Modeling the Performance of the BN-350 Cesium Traps Available to Purchase

A model was generated to evaluate the performance of the cesium trap system used as part of the BN-350 nuclear reactor decommissioning effort in Aktau, Kazakhstan. A series of cesium traps were designed to remove cesium from the reactor primary circuit sodium and piping to minimize personnel radiological exposure while draining and disposing of the sodium during subsequent decommissioning activities. Cesium was trapped by extracting sodium from the primary circuit, passing it through a block of reticulated vitreous carbon (RVC), and returning the cleaned sodium to the primary circuit. Cesium has a strong affinity for adsorbing onto the surface of carbon and RVC in particular has been proven to be an effective cesium collecting material. A model was created to predict and help explain the performance of the system during operation. The model is effectively split into two components, the reactor primary system component and the cesium trap RVC component. The temperature dependent parameters governing the behavior of the system were continuously updated. The model output effectively described the behavior observed during the operation of the first three cesium traps (the final four traps were used to clean a variety of ancillary system whose initially conditions were not well known and, consequently, did not lend themselves to being modeled). The defining system operating conditions were the primary sodium temperature of approximately 290 °C, trap RVC temperatures range of 150 °C to 260 °C, and dissolved cesium concentrations in the primary sodium ranging from 7.2×10⁻³ Ci/kg to 2.4×10⁻⁴ Ci/kg.