The article presents the results of work on dismantling the large installation equipment of Research Building B at the Bochvar High-technology Research Institute of Inorganic Materials (Bochvar Institute). The works were carried out as part of Building B preparation for decommissioning. The purpose of dismantling the large-sized capacitive equipment was to reconstruct the large installation site for managing radioactive waste generated during Building B decommissioning. The works on decommissioning a radioactively contaminated building within a densely populated district of megalopolis were carried out for the first time.

The characteristics of the large-sized capacitive equipment are presented. Radioactive contamination of the capacitive equipment is determined by long-lived a-emitting isotopes: ²³⁵U, ²³⁸U, ²³⁹Pu. The sequence of works on dismantling the radiation-contaminated capacitive equipment includes preparatory work, dismantling the tank piping, localizing radioactive contamination of the external surface of the equipment as well as dismantling and moving it into a transport container.

Dismantling and decontamination of the large-sized capacitive equipment was carried out by the Bochvar Institute Decommissioning Department. The following tools were used during the works: (1) a mobile foam decontamination facility to perform decontamination works and (2) a mobile high pressure facility to apply localizing and decontaminating film coatings. The tanks were dismantled by means of low-spark tools, i.e., reciprocating saws. Crane runways were made in order to move the dismantled equipment into transport containers: the movement was carried out with the help of a winch.

The main results of dismantling and decontaminating the radioactively contaminated tanks are the dismantling of four units of long-length column-type equipment with heights from 4.2 to 6.4 m and 26 units of capacitive equipment (maximum capacity = 8 m³) as well as decontamination of the internal surfaces of radiation-contaminated equipment (decontamination factor = 25–70). As a result, the activity of the accumulated radioactive waste was reduced (the RW class was changed from 3 to 4).

The main conclusion regarding the managment of large-sized radiation-contaminated tanks during Building B decommissioning is as follows: the works were organized and carried out at a high technical level, using modern decontamination and dismantling equipment and modern methods to ensure work safety at the Bochvar Institute site in the city of Moscow.

Decommissioning, radiation-contaminated equipment, tank, extraction column, dismantling, uranium, plutonium, foam decontamination, radioactive waste

Successfully completed in 2015, the Federal Target Program “Ensuring nuclear and radiation safety for 2008 and for the period up to 2015” was an example of a systematic approach to ensuring the safety of nuclear facilities (Order No. 484-p 2007, FTP NRS-2 Archives). One of the FTP NRS objectives was to reduce radiation hazards of enterprises located in populated areas (Federal Law of the Russian Federation). One of such enterprises is the Bochvar High-technology Research Institute of Inorganic Materials (Bochvar Institute): works with nuclear materials and radioactive substances had been carried out in its research buildings since the late 1940s. In 2010, due to the reduction of work with nuclear materials and radioactive wastes, it was decided to decommission Research Building B, the laboratories and facilities of which had been involved in developing SNF hydrometallurgical processing technologies (Sukhanov et al. 2013a, 2013b, Kuznetsov et al. 2012, 2017).

The experimental base for research, development and testing works on SNF extraction processes, equipment and methods for managing and controlling SNF processing was a large radiochemical facility located on Building B a few decks (from the first to the forth). In 2012, LRWs previously accumulated during operation (190-FZ) were removed from the tanks of the facility and transferred to FSUE RosRAO. The capacitive equipment was also to be removed as part of the decommissioning works (Kuznetsov et al. 2014).

The paper describes the technology for managment the large-sized radiation-contaminated tanks during Building B decommissioning at the Bochvar Institute site.

The radiochemical facility had four decks. The floor of the lowermost deck was concrete and the floors of upper deck were made of corrugated metal sheeting. The facility area on the lowermost deck floor is 138.6 m². The entrance to the facility was from the second deck. The main equipment of the facility included tanks, pumps, pipelines, receivers, pulsators, electrical appliances, and instrumentation and automated control systems (Fig. 1). A list and brief characteristics of the capacitive equipment are given in Tab. 1.

Figure 1. 

Radiochemical facility equipment.

Table 1.Download as CSV 

A list and brief characteristics of the capacitive equipment.

