Cementing is the most simple and widely used method of ash residue (AR) conditioning. Traditional cementing is realized by mixing of AR with grout in a mixer or directly in a container.
Moscow SIA “RADON” has developed the method of ash residue (AR) conditioning with high penetrating cement grout (HPCG) (1). The idea of the method is the following. After having fed the ash into a container, the cement grout is pumped under pressure of 0,1 MPa through the feeding pipe into the bottom of container. The cement grout impregnates ash residue and fills the pores. As a result, a durable cement monolith with high content of ash residue is formed. This method has a number of advantages in comparison with the traditional cementing:
• this technological process does not require sorting, batching, shredding and mixing of the ash with grout;
• complicated and expensive equipment is not required;
• no secondary waste is produced;
• the final conditioned volume does not increase in comparison with the initial bulk volume of AR;
• the nuclear safety is high.
High penetrating grout is a suspension in a solid phase, dispersed in water. Its chemical and mineralogical composition is similar to Portland cement, but the particle size 1–6 mm. The basic element of high penetrating grout is the binder consisting of super thin particles, which are with a special technology (2). Super high dispersion of the binder provides the grout high permeability comparable with chemical solution, and gives a high durability and waterproofness to the cement matrix (3).
At present at the Moscow SIA “Radon”:
• laboratory analysis of high penetrating grouts are performed and the range of their compositions, suitable for impregnation of AR are defined;
• laboratory and pilot equipment are developed and methods of AR impregnation with high penetrating grouts are tested (Fig. 1,2);
• technological parameters of the method and physico and mechanical properties of the obtained cement compounds are investigated.
The further researches have to be directed to more exact consideration of mechanism of impregnation of porous materials.
The carried out researches have shown, that the offered method is reliable and applicable for AR cementing, that is does not require the complicated expensive equipment and excepts radiation dangerous operations. The method allows obtaining cement compounds with amount of AR about 50–60% by mass, and final volume does not increase in comparison with AR initial bulk volume.
Today an industrial plant for cementing the AR from solid radioactive waste incinerators is under development at Moscow SIA “Radon”. Besides, the feasibility of this technology at some NPPs is considered.