METHOD FOR PROCESSING LIQUID TRITIUM-CONTAINING RADIOACTIVE WASTE

Abstract

The invention relates to technology for processing liquid radioactive waste containing, inter alia, tritium isotopes, which are formed in various nuclear industry plants, and also during decommissioning of such plants. The technical result of the claimed invention consists in simplifying the technological procedure for processing liquid radioactive waste containing, inter alia, tritium isotopes by excluding complicated and lengthy operations associated with testing a concrete mixture produced from deactivated liquid radioactive waste, and also in increasing the ecological safety by reducing the size of areas for storage of the waste produced during the processing of the liquid radioactive waste. The claimed technical result is achieved in that a method for processing liquid radioactive waste containing, inter alia, tritium isotopes involves removing radioactive substances from the liquid radioactive waste so as to produce a low-level waste solution, and introducing a binder into the low-level waste solution produced in order to prepare a concrete mixture which complies with structural, radioecological, and sanitary and hygiene requirements, wherein components that have a negative effect on the technical characteristics of the concrete mixture being produced are removed from the low-level waste solution before the binder is added.

Claims

1. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes comprising removal of radioactive substances from the liquid radioactive wastes so as to produce a decontaminated low-level waste solution, and introducing a binder into the low-level waste solution produced in order to prepare a concrete mixture which complies with structural, radioecological, and sanitary and hygiene requirements characterized in that components that have a negative effect on the technical characteristics of the concrete mixture being produced are removed from the low-level waste solution before the binder is added.

2. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the composition of the low-level waste solution is pH-corrected before being used as a mortar for the concrete mixture in order to ensure the required parameters.

3. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the low-level waste solution is further diluted by utility water, condensate, sea water.

4. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein cement, silicates, gypsum, bituminous concrete, polymer concrete, sulfur concrete, ash, bentonite are used as a binder, while sand, crushed rocks, pebbles are used as an aggregate.

5. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the low-level waste solution is further introduced with additives, namely, mineral aggregates, water reducers, stabilizers.

6. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the produced concrete mixture is used to make normal and special concrete used for construction blocks and various structures.

7. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the radioactive substances removed from LWR are conditioned into a form satisfying the acceptability criteria for disposal.

8. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the low-level waste solution is treated from components negatively affecting the quality of the produced concrete mixture by using ion exchange, evaporation, mechanical or membrane filters or combination of these methods before the binder is added.

9. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the low-level waste solution is treated before adding the binder from components negatively affecting the quality of the produced concrete mixture such as compression strength, axial elongation strength, frost resistance, water tightness, mean density.

10. A method for processing liquid radioactive wastes containing, inter alia, tritium isotopes according to claim 1 wherein the solution is treated from soluble salts impairing technical characteristics of the produced concrete mixture before the binder is added to the decontaminated solution.

11. A method for processing liquid radioactive waste containing, inter alia, tritium isotopes according to claim 1 wherein the solution is treated from suspended solids impairing technical characteristics of the produced concrete mixture before the binder is added to the decontaminated solution.

12. A method for processing liquid radioactive waste containing, inter alia, tritium isotopes according to claim 1 wherein the components negatively affecting the quality of the produced concrete mixture are removed before LWR decontamination.

Description

EXAMPLE 1

[0032] Liquid radioactive wastes containing radionuclides of tritium, cesium, strontium, iodine, antimony and uranium were treated according to the method described in Russian patent No. 2577512. The decontaminated solution comprised 3.2 g/l of chlorides, 4.1*105 Bq/kg of tritium with the total activity of gamma and alpha-emitting isotopes below 100 Bq/kg. To manufacture prestressed reinforced concrete structures, the mixing water may contain no more than 500 mg/l of chloride ions (GOST 23732-2011), so the decontaminated solution was further treated at the membrane unit to obtain the chloride ion concentration below 50 mg/l. The said solution was then used to make a concrete mixture for prestressed reinforced concrete structures complying with all necessary standards. Tritium concentration in the resulting structures was below 9.2*104 Bq/kg, which complies with IAEA standards (GSR Part 3).

EXAMPLE 2

[0033] Liquid radioactive wastes produced by disposal of solution from the storage pool of fuel elements stored at the NPP containing 7.2 g/l of boron acid, isotopes of tritium, cesium, silver, cobalt and antimony were decontaminated using the method described in Russian patent No. 2577512. The decontaminated solution comprised 4.2 g/l of boron acid, 4.8*105 Bq/kg of tritium with the total activity of gamma and alpha-emitting isotopes below 100 Bq/kg and pH=3.1. According to GOST 23732-2011 Water for Concrete and Mortars, mixing water pH cannot be less 4, so utility water with pH=7.9 was added to the decontaminated solution (200 g of water per 1 kg of solution), which resulted in pH=4.7 in the decontaminated solution, and this solution could be used to produce concrete mixtures having bactericide properties preventing destruction of concrete structures by bacteria.

EXAMPLE 3

[0034] Liquid radioactive wastes produced by collection of ground waters containing 3 g/kg of suspended solids, 14.2 g/kg of soluble salts, isotopes of tritium, cesium, strontium, cobalt and uranium were decontaminated using the method described in Russian patent No. 2577512. The decontaminated solution was evaporated at the evaporation unit, and the resulted condensate contained 4.2*105 Bq/kg of tritium and complied with GOST 23732-2011 requirements to mixing water of concrete mixtures for producing concrete non-reinforced structures and structures with no prestressed reinforcement.

[0035] The studies of the concrete specimens obtained in examples 1-3 have shown that they have strength class B35 (42-46 MPa), frost resistance grade F200, moisture absorption (% by weight) 1.23÷1.25, water tightness (MPa) 1.73÷1.75 (W4). Leaching of radionuclides from the studied specimens evaluated using standard methods is below regulatory limits.

[0036] Characteristics of the produced concrete mixtures confirm that the concretes can be used as normal concretes (for industrial and civil buildings) as special concretes (hydraulic, road, heat insulation, decorative) and special-purpose concretes (chemically resistant, heat resistant, sound absorbing, for radioactive waste storages, etc.).

[0037] Processing of 100 m.sup.3 of liquid radioactive wastes containing, inter alia, tritium isotopes, using the proposed method will result in about 3.5 m.sup.3 (together with the package) conditioned radioactive wastes that will be sent in non-returnable containers to special storages of radioactive wastes and about 450 m.sup.3 of normal and special concrete used for construction blocks and various structures.

[0038] In this manner, the claimed invention, namely the method for processing liquid radioactive wastes containing, inter alia, tritium, ensures simplified processing of liquid radioactive wastes by avoiding complex and energy-intensive conditioning of the low-level waste solution treated from radionuclides and improves environmental safety by reducing the area for storage of wastes produced in processing of liquid radioactive wastes.