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Liquid Low-Level Waste Processing

#3535


Development of Microspherical Materials Based on Cenospheres for Processing Liquid Low-Level Waste of Nuclear Plants

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment

Status
8 Project completed

Registration date
01.06.2006

Completion date
17.02.2011

Senior Project Manager
Rudneva V Ya

Leading Institute
Siberian Branch of RAS / Institute of Chemistry and Chemical Technology, Russia, Krasnoyarsk reg., Krasnoyarsk

Supporting institutes

  • Mining and Chemical Complex, Russia, Krasnoyarsk reg., Zheleznogorsk

Collaborators

  • Lawrence Livermore National Laboratory, USA, CA, Livermore\nNuclear Safety Solutions Limited, Canada, ON, Toronto

Project summary

The typical scheme of the low-level waste (LLW) processing at radiochemical plants producing plutonium in Russia (for example, Industrial Association "Mayak", Siberian Chemical Combine, Mining and Chemical Combine) includes the successive application of the dredge coagulation with the use of coagulants (iron sulphate), sedimentation, filtration, and two- or three-step purification on ion exchange resins. The radioactive hydroxide pulps being formed and purified water with some remaining activity go to open-air pools for storage. The existing technology comes into conflict with environmental challenges for nuclear plants by the reason of a huge amount (2-3% of LLW being processed) of tail wastes inherent for the existing technology (hydroxide pulps, solutions of column regeneration, spent ion exchange resins) and the necessity to utilise open-air pools to store the hydroxide pulps.

The goal of the proposed project is to gain input specifications required to develop the technology for LLW processing, which provides (i) the significant reduction of wastes inherent to the technology, (ii) elimination of using open-air pools for liquid radioactive waste (LRW) storage and depositories of radioactive salt concentrates, and transformation of radioactive waste into the stable form suitable for the long-term storage or disposal.

For a number of years the Institute of Chemistry and Chemical Technology SB RAS (ICCT SB RAS) and Federal State Unitary Enterprise “Mining and Chemical Combine” (FSUE MCC) have been developing a novel approach to liquid radioactive waste management, which is based on utilisation of coal fly ash components, first of all, hollow silica-alumina microspheres (cenospheres). In the ICCT SB RAS, a number of cenospheres-derived porous materials for LRW immobilization and long-term isolation were produced. Among them, the molded open-cell porous material patented in Russia and the USA has been mostly advanced in Russia and abroad (Patents RU21651 of April 10, 2001; RU2190890 of October 10, 2002; RU2196119 of January 10, 2003; US6444162 of September 03, 2002; and US6472579 of October 29, 2002). The proposed project is a further progress of this approach and provides for development of active cenosphere-derived filter materials having coagulation and sorption properties as well as being able to trap specific components of LLW thus allowing for their fixation in the structure of stable mineral-like compounds. At the same time, the fundamental possibility to avoid the coagulant utilization by means of prior ozonation at an initial step of LLW processing was demonstrated at MCC (RU 2083009, priority of June 23, 1993). According to the tentative assessment, combination of an active filtration step with the prior ozone treatment of liquid LLW could provide a significant decrease of radioactive pulp amount and reduction of the bulk activity of LLW being purified.

The essence of the proposed technical approach is to replace the low effective stages of coagulation – sedimentation, which result in radioactive pulp formation, with the more efficient ozonation step for destruction of the organic constituent of LLW followed by filtration through active filters prepared from cenospheres of coal fly ash. As a result of ozonation, oxidation of metals up to the state of the highest oxidation degree, in which they are hydrated, will take place with formation of hydroxides. The ozonation option must exclude the formation of carboxylic acids, which form the complex compounds with radionuclides and, in that way, prevent from their sorption on ion-exchange materials. Ozonated solution is clarified on active cenospheres-derived filters due to removal of dredges and colloids and then goes to microspherical zeolite sorbents (MZS) trapping the dominant part of the determinative radionuclide and also other radionuclides, providing the considerable decrease of the solution bulk activity before purification on ion exchange resins. Then the solution is filtered through the cascade of alternate cation- and anion exchange resins followed by discharging the purified water into the open hydro system. The advantage of the proposed scheme is the absence of the coagulation step with use of coagulants and sedimentation of dredges, as well as the decrease of the radioactive load on the ion exchange resins. It provides the possibility of their more prolonged exploitation. Due to the more efficient trapping of radionuclides at the subsequent filtration step, the high level of water purification will be achieved. The additional environmental premium is achieved owing to the processing of radioactive salt solutions resulted from resin regeneration with the use of spent silica-alumina cenosphere filters and MZS, which act as matrices for fixation and solidification of all solution active components followed by immobilization in cement, ceramic or glassy compounds.

The initial material to prepare the active filters and MZS is close-cut fractions of cenospheres, which will be isolated from cenosphere concentrate according to the scheme combining steps of grain-size classification, hydrodynamic and magnetic separations with the use of equipment, such as the vibrating sifter with a set of sieves, 138T magnetic separator and hydrodynamic separator of periodic operation. To obtain the active materials, cenospheres will be chemically modified by different methods (acid etching, hydrothermal treatment, impregnation of active components). The materials obtained will be characterized by different physicochemical methods, such as chemical and X-ray diffraction analyses, optical and scanning electron microscopies, infra red and Mossbauer spectroscopies, measurement of their porous structure, determination of sorption parameters, distribution coefficients, isotherms, etc.).

During the implementation of the project the scope of activities will include works on synthesis and selection of active filter materials, adjustment of their parameters to the technological requirements for the industrial liquid LLW processing, as well as on development of engineering solutions and finalizing of process variables for liquid LLW treatment. As a result, the pilot tests of the actual liquid LLW purification will be carried out and the source data for development of the technology for liquid LLW processing will be produced.

The data obtained in the framework of the project implementation will be used for development of the liquid LLW processing technology at plants of a nuclear industry, but for all that the radiochemical plant of MCC is a proving ground for industrial testing of the lab-scale results. At the same time, combination of the ozonation of organic impurities, sorption of metal cations with the use of effective selective sorbents, and deep desalting on the ion exchange resins gives an universality to the technological scheme. That makes it possible to use the project results in the technology for water preparation (for example, water for the primary cooling circuit of water-water energetic reactors (WWER), water for high-pressure boilers at hydro power plants). In the presence of suggestions for collaboration the results obtained will be presented to radiochemical and nuclear power plants both in Russia and abroad.

The project is meeting ISTC goals and objectives, as the MCC scientists and engineers related to weapon plutonium production take part in the overall project realization. This project provides the weapon scientists with the opportunity to redirect their talents to peaceful activities in the area of environmental protection.

Foreign collaborators will promote the realization of the project in the frame of the role presented in their letters. In the course of project implementation the scope of cooperation with collaborators will include information exchange, conduction of joint seminars, assistance for the project participants to join international meetings. Collaborators having a free access to the new results of the project can check this technology for their own LLW processing or for water treatment. If the positive effects in this area will be achieved, then an agreement about the joint patenting and commercialization of the technology will be realised.


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