RS-15-013, Exemption Request to Load and Store Thoria Rod Canister in a Holtec 68M Multi-Purpose Canister
| ML15029A334 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 01/29/2015 |
| From: | Simpson P Exelon Generation Co |
| To: | Document Control Desk, NRC/NMSS/SFST |
| References | |
| RS-15-013 | |
| Download: ML15029A334 (9) | |
Text
10 CFR 72.7 RS-15-013 January 29, 2015 A TIN: Document Control Desk Director, Division of Spent Fuel Storage and Transportation Office of Nuclear Material Safety and Safeguards U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Dresden Nuclear Power Station, Units 1, 2, and 3 Facility Operating License No. DPR-2 Renewed Facility Operating License Nos. DPR-19 and DPR-25 NRC Docket Nos.50-010. 50-237, 50-249, and 72-37
Subject:
Exemption Request to Load and Store Thoria Rod Canister in a Holtec 68M Multi-Purpose Canister In accordance with 10 CFR 72.7, "Specific exemptions," Exelon Generation Company, LLC (EGC) is requesting NRC approval of a one-time exemption for the Dresden Nuclear Power Station (DNPS) Independent Spent Fuel Storage Installation (ISFSI) from the requirements of 10 CFR 72.212(b)(3) and (b)(11 ). Specifically, EGC requests authorization to load and store the DNPS Unit 1 Thoria Rod Canister containing 18 DNPS Unit 1 thoria rods (Thoria Rods) in a Holtec International, Inc. (Holtec) Multi-purpose Canister (MPC)-68M, which is not currently permitted under Certificate of Compliance (CoC) Number (No.) 1014, Amendment 8, Appendix B, "Approved Contents and Design Features." The regulations require, in part, compliance to the terms and conditions of CoC No. 1014.
EGC has evaluated loading and storing the 18 Thoria Rods in the DNPS Unit 1 Thoria Rod Canister, within an MPC-68M. This evaluation concluded that the proposed loading configuration does not impact the criticality control, shielding, structural, confinement, or thermal design functions of the loaded MPC-68M.
January 29, 2015 U.S. Nuclear Regulatory Commission Page 2 As a result, the proposed exemption will not endanger life or property, or the common defense and security, and is otherwise in the public interest. Therefore, the exemption is authorized by law.
The attachment to this letter describes the need and justification for the issuance of an exemption, as well as a safety analysis and environmental assessment of the proposed action.
EGC requests approval of the proposed exemption by January 29, 2016 to support development of fuel loading documentation for the Spring 2016 DNPS spent fuel loading campaign.
There are no regulatory commitments in this submittal.
If you have any questions or require additional information, please contact Mr. John L. Schrage at (630) 657-2821.
\i2K Patrick R. Simpson Manager - Licensing cc: NRC Regional Administrator - Region Ill
Attachment:
10 CFR 72.7 Exemption Request, Dresden Nuclear Power Station Independent Spent Fuel Storage Installation
Attachment 10 CFR 72.7 Exemption Request Dresden Nuclear Power Station Independent Spent Fuel Storage Installation
- 1) Background The Holtec International, Inc., (Holtec) HI-STORM 100 dry cask storage (DCS) system is designed to hold and store spent fuel assemblies for independent spent fuel storage installation (ISFSI) deployment. The system is listed in 10 CFR 72.214 as Certificate of Compliance (CoC) Number (No.) 1014. This system is currently installed and in use by Exelon Generation Company, LLC (EGC) at the Dresden Nuclear Power Station (DNPS), in accordance with 10 CFR 72.210, "General license issued."
During the 2016 DNPS spent fuel loading campaign (SFLC), EGC will load and store HI-STORM 100 spent fuel casks utilizing Amendment 8 to Coe No. 1014. In Amendment 8 to CoC No. 1014, the NRC approved the use of the (Holtec) Multipurpose Canister (MPC)-
68M to store BWR spent fuel assemblies. Specifically, the NRC revised Appendix B, "Approved Contents and Design Features," Table 2.1-1, "Fuel Assembly Limits." This revision added, to Table 2.1-1, a new Section VI, "MPC MODEL: MPC-68M." EGC will utilize the MPC-68M during the 2016 SFLC to load and store spent fuel assemblies, as well as a DNPS Unit 1 Thoria Rod Canister containing 18 DNPS Unit 1 thoria rods (Thoria Rods).
