The Chernobyl Nuclear Power Plant accident : its decommissioning, the Interim Spent Fuel Storage ISF-2, the nuclear waste treatment plants and the Safe Confinement project. by Dr. Ing. Fulcieri Maltini Ph.D. SMIEEE, life, PES, Comsoc FM Consultants Associates, France Keywords Nuclear power, Disaster engineering, Decommissioning, Waste management & disposal, Buildings, structures & design. Abstract On April 26, 1986, the Unit 4 of the RBMK nuclear power plant of Chernobyl, in Ukraine, went out of control during a test at low-power, leading to an explosion and fire. The reactor building was totally demolished and very large amounts of radiation were released into the atmosphere for several hundred miles around the site including the nearby town of Pripyat. The explosion leaving tons of nuclear waste and spent fuel residues without any protection and control. Several square kilometres were totally contaminated. Several hundred thousand people were affected by the radiation fall out. The radioactive cloud spread across Europe affecting most of the northern, eastern, central and southern Europe. The initiative of the G7 countries to launch an important programme for the closure of some Soviet built nuclear plants was accepted by several countries. A team of engineers was established within the European Bank for Reconstruction and Development were a fund was provided by the donor countries for the entire design, management of all projects and the plants decommissioning. The Chernobyl programme includes the establishment of a safety strategy for the entire site remediation and the planning for the plant decommissioning. Several facilities that will process and store the spent fuel and the radioactive liquid and solid waste as well as to protect the plant damaged structures have been designed and are under construction. The author has been responsible for the programme with the EBRD Nuclear Safety Account team. This paper describes the design and construction of a new interim spent fuel storage, the liquid and solid radioactive treatment plants and the construction of a unique and very large New Safe Confinement that, when completed, will be moved over of the reactor Unit 4. 1. Introduction In 1993 following the 26 April 1986 Chernobyl accident, the G7 launched an initiative on the prevention of nuclear accidents within Russian built plants and agreed that the EBRD - European Bank for Reconstruction and Development, establishes a fund aimed at the closure and decommissioning of some Russian built Nuclear Power plants of the RBMK and VVER 440-230 type. The initiative included initially the plants of Ignalina units 1 and 2 in Lithuania, Kozloduy units 1, 2, 3 and 4 in Bulgaria, Saint Petersburg units 1, 2, 3, and 4 in the Russian Federation. In 1996, Chernobyl three remaining units in Ukraine were added to the scope. The fund contributors included the G7 countries, the EU, Belgium, Denmark, Finland, the Netherlands, Norway, Sweden and Switzerland. Initial contributions were in excess of € 285 million. As of today 40 countries and the European Community are contributing with grants for the safety upgrades and the decommissioning of the above nuclear power plants. The concept, that had been accepted by the plants countries, included for each plant a nuclear safety assessment, the construction of an essential number of short terms safety improvements facilities and the final closure of the plant. Later an additional special fund was established for the decommissioning of each plant. 2 Fig. 1 The Chernobyl Nuclear power plant including four RBMK-1000 reactors – dated 1985 prior to the accident (source chnpp.gov.ua) 3 Fig. 2 Nuclear power plants in Ukraine (source IAEA) 2. The Chernobyl Nuclear Power Plant The Chernobyl Nuclear Power Plant (ChNPP) included four graphite moderated RBMK-1000 MWe reactors. The “beyond design-basis accident” occurred on 26 April 1986 during an experiment on Unit 4, which studied a potential of using “runout” of a turbine to ensure Unit’s needs at emergency shutdown. The reactor became in an unstable condition, provoking the explosion of the entire structure. The explosion and fires released at least 5% of the radioactive reactor core into the atmosphere. Fig. 3 Schematics of RBMK-1000 reactor (source IAEA) 4 Fig. 4 The Chernobyl NPP Unit 4 after the accident (source chnpp.gov.ua) Unit 4 was destroyed and the radiation levels in some areas of the reactor building have been estimated to be 0,056 sieverts per second (Sv/s) (1.4 mA/Kg), equivalent to more than 200 sieverts per hour (Sv/hr). A lethal dose is around 5 sieverts over 5 hours, so in some areas, unprotected workers received fatal doses in less than a minute. A dosimeter capable of measuring up to 10 Sv/s (0.3 A/kg) was buried in the rubble of a collapsed part of the building. All remaining dosimeters had limits of 10 exp-5 sv/s (0.3 µA/kg) and therefore read "off scale". The reactor crew could ascertain only that the radiation levels were somewhere above 10 exp-5 sv/s (0,0036 sv/h, or 0.3 µA/kg), while the true levels were much higher in some areas. During the accident and the following days a significant cloud containing mostly Caesium, Strontium and other fission products, including Plutonium, spread across Ukraine, northern, eastern, central and southern Europe. Fig. 5 shows a representation of the radioactive cloud eight days after the accident. 