ML23292A172
Text
SSES-FSAR Text Rev. 62
11.7 INDEPENDENT Dry Fuel Storage
11.7.1 Design Basis
Independent Dry Fuel Storage is necessary to provide temporary on-site spent fuel dry storage at Susquehanna Steam Electric Station (SSES). This storage capacity is required as a result of the unavailability of an off-site repository. The original plant design provided spent fuel storage capacity in the spent fuel pools based on the assumption the spent fuel would be continuously shipped off-site to a repository for disposal. The Independent Dry Fuel Storage system allows for the temporary storage of spent fuel without impacting plant operations.
The Independent Dry Fuel Storage system is composed of the Independent Spent Fuel Storage Installation (ISFSI), the NUHOMS Dry Spent Fuel Storage system and the Holtec HI-STORM FW Dry Spent Fuel Storage system. Although many portions of the ISFSI, NUHOMS system and Holtec system are considered Important to Safety, only the Lifting Yokes are considered Safety-Related. No other component of the ISFSI and NUHOMS system and Holtec system is considered Safety-Related.
The Dry Fuel Storage System implements two separate technologies for the ISFSI: the NUHOMS Horizontal Modular Dry Fuel Storage System (NUHOMS System) offered by ORANO (formerly Transnuclear and Vectra Technologies) and the Holtec HI-STORM FW Dry Fuel Storage System offered by Holtec International.
The components which make up the Transnuclear NUHOMS Dry Storage System conform to all requirements of:
- 1. 10CFR72 as documented in Transnuclear NUH-003 - Safety Analysis Report for the Standardized NUHOMS Horizontal Modular System for Irradiated Nuclear Fuel (known as the Certified Safety Analysis Report [CSAR]),
- 2. USNRC Safety Evaluation Report of Vectra Technologies Safety Analysis Report for the Standardized NUHOMS Horizontal Modular Storage System for Irradiated Nuclear Fuel (SER) and
- 3. USNRC Certificate of Compliance for Dry Spent Fuel Storage Casks Number 1004 (C of C).
The components which make up the Holtec HI-STORM FW Dry Fuel Storage System conform to all requirements of:
- 1. 10CFR72 as documented in Holtec Report HI-2114830 - Final Safety Analysis Report (FSAR) on the HI-STORM FW MPC Storage System,
- 2. USNRC Final Safety Evaluation Report (SER) of Holtec Interational HI-STORM Flood/Wind Multi-Purpose Canister Storage System and
- 3. USNRC Certificate of Compliance for Spent Fuel Storage Casks Number 1032 (C of C).
The NUHOMS and Holtec HI-STORM FW Dry Fuel Spent Storage Systems are constructed and operated in accordance with general license requirements of 10CFR72. The NUHOMS and Holtec SSES Spent Fuel Storage Project 10CFR72.212 Evaluations demonstrate that the
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spent fuel transfer and storage process, equipment and facilities meet the conditions and the requirements of their respective C of C.
Codes and standards applicable to the ISFSI are listed in Table 3.2-1, Transnuclear CSAR (Safety Analysis Report for the Standardized NUHOMS Horizontal Modular Storage System for Irradiated Nuclear Fuel [NUH-003]) and Holtec FSAR (Final Safety Analysis Report on the HI-STORM FW MPC Storage System [HI-2114830]).
11.7.2 Dry Storage System Description (NUHOMS System and Holtec System)
The NUHOMS Horizontal Modular Dry Storage System (NUHOMS System) provides for horizontal, dry storage of canisterized spent fuel assemblies in a concrete storage module.
Three canister models are utilized at SSES, t he 52B, 61BT and 61BTH. Each canister is capable of housing either fifty-two or sixty-one spent fuel assemblies. The 61BT and 61BTH canisters are transportable and the 61BTH canister is capable of housing High Burnup Rate fuel. Each concrete storage module houses one canister. The main components of the NUHOMS System are the Independent Spent Fuel Storage Installation (ISFSI), Horizontal Storage Modules (HSM), Dry Shielded Canisters (DSC) and associated transfer / auxiliary equipment. The ISFSI is comprised of HSMs (125 maximum), basemats, approach slabs, roads, fencing, drainage system, lighting, lightning protection and Temperature Monitoring System. The transfer equipment consists of an On-Site Transfer Cask (TC), Transfer Cask Lifting Yoke, Transfer Trailer and rigging assemblies. The transfer equipment interfaces with the existing SSES Reactor Building Refueling Floor equipment, Unit 1 Reactor Building Crane and overall plant infrastructure. The auxiliary equipment consists of the Vacuum Drying System, the Helium Leakage Testing System and the Automatic Welding System.
The Holtec HI-STORM FW Dry Storage System augments the NUHOMS -52B, NUHOMS-61BT, and NUHOMS-61BTH Dry Storage System casks already in service at the ISFSI. The main components of the Holtec HI-STORM FW system are the Multi-Purpose Canister (MPC),
HI-STORM FW overpack and HI-TRAC VW transfer cask. The MPC is loaded with spent fuel assemblies and stored within the HI-STORM FW overpack. The MPC-89 canister model is utilized at SSES. This canister is capable of housing eighty-nine BWR spent fuel assemblies.
