated for minimum (tolerance only), nominal, increased value and a bounding with deformation. The wall thickness is evaluated for nominal and minimum values.
Based on the calculations, the conservative dimensional assumptions listed in Table 6.3.3 were determined for the basket designs. Because the reactivity effect (positive or negative) of the manufacturing tolerances is not assembly dependent, these dimensional assumptions were employed for all criticality analyses.
The basket is manufactured from individual slotted panels. The panels are expected to be in direct contact with each other (see Drawings in Chapter 1). However, to show that small gaps between panels would have essentially no effect on criticality, calculations are performed with a postulated 0.06 gap between panels, repeated in the axial direction every 10 in all panels. Since it is expected that the effect of these gaps would be small, these calculations were performed with a larger number of particles per cycle, larger number of inactive cycles, and a larger total number of cycles to improve the statistics of each run, so the real reactivity effect could be better separated from the statistical noise. The results are summarized in Tables 6.3.6 and show that the METAMIC gap has a very small effect. Therefore, all calculations are performed without any gaps between panels.
Variations of water temperature in the cask were analyzed using CASMO-4. The analyses were HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 6-42 Proposed Rev. 9
To identify the configuration or configurations leading to the highest reactivity, a bounding approach is taken which is based on the analysis of regular arrays of bare fuel rods without cladding. Details and results of the analyses are discussed in the following subsections.
Note that since a modeling approach is used that bounds both damaged fuel and fuel debris without distinguishing between these two conditions, the term damaged fuel as used throughout this chapter designates both damaged fuel and fuel debris.
Note that the modeling approach for damaged fuel and fuel debris is identical to that used in the HI-STORM 100 and HI-STAR 100.
Bounding Undamaged Assemblies The undamaged assemblies assumed in the basket in those cells not filled with DFCs or DFIs are those that show the highest reactivity for each group of assemblies, namely
- 9x9E for BWR 9x9E/F, 8x8F and 10x10G assemblies
- 10x10F for BWR 10x10F assemblies
- 10x10J11x11A for BWR 10x10I, 10x10J and 11x11A assemblies;
- 10x10A for all other BWR assemblies;
- 16x16A for all PWR assemblies with 14x14 and 16x16 arrays;
- 15x15F for all PWR assemblies with 15x15 and 17x17 arrays; and
- 16x16D for all PWR assemblies qualified for MPC-32ML; and.
- 14x14B for all PWR assemblies qualified for MPC-44.
Since the damaged fuel modeling approach results in higher reactivities, requirements of soluble boron for PWR fuel and maximum enrichment for BWR fuel are different from those for undamaged fuel only. Those limits are listed in Table 6.1.4 (PWR) and Table 6.1.5 (BWR) in Section 6.1. Also, those limits are applicable to the basket loading configurations, considered in Tables 6.1.7 (PWR) and Tables 6.1.8 (BWR) in Section 6.1. Note that for the calculational cases for damaged and undamaged fuel in the MPC-89, the same enrichment is used for the damage and undamaged assemblies.
Note that for the first group of BWR assemblies listed above (9x9E/F, 8x8F and 10x10G),
calculations were performed for 8x8F,both 9x9E and 10x10G as undamaged assemblies, and assembly class 9x9E showed the higher reactivity, and is therefore used in the design basis analyses. This may seem contradictory to the results for undamaged assemblies listed in Table 6.1.2, where the 10x10G shows a higher reactivity. However, the cases in Table 6.1.2 are not at the same enrichment between those assemblies.
All calculations with damaged and undamaged fuel are performed for an active length of 150 inches. There are two assembly classes (17x17D and 17x17E) that have a larger active length for the undamaged fuel. However, the calculations for undamaged fuel presented in Table 6.1.1 show that the reactivity of those undamaged assemblies is at least 0.0050 delta-k lower than that HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 6-69 Proposed Rev. 9