 Department of Energy Richland Operations Office |
Environmental Assessment Lead Test Assembly Irradiation & Analysis July 1997 |
DOE/EA-1210
Department of Energy Richland Operations Office |
Environmental Assessment Lead Test Assembly Irradiation & Analysis July 1997 |
2.0 Proposed Action
The Department of Energys Proposed Action is described in the following sections.
2.1 Background
Irradiation of TPBARs in a CLWR is being evaluated as a reasonable alternative for meeting the need to replenish the supply of tritium for nuclear weapons. It is also being considered as a backup source, should the accelerator alternative be selected as the primary tritium source, in order to ensure that adequate supplies of tritium would be available. The TPBARs used in the proposed tests would both replace and function as a standard burnable absorber assembly in a CLWR. The function of the reactor, the absorber assembly and the TPBARs is described below.
The TPBARs have been designed for use in a pressurized water reactor (PWR) of the type developed commercially by Westinghouse. The LWRs used to generate electric power in the United States utilize both PWR and boiling water reactor (BWR) technologies. However, use of a BWR to produce tritium would require technology different from that involved in using a PWR of the design proposed for this test. Specifically, to produce tritium most BWR designs would require production of specially designed fuel or reconfiguration of the reactor core to accommodate separate tritium targets. As a result of these considerations, and because of the extensive research and development that has already occurred using PWR technology, the Proposed Action described in this EA involves the use of a PWR.
Commercial PWRs produce electricity by creating steam to drive a steam turbine generator. In a typical large PWR, heat is generated by nuclear fission in the reactor core and transferred to the turbine via steam produced in a heat exchanger. The side of the heat exchanger that is connected to the reactor vessel (referred to as the primary side) is isolated from the side that supplies steam to the turbine (the secondary side of the heat exchanger) so that water in contact with the reactor core is effectively contained within the reactor vessel and the primary side of the heat exchanger under normal operating conditions.
The reactor core contains fuel assemblies, coolant, a neutron moderator (a material that slows neutrons), and devices to control the nuclear fission reaction. In U.S. commercial power reactors, the fuel consists of uranium slightly enriched (less than 5%) in the fissile isotope uranium-235 (U-235), which is typically fabricated into fuel elements as a series of stacked pellets within a cylindrical metal cladding. A number of individual fuel elements are then bundled into a larger unit, referred to as a fuel assembly, for ease of handling during shipping and refueling.
Water provides both the coolant and neutron moderator functions in a LWR. The moderator in a reactor serves to reduce the energy of neutrons generated by the fission process. The lower energy neutrons are more readily absorbed by U-235 in the fuel to produce additional fissions, thereby sustaining a fission chain reaction. The primary coolant circulates through the reactor core to remove heat and carry it to the heat exchanger, where the heat is transferred to the secondary coolant (also water in the case of commercial PWRs) which is converted to steam to drive the turbine generator.
The power level in the core of the reactor is regulated in part by devices that contain neutron-absorbing materials, typically cadmium or boron, which prevent neutrons from interacting with fuel to produce fission reactions. These materials are incorporated into control rods which can be inserted into spaces within or between the fuel assemblies to control the power level in that region of the core. The control rods are configured in such a way that the nuclear reaction is completely shut down when all of the control rods are fully inserted.
The power level in the region of new fuel assemblies can also be regulated by incorporating neutron absorbing materials directly into the fuel elements or assemblies, thereby maintaining a more uniform power density throughout the core and extending the useful life of the new fuel elements. The absorbers in the fuel assemblies consist of isotopes that readily absorb neutrons, and in the process are transformed into different isotopes that absorb neutrons less efficiently (hence, they are referred to as burnable absorbers). As the active fuel in the assembly is depleted, the neutron absorber in the assembly is also depleted. When a fuel assembly becomes sufficiently depleted of fissile material that it cannot sustain the required power level, it must be removed from the reactor and replaced by a new fuel assembly. CLWRs typically replace part of their fuel on a rotating schedule every 12-18 months, a process referred to as the refueling cycle.
The fuel assemblies in PWRs of the design proposed for the TPBAR irradiation consist of fuel element lattices that contain spaces in the lattice into which either burnable absorber rods or control rods may be inserted. If the fuel assemblies are to contain burnable absorbers, the absorber material is incorporated into separate rods that fit into the lattice openings. The absorber material used for many commercial PWRs consists of borosilicate glass encased in a stainless steel cladding. The absorber rods are attached to a hold-down plate that, in turn, fits into the top of the fuel assembly. The burnable absorber assemblies can be removed from the fuel assemblies after the fuel has been through one operating cycle. This fuel configuration is convenient for the proposed tests because the TPBARs can be incorporated into fuel assemblies in place of the conventional burnable absorber rods. The major difference between conventional PWR burnable absorber rods and the TPBARs would be the use of a lithium aluminate ceramic as a neutron absorber in place of the standard borosilicate glass. At the end of the operating cycle, the TPBAR assemblies could then be removed from the host fuel assemblies and shipped for examination without the need to transport or handle the irradiated fuel.