No.	Component	Overall dimensions, mm	Quantity	Weight u/kg	Wall thickness, mm	Contaminations
The lowermost deck
1	Tank	Ø 1000×1390	1	350	Up to 4 mm, upper part: up to 8 mm	U-238 up to 103 Bq/g
2	Tank	Ø 800×1160	1	350	Up to 5 mm, upper part: up to 8 mm	U-238 up to 103 Bq/g
3	Tank	Ø 800×1970	1	350	Up to 4 mm, upper art: up to 8 mm	U-238 up to 103 Bq/g
4	Agitation tank	Ø 1000×1500	2	1700	Up to 10 mm	U-238 up to 103 Bq/g
5	Tank	Ø 700×1390	1	235	Up to 5 mm, upper part: up to 8 mm	U-238 up to 103 Bq/g
6	Tank	Ø 800×1490	1	350	Up to 5 mm, upper part: up to 8 mm	U-238 up to 103 Bq/g
7	Tank	Ø 1000×1730	4	460	Up to 5 mm, upper part: up to 8 mm	Two tanks: U-235 up to 103 Bq/g (enriched up to 1,66%), 2 tanks: U-238 up to 102 Bq/g
8	Tank	Ø 1900×2300	2	1270	Up to 20 mm	U-238 up to 103 Bq/kg
9	Pump	500×300×400	1	50	–	U-238 up to 104 Bq/g
The second and the third decks
10	Tank	Ø 1000×1730	1	450	Up to 5 mm, upper part: up to 8 mm	U-238 up to 103 Bq/g
11	Tank	Ø 400×1160	3	92	Up to 5 mm, upper part: up to 8 mm	Two tanks: U-238 up to 103 Bq/g 1 tank: Pu-239 up to 102 Bq/g
12	Tank	Ø 700×1390	6	235	Up to 5 mm, upper part: up to 8 mm	5 tanks: Pu-238 up to 102 Bq/g 1 tank: U-238 up to 103 Bq/g
13	Tank	Ø 800×1970	2	350	Up to 5 mm, upper part: up to 8 mm	Pu-239 up to 102 Bq/g
14	Tank	Ø 1400×2730	1	1375	Up to 10 mm	Pu-239 up to 102 Bq/g
Equipment located on several decks
15	Vibration absorption unit	Ø 2000×4500	1	2500	Up to 5 mm	U-238 up to 103 Bq/g
16	Pulsation unit	Ø 1300×6400	1	1980	Up to 5 mm, upper part: up to 8 mm	U-235 up to 104 Bq/g (enriched up to 1,66%),
17	Extraction column	Ø 200×4200	1	200	Plexiglas (thickness up to 5 mm), metal – frame	U-238 up to 103 Bq/g
18	Extraction column	Ø 200×4200	1	250	Plexiglas, metal – frame	U-238 up to 103 Bq/g

A radiation survey of the internal equipment surfaces, carried out after the removal of the RW accumulated during the facility operation, showed the presence of sediments and deposits that had accumulated for a long operational period. It has been established that the radionuclides that determine the radioactive contamination of the large-sized capacitive equipment are long-lived a-emitting isotopes: ²³⁵U, ²³⁸U and ²³⁹Pu (Kuznetsov et al. 2016). In the existing infrastructural and technological conditions of Building B, it was not possible to completely remove the contamination of the internal equipment surfaces; therefore, it was decided to dismantle and subsequently transfer the radiation-contaminated capacitive equipment to contractor. To remove the capacitive equipment, it was necessary to carry out a set of measures to ensure its safe dismantling, transporting and loading into transport containers. Special attention was paid to ensuring security during the work, since the enterprise was located within the boundaries of Moscow (Vereschagin et al. 2016).

To ensure radiation safety during the work, a sanitary lock was created to separate clean and dirty areas (NP-057-04). The premises of the facility were previously divided into sections in accordance with the technology adopted in the working documentation (volumes 109001.000Б.120005-ТХ5 and 109001.000Б.120005-ТХ6 of the “Bochvar Institute Building B Decommissioning” project, JSC RAOPROEKT, 2012). The sanitary lock was equipped with radiometric control devices and plastic containers were installed to collect contaminated overalls.

The equipment and pipelines were brought to a state suitable for safe dismantling; in particular, the large installation communications were blown with compressed air to remove residual process media (Savin et al. 2013, Sukhanov et al. 2013c, Efremov et al. 2015).

