A spare mixing pump from the Hanford Grout Program was installed in Hanford double-shell waste Tank 241-SY-101 on July 3, 1993, after being modified to take advantage of waste stratification. It was anticipated that pump mixing would prevent large episodic flammable gas releases that had been occurring about every 100-150 days. A cautious initial test plan, called Phase A, was run to find how the pump and tank would behave in response to very brief and gentle pump operation. No large gas releases were triggered, and the pump performed well except for two incidents of nozzle plugging. On October 21, 1993, the next test series, Phase B, began, and the pump was applied more aggressively to mix the tank contents and mitigate uncontrolled gas releases. Orienting the pump in new directions , released large volumes of gas and reduced the waste level to a near-record low. Results of the entire period from pump installation to the end of Phase B on December 17, 1993, are presented in detail in this document. Though long-term effects require furtherevaluation, we conclude from these data that v the jet mixer pump is an effective means of controlling flammable gas release and that it has met the success criteria for mitigation in this tank. iii SZrMMARY A mixer pump was found to be effective in controlling and possibly eliminating large episodic flammable gas releases from Hanford Tank 241-SY-I01. A gas release event (GRE) is apparently initiated when a major portion of the gas-bearing sludge layer accumulates sufficient gas to become buoyant, pull flee from the surrounding material, rise through the surface crust, and release the trapped gas into the dome space. Mixer pump operation is intended to keep enough of the gas-generating material in suspension so that gas is released continuously instead of periodically in large, potentially dangerous GREs.. A spare mixing pump from the HartfordGrout Program was modified and installed in the tank on July 3, 1993, seven days after a typical GRE that met the safety criteria for pump installation. The modifications were made to take advantage of the density stratification in the waste, providing vertical v buoyant motion as well as high jet velocity to promote mixing. The initial pump operations in Phase A testing were extremely gentle, beginning with a series of daily pump 'bumps' intended to keep the pump nozzles clear. Because nozzle plugging did occur, bump speed and duration were increased, eventually arriving at the accepted five-minute period at 1000 rpm on July 26. There has been no nozzle plugging since then. Bumping was initially performed twice a day through mid-August and once a day through the start of Phase B testing October 17. By the end of Phase B, thrice-weekly bumping during nontesting periods became the rule. ACKNOWLEDGMENTS The authors wish to thank Jeanne Lecher for supplying plots of various data under high pressure and short notice, to our editor Sheila Bennett for working extra hours to put all the pieces together, and to Kathy Hildebrant for helping with th...

The Full-Scale Mixer Pump Test Program was performed in Hanford Tank 241-SY-101 from February 4 to April 13, 1994, to confirm the long-term operational strategy for flammable gas mitigation and to demonstrate that mixing can control the gas release and waste level. Since its installation on July 3, 1993, the current pump, operating only a few hours per week, has proved capable of mixing the waste sufficiently to release gas continuously instead of in large episodic events. The results of Full-Scale Testing demonstrated that the pump can control gas release and waste level for long-term mitigation, and the four test sequences formed the basis for the long-term operating schedule. The last test sequence, jet penetration tests, showed that the current pump jet creates flow near the tank wall and that it can excavate portions of the bottom sludge layer if run at maximum power. Pump mixing has altered the 'normal' configuration of the waste; most of the original nonconvective sludge has been mixed wi_ the supernatant liquid into a mobile convective slurry that has since been maintained by gentle pump operation and does not readily return to sludge.

SUBJECTS Light water reactor fuel I High-level radioactive waste management TOPICS Spent-fuel storage Thermal hydraulics models AUDIENCE Fuels engineers I R&D scientists Heat transfer Shielding Testing and Analyses of the TN-24P PWR Spent-Fuel Dry Storage Cask Loaded With Consolidated Fuel Full-scale testing has confirmed that the TN-24P storage cask offers a technically sound and practical method for storing consolidated spent fuel. COBRA-SFS code predictions of cask performance at conditions near its design limits agreed very well with actual test data. BACKGROUND As at-reactor storage basins attain maximum capacity, many utilities are expected to implement dry spent-fuel storage systems. To demonstrate the storage of dry spent fuel in large metal casks, EPRI and DOE have sponsored tests of metal casks loaded with unconsolidated fuel at the Idaho National Engineering Laboratory (INEL). This most recent study was initiated to investigate a TN-24P cask containing consolidated fuel. OBJECTIVES To demonstrate the thermal, shielding, and operational performance of the TN-24P cask loaded with consolidated spent nuclear fuel; to assess the ability of the COBRA-SFS heat transfer code (developed by Pacific Northwest Laboratory) to model the cask system and predict thermal performance. APPROACH Prior to the testing, the TN-24P cask contained 24 unconsolidated PWR assemblies from Virginia Power's Surry nuclear power station. The project team replaced the assemblies with 24 canisters of spent fuel, consolidated at a ratio of two assemblies per canister. INEL's rod consolidation project provided the filled test canisters. Researchers used the COBRA-SFS computer code to predict cask thermal performance. The team then instrumented and tested the cask in horizontal and vertical positions with three internal storage environments (nitrogen, helium, and vacuum). They compared the COBRA-SFS predictions with actual test data, refined the code to reflect test results, and performed posttest predictions. Transnuclear, Inc., the cask manufacturer, sponsored an additional test to simulate the insulating influence of impact limiters. RESULTS The TN-24P cask is well suited to store consolidated spent fuel. Its heat transfer performance was exceptionally good, as peak cladding temperatures for a cask heat load of 23.3 kW were well under 300°C with helium, ORDERING INFORMATION Requests for copies of this report should be directed to Research Reports Center (ARC), Box 50490, Palo Alto, CA 94303, (415) 965-4081. There is no charge for reports requested by EPRI member utilities and affiliates, U.S. utility associations, U.S. government agencies (federal, state, and local), media, and foreign organizations with which EPRI has an information exchange agreement. On request, ARC will send a catalog of EPRI reports.

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Printod inThis document presents a complete description of Cycle 2 of COBRA-SFS, and consists of three main parts. Part I describes the conservation equations, constitutive models, and solution methods used in the code. Part 11 presents the User Manual, with guidance on code applications, and complete input instructions. This part also includes a detailed description of the auxiliary code RADGEN, used to generate grey body view factors required as input for radiative heat transfer modeling in the code. Part I11 describes the code structure, platform dependent coding, and program hierarchy. Installation instructions are also given for the various platform versions of the code that are available.iii