Retrieving solid waste from a legacy building at Chernobyl

Solid radioactive waste generated during normal operation as well as in the aftermath of the Chernobyl Unit 4 accident was placed for interim storage in a storage building with two dedicated compartments for each of three waste categories.

The storage building consists of thick-walled concrete cells, dimensions 9x9x10m, loaded from the top. The roof openings are closed with concrete beams and plugs. The waste amounts held in the building are as follows:

• Low-level waste: 1069 m³
• Intermediate-level waste: 926.5 m³
• High-level waste: 417.7 m³

As the Industrial Complex for Solid Radioactive Waste Management project progressed, NUKEM Technologies developed and implemented a concept for safe retrieval and processing of radioactive waste, factoring in the specific site conditions.

To make sure that the required waste retrieval equipment can be operated safely, providing protection to personnel and environment, the existing building had to be reconstructed and extended.

To this end a service building was erected at the side of the existing storage facility (red part of Figure 1). The next step was to enclose the existing building in a steel framework structure. The steel enclosure and service building were covered by a common roof.

The service building accommodates all process equipment, auxiliary systems (utility services, active ventilation, and so on) and control rooms.
Given the site conditions, the retrieval systems had to be designed with a special credit taken for radiation protection, collective dose budget, local dose uptake, and prevention of contamination spreading. NUKEM Technologies' pool of technical expertise includes a range of eligible technologies. These readily-available solutions were the basis for development of the retrieval concept.

Solid radioactive waste is retrieved via the compartment top.

For retrieval, the compartment plugs need to be remotely removed. A rail track was laid on the roof of the existing building. The rail track carries a mobile caisson, which can shelter all the storage compartment openings. The caisson houses the retrieval, transfer and monitoring equipment. It is designed to achieve the highest safety standards with regard to collective dose budget, local dose uptake and prevention of contamination spreading and to ensure high flexibility of retrieval operations. Equipment inside the caisson includes a crane, a remotely operated vehicle (ROV), cutting and demolition tools, vacuums, transfer devices and measurement and monitoring instrumentation.

Five step retreival processs

The concept for the process of retrieval of solid radioactive waste can be split into five steps:

1. 1. The caisson will be moved over the desired retrieval position.
2. 2. Concrete plugs will be removed from the compartment ceiling slabs using the crane and ROV. Then the compartment will be prepared for retrieval of solid radioactive waste. The relevant section of the building will be safeguarded and monitoring equipment will be remotely installed into the open compartment.
3. 3. Solid radioactive waste will be lifted from the compartment opening and transferred to a 1 m3 skip in a container loading position. While being transferred, the solid radioactive waste will be measured; measured data will be logged into the waste tracking system. The skip, in its transport container, will be moved across the building by a roller conveyor and then lowered into a transfer corridor by crane. Its destination is the solid waste processing facility in the adjacent building.
4. 4. The ROV will be lowered inside the storage compartment to help complete waste retrieval.
5. 5. Finally, the compartment structures will be cleaned.

All handling operations are controlled remotely from the control room via a video system.

For the retrieval concept to be successfully implemented, the existing building structures had to be stabilized and refurbished. For this purpose, the external walls were reinforced with an additional concrete layer (grey walls in Figure 2). Concurrently, the old equipment on the building roof was dismantled as it was not suitable for the retrieval concept.

Reconstruction work included erection of a new service building as a side extension to the existing storage building (shown structurally complete at the right of Figure 2.)

Once the 19x9x5 m caisson had been placed on the building roof, the steel enclosure framework (Figure 3) was installed on newly-laid foundation slabs so that any additional load on the existing storage building could be avoided. The steel enclosure framework was later filled with cladding panels (see Figure 4), followed by roof installation and finishing work.

The mobile caisson mentioned earlier is located within the enclosure under the common roof. It is assembled from prefabricated steel structures on the roof of the storage building. The caisson accommodates all devices and tools required to make sure that the retrieval operations go smoothly.

In 2009, NUKEM Technologies handed over the remotely operated retrieval facility to the customer. The expected retrieval rate is 3m3/day. At the moment, NUKEM Technologies is providing support to the customer during the final commissioning phase for all the facilities constructed under the ICSRM project.