Before starting the main work on dismantling the large-sized equipment, the large installation piping manifolds and process pipelines were dismantled and removed. The manifold connections were partly flanged and partly welded. The total length of the dismantled radiation-contaminated pipelines was about 1500 m (with pipe diameters from 12 to 120 mm). The pipes were made of stainless steel, rubber, plastic, and ferrous metal. The piping manifolds were removed both using a hydraulic tool and manually (the connector for mating flanges) (Fig. 2). The instrumentation of the monitoring, measuring and control systems was completely dismantled; the instrumentation and automated control cables were disconnected from the sensors and instruments of control, protection and alarm systems, and dismantled.

Figure 2. 

Dismantling the process pipelines.

The radiochemical facility included four units of long-length column-type equipment with heights from 4.2 to 6.4 m:

• one pulsation unit (surface contamination up to 10 ⁴ Bq/g for ²³⁵U);
• one vibration absorption unit (surface contamination up to 10 ³ Bq/g for ²³⁸U); and
• two extraction columns (surface contamination up to 10 ³ Bq/g for ²³⁸U);

To dismantle them in accordance with the design solutions, a monorail hoist was mounted and a winch was installed on the beam channels of the facility the uppermost deck. Hatches were cut into the upper deck floors and the columns were dismantled through these hatches (Fig. 3).

Figure 3. 

Removal of the column-type equipment.

Dismantling was carried out using plasma cutters and a local suction to prevent radionuclides from entering the air of the working area.

In total, during the large installation dismantling, 26 units of capacitive equipment were to be removed. The maximum equipment capacity was 8 m³.

In order to remove large-sized capacitive radioactive wastes from the large installation the lowermost deck, the window opening was expanded. The expanded opening was reinforced with welded metal structures. From the outside, the opening was sealed with two layers of polyethylene film. After the work was completed, a metal shield was installed indoors.

For the mechanized removal of the large-sized capacitive equipment, crane runways and guides were created and carts were used. The crane runways and guides were made in a mobile version to extend them beyond the building for at least one meter, to mechanize the movement of large-sized radioactive waste into the transport container (Fig. 4).

Figure 4. 

Opening in the wall of the radiochemical facility; crane runways.

During the dismantling process, all the holes in the equipment were filled with mounting foam. Polymer coating based on polyvinyl alcohol was applied on the equipment to be removed, to localize surface radioactive contamination. To create a more stable coating, it was applied twice: the second layer was applied after the first layer was completely dried (Fig. 5).

Figure 5. 

Applying polymer localizing coating.

The dismantled large-sized equipment was disconnected from the beds and stands; then, with the help of the hoist and the winch, it was moved onto a cart on the crane runways; afterwards it was fixed on the cart and moved into a transport container (Fig. 6).

Figure 6. 

Dismantling and removal of the large-sized capacitive equipment.

The large-sized process equipment was loaded into the PU-2ETS-ST containers (Fig. 7) and sent to FSUE RosRAO for compaction, conditioning and temporary storage before being transferred to the National Operator for RW and Technological Waste Managment (Vereshchagin et al. 2017).

Figure 7. 

Loading of the large-sized radiation-contaminated equipment into the PU-2ETS-ST transport containers.

During the work on dismantling the equipment of the radiochemical facility, special attention was paid to reducing the amount of accumulated radioactive waste. As mentioned above, it was not possible to completely decontaminate the internal equipment surfaces. Decontamination was carried out by treating the internal equipment surfaces with acidic foam compounds (Fig. 8). The decontamination factor ranged from 25 to 70. As a result of the decontamination works, the radioactive waste activity was reduced (for radiation-determining transuranic radionuclides, the RW class was changed from 3 to 4) (Resolution of the Government of the Russian Federation No. 1069).

Figure 8. 

Foam decontamination of the internal equipment surfaces.

Totally, after dismantling the capacitive equipment of Building B radiochemical facility, 26 units of equipment were dismantled and removed, including two 8 m³ tanks and and four units of long-length column-type capacitive equipment. Treating the internal equipment surfaces with foam-forming decontamination compositions made it possible to change the RW class from 3 to 4. Dismantling the large-sized equipment of the radiochemical facility was a unique task performed by the Bochvar Institute personnel, which later made it possible to reconstruct the facility site for managing radioactive waste accumulated during Research Building B decommissioning, using modern safety methods, under the conditions of the Bochvar Institute site located within a megalopolis, i.e., the city of Moscow.