The New Safe Confinement (NSC or New Shelter) is a structure built to confine the remains of the number 4 reactor unit at the Chernobyl Nuclear Power Plant, which was destroyed during the Chernobyl disaster in 1986. The structure also encloses the temporary Shelter Object (sarcophagus) that was built around the reactor immediately after the disaster. The NSC is designed to prevent the release of radioactive contaminants from the existing shelter, protect the reactor from external influence, facilitate the disassembly and decommissioning of the reactor, and prevent water intrusion.
As part of the Shelter Implementation Plan supported by the Chernobyl Shelter Fund, the NSC was designed with the primary goal of constructing an enclosure capable of confining the radioactive remains of reactor 4 for the next 100 years. It also aims to allow for a partial demolition of the original sarcophagus, which was hastily constructed by Chernobyl liquidators after a beyond design-basis accident destroyed the reactor.
The word confinement is used rather than the traditional containment to emphasize the difference between the containment of radioactive gases--the primary focus of most reactor containment buildings--and the confinement of solid radioactive waste that is the primary purpose of the New Safe Confinement.
In 2015, the European Bank for Reconstruction and Development (EBRD) stated that the international community was aiming to close a EUR100 million funding gap, with administration by the EBRD in its role as manager of the Chernobyl decommissioning funds. The total cost of the Shelter Implementation Plan, of which the New Safe Confinement is the most prominent element, is estimated to be around EUR2.15 billion (US$2.3 billion). The New Safe Confinement accounts for EUR1.5 billion.
The French consortium Novarka with partners Vinci Construction Grands Projets and Bouygues Travaux Publics designed and built the NSC. Having been moved into place, it is scheduled to be completed by the end of 2018.
Video Chernobyl New Safe Confinement
Legacy structure
The original shelter, formally referred to as the Object Shelter and often called the sarcophagus, was constructed between May and November 1986. It was an emergency measure to confine the radioactive materials within reactor 4 at the Chernobyl nuclear power plant (ChNPP). The shelter was constructed under extreme conditions, with very high levels of radiation, and under extreme time constraints. The Object Shelter was moderately successful in confining radioactive contamination and providing for post-accident monitoring of the destroyed nuclear reactor unit; it has been estimated that up to 95% of the original radioactive inventory of reactor 4 remains inside the ruins of the reactor building.
The Object Shelter is primarily supported by the damaged remains of the reactor 4 building. These are largely considered to be structurally unsound as a result of explosive forces caused by the accident. Three major structural members support the roof of the Object Shelter. Two beams, usually referred to as B-1 and B-2, run in an east-west direction and support the roof beams and panels. A third, more massive member, the "Mammoth Beam", spans the largest distance across the roof from east to west and assists in supporting the roof beams and panels. The roof of the shelter consists of 1 metre (3 ft 3 in) diameter steel pipes laid horizontally north to south, and steel panels that rest at an angle, also in the north-south direction.
The Object Shelter was never intended to be a permanent containment structure. Its continued deterioration has increased the risk of its radioactive inventory leaking into the environment. Between 2004 and 2008, workers stabilized the roof and western wall of the shelter. However, construction of the NSC was necessary to continue confining the radioactive remains of ChNPP reactor 4.
Further upgrades to the area in preparation for NSC construction were completed in 2010. These included road and rail connections, site services (power, water, drains, and communications), facilities for workers (including medical and radiation protection facilities), and the installation of a long-term monitoring system.
Maps Chernobyl New Safe Confinement
NSC structural design
The NSC design is an arch-shaped steel structure with an internal height of 92.5 metres (303.5 ft) and a 12-metre (39.4 ft) distance between the centers of the upper and lower arch chords. The internal span of the arch is 245 metres (803.8 ft), and the external span is 270 metres (885.83 ft). The dimensions of the arch were determined based on the need to operate equipment inside the new shelter and decommission the existing shelter. The overall length of the structure is 150 metres (492.1 ft), consisting of 13 arches assembled 12.5 metres (41 ft) apart to form 12 bays. Vertical walls assembled around, but not supported by the existing structures of the reactor building seal the ends of the structure.
The arches are constructed of tubular steel members and are externally clad with three-layer sandwich panels. These external panels are also used on the end walls of the structure. Internally, polycarbonate panels cover each arch to prevent the accumulation of radioactive particles on the frame members.
