[en] Accumulation of radioactive corrosion product deposits leads to radiation buildup in the various systems of the water cooled nuclear reactors. As a maintenance means to mitigate these problems, satisfactory decontamination is achieved by way of chemical dissolution of the active deposition. This paper summarizes the various in-situ chemical decontamination processes and traces the Indian programme in relation to international scene. (author)

[en] Envisaging the diverse needs of the nuclear industry with respect to decontamination and decommissioning, an organised Research and Development programme was undertaken in India. Under the IAEA Co-ordinated Research Programme, studies were initiated on different areas of Decontamination and Decommissioning. These studies comprised of chemical and electrochemical processes for decontamination. This report summarises the results obtained during different studies carried out in these areas. Laboratory studies on dissolution of magnetite/nickel ferrite powders and oxide films deposited on metal specimens resulted in identifying suitable dilute chemical formulations based on EDTA, oxalic acid, citric acid, ascorbic acid, etc. Studies on the behaviour of ion exchange resins indicated that it is possible to effectively remove the activity with simultaneous regeneration of the formulation chemicals by the cation exchange resins and complete elimination of all the organic acids on mixed bed resins. Study on compatibility of the formulations with the different materials of construction is also reported. Electrochemical parameters have been established for electropolishing of stainless steel components in an electrobath. Creation of a decontamination data base and its usefulness is also reported. (author). 4 refs, 3 figs, 1 tab

[en] A selective and strong in-house chelator has been studied w.r.t. basic parameters like concentration, time, and elution. De-contamination of cadmium, mercury, chromium, lead etc by using high uptake values fro cadmium ions proves its selectivity with high elution ratio ensures further decontamination of run-off water during natural calamities. In three step cascade use the concentration of original cadmium solution (500 ppm) decocted to safe disposable attribute. This polymeric ligand exchanger displayed outlet effluent concentration to 1 ppm and less than 200 ppb when treated for inlet feed concentration of 50 ppm and 500 ppm respectively. (author)

[en] Short communication

[en] Laboratory powder dissolution studies have been carried out on moderately sintered α-Fe₂O₃ (haematite) in citric acid - EDTA - ascorbic acid (CEA) mixtures of different compositions to identify the role of each component and arrive at an optimum composition to effect fast and quantitative dissolution. Experiments involving other reducing agents (in place of ascorbic acid) and chelating agents (in place of EDTA) revealed that there are no better substitutes for these two reagents. Samples prepared by heating ferrous hydroxide at different temperatures from 373 - 1073 K exhibited vastly different dissolution behaviour. chromium substituted iron oxides prepared by heating the coprecipitated mixture of the two hydroxides at high temperature in the required proportions were having low solubility in the CEA mixtures. Pretreatment of these by alkaline permanganate (AP) rendered them somewhat more soluble, particularly in CEA mixtures containing higher ascorbic acid concentrations. Comparative evaluation of the efficacy of single and multi-step AP-CEA and AP-LOMI processes has been made by carrying out experiments on decontamination of contaminated specimens of oxide coated SS-304 surfaces from the reactor water clean-up circuit piping of Tarapur Atomic Power Station (TAPS) BWRs both in one through and closed loop circulation modes. A methodology has been worked out for compaction of the radwastes arising from chemical decontaminations employing AP-CEA and AP-LOMI processes - this involves simply mixing of the AP and CEA or LOMI effluents in proper proportions and digesting at 363 K when MnO₂ precipitates out carrying with it more that 99% of the radioactivity. (author)

[en] Decontamination and decommissioning features which are significantly different for non-reactor facilities as compared to nuclear reactors can be summarised as: potentially high levels of chemical toxicity and radiotoxicity of the alpha emitting radioisotopes, need for criticality control throughout, higher potential for spread of contamination, prompt decontamination/ decommissioning preferred over mothballing or entombing alternatives, complex radiological mapping and characterization situations and complex radiological protection requirements for occupational workers. A brief review of the various aspects of decommissioning of various nuclear installations are given. 7 refs

[en] Natural minerals and some industrial wastes are used as low cost sorbents for removal of metal ions from effluent streams. Apatite as natural mineral and red mud as an industrial waste have been tested for their sorption properties with respect to two important fission products ¹³⁷Cs and ⁹⁰Sr. Their ion exchanging capacity was tested after every 4 hours till 24 hours. The material gets saturated after 4-8 hours. Hence these materials can be considered for treating in treating LLW before discharge, industrial waste treatment and as backfill or admixture material for shallow land repository. (author)

[en] Partitioning of plutonium from uranium is an important step in the reprocessing of spent fuel by PUREX process of solvent extraction using 30% TBP-dodecane. This is achieved by selectively reducing the Pu in solution to least extractable trivalent state by uranous nitrate as the reductant. The latter is conventionally produced by electrolytic reduction of uranyl ion in presence of hydrazine nitrate as uranous nitrate stabilizer using Pt-coated titanium as the anode. The anode plating wears out after period of operation thus affecting the process efficiency and hence the quality control testing of platinum plated electrode becomes important. This article describes the use of Beta backscattering method with strontium-90 radioisotope as non-destructive testing tool for measuring the coating thickness of the sample Ti electrode. The surface characteristics and coating morphology were also examined by scanning electron microscope and the micrographs are presented. (author)

[en] Partitioning of plutonium from uranium is an important step in the reprocessing of spent fuel by PUREX process of solvent extraction using 30% TBP-dodecane. This is achieved by selectively reducing the Pu in solution to least extractable trivalent state by the addition of uranous nitrate as the reductant. The latter is conventionally produced by electrolytic reduction of uranyl ion in presence of hydrazine nitrate as uranous nitrate stabilizer. This is accomplished in an electrolyser cell of Ti-vessel as the cathode and Pt-coated Titanium as the anode. The plating of the anode wears out after period of operation thus affecting the process efficiency and hence the quality control testing of platinum plated electrode becomes important

[en] India's nuclear power program in the third stage relies on Advanced Heavy Water Reactor (AHWR) where mixed oxide (MOX) containing ²³⁹PuO₂ and ²³³UO₂ with thoria (ThO₂) would be used as fuel. Chemical dissolution of ThO₂ was studied in the laboratory to simulate dissolution stage during reprocessing of spent fuel. In earlier studies dissolution of ThO₂ is conducted in boiling 13M HNO₃ in the presence of 0.03MNaF as catalyst and 0.1M Al(NO₃)₃ under reflux. Al⁺³ is added to complex free F^- ion in the solution and reduce corrosion of dissolver vessel made of SS 304-L. Al at 0.1M concentration poses waste loading and viscosity problems during vitrification of high level waste at < 1000 deg C. Considering stability constants of F^- complexes that follow decreasing order of sequence as Zr(IV)>Th(IV)>Al(III)>Be(II)>H⁺, it was felt that Al⁺³ addition can be substituted by addition of small amount of Th(NO₃)₄ prior to dissolution. Reduction in F^- concentration from 0.03M is beneficial from corrosion point of view. Hence studies were conducted with a view to reduce F^- concentration and avoid Al addition. Dissolution characteristics for the pellet as well as pieces are reported here