The nuclear arms race which characterised the late 1940s, 1950s and 1960s resulted in the construction in both the USA and Russia of reactors specifically designed to produce plutonium. In the USA, nine graphite moderated reactors were built at the Hanford site near Richland in Washington State, and five heavy water reactors were built at the Savannah River Plant (SRP) in South Carolina. In Russia, eight uranium graphite production reactors were constructed – three at the Mining & Chemical Combine (MCC) in Zheleznogorsk (Krasnoyarsk) and five at the Siberian Chemical Combine (SCC) in Seversk. All these reactors have now been closed and are at various stages of decommissioning.

At Hanford, the B reactor, which began operation in 1944, was the world’s first production reactor. It was joined over the next decade by the D, F, DR, H, C, K west and K east reactors. These had all been closed down by 1970. In 1963 the ninth reactor, designated N, was built – the only US production reactor which also generated electricity. It operated until 1987.

All but one of the Hanford plutonium production reactors have now been entombed, or cocooned, to allow radioactive materials to decay over the next several decades. Surrounding structures have been removed and buried. This entailed removing hundreds of tonnes of asbestos, concrete, steel and contaminated soil. The pumps and tunnels were dug up and razed, along with the auxiliary buildings. This left the reactor core and shields. These were sealed up and a sloped steel roof constructed over them to draw off rainwater. Cocooning of C Reactor began in 1996, and was completed in 1998. D Reactor followed in 2002, F Reactor in 2003, DR Reactor in 2004, H Reactor in 2005 and N Reactor in 2012. K East was entombed in 2022.

B Reactor, however, was listed on the National Register of Historic Places in 1992 and it was designated a National Historic Landmark by the National Park Service in 2008.

In 2015, it became part of the Manhattan Project National Historical Park alongside other sites at Oak Ridge and Los Alamos.

The five reactors at the SRP were moderated with heavy water instead of graphite and were intended to produce tritium as well as plutonium. The first, R Reactor, began operation in 1953 followed by the similar P Reactor in 1954. R and P were the largest of the five. L and K, which also began operation in 1954, represented a next generation of reactor and C Reactor, the last to begin operation in 1955, represents a third type. R operated for a decade and was closed in 1964. In 1968 L was closed, but it was refurbished and restarted in 1985 to replace C Reactor, which was closed in 1986 after suffering numerous heat exchanger leaks. K, L, and P were all shut down in 1988 and the following year SRP was renamed the Savannah River Site (SRS) K Reactor was refurbished in the early 1990s and started briefly in 1992 but was shut down almost immediately.

Currently, the P and R reactor facilities have been permanently decommissioned. By the end of 2011, they had been fully grouted (filled with concrete) and permanently sealed – a process known as In-situ Decommissioning (ISD) This avoided the potential hazards and cost associated with generating and disposing of an estimated 137,000 tonnes of contaminated debris for each reactor. DOE said the buildings’ radiological contamination, heights, extensive basements, and thick concrete walls made the effort complex and difficult. Extensive planning and hazard analysis ensured the ISD was completed safely. Actual, fully-burdened costs for each of the reactor ISD project was about $73m, significantly less than the estimated cost of about $250m for full demolition including reactor vessel removal and below-grade decontamination of each reactor complex.

In 2012, contractors completed placement of about 1,700 truckloads of concrete into the C Reactor building. The reactor’s huge, below-ground disassembly basin required more than 2.8m gallons of grout designed to permanently seal the area. Before the area could be grouted, the contractor, Savannah River Nuclear Solutions, had to remove about 2m gallons of water through an evaporation process. The rest of the facility was scheduled to be preserved but in 2015, the US Department of Energy (DOE) said it planned to decommission the facility due to deterioration, mould damage, water damage and a lack of maintenance over 25 years.

Both L and K reactors are now used for other purposes. L Reactor is used to store used nuclear fuel and is expected to continue to do so until 2034. K Reactor has been modified to store plutonium that was intended to be used by the cancelled Mixed-Oxide Fuel Fabrication Facility.

