Channel removal work trialled at Chernobyl

12 November 2018

A fuel channel, together with a control and protection system channel, have been removed from the reactor of unit 1 at the Chernobyl nuclear power plant in Ukraine. The work was carried out as part of research into developing a plan for dismantling the three undamaged units at the plant.

Channel removal work at Chernobyl unit 1 (Image: ChNPP)

The Chernobyl plant consisted of four nuclear reactors of the RBMK-1000 design. Units 1 and 2 were constructed between 1970 and 1977, while units 3 and 4 of the same design were completed in 1983. Two more RBMK reactors were under construction at the site at the time of the 1986 accident at unit 4. After the last Chernobyl reactor shut down in December 2000, in mid-2001 a new enterprise, SSE ChNPP was set up to take over management of the site and decommissioning from Energoatom.

One of the principal distinguishing characteristics of the RBMK reactor type is that each fuel assembly is housed in an individual pressure tube called a 'fuel channel' or 'technological channel'.

"The dismantling and processing of these channels is of practical importance for determining the duration of decommissioning works, the period of preservation and ageing of the reactors," ChNPP said.

Under the current programme for implementing the second stage in the final closure and preservation of the Chernobyl plant, removal of all the fuel channels and control and protection system channels from units 1-3 is expected to be completed in 2028.

ChNPP said the duration of the second stage in the four-stage programme will be determined by, among other things, the time it takes to carry out that work in each of the units. There are between 1661 and 1693 fuel channels, as well as 227 control and protection system channels in each of the three reactors.

It is assumed that the fragmentation of the extracted channels will be carried out on the up-graded grinding line for long-lived special waste (LDP). At this facility, pieces of equipment will be fragmented, placed in packages, characterised and loaded into transport containers. ChNPP said the duration of the dismantling and processing of special wastes is determined by the capacity of the LDP, which can currently only process two channels per day.

"Due to the delay in the implementation of the project to create a modernised grinding line for long-lived waste at the Chernobyl nuclear power plant, we are forced to look at ways to accelerate work," said Deputy Technical Director Volodymyr Peskov. "In particular, the processing time of long-lived waste can be reduced by removing it from the special-purpose drying operations and reducing the number of transport operations, since the technical conditions created at the Chernobyl plant during decommissioning make it possible to make appropriate adjustments to previously adopted technical solutions."

He noted that work to remove the fuel channels and the control and protection system channels was routinely carried out during repairs at the Chernobyl plant whilst it was in operation. He said this work will help determine the qualification level of the workers that will be involved in the work, the doses involved, as well as the availability of the necessary equipment to extract the channels from the reactor.

"At the moment, there are not many specialists at the plant who are capable of this work," Peskov said. "Therefore, the transfer of experience, how exactly to carry out the extraction of the channels, from experienced workers to young people, is a very important part of today's work."

The programme for decommissioning the Chernobyl plant was approved by the Ukrainian parliament in 2009. A strategy of 'postponed phased dismantling' has been adopted. The programme involves four stages. Fuel removal and preparatory work for decommissioning was carried out in the first stage between 2000 and 2015. Under the current second stage, sources of ionising radiation will be removed, and the reactor and the most contaminated equipment will be preserved. This stage will run until 2028. In the third stage, running until around 2045, the plant will be left for radiation levels to decline due to the natural decay of some radionuclides. In the final stage, up until 2064, equipment will be dismantled and the site cleared.

Researched and written by World Nuclear News