Large parts of the arches were shop-fabricated and transported to the assembly site 180 metres (590 ft) west of reactor 4. Each of the steel tubes are made of high-strength steel to reduce cost and assembly weight. The steel used in the construction of the tubular members has a yield strength of no less than 2,500 kg/cm2 (250 MPa; 36,000 psi).
Warm, dry air will be circulated in the gap between inner and outer roof sections to prevent condensation, which will reduce corrosion and to prevent water from dripping into the interior.
Design goals
The New Safe Confinement (NSC) was designed with the following criteria:
- Convert the destroyed ChNPP reactor 4 into an environmentally safe system (i.e. confine the radioactive materials at the site to prevent further environmental contamination).
- Reduce corrosion and weathering of the existing shelter and the reactor 4 reactor building.
- Mitigate the consequences of a potential collapse of either the existing shelter or the reactor 4 reactor building, particularly in terms of confining the radioactive dust that would be produced by such a collapse.
- Enable safe demolition of unstable structures (such as the roof of the existing shelter) by providing remotely operated equipment for their demolition.
- Qualify as a nuclear entombment device.
Foundation design
The foundations of the NSC were designed to meet the primary requirements:
- They must support the weight of the arches of the NSC.
- They must support rail tracks across which the NSC can roll 180 metres (590 ft) from the construction site into place over reactor 4.
- They must minimize the amount of digging and cutting into the upper layers of the ground, as the upper soil is heavily contaminated with nuclear material from the disaster.
The site of the NSC is slightly sloped, ranging in elevation from 117.5 metres (385 ft) on the eastern side to 144 metres (472 ft) on the western side. The foundation was required to account for this difference without extensive site leveling.
The ground upon which the foundation was built is unique in that it contains a technogenic layer just below the surface that is approximately 2.5 to 3 metres (8 to 10 ft) in overall depth. Radioactive contamination from the accident created the technogenic layer. It consists of various materials including nuclear material, stone, sand, loamy sands, unreinforced concrete, and construction wastes. It is considered unfeasible to determine the geotechnical characteristics of this soil layer. As a result of this, no assumptions about the load-bearing properties of the technogenic layer were made during the design of the foundation.
The water table at ChNPP fluctuates from 109.9 metres (360.6 ft) on average in December to 110.7 metres (363.2 ft) on average in May.
Several options were considered for the foundation design for the NSC. Ultimately, the final design was specified as consisting of three lines of two 4.50-by-1.00-metre (14.76 by 3.28 ft) foundation panels, each 21 metres (68.9 ft) in length, and a 4-metre (13.1 ft) high pile cap that reaches to a height of 118 metres (387 ft) of elevation. This option was selected to minimize the cost of the foundation, the number of cuts into radioactive soil layers, dose uptake of workers, and risk to the environment from further contamination. The foundation has a slight elevation difference between the area in which the NSC was constructed and the final resting area around reactor 4.
Special consideration was necessary for the excavation required for foundation construction due to the high level of radioactivity found in the upper layers of soil. The conceptual designers of the NSC recommended the use of rope operated grabs for the first 0.3 metres (11.8 in) of pile excavation for the Chernobyl site. This reduced the direct exposure of workers to the most contaminated sections of the soil. Deeper excavation for the foundation piles were accomplished using hydraulic clam shells operated under bentonite slurry protection.
The foundation is designed to withstand horizontal acceleration structural loads of up to 0.08 g, as well as to withstand an F3 tornado. The original design for the structure required it to withstand an F1 tornado until an independent beyond-design-basis analysis was carried out to evaluate the effects of an F3 tornado on the structure.
Assembly process
The system used in the assembly of the NSC derived from civilian bridge launching and bridge cantilever methods. The NSC was assembled in the following steps:
- Stabilization of the Object Shelter to prevent collapse during construction.
- Excavation and construction of the foundation.
- Assembly of first and second arches to form Bay 1, installation of east wall on arch 1.
- Bay 1 was slid East to accommodate the construction of arch 3 and Bay 2.
- Subsequent sliding of the complete structure and adding of arches and bays to complete the structure.
- Installation of cranes and large maintenance equipment.
- Installation of the west wall.
- Final slide into place over reactor 4.
- Deconstruction of the fragmentation, decontamination, and auxiliary buildings. (planned)
This process of assembly was deemed advantageous because it took advantage of the designed mobility of the structure to maximize the distance between workers and the reactor building, thereby minimizing their exposure to radiation.
