DOE OSTI2012
Spent ion-exchange resins are considered to be problematic waste that, in many cases, requires special approaches and precautions during their conditioning to meet the acceptance criteria for disposal. In Belgium, for economical reasons, the Volume Reduction Factor is a key criterion. After Tractebel Engineering performed a technical and economical comparison of the industrially available systems, Tihange NPP decided to install a spent ion-exchange resins hot supercompaction unit with Tractebel Engineering in the role of architect-engineer. The treatment and conditioning unit processes the spent ion-exchange resins through the following steps: dewatering of the resins, drying the resins under deep vacuum, discharging the dried resins into compactable drums, super-compacting the drums to generate pellets, grouting the pellets into standard 400 litres waste drums (overpacks) licensed for final disposal in the near-surface repository in Belgium. Several developments were required to adapt the reference process and equipment to PWR spent ion-exchange bead resins and Belgian radioactive waste acceptance criteria. In order to avoid cracks on the compacted drum, and external surface contamination from resin leaks, some improvements were achieved to minimize spring-back as well as the risk of cracking the drum wall. Placing the compactable drum inside a second, slightly larger drum, guarantees clean and reproducible pellets. Currently the commissioning phase is on-going. Numerous process validation tests have been completed. An acceptance file was transmitted to the Belgian Waste Management Authority recently. This will be followed by demonstration tests necessary to obtain their final acceptance of the installation. More than 3 800 drums of mixed powdered and bead resins have been processed by the reference Hot Compaction process, achieving a Volume Reduction Factor (VRF) of 2.5. The equipment has been proven to be a reliable technology with low operation and maintenance costs. Tractebel Engineering has managed the construction of a new application of this process in Belgium at Tihange NPP. Several developments were required to adapt the reference process and equipment to PWR spent ion-exchange bead resins and Belgian radioactive waste acceptance criteria. The chosen method of conditioning (draining, drying and compaction of the spent resins followed by grouting of the pellets in a 400 litres drum) immobilizes the spent resins under the form of a solid, compact, stable, and non dispersible block free of interstitial water. The various series of inactive tests which were conducted at Tihange NPP, helped among others to determine the best design of the compactable drum and lid and to set the value of critical parameters such as vapour temperature at the end of drying, speed, force and duration of compaction. In an environment of very limited space for interim storage and in the absence of an operational final repository site, or in the case of high final disposal costs, the process exhibits the following key advantages: - Achieving a Volume Reduction Factor (VRF) close to 1 (overpack included) for the interim storage instead of increased volumes observed with other currently available processes; - Achieving a water free end product; - Creating a flexible waste product for interim storage (pellet), which can be retrieved and routed into alternative types of package later, if not initially grouted; - Using well proven standard technologies like drying and compaction; - Flexible use of the system components for the supercompaction of other operational solid waste streams when not conducting resins conditioning campaigns. (authors)
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