The MPC is transportable and is capable of housing High Burnup Rate fuel. The HI-STORM FW overpack houses one MPC and provides structural protection, cooling and radiological shielding for the MPC. The HI-STORM FW overpacks will be stored on Basemat 4 and Basemat 5 of the ISFSI. Basemat 4 will be used to store both existing NUHOMS HSMs and HI-STORM FW overpacks. The HI-TRAC VW, which is used exclusively inside the Reactor Building, is the transfer cask used to house the MPC during fuel loading, unloading, drying, sealing and on-site transfer operations to a HI-STORM FW overpack for long-term storage. The transfer equipment interfaces with the exis ting SSES Reactor Building Refueling Floor equipment, Unit 1 Reactor Building Crane and overall plant infrastructure. All spent fuel transfers outside the Reactor Building utilizes the HI-STORM FW overpack.
11.7.3 ISFSI Source Terms
11.7.3.1 Radiation Source Term
The neutron and gamma radiation sources include the BWR spent fuel, activated portions of the fuel assembly, and secondary gamma radiation. All sources, except secondary gamma
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radiation, are considered physically bound in the source region. Secondary gamma radiation is produced by radiation passing through shielding regions.
Spent fuel assemblies with various combinations of burnup, enrichment, and cooling times can be stored in the DSCs and MPCs. The criteria for spent fuel assembly parameters for each DSC model is specified in C of C No. 1004. Spent fuel assemblies which meet these criteria are bounded by the source strengths used in the design analysis for the NUHOMS System and meet the criteria established in 10CFR72.104. The criteria for spent fuel assembly parameters for each MPC model is specified in C of C No. 1032. Spent fuel assemblies which meet these criteria are bounded by the source strengths used in the design analysis for the Holtec System and meet the criteria established in 10CFR72.104.
11.7.3.2 Airborne Radioactive Material Source Term
11.7.3.2.1 NUHOMS System
The release of airborne radioactive material is addressed for three phases of NUHOMS System operation: irradiated fuel handling in the Reactor Building Cask Storage Pit and Spent Fuel Storage Pools, drying and sealing of the DSC, and DSC transfer and storage.
Potential airborne releases from irradiated fuel assemblies in the Reactor Building Cask Storage Pit and Spent Fuel Storage Pools are discussed in Section 12.2.2.
DSC drying and sealing operations are performed using procedures which prohibit airborne leakage. During these operations, all vent lines are routed to the plant's existing radwaste systems. Once the DSC is dried and sealed, there are no design basis accidents which could result in the release of airborne radioactivity.
During transfer of the sealed DSC and subsequent storage in the HSM, the only postulated mechanism for the release of airborne radioactive material is the dispersion of non-fixed surface contamination on the DSC exterior. By filling the TC/DSC annulus with demineralized water, placing an inflatable seal over the annulus, and utilizing procedures which require examination of the annulus surfaces for smearable contaminat ion, the contamination limits on the DSC are below the permissible level for off-site shipments of fuel. Therefore, there is no possibility of significant radionuclide release from the DSC exterior surface during transfer or storage.
11.7.3.2.2 Holtec System
The release of airborne radioactive material is addressed for three phases of HI-STORM FW System operation: irradiated fuel handling in the Reactor Building Cask Storage Pit and Spent Fuel Storage Pools, drying and sealing of the MPC, and MPC transfer and storage.
Potential airborne releases from irradiated fuel assemblies in the Reactor Building Cask Storage Pit and Spent Fuel Storage Pools are discussed in Section 12.2.2.
MPC drying and sealing operations are performed using procedures which prohibit airborne leakage. During these operations, all vent lines are routed to the plant's existing radwaste systems. Once the MPC is dried and sealed, there are no design basis accidents which could result in the release of airborne radioactivity.
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During transfer of the sealed MPC and subsequent storage in the HI-STORM FW, the only postulated mechanism for the release of airborne radioactive material is the dispersion of non-fixed surface contamination on the MPC exterior. By filling the HI-TRAC VW/MPC annulus with demineralized water, placing an inflatable seal over the annulus, and utilizing procedures which require examination of the annulus surfaces for smearable contamination, the contamination limits on the MPC are below the permissible level for off-site shipments of fuel. Therefore, there is no possibility of significant radionuclide releas e from the MPC exterior surface during transfer or storage.
11.7.4 NUHOMS Dry Shielded Canister (DSC) and Holtec Multi-Purpose Canister (MPC)
11.7.4.1 NUHOMS System
The NUHOMS BWR Dry Shielded Canisters (DSCs) used to store spent fuel in the Horizontal Storage Modules (HSMs) at the ISFSI are designed to preclude or reduce the occurrence of uncontrolled releases of radioactive materials due to handling, transfer or storage of spent fuel.
NUH-003 describes the principal design features and design parameters for the DSC. The cylindrical shell, and the top and bottom cover plate assemblies form the pressure retaining containment boundary for the spent fuel. The DSC is equipped with two shield plugs so that occupational dose at the ends is minimized during drying, sealing, and transfer operations.
The DSC has double, redundant seal welds that join the shell and the top and bottom covers to form the containment boundary. The bottom end assembly containment boundary welds are made during fabrication of the DSC. The top end assembly containment boundary welds are made after spent fuel loading. Both top plug penetrations (siphon and vent ports) are redundantly sealed after DSC drying operations are complete. This assures that no single failure of the DSC top or bottom end assemblies will breach the DSC containment boundary.