As each bay was completed, infrastructure equipment--including that for ventilation systems, radiation monitoring, plumbing, and electrical was installed.
Positioning
The NSC was constructed 180 metres (590 ft) west of reactor 4, and slid into place. Sliding of the structure along foundation rails was a difficult process. It was pushed on teflon pads by hydraulic pistons, and guided by lasers. As of 2018, the NSC is the world's largest movable land-based structure.
Two options were initially considered for moving the structure: hydraulic jacks to push the structure forward, or pulling the structure with large, multi-stranded steel cables. The first option would require the relocation of the hydraulic jacks after each push. This process would necessitate more worker interaction with the system and a greater worker exposure to radiation. The second option was initially chosen because it would expose workers to a lower radiation dose, and would have moved the structure into its final position in less than 24 hours. However, the structure was moved using hydraulic jacks, beginning the 327-metre (1,073 ft) move on November 14, 2016, and finishing on November 29.
Demolition of existing structures
The operational phase of the NSC involves the demolition of the unstable structures associated with the original Object Shelter. The goal of demolition has imposed significant requirements upon the load carrying capacity of the arches and foundation of the NSC, as these structures must carry the weight of not only the suspended cranes to be used in demolition, but also loads of those cranes.
Demolition equipment
The NSC design includes two bridge cranes suspended from the arches. These cranes travel east to west on common runways and each has a span of 84 metres (276 ft).
Each crane can carry a variety of interchangeable carriages. Three types of carriages have been designed for the NSC:
- One typical lifting carriage with a 50-tonne (55-ton) carrying capacity.
- One secure lifting carriage for shielded transportation of personnel, with a 50-tonne (55-ton) carrying capacity.
- One carriage suspends a mobile tool platform, extending up to 75 metres (246 ft), that can be fitted with a variety of end actuators useful for demolition.
The cranes' carriage interchangeability allows the rotation of the largest members to be demolished, reducing the overall size of the NSC by approximately one arch bay.
After the members to be demolished are removed by crane they must be fragmented into pieces small enough to decontaminate. It is expected that the primary contamination of most demolished elements will be loose surface dust and can easily be removed. Decontamination will take place using vacuum cleaners with HEPA filters, grit blasting (for steel elements), and scarifying (for concrete elements). Once decontaminated to the maximum extent practical, pieces will be further fragmented for eventual disposal. Fragmentation tools include plasma arc cutting torches, diamond circular cutting wheels, and diamond wire cutting. The tools selected for the demolition process were selected based on a number of factors including minimization of individual and collective radiation exposure, the amount of secondary waste generated, the feasibility of remote operation, the cutting efficiency, fire safety, capital cost and operating costs.
The exact methods for disposing of wastes generated by the demolition process have not been determined, and may include on-site burial outside the NSC for low-level waste, and long-term storage inside the NSC for medium and high-level wastes. As of 2018 no policy has been decided for the disposal and processing of fuel containing materials.
Elements to be demolished
The following elements of the Object Shelter are planned for demolition:
Types of materials to be demolished
The elements that are to be demolished fall into several broad material types:
- Steel
- Flat (roof panels)
- Three-dimensional (pipes, trusses, beams)
- Reinforced concrete
- Pre-cast
- Cast in place
- Debris
- Fragments of steel structures and equipment
- Fragments of reinforced concrete structures
- Materials added after the Chernobyl accident to mitigate its consequences.
Waste storage
Near to the Chernobyl site, the Vector Radioactive Waste Storage Facility is being built, consisting of the Industrial Complex for Solid Radwaste Management (ICSRM), a nuclear waste storage site. It is being constructed by Nukem Technologies, a German nuclear decommissioning company, a subsidiary of the Russian Atomstroyexport. This storage is reported to be able to contain 75,000 cubic metres (98,000 cubic yards). The storage is for both temporary high level waste as well as low and intermediate long-term level waste storage.
Worker safety and radioactive exposure
Radioactive dust in the shelter is monitored by hundreds of sensors. Workers in the 'local zone' carry two dosimeters, one showing real-time exposure and the second recording information for the worker's dose log.
Workers have a daily and annual radiation exposure limit. Their dosimeter beeps if the limit is reached and the worker's site access is canceled. The annual limit (20 millisieverts) may be reached by spending 12 minutes above the roof of the 1986 sarcophagus, or a few hours around its chimney.