Russian reactors

In Russia, a total of five industrial uranium-graphite plutonium production reactors operated at SCC: I-1, EI-2, ADE-3, ADE-4, ADE-5. The first (I-1) was launched in 1955 followed by EI-2 in 1958. Together they formed the first dual-purpose nuclear power plant producing both weapons-grade plutonium and 100 MWe of electricity. In the 1960s SCC put three more dual-purpose reactors into operation – ADE-3 (1961), ADE-4 (1964) and ADE-5 (1965) boosting power production to 600 MWe.

Under a Russia-US agreement to end production of military-grade plutonium, I-1 was closed in 1990, EI-2 in 1991 and ADE-3 in 1992. ADE 4 and ADE 5 continued operating until 2008 as they also provided power to the site. SCC in 2010 established UDC UGR, which, in co-operation with leading research centres of the Russian Academy of Sciences, developed a unique decommissioning technology whereby all reactor cavities were filled with a mix of natural clays.

The decommissioning of EI-2 was formally accepted as completed by a government commission in 2015. It was expected that the withdrawal of the remaining four shutdown reactors at SCC would take about five years but this was extended by a year. In 2021, Rosatom signed a state contract with UDC UGR, which was tasked with dismantling and fragmentation of radiation-contaminated equipment and pipelines, as well as concreting of the ADE-5 sub-reactor space. The work was expected to take two years.

In the course of the work, some 1,500 tonnes of equipment and pipelines of the first and second circuits of the ADE-4 and ADE-5 reactors were dismantled and fragmented, packaged in containers and placed on a specially prepared temporary storage site. Part of the dismantled pipelines was deactivated and returned to the national economy as scrap metal.

A lot of preparatory work was carried out to concrete the sub-reactor space of the ADE-5 reactor mine: access roads for concrete trucks and concrete pump installation sites were organised, walkways and open-air openings were made in the walls and inter-story floors. During preparation of the premises for concreting, 107 tonnes of equipment and metal structures, about eight tonnes of plastic and more than two tonnes of electric cable were dismantled. When concreting the reactor cavity, heavy concrete with a waterproofing additive was used. In total, more than 2,500 cubic metres of concrete was required for the bottom of the reactor. The work was carried using the ‘on-site burial’ option developed by the All-Russia Science Research and Design Institute of Power Engineering Technology (VNIPIET).

As well as the three uranium graphite reactors built at SCC, three others were constructed at the Mining and Chemical Combine (MCC) in Zheleznogorsk (Krasnoyarsk). The first AD reactor was launched in 1958 at MCC. The second, ADE-1, launched in 1961, was intended also to produce electricity but never did so as the combined heat and power plant (CHPP) had not been completed. ADE-2 began operation in December 1963 after the CHPP was in place. All three reactors were built underground and used cooling water from the Yenisei River.

In 1992, the AD and ADE-1 reactors at MCC were shut down. MCC has been key to the development of new technologies and equipment for the liquidation of the nuclear legacy. Practical work began there in 2015 with the concreting of AD, and in 2020, concreting work began on ADE-1. Decommissioning includes the construction of the necessary infrastructure facilities, the extraction and processing of radioactive waste (RW), and the establishment of safety barriers around the underground part of the reactor, namely localisation of the graphite stack.

The process involves laying a barrier of 8,700 cubic metres of concrete and 37,430 cubic metres of clay material in each reactor. Additional security barriers are also put in place and there is also natural protection in a reliable rock mass as they were built underground. The volume of waste from dismantling is minimal, which means that there is no need to build new RW storage facilities. This technology was patented by MCC specialists in 2010. By contrast, decommissioning of the reactors at SCC presented more complex waste disposal problems since they were not built underground.

ADE-2 was the last of Russia’s dual purpose plutonium production reactors to be closed in 2010. It also provided heat and electricity to Zheleznogorsk and nearby areas, which was its main function after 1993. in 2021 ADE-2 sealed its legacy, becoming a nuclear industry museum.