5 Fig. 6 shows the levels of contamination in various countries in Europe. Fig.5 Pattern of Cesium 137 concentration levels (Bq/sqm) on 4th May 1986 across Europe following the accident (source IRSN) 6 Fig. 6 Radiation levels across Ukraine and Europe following accident. (source WHO/IAEA) The French government strongly denied that the radioactive cloud had “entered” the country territory. However, as shown in Fig 7 it was obliged later to admit that large part of east and southern land was contaminated by Cesium 137. 7 Fig. 7 Mean concentration of cesium-137 in the air over France between 30th April and 6th May 1986 (source IRSN). ). Official document released five years after the accident. The structure of the reactor collapsed due to the fire (Fig. 8) and the reactor core melted due to temperatures exceeding 2600 °C. The corium, also called “fuel containing material (FCM)”, a lava-like molten mixture of portions of nuclear core, was collected in the lower reactor structure (Fig.9)- 8 Fig. 8 Schematics of the collapsed reactor after the accident (source chnpp.gov.ua) 9 . Fig. 9 Reactor corium lava flow formed in the basement of the plant below (source chnpp.gov.ua) 10 Fig 10 Storage of abandoned contaminated vehicles and helicopter used for throwing sand and other materials on the burning reactor (source chnpp.gov.ua) Human Consequences. About 130,000 people were evacuated immediately after the initial event, and in total about 400,000 people were eventually dislocated. Around 550.000 poorly trained workers called “liquidators”, engaged by the Soviet army in disaster management, received amongst the highest doses. Health Consequences. A recent independent assessment expects a total of 40,000 fatal cancers over the coming 50 years caused by Chernobyl fallout. Over 6,000 thyroid cancer cases have been identified so far, another 16,000 are expected in the future. Similarly, 500 % increases were observed in leukemia risk in both Belarus and Ukraine. Some new evidence indicates increased incidences of cardiovascular effects, stroke, mental health effects, birth defects and various other radiogenic effects in the most affected countries. Strong evidence has been published on Chernobyl related effect on children, including impaired lung function and increased breathing difficulties, lowered blood counts, high levels of anemias and colds and raised levels of immunoglobulins. 11 Fig.11 45,000 people abandoned the town of Pripyat (source chnpp.gov.ua) Fig.12 The abandoned town of Pripyat (source chnpp.gov.ua) Six months after the accident, a "Sarcophagus" also called “Object Shelter”, was built to cover the damaged Unit 4. (Fig. 10, 11, 12). At term, this was considered highly unsafe. The other three units of the plant were shut down respectively in 1991 (2), 1996 (1) and 2000 (3). 12 Fig. 13 Construction of the «Sarcophagus» (source chnpp.gov.ua) Fig. 14 Completion of the «Sarcophagus» (source chnpp.gov.ua) 13 Fig.15 Cross section of the “Sarcophagus” (source chnpp.gov.ua) Fig. 16 View of Chernobyl plant following the completion of “sarcophagus” (source: chnpp.gov.ua ) 14 3. EBRD Nuclear Safety Fund Following the Chernobyl accident, the G7 launched an initiative in 1993 aimed at the prevention of nuclear accidents within Russian built Nuclear Power Plants. The EBRD- European Bank for Reconstruction and Development was appointed to manage a Fund created by more than 40 donor countries. The RBMK and VVER-230 reactor types targeted by the Fund were: - Ignalina Units 1,2 Lithuania - Kozloduy Units 1,2,3,4 Bulgaria - Saint Petersburg Units 1,2,3,4 Russian Federation - Chernobyl 1,2,3,4 Ukraine added in 1996 A budget of € 285 million was initially established. Today the Fund includes more than 40 countries. The purpose of the Fund was to decommission the selected soviet built nuclear power plants by initially providing a strategy for the site remediation and building several safety facilities. Among them, interim spent fuel storages, radioactive liquid and solid waste treatment and storage plants as well as several protection structures on the plants. In charge of the operation, EBRD established a team called the Nuclear Safety Account including engineers and nuclear specialists. The author of this paper has been a member of the team and has been responsible for the entire decommissioning programme of the Chernobyl an Ignalina power plants. The co-author has been in charge for the Chernobyl Nuclear Power Plant of various tasks including the site remediation, the design of the “object” shelter and the construction supervision of the facilities.