However, Table 2.1-1,Section VI does not include, as an allowable content in the MPC-68M, Thoria Rods (i.e., Th0 2 and U02) that are placed in a DNPS Unit 1 Thoria Rod Canister.
- 2) Request for Exemption Holtec Coe No. 1014, Amendment 8, Appendix B, Table 2.1.1, Item VI, "MPC Model:
MPC- 68M," does not include DNPS Unit 1 Thoria Rods as an allowable content. Therefore, in accordance with 10 CFR 72.7, "Specific exemptions," EGC is requesting NRC approval of an exemption from the following requirements, which will enable EGC to load and store the DNPS Unit 1 Thoria Rod Canister, containing the 18 Thoria Rods, in a Holtec MPC-68M.
- 10 CFR 72.212(b)(3), which states the general licensee must "[e]nsure that each cask used by the general licensee conforms to the terms, conditions, and specifications of a Coe or an amended Coe listed in § 72.214."
- The portion of 10 CFR 72.212(b)(11) which states that" The licensee shall comply with the terms, conditions, and specifications of the Coe .... "
- 3) Basis for Approval of Exemption Request In accordance with 10 CFR 72.7, the NRC may, upon application by any interested person or upon its own initiative, grant such exemptions from the requirements of the regulations in this part as it determines are authorized by law and will not endanger life or property or the common defense and security and are otherwise in the public interest.
a) Authorized by Law This exemption would allow EGC to load and store a DNPS Unit 1 Thoria Rod Canister containing 18 DNPS Unit 1 Thoria Rods in a Multi-purpose Canister that is not currently approved for storage of this type of spent fuel rods (i.e., the Holtec MPC-68M).
The NRC issued 10 CFR 72.7 under the authority granted to it under Section 133 of the Nuclear Waste Policy Act of 1982, as amended, 42 U.S.C. § 10153. Section 72.7 allows the NRC to grant exemptions from the requirements of 10 CFR Part 72. Granting the Page 1 of 7
Attachment 10 CFR 72. 7 Exemption Request Dresden Nuclear Power Station Independent Spent Fuel Storage Installation proposed exemption provides adequate protection to public health and safety, and the environment. As described below, the proposed exemption will not endanger life or property, or the common defense and security, and is otherwise in the public interest.
Therefore, the exemption is authorized by law.
b) Will not Endanger Life or Property or the Common Defense and Security EGC has evaluated loading and storing 18 Thoria Rods in a DNPS Unit 1 Thoria Rod Canister, within an MPC-68M. This evaluation concluded that the proposed loading configuration does not impact the criticality control, shielding, structural, confinement, or thermal design functions of the loaded MPC-68M, as described in the Safety Analysis section below. Therefore, the proposed exemption does not endanger life or property or the common defense and security. In addition, EGC has determined that neither the proposed action nor the alternative to the proposed action will have an adverse impact to the environment c) Otherwise in the Public Interest It is in the public's interest to grant an exemption, since dry storage of the Thoria Rods places them in an inherently safe, passive system, and the exemption would permit this storage without the unnecessary burden and impact of requesting and approving a license amendment.
- 4) Safety Analysis The Holtec HI-STORM 100 DCS system (i.e., a loaded MPC, stored within a HI-STORM overpack) provides criticality control, shielding, heat removal, and confinement functions, independent of any other facility structures or components. The structural design of the cask system also maintains the integrity of the fuel during storage.
The MPC design requires certain limits on spent fuel parameters, including fuel type, assembly weight, initial enrichment, maximum burnup, maximum decay heat, minimum cooling time, and physical condition to safely store the spent fuel. These limitations are included in the thermal, structural, radiological, and criticality evaluations for the cask.