When a utility desires to implement design modifications in a commercial reactor that may affect fuel performance or other systems that provide reactivity control (such as substituting TPBARs for the conventional burnable absorber rods), a lead test assembly (LTA) program can be conducted to confirm specific expected behavior in a reactor. An LTA program usually consists of a limited number of assemblies of the proposed new design (typically an even number for symmetry), which are inserted into the reactor core at the beginning of an operating cycle in order to demonstrate satisfactory performance of the components. Such a program is appropriate for the use of TPBARs containing lithium in place of the standard boron neutron absorbers in a PWR burnable absorber assembly.
The Proposed Action expands upon more than ten years of DOE research and development activities associated with tritium production targets for LWRs. As part of this research, target irradiation, PIE, and safety testing has been performed entirely at DOE facilities. During the Proposed Action, the NRC would oversee activities that take place at its licensee facilities. The NRC has reviewed a technical report prepared by DOE to document the performance and safety basis for the TPBAR design (Erickson et al 1997), and has issued a safety evaluation report with regard to the proposed tests. (NRC 1997).
2.2 Description of the Proposed Action
The Proposed Action would confirm the results of developmental testing conducted previously at DOE facilities and provide DOE with information regarding the actual performance of the TPBARs in a CLWR. It would also demonstrate that tritium production could be carried out within the normal operating and regulatory constraints associated with a commercial nuclear power facility, without affecting the plants safety systems, production capacity, or normal operations. These activities would provide added confidence to the utilities and the NRC, which regulates commercial power reactors, that tritium production in a CLWR could meet national security needs in a technically straightforward, safe and cost effective manner.
Activities associated with the Proposed Action include replacing four conventional PWR burnable absorber assemblies with assemblies containing the TPBARs (referred to as TPBAR-LTAs) during the next refueling outage at the Watts Bar Nuclear plant (WBN), Unit 1 (operated by the Tennessee Valley Authority (TVA)) in southeastern Tennessee. See Figure 2.1 for a graphical depiction of the Proposed Action. The TPBARs would be shipped from the Hanford Site near Richland, Washington to the Westinghouse fuel fabrication facility in Columbia, South Carolina, for assembly into TPBAR-LTAs (see Figure 2.2). The TPBAR-LTAs would be inserted into four new fuel assemblies at Westinghouse. The fuel assemblies with the TPBAR-LTAs (hereafter referred to as integrated assemblies) would then be shipped to WBN with the rest of the new fuel and stored until the next refueling outage, when they would be inserted into the reactor. A typical fuel reload would contain more than 1000 burnable absorber rods, of which 32 would be replaced by the TPBARs in the proposed test.
The TPBAR-LTAs would be irradiated for one complete operating cycle (approximately 18 months), following which they would be removed from the integrated assemblies and stored in the spent fuel pool. The fuel assemblies would be placed back in the reactor as part of the refueling process. The TPBAR-LTAs would be shipped to the Pacific Northwest National Laboratory (PNNL) at Hanford for post-irradiation examination (PIE). Because the fuel assemblies from the integrated assemblies could be returned to the reactor core during refueling, no shipment or disposal of spent nuclear fuel would be required as part of the Proposed Action.
As part of the PIE activities at Hanford, the TPBARs would be removed from the remaining hardware. The TPBARs would then be subjected to non-destructive evaluation (NDE), including a visual inspection and gamma radiography. The TPBARs would also be punctured to collect and analyze any gases that accumulate during irradiation, and the penetrations would be sealed before the TPBARs are stored or processed further.
After the initial NDE at PNNL, the TPBARs may also be examined by neutron radiography at a facility yet to be determined. For the purposes of this analysis, neutron radiography was assumed to take place at the Hot Fuels Examination Facility (HFEF) located at the Argonne National Laboratory-West (ANL-W) near Idaho Falls, Idaho. Upon completion of the neutron radiography, the TPBARs would be returned to PNNL for destructive examination. For this evaluation, laboratory wastes that result from the destructive examinations, intact spent TPBARs, and residual equipment and materials that remain from cleaning out the facilities are assumed to be dispositioned as waste at the Hanford Site. The small quantities of radioactive waste that may be generated at other locations would be disposed with similar wastes from those facilities. Additional information about each phase of the Proposed Action is provided in the following sections.
