Cleaning residual NaK in the fast flux test facility fuel storage cooling system
- Fluor Hanford, PO Box 1000, Richland, Washington, 99352 (United States)
- Fluor Government Group, PO Box 1050, Richland, Washington, 99352 (United States)
The Fast Flux Test Facility (FFTF), located on the U.S. Department of Energy's Hanford Reservation, is a liquid metal-cooled test reactor. The FFTF was constructed to support the U.S. Liquid Metal Fast Breeder Reactor Program. The bulk of the alkali metal (sodium and NaK) has been drained and will be stored onsite prior to final disposition. Residual NaK needed to be removed from the pipes, pumps, heat exchangers, tanks, and vessels in the Fuel Storage Facility (FSF) cooling system. The cooling system was drained in 2004 leaving residual NaK in the pipes and equipment. The estimated residual NaK volume was 76 liters in the storage tank, 1.9 liters in the expansion tank, and 19-39 liters in the heat transfer loop. The residual NaK volume in the remainder of the system was expected to be very small, consisting of films, droplets, and very small pools. The NaK in the FSF Cooling System was not radiologically contaminated. The portions of the cooling system to be cleaned were divided into four groups: 1. The storage tank, filter, pump, and associated piping; 2. The heat exchanger, expansion tank, and associated piping; 3. Argon supply piping; 4. In-vessel heat transfer loop. The cleaning was contracted to Creative Engineers, Inc. (CEI) and they used their superheated steam process to clean the cooling system. It has been concluded that during the modification activities (prior to CEI coming onsite) to prepare the NaK Cooling System for cleaning, tank T-914 was pressurized relative to the In-Vessel NaK Cooler and NaK was pushed from the tank back into the Cooler and that on November 6, 2005, when the gas purge through the In-Vessel NaK Cooler was increased from 141.6 slm to 283.2 slm, NaK was forced from the In-Vessel NaK Cooler and it contacted water in the vent line and/or scrubber. The gases from the reaction then traveled back through the vent line coating the internal surface of the vent line with NaK and NaK reaction products. The hot gases also exited the scrubber through the stack and due to the temperature of the gas, the hydrogen auto ignited when it mixed with the oxygen in the air. There was no damage to equipment, no injuries, and no significant release of hazardous material. Even though the FSF Cooling System is the only system at FFTF that contains residual NaK, there are lessons to be learned from this event that can be applied to future residual sodium removal activities. The lessons learned are: - Before cleaning equipment containing residual alkali metal the volume of alkali metal in the equipment should be minimized to the extent practical. As much as possible, reconfirm the amount and location of the alkali metal immediately prior to cleaning, especially if additional evolutions have been performed or significant time has passed. This is especially true for small diameter pipe (<20.3 centimeters diameter) that is being cleaned in place since gas flow is more likely to move the alkali metal. Potential confirmation methods could include visual inspection (difficult in all-metal systems), nondestructive examination (e.g., ultrasonic measurements) and repeating previous evolutions used to drain the system. Also, expect to find alkali metal in places it would not reasonably be expected to be. - Staff with an intimate knowledge of the plant equipment and the bulk alkali metal draining activities is critical to being able to confirm the amount and locations of the alkali metal residuals and to safely clean the residuals. - Minimize the potential for movement of alkali metal during cleaning or limit the distance and locations into which alkali metal can move. - Recognize that when working with alkali metal reactions, occasional pops and bangs are to be anticipated. - Pre-plan emergency responses to unplanned events to assure responses planned for an operating reactor are appropriate for the deactivation phase.
- Research Organization:
- American Nuclear Society, 555 North Kensington Avenue, La Grange Park, Illinois 60526 (United States)
- OSTI ID:
- 21144240
- Resource Relation:
- Conference: DD and R 2007: ANS Topical Meeting on Decommissioning, Decontamination, and Reutilization 2007, Chattanooga, TN (United States), 16-19 Sep 2007; Other Information: Country of input: France; Related Information: In: Proceedings of the 2007 ANS Topical Meeting on Decommissioning, Decontamination, and Reutilization - DD and R 2007, 336 pages.
- Country of Publication:
- United States
- Language:
- English
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