CoC No. 1014, Appendix B, Table 2.1-1,Section II, "MPC MODEL: MPC-68F," Item A.7, and Section Ill, "MPC MODEL: MPC-68 and MPC-68FF," Item A.3, both specify, as an allowable content:
"Thoria rods (Th02 and U02) placed in Dresden Unit 1 Thoria Rod Canisters and meeting the following specifications:"
Sub-Item b., "Composition," in both Items 11.A.7 and 111.A.3, specifies a maximum allowable composition for the DNPS Unit 1 Thoria Rod Canisters of 98.2 wt.% Th02 and 1.8 wt.%
U02, with a maximum enrichment of 93.5 wt.% 235 U. The required post-irradiation cooling time is specified as greater than or equal to 18 years, the decay heat is limited to less than or equal to 115 Watts per canister, and the average burnup limit is specified as less than or equal to 16 GWd/MTIHM (gigawatt days per metric tonne of initial heavy metal).
The allowable combinations of composition, enrichment, cooling time, decay heat, and burnup that are specified in Coe No. 1014, Appendix B Table 2.1.1-1, Sections 11 and 111 ensure that the criticality control, thermal, shielding, and confinement design functions for a Page 2 of 7
Attachment 10 CFR 72.7 Exemption Request Dresden Nuclear Power Station Independent Spent Fuel Storage Installation loaded DNPS Unit 1 Thoria Rod Canister are bounded by those evaluated in the Final Safety Analysis Report (FSAR) for the design basis fuel assembly.
- Criticality The DNPS Unit 1 Thoria Rod Canister is equipped with an internal separator assembly containing 18 Thoria Rods with an approved average composition of 98.2 wt.% Th02 and 1.8 wt.% U02. The analyzed keff value for a similar MPC (i.e., the MPC-68, the MPC-68F, or the MPC-68FF) filled with 68 Thoria Rod Canisters, each containing 18 Thoria Rods with the average approved composition of Th02 and U02, is calculated to be 0.1813.
This low reactivity is attributed to the relatively low content in 2s5U (i.e., equivalent to U02 fuel with an enrichment of approximately 1. 7 wt.% 235 U); the large spacing between the rods (i.e., the pitch is approximately 1 inch and the cladding OD is 0.412 inches); and the absorption in the separator assembly. Together with the bounding maximum keff values, this low reactivity demonstrates that the keff for a Thoria Rod Canister loaded into the MPC-68, MPC-68F, or the MPC-68FF, together with other approved fuel assemblies or Damaged Fuel Canisters, will remain well below the regulatory requirement of keff < 0.95.
The MPC-68M design consists of a Metamic-HT BWR fuel basket inside the existing MPC enclosure vessel. The Metamic-HT in the MPC-68M serves as the structural material of the basket and provides the necessary neutron absorption for maintaining the fuel in a sub-critical condition.
The incorporation of Metamic-HT in the MPC-68M fuel basket results in a much greater Boron (B)-10 concentration than is available in fuel baskets designs with "attached" neutron absorber (i.e., the MPC-68, MPC-68F, and MPC-68FF). This accrues three major safety and reliability advantages:
o The BWR basket may store high enrichment fuel (i.e., fuel with up to 4.8 wt.%
2s5U initial planar enrichment) without reliance on gadolinium or burn-up credit.
o The neutron absorber cannot detach from the basket or displace within it.
o Axial movement of the fuel with respect to the basket due to internal clearances has no reactivity consequence because the entire length of the basket contains the same concentration of the B-1 O isotope.
These design benefits ensure that the MPC-68M has equal or better criticality performance than the MPC-68, MPC-68F, or MPC-68FF, due to the basket itself being made from the Metamic-HT.
However, while only a single DNPS Unit 1 Thoria Rod Canister will be loaded and stored in an MPC-68M, the criticality analysis described above assumes loading such a canister in every basket cell, which would result in the very low reactivity of 0.1813 maximum keff.
The criticality analysis above for an MPC-68, MPC-68F, or MPC-68FF assumes that the composition of the 18 Thoria Rods in each DNPS Unit 1 Thoria Rod Canister is at the Appendix B, Table 2.1-1 approved composition of 98.2 wt.% Th0 2 and 1.8 wt.% U02.