2.2.1. Pre-Irradiation Transport and Assembly of TPBAR-LTAs
Initially, the TPBARs would be shipped from the Hanford Site to the Westinghouse fuel fabrication facility for assembly into the TPBAR-LTAs and integrated assemblies. Prior to placement in the reactor, the TPBARs are not radioactive nor do they contain hazardous materials as defined by the Department of Transportation (DOT) in 49 CFR Part 171-178. (Figure 2.3 depicts transportation route options for the Proposed Action.)
Thirty-two TPBARs (plus a limited number of spares) would be required for the Proposed Action. General information regarding the TPBAR design is included in this section; Appendix A contains additional information. The exterior dimensions of the TPBAR are compatible with those of a standard Westinghouse burnable absorber rod - approximately 0.381 inch (1 cm) in diameter and 152 inches (390 cm) long. The TPBARs contain lithium aluminate absorber in the form of stacked cylindrical elements, a Zircaloy-4 liner, and a nickel-plated zirconium getter to trap and retain the tritium in a solid matrix. The getter is an effective mechanism to contain the tritium. In fact, it is extremely difficult to extract the tritium from the getter which requires very high temperatures for an extended period of time. The TPBAR cladding consists of Type 316 stainless steel with a wall thickness of 0.0225 inch (0.057 cm). The cladding also has an aluminum coating to minimize permeation of hydrogen through the cladding. The TPBAR end plugs are of a standard Westinghouse design and are seal-welded in place.
At the Westinghouse fuel fabrication facility, 8 TPBARs and 16 thimble plugs would be attached to a hold-down assembly to make up a single TPBAR-LTA (which contains 24 possible burnable absorber rod locations). Figure 2.2 depicts the TPBAR-LTA. Each TPBAR-LTA would undergo a standard acceptance inspection before incorporating it into an integrated fuel assembly. Four TPBAR-LTAs would be prepared, each of which would be placed into one fuel assembly to provide the four integrated assemblies required for the LTA program. The integrated assemblies containing the TPBAR-LTAs would be loaded into standard unirradiated fuel shipping containers and transported to WBN. The shipments would likely utilize a commercial carrier authorized to transport radioactive materials of low-specific-activity on interstate highways.
2.2.2. Irradiation
The integrated assemblies containing the TPBAR-LTAs would be received at WBN and transported through the truck bay door, into the truck bay, and through the truck bay overhead hatches to the refueling floor. The integrated assemblies and the rest of the new fuel would undergo a receiving inspection, following which they would be stored in preparation for loading into the reactor core during the refueling outage.
The TPBAR-LTAs would remain in the core for one operating cycle and would receive approximately 450 to 550 effective full power days of exposure. After one cycle of irradiation, during the next refueling outage, the integrated assemblies would be removed from the reactor core and transported under water to the spent fuel pool. The TPBAR-LTAs would then be removed from the integrated assemblies, and the fuel assemblies that held the TPBAR-LTAs would be reloaded into the reactor core with the new reload fuel.
2.2.3. Post-Irradiation Transportation
Following the refueling, an NRC-certified Type B shipping cask would be shipped to WBN and transported to the spent fuel pool floor through the previously described path. No cool down period is necessary for transport of the TPBAR-LTAs; therefore, the shipment would likely occur after the refueling outage to minimize operational impacts on the WBN restart. The cask would be placed in the fuel cask loading area in the spent fuel pool, and one or two of the TPBAR-LTAs would be loaded into the cask under water. The loaded cask would be lifted out of the spent fuel pool and moved to the cask wash down area. The cask would be washed down, drained, decontaminated, transported to the truck bay, and loaded on a truck. Up to 4 exclusive use shipments would be used to transport the cask containing the irradiated TPBAR-LTAs to the 325 Building at Hanford.
2.2.4. Post-Irradiation Examination
Post-irradiation examinations would be performed at the Hanford Site 325 Building and possibly at a neutron radiography facility to be identified in the future. PNNL would conduct all PIE activities other than the neutron radiography.
The 325 Building in the Hanford Site 300 Area houses a variety of laboratories, three hot cells and a cask unloading gallery in the rear of the cells. (See Figure 2.4) Some construction would be necessary in order to accept and unload the shipping cask at the 325 Building. The construction would consist of making a new penetration in the south wall of the A hot cell and installing an access door. Some additional modifications would be required to relocate a stairway inside the building but external to the hot cell. However, all of the planned construction activities would be performed inside the current building footprint, and no construction external to the building would be required.
