On 26 April 1986, a serious nuclear accident occurred in Unit 4 of the Ukrainian Chernobyl nuclear power plant. During an experiment, the reactor's power output increased excessively due to a series of operator errors. The fuel overheated. Several explosions and a fire were the result. About eight tons of radioactive fuel escaped from the reactor core into the environment.
Shortly after the disaster already, GRS started with the analysis of the accident and its consequences. In June 1986, it was one of the first institutions worldwide to submit a report on the accident sequence and its consequences. In the years that followed, GRS intensively studied the radiological situation at the site and investigated issues regarding the stability of the Sarcophagus that had been hastily erected under the then prevailing extreme conditions. In this context, GRS also supported the Ukraine and other Eastern European countries in establishing nuclear licensing and supervisory authorities.
On behalf of the Federal Ministry for the Environment, the European Union and international organisations - such as the European Bank for Reconstruction and Development (EBRD) - GRS was and still is active in various projects for Chernobyl. The aim of these projects in the long run is to transform the Chernobyl site and its surroundings into an ecologically safe state. The dismantling of parts of the Sarcophagus and the disposal of nuclear-fuel-containing materials from the destroyed Unit 4 play a central role in this process.
New Safe Confinement
In order to secure the severely damaged building of Unit 4 and isolate it from the environment and to resume operation of the other reactor units, the so-called "Sarcophagus", a reinforced-concrete structure, was erected in 1986 in just under six months construction time.
Since the old Sarcophagus was not stable in the long run, the G7 countries, the EU and the Ukraine created the "Shelter Implementation Plan" (SIP) in 1997. Its aim was to stabilise the Sarcophagus and build a new, larger protective cover over it: the "New Safe Confinement" (NSC). 45 countries financed the project at a total sum of 2.1 billion euros.
In 2016, after six years of construction, the New Safe Confinement was pushed on rails over the old Sarcophagus. A double-walled outer skin now enshrouds the building and protects it from external influences.
The destroyed reactor is to be dismantled under the new protective cover. A ventilation system is to ensure that the steel framework construction is air-conditioned in the area between the inner and outer cover of the shell. For this purpose, the air blown in is first "dried" to such an extent that the humidity in this area does not exceed 40%. This is to ensure that the structure remains free of corrosion. An integrated crane system is to shift the large building and plant components during dismantling.
From 1998 until early 2013, GRS supported the Ukrainian supervisory and licensing authority in the expert assessment of safety-relevant issues regarding the Shelter Implementation Plan and the planning, construction and completion of the new protective cover.
Collection of data on the radiological situation on site
In order to transfer Chernobyl to an ecologically safe state, precise knowledge of the radioecological situation at the site is required. Since the mid-1990s, GRS has been involved in the collection of such data, first for the German-French Initiative (DFI) and later in bilateral projects. Since 2006, GRS has been developing the "Shelter Safety Status Database (SSSDB)" together with Ukrainian scientists. In this database, data on the radiological situation on site are systematically compiled. This database is used by expert institutions in Germany and abroad as well as the by the operator of the Chernobyl nuclear power plant.
Further focal points of the work include questions on radioecological aspects, such as radionuclide activities in ground and surface water, in surface-near air or in biological samples in the vicinity of the New Safe Confinement as a result of the decommissioning of the cooling pond, of forest fires, and of so-called "waste dumps" in Chernobyl. These data were also collected in cooperation with Ukrainian experts and integrated into the SSSDB together with the associated geographical data. With the help of the SSSDB, geographically correct overview maps can be viewed, showing measured values as well as three-dimensional views of the site, including the Sarcophagus and the New Safe Confinement .
Decommissioning and dismantling of Units 1 to 3
In addition to the destroyed Unit 4, Units 1 to 3 of the Chernobyl nuclear power plant are also to be dismantled and disposed of. At the Naples Summit in July 1994, the G7 countries decided to enable the Ukraine through broad-based cooperation to decommission the entire Chernobyl nuclear power plant. On 15 December 2000, the last unit was finally shut down.
The units have initially been transferred to a monitored state of "safe enclosure" that will last for several decades. During this period, the radioactivity inside the plants will decay. Afterwards, the actual decommissioning of the reactors will begin. Plant components that are no longer required and whose activity inventory allows manual handling are already dismantled during the safe enclosure phase.
Treatment and storage of radioactive waste
A major challenge in the remediation of the site is the safe disposal of radioactive waste from operation and dismantling. The cooperation programme of the G7 states and the European Union with the Ukraine therefore also includes projects relating to the treatment and storage of such waste:
- In the "Interim Spent Fuel Storage Facility" (ISF-2), all spent fuel assemblies on the power plant site are to be stored temporarily. As soon as the facility is completed, the spent fuel assemblies of Units 1 to 3 are to be transferred from the existing wet storage facility (ISF-1) to ISF-2.
- At the "Liquid Radwaste Treatment Plant" (LRTP), liquid radioactive waste is to be conditioned, i.e. brought into a form suitable for storage or disposal. This waste comes from the operation of the four reactor units and has been stored at the site for more than 30 years in some cases. The LRTP has been handed over to the power plant operator; the operating licence was granted in December 2014.
- In the "Industrial Complex for Solid Radwaste Management" (ICSRM), solid radioactive waste is to be conditioned. This is initially waste from the former Chernobyl NPP operation.
Together with other expert organisations, GRS has supported the nuclear licensing and supervisory authority of the Ukraine in safety assessments within the framework of licensing procedures for these plants.
Low and medium-level radioactive waste
In addition to the waste from the operation and decommissioning of the reactor units, low and medium-level waste collected after the Chernobyl accident must also be safely stored. Some of this waste is currently being stored at the Buryakovka long-term interim storage facility. The 90-hectare facility is located 13 kilometres from the nuclear power plant site and is thus still within the 30-km exclusion zone around Chernobyl. This storage facility has been expanded to accommodate further low-level waste from the decommissioning of the Chernobyl nuclear power plant.
(as at: April 2020)