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Attachment 10 CFR 72.7 Exemption Request Dresden Nuclear Power Station Independent Spent Fuel Storage Installation During a review of DNPS fuel characterization data, EGC identified that the weight percentage of Th0 2 in nine of the 18 Thoria Rods was slightly higher than the maximum approved Th0 2 value, while the weight percentage of U02 in these nine Thoria Rods was slightly lower than the maximum approved U02 value.
Specifically, these nine Thoria Rods have a composition of 98.8 wt.% Th02 and 1.2 wt.%
U0 2. When combined with the nine Thoria Rods that comply with the Coe-authorized composition (i.e., 98.2 wt.% Th02 and 1.8 wt.% U0 2), the average composition in the DNPS Unit 1 Thoria Rod Canister would be 98.5 wt.% Th02 and 1.5 wt.% U02.
Although this maximum calculated keff of 0.1813 assumes an average Th02 content of 98.2 wt.%, compared to the average Th0 2 content of 98.5 wt.%, it is also based on a U02 content of 1.8 wt.%. Reducing the U0 2 content from 1.8 wt.% to the average value of 1.5 wt.% would result in a reduction of the already low reactivity, due to the reduction in the fissile material.
Therefore, EGC has concluded that loading and storing the 18 Thoria Rods in an MPC-68M canister would not significantly increase the cask reactivity, which would continue to remain below the regulatory limit.
- Shielding The radiological analysis of the DNPS Unit 1 Thoria Rod Canister is described in Section 5.2.6 and Section 5.4.8 of the HI-STORM 100 FSAR. Specifically, the DNPS Unit 1 Thoria Rod Canister was analyzed to determine if it was bounded by the design basis 6x6 source terms for DNPS Unit 1 fuel. The results indicate that the design basis source terms bounded the Thoria Rod source terms in all neutron groups and in all gamma groups except the 2.5 to 3.0 MeV group (i.e., due to a high energy gamma from the decay of 2oaTl, a daughter nuclide in the 2ssU decay chain).
In order to demonstrate that the gamma spectrum from the single DNPS Unit 1 Thoria Rod Canister is bounded by the gamma spectrum from the design basis 6x6 fuel assembly, the gamma dose rate on the outer radial surface of the HI-STORM overpack was estimated conservatively assuming an MPC-68F full of DNPS Unit 1 Thoria Rod Canisters, each with 18 Thoria Rods at the average approved composition of 98.2 wt.%
Th02 and 1.8 wt.% U02.
The calculated gamma dose rate was compared to an estimate of the dose rate from an MPC full of design basis 6x6 fuel assemblies. When compared to the design basis 6x6 fuel assemblies, the gamma dose rate on the outer radial surface from an MPC full of Thoria Rod Canisters was only 15% higher than the design basis dose rate.
When applied to a calculated maximum design basis dose rate, this would raise the expected dose rate on the external surface of a HI-STORM loaded with DNPS Unit 2 or Unit 3 fuel bundles, all with a post-irradiation time of five years, from 21.3 mrem per hour (mrem/hr) to approximately 24.5 mrem/hr. Technical Specification 5.7.4 in Appendix A of the CoC limits the total radiation dose rate, on the external surface of a loaded HI-STORM 100, to less than 300 mrem per hour (mrem/hr). Therefore, even with a 15%
increase, the maximum expected dose rate would still be well below the CoC limit.
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Attachment 10 CFR 72.7 Exemption Request Dresden Nuclear Power Station Independent Spent Fuel Storage Installation The conservative analysis assuming a HI-STORM completely filled with Thoria Rod Canisters, in conjunction with the significant margin in neutron spectrum and the fact that there is only one DNPS Unit 1 Thoria Rod Canister placed into the MPC-68M, demonstrates that a single DNPS Unit 1 Thoria Rod Canister containing 18 Thoria Rods, at the approved average composition (i.e., 98.2 wt.% Th02 and 1.8 wt.% U02), and 67 design basis spent fuel assemblies (i.e., in compliance with Coe No. 1014, Amendment 8, Appendix B requirements) are acceptable for storage in the MPC-68M fuel cask.