The internal basket assembly of the DSC contains a storage position for each of the spent fuel assemblies. Fixed neutron absorbing material is used for criticality control in the DSC.
Subcriticality during wet loading, drying, sealing, transfer and storage operations is maintained through the geometric separation of the fuel assemblies by the DSC basket assembly and the neutron absorbing capability of the DSC materials of construction.
11.7.4.2 Holtec System
The Holtec BWR Multi-Purpose Canisters (MPCs) used to store spent fuel in the HI-STORM FW overpacks at the ISFSI are designed to preclude or reduce the occurrence of uncontrolled releases of radioactive materials due to handling, transfer or storage of spent fuel.
HI-2114830 describes the principal design features and design parameters for the MPC. The MPC assembly consists of a honeycomb fuel basket, a baseplate, a canister shell, a lid, and a closure ring. The MPC enclosure vessel is a fully welded enclosure, which provides the confinement for the stored fuel and radioactive material. The confinement boundary is defined by the MPC baseplate, shell, lid, port covers, and closure ring.
The MPC incorporates a redundant closure system. The MPC lid is edge-welded to the MPC outer shell. The lid is equipped with vent and drain ports that are utilized to remove moisture from the MPC and backfill the MPC with a specified amount of inert gas (helium). The vent and
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drain ports are closed tight and covered with a port cover (plate) that is seal welded before the closure ring is installed. The closure ring is a circular ring edge-welded to the MPC shell and lid; it covers the MPC lid to shell weld and the vent and drain port cover plates. The MPC lid provides sufficient rigidity to allow the entire MPC loaded with spent fuel to be lifted by the suitably sized threaded anchor locations in the MPC lid.
All components of the MPC assembly that may come into contact with spent fuel pool water or the ambient environment are made from stainles s steel alloy or aluminum/aluminum alloy materials. Prominent among the aluminum based materials used in the MPC is the Metamic-HT neutron absorber lattice that comprises the fuel basket.
11.7.5 NUHOMS Horizontal Storage Module (HSM) and Holtec HI-STORM FW Overpack
11.7.5.1 NUHOMS System
Prefabricated Horizontal Storage Modules (HSMs) are utilized to form an array of HSMs at the ISFSI. Each HSM provides a self contained modular structure for storage of spent fuel in a single DSC. NUH-003 describes the principal design features and design parameters for the HSM.
The HSM is constructed from precast reinforced concrete and contains a structural steel support for the DSC and heat shields. Adequate radiation shielding is accomplished by adding shield walls at each end of a row of HSMs and/or adding a shield wall at the rear of each HSM if configured as single row of HSMs.
The HSM provides a means of removing spent fuel decay heat by a combination of radiation, conduction, and convection. By design, ambient air enters the HSM through openings below the loaded DSC and exits through openings above the loaded DSC. The passive cooling system for the HSM is designed to assure that peak cladding temperatures during long term storage remain below acceptable limits to ensure fuel cladding integrity.
The HSMs are constructed on a load bearing foundation, which consists of a reinforced concrete basemat on compacted fill.
11.7.5.2 Holtec System
The HI-STORM FW overpack houses one MPC and provides structural protection, cooling and radiological shielding for the MPC at the ISFSI. HI-2114830 describes the principal design features and design parameters for the HI-STORM FW overpack.
HI-STORM FW is a vertical ventilated module engineered to be fully compatible with the HI-TRAC VW transfer cask and the MPC. The HI-S TORM FW overpack consists of two major parts: a dual wall cylindrical container with a set of inlet ducts near its bottom extremity and an integrally welded baseplate, as well as a removable top lid equipped with a radially symmetric exit vent system.
The HI-STORM FW overpack is a rugged, heavy-walled cylindrical vessel. The main structural function of the storage overpack is provided by carbon steel, and the main shielding function is provided by plain concrete. The overpack plain concrete is enclosed by a steel weldment of cylindrical shells, a thick baseplate, and a top annular plate. A set of four equally spaced radial
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connectors join the inner and outer shells and define a fixed width annular space for placement of concrete. The overpack lid also has concrete to provide neutron and gamma shielding.
The HI-STORM FW overpack consist of eight angled inlet ventilation ducts. These inlet ducts are straight channels with horizontal vents. This duct design reduces streaming through the angled design and slightly elevating the MPC on bottom support guides. Additional streaming is reduced through the use of a perforated steel plate as the inlet vent screen.
11.7.6 Transport Equipment
11.7.6.1 NUHOMS On-Site Transfer Cask
The On-Site Transfer Cask (TC) used in the NUHOMS System provides shielding and protection from potential hazards while the DSC is loaded with spent fuel. The fully loaded TC has a gross weight of approximately 100 tons and is limited to on-site use under 10CFR72.
The TC is designed to provide sufficient shielding to ensure that dose rates are ALARA.
Two lifting trunnions are provided for handling the TC in the Reactor Building using a Lifting Yoke and the Unit 1 Reactor Building Crane. Lower support trunnions are provided on the TC for pivoting the TC from/to the vertical and horizontal positions on the Transfer Trailer.
