Results of Computational and Experimental Studies on the Long-Term Safety Justification of Deep Disposal Facilities for LRW

Abstract

The article overviews the findings of individual studies under the Program of Calculation and Experimental Research Seeking to Demonstrate and Assess the Long-term Safety of Deep Disposal Facilities for Liquid Radioactive Waste Aiming to Implement the Recommendations of the IAEA Peer Review of the Deep Well Injection Practice for Liquid Radioactive Waste in the Russian Federation. To demonstrate the long-term safety of the Zheleznogorsk, Seversk and Dimitrovgrad deep disposal facilities for liquid radioactive waste (hereinafter referred to as the DDF LRW), data on the geological and hydrogeological conditions in the regions and at the DDF LRW sites were collected and systematized; the processes occurring in DDF LRW near and far zones, including those involved in radioactive waste (RW) component transport, were studied; evolution scenarios for the RW disposal system were developed, including a forecast describing potential climate changes in the DDF LRW areas covering a period of up to 100,000 years; conceptual and mathematical DDF LRW models were developed; computer software was used in predictive calculations focused on the migration of liquid RW components in the operational DDF LRW horizons with the potential radiation impact on the population been assessed. The study also involved some computational and experimental research focused on the evolution of backfill materials to develop the designs of some additional engineered safety barriers to be installed during DDF LRW DGR well abandonment; the paper also presents the approaches to the development of the DDF LRW closure concept.

Transformation of the Geological Environment under the Influence of Liquid Radioactive Waste (Russian Experience in Studying Historical Nuclear Disposal)

“…One of the LRW disposal sites operates on the territory of the Siberian Chemical Combine, where isolation takes place in deep-lying (350-550 m from the surface) sandy silt reservoirs located between thick clay horizons [4,[11][12][13][14][15]. The geological structure in the disposal site has a synclinal structure and is characterized by the absence of tectonic disturbances.…”

“…LRW is a thermodynamically non-equilibrium weakly alkaline (pH = 8-10.5) and acidic (pH = 3-4) solution with a total salt value of up to 30 g/L; the cationic composition is determined by sodium, ammonium, and alkaline-earth metals, and the anionic composition is determined by nitrate, sulfate, chloride, and bicarbonate. Also, the solutions contain dissolved corrosion products, small amounts of phosphorus-containing compounds, and silicon in the form of orthosilicic acid and fission products; acidic solutions contain acetic acid [12,13,16]. When LRW enters the reservoir, a specific natural technogenic system is formed in which all its constituent components are transformed, including mineral particles, dissolved components, and the composition of the aqueous solution.…”