Project timeline
The New Safe Confinement (NSC) was originally intended to be completed in 2005, but the project has suffered lengthy delays.
- March 2004
- An international tender for NSC design and construction was announced. Two bid candidates were identified, but in September 2006 the plant's general director Ihor Hramotkyn announced his intent to annul all bids on the project.
- September 17, 2007
- The project contract was signed, with French consortium Novarka (consisting of Vinci Construction Grands Projets and Bouygues Construction as 50/50 partners) constructing the 190 by 200 metres (620 by 660 feet) arch structure. Construction costs were estimated at $1.4bn with a project time of five years. The estimated time for completion was given as 53 months, including 18 months of planning and design studies, with a projected completion in mid-2012.
- 2009
- Progress was made with stabilization of the existing sarcophagus, which was then considered stable enough for another 15 years.
- September 2010
- Novarka began construction.
- April 2011
- Some project milestones, including infrastructure and preparatory work such as the NSC pilings, were completed.
- April 2012
- Steel erection began.
- November 26, 2012
- The first sections were raised.
- June 13, 2013
- The second lifting operation on the eastern arch was performed.
- April 2014
- The fully lifted eastern arch was moved 112 metres (367 feet) eastward on its rails to a parking position to clear the construction area for building the western arch.
- August 4, 2014
- The western arch completed the second of three lifting operations which raised the height of the arch.
- November 12, 2014
- Successfully completed the third ascent of the western part arches.
- April 2015
- The two arches were fused, and the west wall was under construction.
- April 2016
- Construction of the arches was completed.
- November 14, 2016
- The arch slipping procedure began.
- November 29, 2016
- The NSC slipping was completed, taking a total of fifteen days. It was pushed on teflon pads by hydraulic pistons, guided by lasers.
- November 2017
- Development company Rodina began the construction on the first PV project to be developed within the Chernobyl exclusion zone. 3,762 solar modules would be installed at the site with a generation capacity of 1 MW.
- December 2017
- According to a project official, construction completion will be delayed until late 2018 due to a contractor being unable to finish its work in time. The reason is the extremely high level of radiation, forcing workers to limit their presence at the site to a minimum.
International competition
In 1992, Ukraine's government held an international competition for proposals to replace the sarcophagus.
In the autumn of 1992, Design Group Partnership (DGP) of Manchester was invited to assist the Atomic Energy Authority (AEA) for the UK's submission for the international competition organized by the Ukrainian government.
DGP's senior management was assembled to generate a solution. David Haslewood suggested an arch, built off-site, and then slid over the existing Soviet-built sarcophagus because:
- Off-site construction would minimize radiation doses of construction workers.
- An arch would fit snugly over the damaged reactor excluding its chimney.
- An arch would be easier to slide than a square box.
Of the 394 entries, only the British submission proposed a sliding arch approach. There was no top design choice, but the French submission came as second best with the UK and German proposals coming joint third.
Subsequently, a pan-European study (the TACIS programme) re-examined the proposals of the competition's top three finalists. The study selected the sliding arch proposal as the best solution for their further investigations and recommendations, primarily to reduce the chance of the construction workers receiving a harmful dose of radiation.
On 17 September 2007 Vinci Construction Grands Projets and Bouygues Travaux Publics announced that they won the contract to build the New Safe Confinement as 50/50 partners of a French consortium named Novarka. The original 432 million euros contract comprises the design and construction of the NSC and planned to employ 900 people at its peak.
The project has involved workers and specialists from at least 24 countries in addition to Ukraine.
Responsible organizations
The European Bank for Reconstruction and Development (EBRD) is responsible for managing the Shelter Implementation Plan, including overseeing the construction of the New Safe Confinement.
See also
- List of nuclear and radiation accidents
References
Notes
Further reading
External links
- Official website: Chernobyl Nuclear Power Plant (CNPP)
- Description of the New Safe Confinement. Design of the new protective shield under Sarcophagus.
- Chernobyl 25 years on on YouTube European Bank for Reconstruction and Development, Computer rendered video of the construction process, Novarka, October 2009
- November 2014, Chernobyl Story on CBS 60 Minutes
- NSC site live camera
- Unique engineering feat concluded as Chernobyl arch has reached resting place on YouTube showing of NSC being slid into position, 14-29 November 2016, European Bank for Reconstruction and Development channel
Source of article : Wikipedia
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