11.7.6.2. NUHOMS Transfer Trailer
The Transfer Trailer consists of a heavy haul industrial trailer, support skid assembly/positioning system and hydraulic ram. The Transfer Trailer is designed to ride as low to the ground as possible to ensure that the TC height during transport is less than the 80 inch drop height used as the accident drop design basis for the TC/DSC. A conventional heavy haul tractor or other suitable mover is used to tow the Transfer Trailer.
11.7.6.3 Holtec HI-TRAC VW Transfer Cask
The HI-TRAC VW transfer cask is engineered to be used to perform all short-term loading operations on the MPC beginning with fuel loading and ending with the emplacement of the MPC in the storage overpack. The HI-TRAC VW is also used for short term unloading operations beginning with the removal of the MPC from the storage overpack and ending with fuel unloading. The HI-TRAC VW is used exclusively inside the Reactor Building.
The HI-TRAC VW is designed to provide maximum shielding to the plant personnel engaged in conducting short-term operations, provide protection of the MPC against extreme environmental phenomena loads, such as tornado-borne missiles, during short-term operations and serve as the container equipped with the appropriate lifting appurtenances in accordance with NUREG-0612 to lift, move, and handle the MPC.
11.7.6.4 Holtec HI-PORT
The HI-PORT is a self-propelled low-profile transporter. During transport operations, the HI-PORT is used to transport the loaded HI-STORM FW from the Railroad Bay to the ISFSI. When the HI-STORM FW reaches the ISFSI on the HI-PORT, the VCT is used to lift the HI-STORM FW and move it to its storage location. All spent fuel transfers outside the Reactor Building utilizes the HI-STORM FW overpack.
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11.7.6.5 Holtec Vertical Cask Transporter (VCT)
A Vertical Cask Transporter (VCT) is used to lift the loaded HI-STORM FW from the HI-PORT and place it on the ISFSI, as well as to lift an empty HI-STORM FW from the ISFSI pad and place it on the HI-PORT. The VCT is qualified for lifting the HI-STORM FW in accordance with HI-2114830. HI-STORM FW Lift Brackets will be used with the VCT to lift a loaded HI-STORM FW.
11.7.7 NUHOMS and Holtec System Operation
11.7.7.1 NUHOMS System
The primary operations (in sequence of occurrence) for the NUHOMS System are described in the following sections:
11.7.7.1.1 On-Site Transfer Cask (TC) Preparation
TC preparation includes exterior washdown and interior decontamination. These operations are performed in the Steam Dryer and Separator Storage Pit.
11.7.7.1.2 Placement of DSC in Cask
The empty DSC is inserted into the TC ensuring proper alignment by visual inspection of the alignment match marks on the DSC and TC.
11.7.7.1.3 Fill TC/DSC Annulus with Water and Seal
The TC/DSC annulus is sealed prior to placement in the Cask Storage Pit to prevent contamination of the DSC outer surface.
11.7.7.1.4 TC Movement to the Cask Storage Pit
The TC/DSC is moved to the Cask Storage Pit using the Unit 1 Reactor Building Crane.
Alternately, the Cask Storage Pit water level can be lowered for this process by installing the Cask Storage Pit Gates and draining the water from the Pit in accordance with procedures as described in Section 9.1.3.3.
11.7.7.1.5 DSC Spent Fuel Loading
Prior to transferring spent fuel, the Cask Storage Pit water level is maintained at normal level.
Spent fuel assemblies are placed into the DSC using the Refueling Platform. Upon completion of 61BT or 61BTH DSC Spent Fuel loading, a hold down ring is installed. The 52B DSC does not require a hold down ring.
11.7.7.1.6 DSC Top Shield Plug Placement
This operation consists of placing the DSC top shield plug onto the DSC using the Unit 1 Reactor Building Crane.
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11.7.7.1.7 Lifting TC from Cask Storage Pit
The loaded TC/DSC is moved to the Steam Dryer and Separator Storage Pit. Alternately, the Cask Storage Pit water level can be lowered for this process by installing the Cask Storage Pit Gates and draining the water from the pit in accordance with procedures as described in Section 9.1.3.3.
11.7.7.1.8 Inner DSC Top Cover Plate
Using a pump, the water level in the DSC is lowered below the inside surface of the DSC top shield plug. The inner top cover plate is put in place and welded.
11.7.7.1.9 DSC Drying and Backfilling
The initial blow-down of the DSC is accomplished by pressurizing the vent port with nitrogen, helium or shop air. The remaining liquid water in the DSC cavity is forced out the siphon tube and routed back to the pool or to the plant radwaste processing system. For the 52B, the DSC is then evacuated to remove any residual liquid water and water vapor in the DSC. The DSC is backfilled with helium and slightly pressurized. A helium leak test of the inner seal weld is then performed and the drain and fill port penetrations seal welded closed.
11.7.7.1.10 Outer DSC Top Cover Plate
The DSC outer top cover plate is installed and welded. For the 61BT or 61BTH, the DSC is then backfilled with helium and slightly pressurized. A helium leak test of the inner seal weld is then performed and the drain and fill part penetrations seal welded closed.
11.7.7.1.11 TC/DSC Annulus Draining and Top Cover Plate Placement
The TC is drained, removing the water from the TC/DSC annulus and flushing the TC/DSC annulus to remove any contamination left on the DSC exterior. The TC top cover plate is then put in place and bolted.
