Gas Retention, Gas Release, and Fluidization of Spherical Resorcinol-Formaldehyde (sRF) Ion Exchange Resin

Abstract

Executive SummaryThe Low-Activity Waste Pretreatment System (LAWPS) is being developed to provide treated supernatant liquid from the Hanford tank farms directly to the Low-Activity Waste (LAW) Vitrification Facility at the Hanford Tank Waste Treatment and Immobilization Plant. The design and development of the LAWPS is being conducted by Washington River Protection Solutions, LLC. A key process in LAWPS is the removal of radioactive Cs from LAW liquids using ion exchange (IX) columns filled with spherical resorcinol-formaldehyde (sRF) resin. When loaded with radioactive Cs, radiolysis of water in the LAW liquid will generate hydrogen gas. In normal operations, the generated hydrogen is expected to remain dissolved in the liquid and be continuously removed by liquid flow. One accident scenario being evaluated is the loss of liquid flow through the sRF resin bed after it has been loaded with radioactive Cs and hydrogen gas is being generated by radiolysis. For an accident scenario with a loss of flow, hydrogen gas can be retained within the IX column both in the sRF resin bed and below the bottom screen that supports the resin within the column, which creates a hydrogen flammability hazard. Because there is a potential for a large fraction of the retained hydrogen to be released over a short duration as a gas release event, there is a need to quantify the size and rate of potential gas release events. Due to the potential for a large, rapid gas release event, an evaluation of mitigation methods to eliminate the hydrogen hazard is also needed. One method being considered for mitigating the hydrogen hazard during a loss of flow accident is to have a secondary flow system, with two redundant pumps operating in series, that recirculates liquid upwards through the bed and into a vented break tank where hydrogen gas is released from the liquid and removed by venting the headspace of the break tank. The mechanism for inducing release of gas from the sRF bed is to fluidize the bed, which should allow retained bubbles to rise and be carried to the break tank.Currently, neither the ability of fluidizing a settled sRF bed to release gas nor the quantity of hydrogen gas that can be retained and the corresponding potential for large, rapid gas release events has been tested and evaluated. Accordingly, the purpose of this study was to conduct experiments and develop models that evaluate the ability of a re-circulating flow system to fluidize an sRF resin bed as a method to release retained hydrogen gas and maintain hydrogen gas retention at low levels, thereby avoiding conditions where hydrogen gas poses a flammability hazard. The purpose of the study was also to determine if effective hydrogen gas release would occur using a single constant fluidization velocity, because this is the most simple safety system to implement, for the range of fluid and sRF resin conditions anticipated in the column (because a velocity that is effective for one fluid/resin pair can be ineffective for different resin/fluid pairs). Finally, the study...