Igor A.Sobolev, Vyacheslav .I. Demkin, Vladimir .I. Panteleyev, Dmitriy .V. Adamovich, Eugenie M. Timofeyev,
Yurii .T. Slastennikov, Alexander .V. Sumenko, Victor .Yu. Flit
Moscow Scientific and Industrial Association "Radon" The 7-th Rostovsky lane, 2/14
Moscow,119121, Russia
Fax (095) 248 1941
E-mail: root@nporadon.msk.ru

During repair and maintenance of atomic submarines at State Engineering Enterprise GMP "Zvezdochka" liquid radioactive waste (LRW) is generated. In February 1996 the Moscow SIA "Radon" processed 400 m³ of low level LRW at Facility 159 of GMP Zvezdochka in Severodvinsk. Results of this work are described in the paper.

During repair and maintenance of atomic submarines at State Engineering Enterprise GMP "Zvezdochka" liquid radioactive waste (LRW) is generated. In February 1996 the Russian State Center of Atomic Ship Building contracted the Moscow SIA "Radon" to process 400 m³ of low level LRW at Facility 159 of GMP Zvezdochka in Severodvinsk. The initial stage of this work comprises radiochemical, spectrometric and chemical analyses of LWR to be treated. Table I shows the results of the radiochemical and spectrometric analysis of initial LRW. Table II shows the chemical composition of this waste. As follows from Table I, the concentrations of certain radionuclides exceed permissible concentrations (PCb) of radionuclides (2). Also, GMP Zvezdochka currently has to comply with Instructions on the collection of industrial water waste in the sewage system (No. 585.01-01-02-95), which define the permissible concentration levels of chemical ingredients in order to achieve a safe level of water pollution in fish breeding waters.

* Environmental Radiation Control at Enterprises Involved in Repairing and Modernizing Nuclear Ships and Vessels /Instructions/.

In order to achieve the above it was recommended to use the sorption-membrane technology of salt LRW decontamination and concentration followed by the cementation of the concentrate and its disposal in the repositories of SIA Radon.

Among the known methods of the decontamination of industrial low mineral level water the membrane (electrodialysis) method is one of the most ecological and economical efficient. This was confirmed by research and tests carried out by SIA Radon from 1970 onwards (3), (4), (5).

Figure 1 shows the flow-sheet of salt LRW processing used in the EKO-3 mobile plant which was built in a sea container at Facility 159 at GMP Zvezdochka.

A special feature of this method is the electroosmotic concentration unit with two non-flow type brine chambers. It increases the concentration of small amounts of low-level LRW and improves the operational reliability of the unit. Dialyzate loop of this unit is a by-pass pipeline of pump for circulation of liquid through electrodialyzer brine loop. As a result a salt solution with a concentration over 200 g/l is produced in tank 14.

The choice of sorbents for preliminary decontamination of salt LRW is determined by the following three factors:

• radionuclide composition of initial LRW;
• the need for eliminating sedimentation in electrodialysis and electroosmotic units;
• maximum reduction of dose rate at work places.

As follows from Tables I and II, the initial LRW in tank A02/1 at GMP Zvezdochka is a salt low level radioactive solution. Among the radionuclides found there only four exceed the permissible concentration PCb according to NRB-76/87, namely Cs-137 by a factor of 70, Sr-90 by a factor of 3, tritium by a factor of 12 and Cs-134 by a factor of 3.5. The total a -activity is below permissible concentration of any one of the radionuclides. Among the b -radionuclides, C-14 and Ni-63 were also found.

Proceeding from the radionuclide composition the following sorbents were chosen:

• for cesium - ferrocyanide sorbent produced by SIA "Radon" - "Phoenix-A";
• for strontium - highly acid cationite KA-11 in the sodium form (equivalent to KU-2-8).This cationite possesses selectivity in relation to cobalt ions against the background of sodium ions;
• natural substance clinoprilonite is less effective than synthetic sorbents, however, it costs less and has selectivity in relation to cesium, strontium and cobalt ions. This is why it is also used for loading filters 3.

In order to prevent the formation on ion exchange membranes of compounds which are hard to dissolve, two sorption filters with capacities of 450 litres each were loaded with cationite KA-11 in sodium form. These filters are designed to retain calcium, magnesium and ferrous cations, but in practice after processing 60 m3 hard salts reached the electrochemical processing unit. This occurred due to the presence in LRW of compounds which transform the ions of alkali-earth and transition metals into neutral compounds.

The presence of hard salts in solutions which are being processed and which reach the electrochemical unit lead to the formation of hard to dissolve sediments in desalination electrodialyzer, and especially in the electroosmoosis concentration unit. This resulted in a sharp decrease of operational current and the reduction of effective operation. In order to eliminate the sedimentation a chemical washing and ion exchange membranes regeneration procedure was developed which enabled the unit to work without the reduction of the effective operation.

In order to reduce the radiation dose cesium was eliminated at the first stage in the first sorption filter filled with 200 litres of "Phoenix-A" . However, despite the fact that the filter was at some distance from the operator's workplace, the dose rate at the workplace (by comparison with other sorption filters) was 2 m R/hour already after the first hundred of cubic meters of LRW was processed (Figure 2).

