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The Chernobyl nuclear power plant’s (NPP) number four reactor exploded on 26 April 1986, sending a radioactive cloud across much of Europe. Radioactivity with an intensity equivalent to 500 of the bombs that destroyed Hiroshima, Japan, at the end of World War Two was measured in the atmosphere following the explosion.

In 2005, the International Atomic Energy Agency (IAEA) and World Health Organisation (WHO) reported that 56 people died directly from the incident, mainly workers at the accident site. They estimated another 4,000 deaths among workers and local residents. According to unofficial statistics, though, at least 15,000 people died as a direct result of the explosion.

The power station is still seen by critics as a time bomb, and work has been carried out ever since to try and make the site safe. The Ukrainian Government initiated a long-term plan to protect the Chernobyl shelter from the radiation.

Russia initiated a military operation against Ukraine in February 2022 and entered the Chernobyl site, which led to a rise in the levels of gamma radiation in the area. The State Nuclear Regulatory Inspectorate of Ukraine (SNRIU) reported that heavy military machinery movement at the site disturbed the topsoil layer and raised the radiation levels in the area, but that the nuclear facility’s condition remained stable.

Project decommissioning

Following the 1986 accident, the number four reactor at Chernobyl was encased in a giant concrete ‘sarcophagus’ to prevent further leakage of radioactive material. Hundreds of thousands of mobilised soldiers and civilian experts constructed the sarcophagus above the destroyed reactor, and the plant was re-opened in late 1986. A huge fire in the second reactor led to its closure in 1991. The number one reactor was shut down in 1996 as it had reached the end of its lifespan.

Reactor 2 was also taken offline and decommissioned in 1996, following the fire in 1991. Reactor 3, the last reactor, was switched off in 2000 to close the plant, after which the decommissioning of the three reactor units began.

The sarcophagus built in 1986 was unstable and needed further repair. In December 2000, the US promised to contribute the largest G7 funding to repair the sarcophagus. In 2001, construction began on a waste management facility for the treatment of fuel and other wastes from the decommissioned units one to three. A stabilising steel structure was extended in December 2006 to spread some of the load on the walls damaged by the explosion.

The fuel mass at the reactor has also been enclosed in EKOR, a radiation-resistant material developed by the UK-based company Eurotech. The material was applied during March 2000 to maintain an isolation coating and seal of the pile, preventing further dusting and leaching of contamination to the environment.

After two months, EKOR exceeded the longevity of all previously applied materials, which degraded rapidly in the severe-radiation environment and lost isolation effectiveness.

The EKOR-encapsulated fuel pile had radiation readings in the range of 1,000 rads on contact, although EKOR was laboratory tested to an accumulated dose of 10 gigarads without loss of physical properties.

In June 1999, Chernobyl Nuclear Power Plant (ChNPP) and a consortium led by Framatone signed a contract to build a facility to store spent fuel. In August 1999, ChNPP signed an agreement with a consortium led by Belgatom for a liquid radwaste treatment plant (LRTP).

Financing

The European Bank for Reconstruction and Development (EBRD) established the Chernobyl Shelter Fund in 1997 to support Ukraine in developing a site for temporary shelter over the destroyed Reactor 4 to make it safe and stable. The fund received more than €1.6bn ($1.9bn) from 45 donors and was closed in late 2020. It helped to support the decommissioning work at the site.

A shelter implementation plan (SIP), including the construction of a new safe confinement (NSC) structure, was chalked out to make the site of the nuclear accident safe. The SIP project was implemented at a cost of €2.15bn ($2.7bn), funded by contributions from more than 40 countries and organisations.

A Bechtel-led consortium, comprising Battelle Memorial Institute and Electricite de France, was selected for the management of the SIP project. NOVARKA, a French joint venture comprising construction companies Bouygues and Vinci, constructed the NSC structure, which was put in place surrounding the sarcophagus and reactor in November 2016.

