WO2019125216A1

WO2019125216A1 - Method for reprocessing liquid radioactive waste

Info

Publication number: WO2019125216A1
Application number: PCT/RU2018/000831
Authority: WO
Inventors: Виктор Павлович РЕМЕЗ
Original assignee: Общество с ограниченной ответственностью Научно-производственное предприятие "Эксорб"
Priority date: 2017-12-19
Filing date: 2018-12-17
Publication date: 2019-06-27
Also published as: RU2675787C1; EP3736819A1; EP3736819A4

Abstract

The invention relates to liquid radioactive waste (LRW) reprocessing technology and can be used for the recycling of radioactive substances at various nuclear industry sites. The technical result of the claimed invention involves increasing the efficiency of a method for reprocessing liquid radioactive waste by reducing the volume of radioactive waste requiring special storage and lowering the radiation exposure of service personnel during the reprocessing of liquid radioactive waste. The claimed technical result is achieved by the fact that a method of purifying liquid radioactive waste includes filtration, oxidation of liquid radioactive waste to obtain an oxidised flow, filtration of said flow, microfiltration and removal of radionuclides by feeding the filtrate into a vessel with granulated selective sorbents, wherein after oxidation, prior to filtration, a selective sorbent is introduced into the oxidised flow, wherein the sorbent is introduced into the liquid radioactive waste only after the oxidation stage.

Description

METHOD FOR PROCESSING LIQUID RADIOACTIVE WASTES

The invention relates to the technology of processing liquid radioactive waste (LRW) and can be used for the disposal of radioactive media at various sites of the nuclear industry.

This method can be used for the processing of low- and intermediate-level liquid radioactive waste at various sites of the nuclear industry, including nuclear power plants; for processing solutions resulting from the decontamination of buildings, structures, equipment, transport, etc; for processing natural water contaminated with radionuclides.

Processing of liquid radioactive waste is aimed at solving two main tasks: cleaning the bulk of the waste from radionuclides and concentrating the latter in a minimal amount.

There is a method of processing liquid radioactive waste from nuclear power plants, in which salt waste is subjected to ozonation and subsequent separation of the radioactive sludge produced during oxidation (see RF Patent for invention Ns 2066493 "Method of processing liquid radioactive waste of nuclear power plants", 6 IPC G21 F 9/08, priority from 13.11.1995, published on 10.09.1996).

The disadvantages of this method include low purification factors from radionuclides remaining in the liquid phase after oxidation in the ionic state, namely, from cesium radionuclides.

There is a method of processing liquid radioactive waste containing radionuclides in ionic and colloidal forms and ballast components of mineral and organic nature in a dissolved and suspended state, consisting in the fact that organic components of liquid radioactive waste are oxidized to gaseous state, and mineral ionic components, including and radionuclides, suspended in the form of metal hydroxides by feeding ozone into the waste stream, the stream of oxidized waste is divided into condensed sludge liquid phase, selective sorbents carry out additional treatment of the liquid phase from the remaining radionuclides in ionic form, and the resulting sludge and spent sorbents are converted to solid form and sent for long-term storage (see RF patent for invention Me 2122753 "Method for processing liquid waste containing radionuclides" , 6 IPC G 21 F 9/06, priority of 30.10.1997, publ. 27.11.1998).

The disadvantage of this method is that in the conditions of the flow-through processing mode, there is no guarantee that the liquid is completely saturated with ozone, which leads to the leakage of the complexed form of radionuclides into the purified liquid phase through selective

SUBSTITUTE SHEET (RULE 26) the sorbent, since neither the separation of the condensed sludge nor the selective sorption delays the complexed radionuclides, which reduces the efficiency of liquid radioactive waste processing as a whole.

There is a method of processing liquid radioactive waste containing radionuclides in ionic and colloidal forms and ballast components of mineral and organic nature in a dissolved and suspended state, namely, that organic components of liquid radioactive waste are oxidized to gaseous state, and mineral ionic components, including and radionuclides, suspended in the form of metal hydroxides by feeding ozone into the waste stream, the stream of oxidized waste is divided into condensed sludge a liquid phase is carried out on selective sorbents additional cleaning liquid phase from remaining in the ionic form of radionuclides, and the formed sludge and spent sorbent is converted into solid form and are sent to the long-term storage. At the same time, before ozone treatment, the waste stream is cleaned from suspended particles by filtration on a mesh filtering material; sorbents carry out membrane microfiliation with the separation of radionuclides from the liquid phase in colloidal form, which are returned to the stream of liquid radioactive waste after the supply of ozone into it (see RF patent for invention JV ° 2268513 "Method for processing liquid radioactive waste", 7 IPC G21F 9/06, G21F 9/20, priority from 12/28/2004, publ. 20.01.2006).

