Use of drum film devices in radioactive waste conditioning technology

V.A. Uzikov

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So far, the common practice of radioactive waste treatment in Russia was controlled temporary storage – the so-called “procrastinated decision”. In Russia, the total amount of accumulated liquid radioactive waste (hereinafter LRW) is 477 million, and 77 millions of solid radioactive waste. However, as the world and Russian practice shows, that the controlled storage of radioactive waste in the long term results their accumulation and is not acceptable as a strategy of RAW treatment. Such strategy does not lead to the final safe solution of the problem, but requires the permanent overhead costs without clear prospect [1].

Thus, high production complexes for LRW treatment are needed. Key consumers interested in of liquid radioactive waste treatment plants are:

• enterprises of spent fuel treatment;
• existing nuclear power plants with power and research reactors;
• enterprises involved to decommissioning of boats and ships with nuclear power plants;
• enterprises involved to decommissioning of nuclear power plants and research reactor
• enterprises involved in the liquidation of the consequences of nuclear accidents
(Chernobyl, Fukushima , etc.).

Nowadays, mainly thermal and sorption methods are used for treatment of liquid radioactive waste. Using these methods, the main part of liquid radioactive waste, produced during the operation of nuclear installations of various purposes and other facilities using radioactive substances, is treated. These methods cannot be called original or specific for the treatment of radioactive waste (hereinafter RAW), because they were taken from various conventional industries and modified. Mainly these are methods, usually used in purification, treatment and desalination of water.
For implementing of treatment methods of non-nuclear industry and their modification, the specific requirements of industries related to radiation must be taken into account [2]:

• leak tightness of the equipment, excluding the possibility of radioactive contamination of buildings, staff and the environment;
• feasibility of the equipment operation to minimize the need for maintenance services in the radiation conditions, which require complicated and expensive works of equipment decontamination.

The most universal method for treatment of almost all types of LRW is a thermal method, in which LRW solution is evaporated to concentrate radioactive products in a small volume.
Practice of LRW treatment shows that the main source of problems in evaporation equipment are the heat exchange pipes. During the operation, their surface is covering inevitably by sediments, which have to be removed periodically by chemical washing, with interruption of the treatment process and at the same time with producing a large amount of secondary LRW. This inevitability is caused by evaporator’s design including heat exchange tubes – the process of sedimentation of the tubes cannot be prevented, it can only be decreased by using different methods: increasing the circulation velocity in heat exchange tubes or addition of special chemicals additives. The inevitability of foam-and-droplets entrainment from the evaporator is also caused by its design, so the additional special equipment have to be used for steam and condensate purification from radionuclides. Moreover, it is necessary to perform periodically the mechanical cleaning of heat exchange tubes which leads to important radiation doses to personnel.
All these problems existing in LRW evaporation technology are well known and studied, and some alternative methods are considered in [2], but it is concluded that these methods have a low productivity and heat transfer because of the lack of an organized circulation of evaporated solution [2].
The ideal comprehensive solution of the problem of LRW treatment is to create a continuous LRW evaporation technology with cementation of the concentrate at the same time, and the possible addition of used sorbents and sludge to the resulting cement compound. The main factor limiting the use of evaporation technology is a high energy costs, but with the appearance at energy market such installations as E-Cat, this problem disappears.
For comprehensive solution of the problems of LRW concentration and its subsequent cementation it is proposed to establish a technological process based on the two following principles:

1. To perform the process of LRW concentration in the evaporator equipment, that helps to prevent droplet entrainment and excludes degradation of technological parameters in time (to exclude interruptions in work of evaporation equipment due to fouling of the heating surface).
2. To make the processes of evaporation (secondary evaporation) and conditioning of LRW (inclusion in cement matrix) sequental and continuous, thereby eliminating the need for a large number of intermediate containers and dosing of separate portions.
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