[en] Coagulation-flocculation, membrane separation and ion-exchange are traditional methods for treatment of radioactive wastewater generated primarily from the front end processes of the fuel cycle. Electrocoagulation presents a robust and novel alternative to conventional coagulation process. The present study involves the establishment of electrocoagulation as a treatment process for thorium bearing non-process effluents in batch mode. This involved an electrolytic reactor with iron electrodes. The non-process effluent was subjected to coagulation and floatation by Fe(II) ions dissolved from the anode with the resultant flocs floating on the surface after being captured by hydrogen gas bubbles generated at the cathode. The effect of various operational parameters like initial pH, residence time, current density and initial thorium concentration on the removal efficiency was investigated. Maximum decontamination factor obtained was of the order of 10"4. (author)

[en] During manufacturing of Mixed Oxide Fuel (MOX) pellets for Advance Heavy Water Reactor (AHWR-LEU), around 30% rejected MOX pellets are generated in every cycle. These rejected MOX pellets are dissolved in nitric acid for recovery of U/Th. The recovered U/Th is recycled for production of MOX pellets. MOX pellets of varying compositions are used in AHWR fuel. Dissolution of MOX pellets in nitric acid is a challenging task because of its low surface area and longer dissolution times. High normal nitric acid is used in order to increase rate of dissolution, which in turn results in generation of high free acidity solution which influences the precipitation characteristics of Uranium (VI) by oxalic acid. Oxalic acid precipitation helps in generation of nitric acid which can be used for dissolution there by effectively facilitating nil effluent generation. Precipitation by oxalic acid unlike ammonia has advantage of zero liquid effluent discharge by complete recycle of oxalate filtrate to dissolution section. In the present work, the effect of various parameters like free acidity, residence time, concentration of oxalic acid, initial concentration of uranium and thorium etc. on the precipitation of U(VI) and Th(IV) in nitrate media by oxalic acid was carried out. The precipitated powder was subjected to various morphological evaluations like particle size etc. Study of various parameters on the co-precipitation of uranium and thorium by oxalic acid was carried out. It was observed that complete precipitation (> 99.9%) of thorium as oxalate does not depend on free acidity range (1- 6 N). Excess oxalic acid is not required for complete precipitation of thorium oxalate. The precipitation of uranyl oxalate varies with initial free acidity of solution. Uranyl oxalate precipitation does not take place at and above 5 N of free acidity

[en] Indigenously designed Advanced Heavy Water Reactor utilises (Th-LEU)O_2 MOX as the fuel. During fabrication of MOX fuel, pellets not meeting the quality requirements will be recycled by wet processing for the recovery of uranium and thorium. The present study investigates the feasibility of various processes on the treatment of thorium bearing effluent arising from wet processing of reject MOX pellets. Process involving the reductive precipitation of uranium by sodium dithionite followed by adsorption of thorium onto inorganic sorbent, MST was developed and optimized. Reproducibility of the process under scale up conditions was also established. Under the optimized parameters, percentage removal obtained for uranium, thorium and radium was 99%, 97% and 98% respectively. (author)