After the cask is unloaded at the Hanford 325 Building, the TPBAR-LTAs would be moved to the A cell facility through the new access port. The TPBAR-LTAs would be disassembled inside the A cell, and all ancillary hardware (such as the hold down assembly, attachment nuts, and thimble plugs) would be packaged and dispositioned as low level radioactive waste. The TPBARs would undergo an initial non-destructive evaluation, including a visual inspection and gamma radiography. All of the TPBARs may then be punctured to collect and analyze any gases that accumulated during irradiation, and the penetrations would be resealed prior to storage or further handling.
If neutron radiography is to be performed, all of the TPBARs would be loaded into an NRC-certified Type B shipping cask and transported to the neutron radiography facility for additional non-destructive examination. The HFEF at ANL-W was analyzed as a representative location for this activity. The HFEF is used by DOE for neutron radiography on a variety of materials including components similar to the TPBARs. The HFEF can only radiograph a 9' 6" (2.9 m) length; thus each rod would be flipped end-to-end such that a radiograph of the full length of the rod can be obtained. Upon completion of neutron radiography, the TPBARs would be reloaded into the shipping cask and returned to Hanford.
The TPBARs would be stored in sealed containers within the 325 Building hot cell facility until they are removed for destructive examination. Destructive examination of the TPBARs involves 2 major activities:
For sectioning, at least one TPBAR from each TPBAR-LTA would be moved into the B cell facility and cut in preparation for examination. Helium, lithium, tritium, and protium assays would be performed on various sections from the TPBARs. Metallographic examinations would also be performed on various components including the cladding. Extraction of tritium from the TPBARs involves puncturing and heating the TPBARs in a closed system to drive off tritium trapped in the solid components. The gases are then collected and analyzed to determine the quantity and chemical state of recovered tritium. In addition to the PIE tests, additional experiments to evaluate the permeability of the TPBAR cladding material to tritium would also be conducted using tritium from a commercial source. Examination of small samples from the TPBARs may take place in other laboratories within the 325 building or at another appropriate laboratory in the 300 Area. Depending on the results of the destructive examinations, additional TPBARs (up to all 32) may be selected for further examination.
2.2.5. Interim Storage and Waste Disposition
Any TPBARs that are not subjected to destructive examination would be stored at Hanford until another use for them is identified or DOE decides to dispose of them. Prior to disposal, the tritium would be extracted from any remaining intact TPBARs and recovered for other purposes or packaged separately for disposal.
Preparation of the integrated assemblies at the Westinghouse fuel fabrication facility would not produce any radioactive or hazardous wastes in addition to those typically generated at the facility. Wastes associated with irradiation of the integrated assemblies at WBN would consist of low-level radioactive liquids and solids generated as the TPBAR-LTAs are removed from the spent fuel pool and packaged for shipment to Hanford. These wastes would be treated as appropriate and disposed of at an NRC-licensed commercial facility with wastes from routine operations at WBN.
Wastes produced during disassembly of the TPBAR-LTAs and NDE of the TPBARs at Hanford would consist of laboratory materials and protective clothing used to prevent possible spread of contamination during receipt, handling, and examination. Those wastes would be disposed of at Hanford in facilities appropriate to the waste type. Likewise, any radioactive waste generated by neutron radiography at ANL-W would consist of small quantities of laboratory materials used to survey the shipping cask for external contamination and disposable protective clothing such as gloves. Waste generated during activities at ANL-W would be managed onsite at the INEEL.
The quantities of low-level radioactive waste generated during PIE of the TPBARs at Hanford would consist of cuttings and small sections of the cladding and internal components, laboratory materials used to control spread of contamination, and either solid molecular sieve or bubbler liquids used to trap the tritium contained in gaseous effluents from the sectioning and extraction processes. Smaller quantities of mixed low-level waste could be produced during liquid scintillation counting of tritium samples, and a small quantity of nonradioactive hazardous wastes would be produced during the laboratory activities as well. Additional radioactive wastes would result from decontamination of the hot cells and removal of unneeded equipment after the work is completed. All radioactive and hazardous wastes generated at Hanford would be disposed of either at the onsite burial grounds or in permitted commercial disposal facilities in accordance with applicable state and federal regulations. Mixed low-level wastes would be stored onsite in permitted facilities. Section 5.3 of this EA contains additional information concerning waste management.
Figure 2.1 General Depiction of the Proposed Action
Figure 2.2 Tritium Producing Burnable Absorber Rods - Lead Test Assembly (TPBAR-LTA)
Figure 2.3 Proposed Action Transportation Routes
Figure 2.4 Hanford Site 325 Building and Hot Cells