Some of the decommissioning infrastructure projects were funded through bilateral aid, while two critical Chernobyl facilities, the Interim Storage Facility 2 (ISF-2) and LRTP, were funded by the Nuclear Safety Account (NSA).

ISF-2 was built at a cost of €400m ($448.7m), through contributions from members of the NSA including the European Union, Belgium, Denmark, France, Germany, Italy, Finland, the Netherlands, Norway, Sweden, Switzerland, Japan, Russia, the UK and the US. The EBRD contributed €235m ($274m) towards the construction of the ISF-2.

New safety confinement details

The NSC structure is a large movable, land-based arch-shaped structure spanning 257m, built to make the accident site safe for a lifetime of 100 years. With a total weight of 36,000t, the structure measures 162m long and 108m high. The safe confinement was built under the SIP at an estimated cost of $1.7bn.

The frame is a huge lattice structure made of tubular steel members and supported by two longitudinal concrete beams. Its sophisticated ventilation system eliminates the risk of corrosion and can withstand even a tornado. It covers the existing containment structure above the reactor and radioactive fuel. The structure was moved into the place in November 2016, while the site was transformed into an environmentally safe and secure state by November 2017.

State law programme to decommission the power plant

On 7 January 2010, the Ukrainian Government passed a state law to transform the Chernobyl shelter facility into an environmentally safe system to protect the surroundings from radiation. The programme is being executed in four stages.

Nuclear fuel was moved to a storage facility in the first stage, which was completed in 2013. All the reactors will be deactivated in the second stage, which will be completed by 2025. The third stage involves maintaining the reactors until radiation drops to an acceptable level, which is envisaged to be completed by 2045. The fourth and final stage involves dismantling the reactors and clearing the site, which is expected to be completed by 2065.

The state law programme is being financed by the EBRD and other international donors.

In addition, a seminar was conducted by IAEA to discuss the decommissioning of the cooling pond, which was highly contaminated after the explosion.

ISF-2 and LRTP details

Framatome was selected by ChNPP for the construction of ISF-2 in 1999, and it was planned for completion in 2003. The contract was, however, terminated due to design flaws and non-compliance to agreement terms.

In 2007, the US-based firm Holtec was selected to build the ISF-2 to store the nuclear waste produced by the Chernobyl nuclear plant. Holtec completed the first phase of the project, which involved preparation of safety and environmental qualification documents that comply with Ukrainian standards. Ukrainian authorities issued a positive safety conclusion on Holtec’s design in November 2010.

The company was permitted to begin the final phase of the project in March 2011. The phase involved the supply of 231 double wall canisters (DWCs) manufactured at Holtec’s facility in Pittsburgh, Pennsylvania, US.

The facility’s construction and comprehensive pre-commissioning programmes (cold tests) were completed in August 2019. SNRIU issued the license permit to ChNPP to begin the commissioning of ISF-2 in September 2020.

From November 2020, Holtec’s technicians placed the first fully-loaded DWC at ISF-2, and in December the second DWC was also loaded at the facility.

The ISF-2 will process, dry and cut more than 21,000 fuel assemblies from reactors one to three and will place them in DWCs to store in concrete modules on site. The DWC is the world’s largest forced gas dehydration system and features an advanced hot cell to dismember the conjugated RMBK fuel assembly.

In April 2021, the SNRIU gave an operating licence to SSE ChNPP to retrieve undamaged used nuclear fuel from the ISF-1 interim used fuel wet storage facility. The ISF-1 facility has a limited-service life as it was not designed for long-term storage of the fuel.

The spent nuclear fuels will be disassembled, packaged in DWCs and moved to the new ISF-2 dry storage facility. The spent fuel will be securely stored for at least 100 years. The existing fuel storage facilities can be decommissioned after the transfer of all fuel to the ISF-2 facility.

The operational LRTP retrieves highly active liquids from their current storage tanks, processes them into a solid state and moves them into containers for long-term storage.

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