In order to continue the work biological protection shielding was mounted at the sorption filter, and two filter containers with 30 litres of non-organic sorbent each were placed before it. These additional filters made at SIA Radon for Zvezdochka solved two problems:

• firstly, removing about 98% of cesium they prevented further accumulation of cesium on other parts of the unit;
• secondly, simplified further treatment of waste, as the filters already reside in containers and are delivered directly to the disposal site without reloading.

Filter containers were replaced after processing every 100 m³ of LRW.

Using the sorption method LRW was decontaminated from cesium by a factor of 1000 and from strontium by a factor of 100 before the electrodialysis unit. The decontamination factor for cobalt was very small as cobalt is usually in the form of stable complexes which can be easily removed after the oxidization of solutions, either by ozone treatment, or by electrochemical activation.

Table III shows the results of radiometric and spectrometric characteristics of decontaminated LRW measured by special analysis techniques team of Department XI of GMP Zvezdochka and confirmed by results obtained by the Informational Processes and Technologies Center team headed by A.I.Sobolev.

* Environmental Radiation Control at Enterprises Involved in Repairing and Modernizing Nuclear Ships and Vessels /Instructions/.

As follows from Table III, the volume activity of decontaminated LRW is below the permissible concentration according to NRB-76/87 except for tritium.

In accordance with OSP-72/87 section 9.7 and in agreement with the Environmental Committee of regional Sanitary Board (SES) it was decided to dilute the decontaminated LRW in the plant's collector 10 times with household sewage before discharging it into the sea; after this the maximum testing radionuclides levels in see water were within the norm specified in Table III.

Taking into consideration high total salt content of the initial LRW and the present of chemical compounds (see Table II), such as chlorides, nitrates, sulfates, phosphates, ammonia, active surface substances, oil products, etc. the concentrations of which exceed the permissible norms for LRW to be discharged in fish breeding waters, preliminary decontaminated LRW was further treated in two electrochemical membrane apparatuses. Technical characteristics of these apparatuses are given in Table IV.

Technological characteristics of membrane apparatuses are given in Table V

As follows from the above table, the total specific power consumption did not exceed 10 kW-h/m³.

As at 01.06.97 407 m³ of salt LRW had been processed and 300 m³ of them discharged into the White Sea. 2300 litres of concentrate had been generated. The concentrate was cemented in 200l containers (drums).

In early March 1997 some of the cemented waste was transported on special vehicles OT-20 belonging to SIA Radon and buried in the repositories of Sergiev-Pasad region under a separate agreement.

Table VI shows the results of chemical analysis after the decontamination of LRW at the EKO-3 plant.

Table VII shows radiation and physical/chemical characteristics of concentrates.

Table VII. Radiation and Physical/Chemical Characteristics of Recovered Concentrates from EKO-3 Plant

This sorption-membrane method (using desalination and concentration electrodyalizers) allows not only to decontaminate salt LRW to maximum permissible concentration, but also dispose of small amounts of concentrates after cementation.

Domestic sorbents and ion exchange membranes for salt LRW were tested in working circumstances, and their useful life before replacement or regeneration was determined.

Following decontamination and disposal of 407 m³ of salt LRW at GMP Zvezdochka initial information was obtained on the techniques for the processing and development equipment for the sorption-membrane method which is to be used for designing and constructing domestic plants of this type.

Approximate cost of the decontamination and disposal of 1 m³ of LRW for the circumstances of GMP Zvezdochka using the EKO-3 experimental plant was $400.

It is necessary to note that only domestic materials and parts were used in the EKO-3 plant.

1. Radioactive Safety Norms NRB-76/87, Moscow, Energoatomizdat, 1988
2. I.A.Sobolev, etc. Mobile Plant for Mineralized Liquid Waste Decontamination. Atomnaya Energya Magazine, v.73, # 6, December, 1992
3. V.I.Demkin, Y.A.Tybashov, V.I.Panteleyev, Y.V.Karlin. Desalination. 1987 v.64, p.367-373
4. V.I.Demkin, V.I.Panteleyev, E.M.Timofeyev and others. Patent No. 176829 kl, St.219/04 of 25.02.91. Liquid Radioactive Waste Decontamination and Concentration Plant.
5. Sanitary Rules For Handling Radioactive Waste (SPORO-85) SanPiN 42-129-11-3938-85 Moscow, 1986.

1. Container for initial LRW, 500 m³

2. sorption filter container (sorbent Fenics)

3. and 3a. sorption filter container (sorbent Fenics )

4. ion exchange filter with a capacity of 450 litres with cationite KA-11 (equivalent to KU-2-8) in sodium form

5. diluate tank

6. brine tank

7. electrodialyzer (n=600 membranes)

8. electroosmotic apparatus for concentration (n=60 membranes)

9., 10., 11. centrifugal pumps

12., 13. constant current rectifiers

14. concentrate container 1 m³

15. container for decontaminated LRW 500 m³

16., 17. pumps available in building 159

BACK