The main disadvantage of this method is that cesium radionuclides, which are in ionic form and make the greatest contribution to the total activity of LRW, are removed only at the final stage of the process - selective sorbents placed in filter containers. Therefore, with the initial activity of cesium radionuclides in LRW 3.7 10 ⁸ Bq / l (10 Ku / m ³ ) through the filter container containing granulated selective sorbent based on nickel ferrocyanide, you can skip no more than 12 m ³ LRW, since the filter resource -container for accumulated radioactivity is 120 Ku (see http.V / nii-izoterm.ru/index. php? option = com content & task = view & id = 72 & Itemid = 51). Under actual conditions at a nuclear power plant after the packaging of LRW, vat residues contain from 3 to 10 Ci / m ³ , therefore for processing 1000 m ^{3 of} such LRW according to the prototype method, it will be necessary to use at least 55 expensive filter containers of complex design. (The cost of one filter container, taking into account its installation and

SUBSTITUTE SHEET (RULE 26) operation is about 2 million rubles). In addition, due to the high activity accumulated in each spent filter container (up to 120 Ku for Cs-l37), their movement, maintenance and storage is very difficult and expensive, since special measures are needed to protect personnel from exposure. To accommodate the storage of such a quantity (55 pcs of filter containers per 1000 m ³ LRW), according to the technological requirements, a special storage of at least 100 m ^{3 is} necessary. Thus, the effective reduction rate of waste during the processing of 1000 m ³ LRW will be no more than 10.

As a prototype, we consider a method for processing liquid radioactive waste and its disposal, including oxidation of waste, separation of sludge, colloids and suspended particles from the liquid phase and removal of radionuclides from the liquid phase for subsequent utilization using selective sorbents and filters, characterized in that before the separation stage from the liquid phase of radioactive waste sludge, colloids and suspended particles are added to the liquid waste with stirring selective sorbents in the form of powders, and then the resulting suspension f liter, pumping through at least one tank designed for waste disposal and equipped at the outlet with at least one filter element separating insoluble substances from the liquid phase, after which the filtrate is passed through at least one tank designed for recycling, with granular selective sorbents, with these containers placed in concrete blocks. An example implementation: in this way was carried out processing of LRW (pH 12.1) containing:

- dry residue (after drying at 105 ° C) 285 g / l;

- suspended solids (blue ribbon separated from the filter) 5.1 g / l;

- specific activity of cesium-137: 1.1 10-3 Ci / l;

- The specific activity of cobalt-60: 1,4 · 10-6 CI / l.

5 m3 of liquid radioactive waste of the above composition was pumped into the tank and a composition consisting of 5 kg of nickel ferrocyanide selective sorbent applied to amorphous silica powder from the Sukholozhskoye deposit with a particle size of 200 to 500 μm and 0.5 kg of nickel sulfate as a coagulant was added with stirring. The combination of amorphous silica and agglomerates formed by the interaction of a coagulant based on nickel and suspended particles of liquid radioactive waste makes it easy to separate the solid phase from the liquid inside Corbric F.

SUBSTITUTE SHEET (RULE 26) After 2 hours of stirring, the suspension consisting of sorbent, suspended particles in LRW and coagulant was applied to Korbrik F (position 2) with two filter elements, and after it the solution was purified from suspension and sent to ozonization (position 3) for the destruction of organic compounds and complexes. To the suspension formed during oxidation, 5 kg of the same sorbent was added as to the tank (position 1) and the resulting suspension was sent to Korbrik F (position 4) with two filter elements. The solution, purified from suspension, was passed through successively connected Corbrics C (positions 5 and 6) with a granular selective sorbent based on nickel ferrocyanide. The purified solution containing less than 10 Bq / l l37Cs and boco was sent for uparka and crystallization (see RF patent for invention N ° 2577512 "Method for processing liquid radioactive waste and their disposal", priority from 12/29/2014, published. 20.03 .2016)

The main disadvantage of the prototype is that when using a sorbent before ozonization, trace amounts of transition metals that make up the sorbent, after filtration, enter the system for ozonation and catalytically destroy ozone. This leads to a significant decrease in the efficiency of ozonation, an increase in the time of ozonation and, in some cases, to the inability to clear LRW of a number of radionuclides.

The technical result of the claimed invention is to increase the efficiency of the method of processing liquid radioactive waste by reducing the volume of radioactive waste requiring special storage and reducing the dose load on the staff during the processing of liquid radioactive waste.

The claimed technical result is achieved in that the method of purification of liquid radioactive waste includes filtration, oxidation of liquid radioactive waste to produce an oxidized stream, its filtration, microfiltration and purification from radionuclides by feeding the filtrate into a container with granular selective sorbents, and after oxidation before filtration into the oxidized stream a selective sorbent is introduced, and the sorbent is introduced into liquid radioactive waste only after the oxidation stage.