11.7.7.1.12 Placement of TC on Transfer Trailer
The TC is then moved to the Transfer Trailer using the Unit 1 Reactor Building Crane and downended to a horizontal position. The TC is secured to the Transfer Trailer for the subsequent transport operations.
11.7.7.1.13 Transport of TC to HSM
The Transfer Trailer is moved to the ISFSI along a predetermined route on plant roads. Upon entering the ISFSI, the Transfer Trailer is positioned and aligned with the HSM in which a DSC is to be stored.
11.7.7.1.14 TC/HSM Preparation
With the TC positioned in front of the HSM, the TC top cover plate is removed and the HSM door is removed. The Transfer Trailer is then backed into close proximity with the HSM and the skid positioning system is used for the final alignment and docking of the cask with the HSM.
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11.7.7.1.15 Loading DSC into HSM
After final alignment of the Transfer Trailer with the HSM, the DSC is pushed into the HSM by the hydraulic ram.
11.7.7.1.16 Spent Fuel Storage
After the DSC is inside the HSM and the Transfer Trailer is pulled away, the HSM door is installed and the DSC axial retainer inserted.
11.7.7.1.17 Spent Fuel Retrieval
For retrieval of the DSC, the TC is positioned at the HSM and the DSC is transferred from the HSM by using the hydraulic ram to pull the DSC into the TC. Once back in the TC, the DSC with spent fuel assemblies is ready for return to the Spent Fuel Storage Pools.
11.7.7.2 Holtec System
The primary operations for the Holtec HI-STORM FW System are described in the following sections:
11.7.7.2.1 HI-TRAC VW Preparation
The HI-TRAC VW is placed in the cask receiving area where receipt inspection and cleanliness verification are performed. The top of the HI-TRAC VW is cleared for installation of the MPC.
11.7.7.2.2 Placement of MPC in HI-TRAC VW
A receipt inspection and cleanliness verification are performed on the empty MPC, and the MPC is installed inside the HI-TRAC VW in accordance with SSES rigging procedures.
11.7.7.2.3 Fill HI-TRAC VW / MPC Annulus with Water and Seal
The HI-TRAC VW / MPC annulus is filled with non-contaminated water and the inflatable annulus seal is installed around the MPC. The MPC is then filled with water to approximately 12 inches below the top of the MPC shell.
11.7.7.2.4 HI-TRAC VW Movement to the Cask Loading Area
The HI-TRAC VW / MPC is placed in the Cask St orage Pit using the Unit 1 Reactor Building Crane.
11.7.7.2.5 MPC Spent Fuel Loading
The MPC is loaded with the pre-selected fuel assemblies in accordance with the approved loading plan. A post-loading visual verification of the assembly identification is performed to confirm serial numbers match the approved loading plan.
11.7.7.2.6 MPC Lid Install
The MPC lid is installed in accordance with site-approved rigging procedures.
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11.7.7.2.7 Lifting HI-TRAC VW from the Cask Loading Area
The lift yoke to the HI-TRAC VW is engaged and the HI-TRAC VW is removed from the Cask Storage Pit while performing decontamination activities in accordance with directions from radiological control personnel. The HI-TRAC VW is then placed in the Steam Dryer and Separator Storage Pit.
11.7.7.2.8 MPC Lid Welding
The MPC annulus is prepared for MPC lid welding by removing the annulus seal, and the MPC water is lowered prior to welding. The MPC lid is prepared for welding and the lid-to-shell weld is performed.
11.7.7.2.9 Drying and Backfilling the MPC
The annulus between the MPC and the HI-TRAC VW is filled with clean water and the drying system is attached to the vent and drain port valves. The drying system is started, and the MPC pressure is slowly reduced. Once the MPC is dry, the vent and drain port valves are closed.
The MPC is backfilled and the drying system is disconnected from the MPC.
11.7.7.2.10 MPC Cover Plates and Closure Ring
The vent and drain port cover plates are welded to the MPC, and the MPC closure ring is installed and welded to the MPC shell and lid.
11.7.7.2.11 HI-TRAC VW / MPC Annulus Draining
The remaining water in the HI-TRAC VW / MPC annulus is drained and surface dose rate measurements are performed in accordanc e with the Technical Specifications.
11.7.7.2.12 Placement of HI-STORM FW
The HI-STORM FW receipt inspection and clean liness verification is performed and the empty HI-STORM FW module is positioned at the Railroad Bay.
11.7.7.2.13 HI-STORM FW Preparation
The mating device is installed on top of the HI-STORM FW and the HI-TRAC VW is aligned above the HI-STORM FW and the components are mated.
11.7.7.2.14 Transport of HI-TRAC VW / MPC to HI-STORM FW
The HI-TRAC VW is transferred to the Railroad Bay. The HI-TRAC VW is positioned and aligned with the HI-STORM FW in which the MPC is to be stored.
11.7.7.2.15 Loading MPC into HI-STORM FW
The MPC is slightly raised, and the bottom lid of the HI-TRAC VW is removed using the mating device. The MPC is then lowered into the HI-STORM FW, and the HI-TRAC VW is removed from the top of the HI-STORM FW.
