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Treatment of Radioactive Wastes

#A-1655


Treatment of Radioactive Wastes of Nuclear Power Plants by their Immobilization into the Stable Matrix Glass-Crystalline Materials – Pyrocerams (Sitalls) on the Base of Natural Minerals

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment
  • CHE-SAS/Safety and Security/Chemistry
  • ENV-EHS/Environmental Health and Safety/Environment
  • ENV-WDS/Waste Disposal/Environment
  • MAT-CER/Ceramics/Materials
  • OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences

Status
3 Approved without Funding

Registration date
17.06.2008

Leading Institute
Yerevan State University, Armenia, Yerevan

Supporting institutes

  • Armenian NPP, Armenia, Metsamor

Collaborators

  • Friedrich-Schiller-Universitat / Institut fur Geowissenschaften, Germany, Jena\nStoller Ingenieurtechnik GmbH, Germany, Dresden\nANDRA, France, Chatenay Malabry\nNational Research Council, Italy, Rome\nQueen's University / Department of Civil Engineering, Canada, ON, Kingston\nSystemanalyse Umwelt-Beratung, Germany, Wernigerode

Project summary

The purpose of the project is the development of the innovative resource-saving technology of conditioning (sitallization) of radwastes (slurries, sorbents, etc.) by their immobilization into the new stable matrix formed Glass-Crystalline-Materials (GCM) such as special sitalls (pyrocerams) on the basis of natural minerals and rocks of Armenia.

The risk of the increased levels of radioactive radiations determines a special attitude to the atomic energy and radwastes (RW) and demands the acceptance of cardinal and operative measures on their isolation from people. Based on the analysis of the incidents at the Nuclear Power Plants (NPP) and other facilities, we can determine three basic trends on RW management:

  • RW processing with the extraction of the radioactive nuclides for their further use;
  • transformation of the liquid radwaste (LRW) into the hard form and their storage;
  • RW entombment in geological formations.

Now the most actual (and not optimally solved) problem is the minimization of concentrated liquid radwaste (CLRW) with their transformation into the stable form. For the reduction of LRW volumes the concentrating by distillation or Deep Evaporation with the reception of middle active and highly-saline CLRW is applied. The CLRW immobilization technology with the use of matrixes such as glass or cement is wildly spread everywhere for the provision of safe storage. Thus, the matrix blocks with the immobilized radioactive nuclides are usually packed into metal or concrete capacities, and the products from the Deep Evaporation Machine (DEM) are placed into the special containers for the subsequent long storage.

The construction of storehouses, the adoption of special measures on their waterproofing, and also the storage of containers with DEM products at the NPP are technologically difficult problems which demand significant expenses and don’t provide the safe storage of CLRW. As regards the glass matrixes, they allow to reduce the volume of the conditioned waste products and to improve sharply physical and chemical properties of the matrix, but at the same time due to an amorphous structure have a number of disadvantages such as: high fragility, presence of numerous structural defects, low homogeneity and density and also rather low radiation resistance.

Within the framework of ISTC project A-485 “Efficient Treatment of Radioactive Liquid Waste by Zeolites Modified through Chemical and Radiation Methods” at Yerevan State University, the researches on the development of LRW sanitation technology of Armenian NPP with the use of various natural sorbents have been successfully executed. During the last stage the optimal regimes of the extraction of radioactive nuclides by zeolites have been specified on the pilot machine. Thus, in the static and dynamic conditions the significant reduction of LRW volumes (up to 400-600 times) with their transformation into a hard phase has been achieved. At the same time, the reduction of LRW volumes was considered by the participants of the above mentioned project as a temporary measure till the development of the technology of sitallization of sorbents with high concentration of radioactive nuclides and slurries got from the Deep Evaporation Machine. This direction of works, on which the prediscovery had been carried out, demands much more time and new financial support.

In the suggested project the high-competent personnel will participate. Particularly the participants of the project made the following steps:

  • for the minimization of Armenian NPP LRW the technology of concentration of LRW by the methods of distillation and Deep Evaporation has been introduced;
  • an experimental-industrial technological setup for LRW disposal with the help of chemical radiation modified zeolites has been developed and tested on NPP;
  • the sorption method of sanitation of the aquatic environment from the radioactive nuclides has been developed (including the use of natural sorbents);
  • the properties, compound and structure of the minerals and rocks taking into consideration their use as radiation protectors for isolation of biologically significant radioactive nuclides from the biosphere has been investigated.

The participants of the project accumulated great experience in:
  • research of the aluminosilicate and other systems for formation of GCM matrixes, the compound of which includes analogues of the soil-formation minerals;
  • development and implementation of the new technology of special sitalls production;
  • development of the technology and the manufacturing of natural sorbents;
  • development of the technology of thermo-chemical and microwave modification of natural sorbents.

The current proposal is offered as an evolution of the above mentioned project. This project is devoted to the development of the innovative sitallization technology of the fully used CLRW (evaporation slurries of the liquid radioactive outlets and zeolites fulfilled with the radioactive nuclides gained after adsorption).

Armenia natural and technogenic materials (volcanic glass, perlite, tuff, slag, litoid pumice, boron-containing travertine, barite and etc., and also alkaline and soil- alkaline magmatic rocks of syenite, phonolites, trachytes, nepheline- syenites, etc.) will be used as an initial raw material for sitalls formation.

For the effective and long-term isolation of the fully used sorbents and slurries (the oozy formations accumulated in settling tanks) from biosphere, the authors of the project offered the sitallization technology by the help of the method of their incorporation into stable (against cataclysms) and durable Glass-Crystalline-Materials - sitalls.

The end product of the researches will be homogeneous, recrystallized microcrystalline GCM compound in which the granules of the radioactive sorbents and the particles of slurries will be equally allocated. The ingredients of the silicate GCM create a matrix compound, which isolates the radioactive sorbents from an environment for a long time due to its high stability to external influence and interaction with silica-alumina sorbents on the border of phase contacts. New formations formed in a silicate matrix material will include in their structure radioactive nuclides, particularly cesium and strontium, as a result of isomorphic replacement. At the sufficient mass contents they form independent isostructural phase distinguished by thermodynamic stability and high resistance to the environment.

Thus, within the framework of this project the following primary objectives will be achieved:

  • the reduction of LRW volumes stored at operating NPPs will be achieved, i.e. the special storehouses’ creation expenses will be decreased;
  • RW more safe storage will be provided, i.e. the factor of their migration into the environment will be excluded, as they will be included in more hard crystalline structure;
  • the durability of GCM containing radioactive nuclides will be increased, due to their modification and getting of new mineral-like compounds;
  • the technology of the radioactive sorbents and slurries conditioning will be simplified and cost reduced due to the use of inexpensive, well-known by their radioactively-stable properties natural minerals (rocks and stone waste products) of Armenia.


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