In that the increase in the average thoria composition in the Thoria Rod Canister due to nine Thoria Rods (i.e., from the approved value of 98.2 wt.% Th02 to the average value of 98.5 wt.% Th02) is a very small fraction of the allowable value (i.e., 0.3%), it is reasonable to conclude that the increase in Thoria will have a negligible effect on the resultant gamma and neutron spectrum.
In addition, the MPC-68M basket consists of homogeneously dispersed boron carbide (10% minimum by weight). The B-10 areal density of the Metamic-HT panels which make up the basket is consistent with the areal density of the Metamic classic neutron poison panels in the MPC-68, and therefore provides equivalent neutron shielding.
From an overall shielding perspective the MPC-68M is expected to provide similar, if not better, shielding characteristics as the MPC-68. The MPC enclosure vessel, overpack, and transfer cask shielding properties are not modified.
Therefore, as stated in the HI-STORM 100 FSAR, Supplement 5.111, the effect of the design differences between MPC-68 and MPC-68M on dose rates is small and all results and conclusions from the MPC-68 are directly applicable. As such, the radiological impact of storing the DNPS Unit 1 Thoria Rod Canister containing 18 Thoria Rods with an average composition of 98.5 wt.% Th02 and 1.5 wt.% U0 2, in the MPC-68M, would be negligible.
- Structural, Thermal, and Confinement The remaining design characteristics of the Thoria Rods and the DNPS Unit 1 Thoria Rod Canister, including dimensions, weights, materials, as well as limits in the CoC, remain unchanged. Since the MPC-68M is bounded by the evaluations for the MPC-68, MPC-68F, and MPC-68FF in these characteristics, no other safety evaluations are affected by either the small change in the fuel composition or by storing the DNPS Thoria Rod canister in the MPC-68M.
Structural The MPC-68M cask is loaded in exactly the same manner as other certified MPCs, and uses the same ancillary equipment, (i.e., lift cleats, lift yokes, Lid Welding Machine, Weld Removal Machine, Cask Transporter, Mating Device, Low Profile Transporter, and Forced Helium Dehydrator). The operational characteristics of the HI-STORM overpack are unaffected. Due to the low density of the Metamic-HT material and the optimized fuel basket design, the loaded weight of the MPC-68M is less than the loaded weight of the MPC-68, MPC-68F, and MPC-68FF. Therefore, the lifting features on the MPC are unchanged and the lifting and handling equipment used to lift and handle the loaded MPC-68, MPC-68F, and MPC-68FF may also be used to lift and handle the loaded MPC-68M.
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Attachment 10 CFR 72.7 Exemption Request Dresden Nuclear Power Station Independent Spent Fuel Storage Installation Thermal and Confinement The MPC-68M, for an identical heat load, is intrinsically capable of more cooling effectiveness than the MPC-68, MPC-68F, and MPC-68FF, due to the higher thermal conductivity of Metamic-HT (i.e., approximately one order of magnitude greater than the thermal conductivity of the alloy used in the MPC-68, MPC-68F, and MPC-68FF), the use of full length aluminum basket shims, and the hard-anodizing of the basket and basket shim materials to obtain high emissivities. The design aspects of the MPC enclosure vessel (i.e., the confinement boundary), including the vent and drain port arrangements in the MPC lid, are unchanged.
Short-term cask operations, including draining of the MPC, welding of the lid, drying and filling of the MPC cavity with inert gas, and handling of the MPC remain unchanged from the existing practice, except that the dried and helium filled MPC-68M may reside indefinitely in the HI-TRAC transfer cask without the aid of the supplemental cooling system. The increased thermal conductivity of the Metamic-HT basket ensures that the steady state fuel cladding temperatures remain below the limits of ISG-11, "Cladding Considerations for the Transportation and Storage of Spent Fuel," Revision 3.