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11.7.7.2.16 HI-STORM FW Transfer
During transport operations, the HI-PORT is used to travel the loaded HI-STORM FW from the Railroad Bay to the ISFSI. When the HI-STORM FW reaches the ISFSI on the HI-PORT, the VCT is used to lift the HI-STORM FW and move it to its designated location on the ISFSI.
11.7.7.2.17 Spent Fuel Long-Term Storage
After the loaded HI-STORM FW is transferred to the ISFSI, the HI-STORM FW temperature monitoring system (if used) and screens are attached.
11.7.7.2.18 Spent Fuel Retrieval
For retrieval of the MPC, the HI-TRAC VW and HI-STORM FW are positioned at the Railroad Bay and the MPC is transferred from the HI-STORM FW to the HI-TRAC VW. Once back in the HI-TRAC VW, the MPC with spent fuel assemblies is ready for return to the Spent Fuel Storage Pools.
11.7.8 Radiological Assessment
11.7.8.1 Introduction
The ISFSI is designed to limit off-site doses from the on-site storage of dry spent fuel to a fraction of the 40CFR190 limits for SSES, and on-site radiation exposure within the guidelines of 10CFR20 and 10CFR72. In all instances, the facility is designed to maintain dose rates ALARA as outlined in Regulatory Guides 8.8 and 8.10. Exposure of on-site workers is minimized by the use of concrete shielding, shielded transfer equipment, and controlled access to the ISFSI.
11.7.8.2 Dose
11.7.8.2.1 NUHOMS System
Compliance with Subpart K of 10CFR72 requires a written evaluation to demonstrate that the annual whole body, organ, and thyroid dose equivalent limits of 10CFR72.104 for an individual beyond the SSES Controlled Area are not exceeded as the result of the combined exposure to radiation from the storage of spent fuel on-site and all other nuclear fuel cycle contributors during normal operations. Evaluation shows that annual dose equivalents from the ISFSI and SSES operation are below the limits of 10CFR72.104 and that the maximum dose equivalent rates from the ISFSI and SSES operation ar e less than the 10CFR20.1301 limits for an Unrestricted Area when controlled in accordance with the SSES Dry Fuel Storage Project 10CFR72.212 Evaluation.
11.7.8.2.2 Holtec System
Evaluation for the Holtec system were performed to demonstrate that the combined dose produced by the NUHOMS HSMs and HI-STORM FWs on the SSES ISFSI will not result in annual doses at the ISFSI controlled area boundary to exceed the limits specified in 10CFR72.104(a) during normal operations and anticipated operational occurrences. The evaluations in the Holtec 10CFR72.212 Evaluation also demonstrate compliance with 10CFR72.104(b) and (c), and C of C No. 1032.
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11.7.8.3 ISFSI Controlled Area
A design basis accident dose limit to the whole body, or to any organ for any individual beyond the nearest controlled area boundary of the ISFSI is established in 10CFR72.106. The ISFSI design/location ensures that the criteria of 10CFR72.106 are satisfied.
11.7.8.4 Fully Loaded ISFSI Dose Assessment
11.7.8.4.1 NUHOMS System
An analysis was performed to determine the expected annual dose to an individual as a result of operation of a fully loaded ISFSI (125 HSMs). Impacted personnel include operators performing daily surveillance of the HSMs and health physi cs personnel performing routine weekly surveys of the ISFSI. An analysis was performed to determine the exposure impact for a loading campaign. The analysis which is included in the SSES Dry Fuel Storage Project 10CFR72.212 Evaluation determined that the maximum annual dose for routine surveillance of the ISFSI and the estimated dose to perform a loading campaign remain within acceptable limits of the Radiological Protection Program.
11.7.8.4.2 Holtec System
An analysis was also performed, as part of an overall integrated analysis with the NUHOMS System, to determine the expected annual dose to an individual as a result of operation of a fully loaded ISFSI with 26 HI-STORM FW overpacks placed on existing Basements 4 and 5.
This installation meets the requirements of 10CFR72.106.
11.7.9 Site Specific Evaluations
11.7.9.1 Average Ambient Air Temperature and Temperature Extremes
11.7.9.1.1 NUHOMS System
The average annual air temperature and air temperature extremes for the SSES are within the NUHOMS System NUH-003 limits.
11.7.9.1.2 Holtec System
Both the average annual temperature and the temperature extremes at SSES are bounded by the allowable temperatures specified in HI-2114830.
11.7.9.2 Earthquake Intensity/Seismic Acceleration
11.7.9.2.1 NUHOMS System
10CFR72 requires an evaluation be performed to establish that the cask storage pads and areas have been designed to adequately support the static load of the stored casks. A seismic evaluation has demonstrated that the design of the SSES ISFSI pad is adequate for all design basis loads for the HSM and DSC loading sequence and is adequate for the site specific loads at SSES due to a seismic event.
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11.7.9.2.2 Holtec System
Holtec seismic evaluations have demonstrated that the design of the SSES ISFSI pad is adequate for all seismic design basis loads for the HI-STORM FW and HI-STORM FW loading sequences and is adequate for the site specific loads at SSES due to a seismic event.
11.7.9.3 Flooding
11.7.9.3.1 NUHOMS System
The maximum water level at SSES, under the effects of probable maximum precipitation with coincident wind induced waves produces a flood level in the Susquehanna River that is well below the ISFSI elevation. The SSES ISFSI is not subject to flooding.