The novelty of the claimed invention consists in adding a sorbent to liquid radioactive waste only after the oxidation stage.

When using a sorbent before oxidation (as in the prototype method), trace amounts of transition metals that make up the sorbent, after filtration, enter the system for ozonation and catalytically destroy ozone. This leads to

SUBSTITUTE SHEET (RULE 26) a significant decrease in the efficiency of ozonation, an increase in the time of ozonation and, in some cases, the impossibility of clearing LRW from a number of radionuclides. At the same time, the efficiency of using sorbents after ozonation is 40-70% higher than before ozonation, therefore, a significant reduction in the amount of sorbents supplied and the amount of radioactive spent sorbents sent for disposal is achieved. We exclude the equipment for supplying the sorbent before the stage of ozonation, and these are tanks, pumps, pipelines, etc., which also requires disposal in the event of a breakdown and relates to radioactive waste.

Thus, the addition of a sorbent to liquid radioactive waste only after the oxidation stage leads to a reduction in the volume of radioactive waste requiring special storage.

In the process of processing liquid radioactive waste in the oxidized stream contribute one or more selective sorbents.

In this case, selective sorbent is introduced into the oxidized stream in the form of a paste or suspension, or in the form of a powder, or in the form of granules.

The introduction after oxidation before filtration into the oxidized stream of a selective sorbent allows the main amount of radionuclides, including cesium radionuclides, to be transferred to the sludge separated during filtration and microfiltration. Thus the activity of radionuclides of cesium in the liquid phase after filtration is reduced to U ^"4 - ¹⁰ May Ku / m ^3, hence a filter container can be cleaned not 12m ³ as in the method-analogue, and to 10000 m ³ LRW accordingly, the effective waste reduction ratio will increase by no less than 100. The number of expensive filter containers required for LRW processing and the cost of their special storage will also decrease by at least 100 times, while the addition of a selective sorbent will increase the amount of waste slightly compared to the original the volume of LRW, moreover, this waste will not be sent for special storage, but will be conditioned in normal mode by the usual cementing technology and buried, which is important.

Technical solutions that coincide with the set of essential features of the claimed invention have not been identified, which allows to make a conclusion about the compliance of the claimed invention with the condition of patentability as "novelty."

The inventive essential features that determine the receipt of the specified technical result, not explicitly follow from the prior art, which allows to make a conclusion about the compliance of the claimed invention to the condition of patentability as "inventive step".

SUBSTITUTE SHEET (RULE 26) The condition of patentability "industrial applicability" is confirmed by examples of specific performance of the proposed method presented below.

Example 1

The inventive method was applied for processing LRW of the following composition: pH = 10.2, total salt content 371 g / l, activity on Cs-l37 - 12.16 Ku / m ³ (1.2 10 ² Ci / l), on Co- 60 - 0.09 Ci / m ³ (9 10 ⁵ Ci / l).

In 10 liters of initial LRW, which, after preliminary filtration on a screen filter (particles separated more than 50 μm) and ozonation, contained Co-60 less than 10 ⁹ Ku / l and 1.1 10 ^-2 Ku / l Cs-l37, 30 g are introduced ( 0.3% by weight of LRW) cesium selective sorbent based on nickel ferrocyanide with a particle size of 100 microns; after stirring for 1 hour, the resulting suspension was first filtered on a mesh filter with filtration fineness less than 5 microns, and then microfiltrated on ceramic membranes with pores 0.2 microns. The content of Cs-l37 in the purified solution was 4.1 10 ⁸ Ku / l. When processing such LRW, the filter container life currently used at NPPs will be at least 1000 m ³ , and in the absence of the powder sorbent application stage, the content of Cs-l37 in the purified solution will be 1.1 10 ^-2 Ku / l, filter container will be less than 10 m ³ LRW.

Example 2

In LRW, the same as in Example 1, after ozonation, 100 g of an aqueous suspension of nickel ferrocyanide sorbent (containing 50 g (0.5% by weight of LRW) colloidal sorbent of nickel ferrocyanide nickel) are added and after two hours of mixing it is filtered as in Example 1. The specific activity of the solution was less than 0.4 · 10 ¹⁰ Ku / l, therefore, based on the radiation safety standards, this solution does not require further purification using filter containers. After evaporation of this solution, the resulting melt can be stored in landfills with non-radioactive chemical materials.

SUBSTITUTE SHEET (RULE 26)

Claims

CLAIM

1. The method of purification of liquid radioactive waste, including filtration, oxidation of liquid radioactive waste to produce an oxidized stream, filtering it, microfiltration and removing radionuclides by feeding the filtrate into a container with granular selective sorbents, which after oxidation, before filtering, contribute to the oxidized stream selective sorbent, and the sorbent is introduced into the liquid radioactive waste only after the oxidation stage.

SUBSTITUTE SHEET (RULE 26)