- 5) Environmental Consideration EGC has evaluated the environmental impacts of the proposed exemption request and has determined that the neither the proposed action nor the alternative to the proposed action will have an adverse impact to the environment. Therefore, neither the proposed action nor*
the alternative require any Federal permits, licenses, approvals, or other entitlements.
a) Environmental Impacts of the Proposed Action The DNPS ISFSI is a radiologically controlled area within the DNPS Protected Area (i.e., the 10 CFR 20 Restricted Area). The area considered for potential environmental impact as a result of this exemption request is the area in, and surrounding the ISFSI.
The interaction of a loaded HI-STORM 100 with the environment is through the thermal, shielding, and confinement design functions for the cask system.
As described above, EGC has verified the following conclusions for proposed storage of the DNPS Unit 1 Thoria Rod Canister, with the 18 Thoria Rods, within an MPC-68M cask:
- Steady state fuel cladding temperatures will remain below the ISG-11, Revision 3 limits.
- Existing radiological evaluations and conclusions in Chapter 5 of the HI-STORM 100 FSAR will remain valid.
- Design aspects of the MPC enclosure vessel (i.e., the confinement boundary) will remain unchanged.
EGG has also determined that there are no gaseous, liquid, or solid effluents (radiological or non-radiological), radiological exposures (worker or member of the public) or land disturbances associated with the proposed exemption. Therefore, approval of the requested exemption has no impact on the environment.
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Attachment 10 CFR 72.7 Exemption Request Dresden Nuclear Power Station Independent Spent Fuel Storage Installation b) Adverse Environmental Effects Which Cannot be A voided Should the Exemption be Approved Since there are no environmental impacts associated with approval of this exemption, there are no adverse environmental effects which cannot be avoided should the exemption request be approved.
c) Alternative to the Proposed Action In addition to the proposed exemption request, EGG has considered the alternative action. Specifically, EGG would need to request the CoC holder to submit a license amendment request, which the NRG would need to review and approve.
While 10 CFR 72.7 does not require a description of "special circumstances," application of the applicable regulations [i.e., 10 CFR 72.212(b)(3) and (b)(11 )] to the particular circumstances would not serve the underlying purpose of the rule, nor is it necessary to achieve the underlying purpose.
The underlying purpose of 10 CFR 72.212 is to allow reactor licensees to utilize dry fuel storage casks that have previously been found to be safe and appropriately analyzed for use by the cask designer, the cask user, and the NRG. As described above, the storage of the 18 Thoria Rods described above in an MPC-68M has been found to be non-safety significant, and in agreement with the underlying purpose of 1o CFR 72.212.
In addition, the required NRG review and approval of a license amendment request would result in an unnecessary delay in the safe loading and storage of the DNPS Unit 1 Thoria Rod Canister. EGG currently plans to load the Thoria Rod Canister during the DNPS 2016 SFLC as part of a program to ensure full core discharge capability. In order to load the Thoria Rod Basket during the 2016 SFLC campaign, EGG must finalize fuel loading package documentation by December 2015.
Based on the amount of time required to review and approve previous CoC amendment requests (i.e., ranging from 18 months to 27 months), NRG review and approval of a license amendment request to allow loading the DNPS Unit 1 Thoria Rod Canister containing 18 Thoria Rods, in an MPC-68M would not provide adequate time for development of fuel loading packages, and quite possibly could extend beyond the scheduled start of the DNPS SFLC campaign in Spring 2016. If not loaded during the 2016 DNPS SFLC, EGG would not be able to be load and store the DNPS Unit 1 Thoria Rod Canister until 2018.
d) Environmental Effects of the Alternatives to the Proposed Action There are no environmental impacts associated with the alternative to the proposed action.
e) Conclusion and Status of Compliance As a result of the environmental assessment, EGG concludes that the proposed action, which will allow EGG to load a DNPS Unit 1 Thoria Rod Canister containing 18 Thoria Rods in an MPC-68M, is in the public interest in that it avoids an unnecessary delay in the safe loading and storage of the DNPS Unit 1 Thoria Rod Canister that would result from the alternative to the proposed action.
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