11.7.9.3.2 Holtec System
The Holtec 10CFR72.212 Evaluation concluded that flooding of rivers and streams will not affect HI-STORM FW operations at SSES, and that the ISFSI is not subject to flooding under the probable maximum flood (PMF) scenarios specified in Section 2.4 of the SSES FSAR.
11.7.9.4 Tornado Wind Pressure and Missiles
11.7.9.4.1 NUHOMS System
The NUHOMS System components are designed and analyzed to perform their intended functions under the extreme environmental and natural phenomena specified in 10CFR72.
The HSMs are designed to withstand the design basis tornado generated missiles defined in 10CFR72 and the tornado missile loading specified by NUREG0800. Supplemental analysis has demonstrated that the HSM design is adequate to withstand all SSES tornado generated missiles. This evaluation also shows that the TC is structurally adequate to withstand the SSES tornado generated missiles.
11.7.9.4.2 Holtec System
The Holtec System components are designed and analyzed to perform their intended functions under the extreme environmental and natural phenomena specified in 10CFR72. The HI-STORM FW is designed for the tornado wind speed and pressure drop defined in HI-2114830. Supplemental reports provided by Holtec demonstrate that the Holtec system remains stable and in compliance with the design requirements for the SSES tornado event conditions. The HI-STORM FW is designed to withstand impacts from tornado-generated missiles in addition to the tornado wind and pressure drop. Holtec supplemental reports conclude that the missiles considered in HI-2114830 bound the postulated missiles at SSES.
These reports evaluate the effects of missile impacts on the HI-STORM FW while the HI-STORM FW is in storage on the ISFSI and st ability of HI-STORM FW due to missile impact while the HI-STORM FW is being transported on the HI-PORT. These supplemental reports conclude the HI-STORM FW will not tip over and will not slide off the HI-PORT deck due to missile impact.
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11.7.9.5 Snow
11.7.9.5.1 NUHOMS System
The NUHOMS System snow load capacity envelops the SSES site criteria for snow loads.
11.7.9.5.2 Holtec System
The snow loading conditions at SSES are bounded by the HI-STORM FW design conditions.
11.7.9.6 Lightning
11.7.9.6.1 NUHOMS System
The review of the SSES site for lightning damage was performed in accordance with the criteria of the National Fire Protection Association (NFPA) 780 Standard for the Installation of Lightning Protection Systems, formerly NFPA 78 "Lightning Protection Code." Lightning protection system is installed on the HSMs which meets code requirements.
11.7.9.6.2 Holtec System
HI-2114830 demonstrates that if the HI-STORM FW is struck by lightning, the electrical surge will discharge through the steel shell of the overpack to the ground. The evaluation in HI-2114830 concludes that this event would have no effect on the spent fuel, confinement boundary of the MPC, or shielding materials of the HI-STORM FW. If the lightning strike occurs while the HI-STORM FW is being handled by the HI-PORT or VCT, this conclusion remains the same, as the charge on the HI-STORM FW shell would discharge through the HI-PORT or VCT and into the ground. Thus, any lightning strike potential at SSES is accommodated by the design of the HI-STORM FW System.
11.7.9.7 Fire and Explosion
11.7.9.7.1 NUHOMS System
10CFR72 requires that the NUHOMS System ISFSI be designed and located so that it can continue to perform its safety functions effectively under credible fire and explosion exposure conditions. The ISFSI is located away from other plant structures and protected by its own chain link fence.
The ISFSI is located near internal Protected Area roads where minimal, essential traffic is experienced. Some of this traffic involves occasional deliveries of materials such as propane and fuel within the Protected Area. Vehicles transiting the roads are continually attended so that any malfunction would be quickly mitigated.
The closest buildings are the Low Level Radwaste Holding Facility (LLRWHF) and the Central Alarm Station (CAS). These buildings are approximately 100 feet and 300 feet away respectively. The LLRWHF was designed and built to store low-level radwaste generated by SSES. Trucks are parked at the LLRWHF door for loading and unloading activities for a minimal time and are continually attended. Due to the distances between the ISFSI and LLRWHF and the minimal time any vehicle is at the LLRWHF, risk of fire or explosion is
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minimal. The CAS does not present a risk to the ISFSI. There are no hazards (e.g.,
compressed gases) in the vicinity that would pose an explosion concern to the ISFSI.
The design of the NUHOMS System does not pose a fire or explosion hazard and provides protection against fire. The concrete and steel construction provides protection against any transient fire that would manage to start. The installed fencing along with the routine inspections of the area will keep any loose combustibles from accumulating in the area of the HSMs.
During the period when a transporter is in use within the storage area, controls will ensure that an attendant is present. Thus the attendant can notify the Control Room should any malfunction occur. The plant fire brigade will respond to the area upon notification of a fire. Manual fire suppression equipment is available for fighting a fire in the area.
The Hydrogen/Oxygen Tank Farm located near the South Gate house is along the transport path of the Transfer Trailer during transit from the Reactor Building to the ISFSI. Evaluation to determine the effects of a postulated accidental hydrogen explosion at the Hydrogen/Oxygen Tank Farm on the TC and Transfer Trailer indicated that the TC/Transfer Trailer are not compromised.
The above review of the NUHOMS System shows that there is no credible fire or explosion exposure that would prevent the system from performing its function.
11.7.9.7.2 Holtec System
HI-2114830 and C of C No. 1032 specify that the casks must be able to withstand the elevated temperatures due to a fire event. A site-specific evaluation of the HI-STORM FW has been performed which demonstrates that the temperature limits for the fuel cladding and HI-STORM FW system components are not exceeded during the most bounding fire scenario.
The potential on-site fire hazards in proximity to the HI-TRAC VW during MPC loading and processing and the HI-STORM FW in transport on the HI-PORT and storage at the ISFSI (as well as effects on HSMs) has been evaluated. This hazards evaluation tabulates the allowable quantities for different flammable materials at various separation distances. These tables are used to evaluate transient hazards in the vicinity of the casks that are not captured in the hazards analysis. Administrative controls are included in Holtec procedures for dry fuel storage campaigns to limit the amount of combustible material permitted around the HI-TRAC VW and HI-STORM FW (and the HSMs, as applicable) during all stages of the loading campaigns.
C of C No. 1032 requires the potential for fire and explosion while handling a loaded HI-STORM FW or HI-TRAC VW to be addressed. A site-specific review and evaluation of potential explosion hazards in proximity to the HI-TRAC VW and the HI-STORM FW determines the credibility of the potential explosion hazards based on their material type and flashpoint of the material. If a hazard is deemed a credible explosion hazard, that hazard is analyzed for the resultant overpressure experienced by the HI-TRAC VW and/or HI-STORM FW at its separation distance from the cask, haul path, and/or ISFSI, as applicable. Credible explosion hazards are evaluated and considered acceptable if the resultant overpressure is less than the acceptable, allowable overpressure specified in HI-2114830 at its separation distance. This hazards evaluation tabulates the allowable quantities for different explosive materials at various separation distances. These tables have been used to evaluate transient hazards in the vicinity of the casks that are not captured in the hazard analysis. Administrative controls are included in Holtec procedures for dry fuel storage campaigns to limit the amount of explosive material
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permitted around the HI-TRAC VW and HI-STORM FW during all stages of the loading campaigns.
11.7.10 Heavy Loads
11.7.10.1 NUHOMS System
All lifting of TC or DSCs in the Reactor Building will utilize the Unit 1 Reactor Building Crane (single failure proof) with rigging/lifting mechanisms meeting the requirements of the SSES Heavy Loads Program and NUREG 0612. The Unit 1 Reactor Building Crane single failure proof certification is maintained via the SSES Preventative Maintenance Program.
11.7.10.2 Holtec System
All lifting of HI-TRAC VW or MPCs in the Reactor Building will utilize the Unit 1 Reactor Building Crane (single failure proof) with rigging/lifti ng mechanisms meeting the requirements of the SSES Heavy Loads Program and NUREG 0612. The Unit 1 Reactor Building Crane single failure proof certification is maintained via the SSES Preventative Maintenance Program.
11.7.11 Auxiliary Systems
11.7.11.1 Electrical Systems
Electrical power is required at the ISFSI for the lighting and for HSM Temperature Monitoring System.
11.7.11.2 Instrumentation
11.7.11.2.1 NUHOMS System
The Independent Spent Fuel Storage Installation contains a Temperature Monitoring System to continuously monitor the temperature of each HSM's concrete roof slab. HSM cooling relies on natural air circulation through the modules, therefore, the roof slab represents the hottest portion of the HSM concrete. Temperature monitoring provides a means to identify abnormal increases in temperature that could threaten proper HSM operation. The normal temperature range of the concrete at the temperature sensor(s) location is predicted in the range of 60° F to 240° F, based on age of contained fuel and ambient conditions.
The Temperature Monitoring System consists of one thermocouple per roof slab to provide a signal to a Data Acquisition based system capable of displaying and recording the concrete temperature for each HSM. A local temperature indicator (gauge) is also installed in each HSM to provide a backup in the event of a thermocouple or PLC/recorder failure. The Temperature Monitoring System provides the means of monito ring temperature to meet the requirements in the C of C Number 1004.
11.7.11.2.2 Holtec System
The HI-STORM FW is a completely passive system with appropriate margins of safety.
Therefore, it is not necessary to deploy any instrumentation to monitor the cask in the storage
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mode. However temperature elements are supplied which may be utilized to monitor the air temperature of the HI-STORM FW overpack exit vents in lieu of routinely inspecting the vents for blockage.
11.7.12 Dry Fuel Storage Aging Management Program (AMP)
Orano Certificates of Compliance (C of C) No. 1004, Revision 1, Renewed for Amendment 0, 4, 8, 9, and 10, and Renewed Amendment 14, direct development of an Aging Management Program for the Dry Fuel Storage System, specifically for the following areas:
DSC External Surfaces Aging Management Program DSC Aging Management Program for the Effects of CISCC (Coastal Locations, Near Salted Roads, or in the Path of Effluent Downwind from the Cooling Tower(s)).
HSM Aging Management Program for External and Internal Surfaces HSM Inlets and Outlets Ventilation Aging Management Program Transfer Cask Aging Management Program High Burnup Fuel Aging Management Program
This program was implemented within the 20-year period following initial loading on the ISFSI pad.
Areas addressed under 10 CFR Part 54, License Renewal Rule, are addressed in Chapter 3, Section 3.14.
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