The New Safe Confinement (NSC or New Shelter) is the structure intended to contain the nuclear reactor at Chernobyl, Ukraine, part of which was destroyed by the Chernobyl disaster in 1986. The idea is to prevent the reactor wreck from leaking radioactive material into the environment. Originally planned to be in place by 2005, as of 2011 the confinement is expected to be completed in 2015.[1]
A part of the Shelter Implementation Plan funded by the Chernobyl Shelter Fund, the NSC is designed to contain the radioactive remains of Chernobyl Unit 4 for the next 100 years. It is intended to replace the present sarcophagus, that was hastily constructed after a "beyond design-basis accident" destroyed reactor 4 on April 26, 1986.
The word "confinement" is used rather than the traditional "containment" to emphasize the difference between the "containment" of radioactive gases that is 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.
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The existing shelter, formally referred to as the Object Shelter and often called the sarcophagus, was constructed between May and November 1986 as an emergency measure to contain the radioactive materials within reactor unit 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 containing radioactive contamination and providing for post-accident monitoring of the destroyed nuclear reactor unit.
The existing Object Shelter is primarily supported by the damaged remains of the Unit 4 Reactor Building, which 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 itself 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 south wall of the Object Shelter is formed by the steel panels of the roof as they make an angle of approximately 115 degrees to become vertical. The east wall of the shelter is formed by the reactor building itself, and the north wall by a combination of the reactor building and concrete segments. The west wall is constructed of large concrete sections reinforced by buttresses. The complexity of the segments of the west wall necessitated their construction off-site; they were then lifted into place by a remotely operated tower crane. It is these buttressed sections of the Object Shelter that are most often recognized in photographs of the sarcophagus.
The Object Shelter was never intended to be a permanent containment structure, despite rumors to the contrary. Its continued deterioration has increased the risk of its radioactive inventory leaking out into the environment. Upgrades to the site made sometime prior to 2007 include pathways for roof access, roof repairs, the installation of a dust control system, and the installation of a long-term monitoring system. However, substantial upgrade or replacement of the shelter will be necessary in the near future in order to continue containing the radioactive remains of ChNPP reactor 4. It has been estimated that up to 95% of the original radioactive inventory of reactor unit 4 still remains inside the ruins of the reactor building.
In 1992, the Ukraine Government held an international competition for proposals to replace the hastily constructed sarcophagus.[2]
Of the 394 entries, only the British submission proposed a sliding arch approach.[3]
Subsequently, a pan-European study (the TACIS programme) re-examined the proposals of the top three finalists of the competition. The study selected the British sliding arch proposal as the best solution for their further investigations and recommendations.
The fact that the sliding arch solution is now to be built confirms the initial view that, by using this method, there is much less chance of the construction workers receiving a dose of radiation.
The New Safe Confinement (NSC) was designed with several design goals in mind:
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 to be 245 metres (803.8 ft), and the external span is to be 270 metres (885.8 ft). The dimensions of the arch were determined based upon 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. The ends of the structure will be sealed by vertical walls assembled around, but not supported by, the existing structures of the reactor building.
The arches are constructed of tubular steel members, and are externally clad with a three layer sandwich panels. These external panels will also be used on the end walls of the structure. Internally, each arch will be covered in polycarbonate (Lexan) to prevent the accumulation of radioactive particles on the frame members themselves.
Large parts of the arches will be shop fabricated and transported to the assembly site, 180 metres (590 ft) west of reactor unit 4. Each of the steel tubes will be high-strength steel in order to reduce cost and assembly weight. The steel used in construction of the tubular members will have a yield strength of no less than 2,500 kg/cm2 (250 MPa; 36,000 psi).
More extensive detail of the structural composition and design of the arches can be found in Section II.B., "Structural Design Process" of Conceptual Design of the Chernobyl New Safe Confinement—An Overview.
The foundations of the NSC must meet the primary design requirements:
The site of the NSC itself 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 must account for this difference without extensive site leveling.
The ground upon which the foundation must be 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. The Technogenic Layer was created by radioactive contamination from the accident and consists of various materials including nuclear material, stone, sand, loamy sands, concrete (probably unreinforced), and construction wastes. It is considered unfeasible to determine the geotechnical characteristics of this soil layer. As a result of this, the load-bearing properties of the technogenic layer are unassumed by 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, and the final design was specified as consisting of three lines of two 4.50-by-1.00-metre (14.8 by 3.3 ft) foundation panels 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 in order 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 differs slightly between the area in which the NSC will be constructed and the final resting area around unit 4.
Special consideration is necessary for the excavation required for foundation construction due to the high level of radioactivity found in the upper layers of soil. The use of rope operated grabs for the first 0.3 metres (11.8 in) of pile excavation has been recommended for the Chernobyl site by the conceptual designers of the NSC. This will reduce the direct exposure of workers to the most contaminated sections of the soil. Deeper excavation for the foundation piles will be 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 a tornado of up to Class F-1.5. However, the design requirement for the structure was later raised to withstand a Class F-3.0 tornado, resulting in a beyond-design-basis analysis that was carried out independently to evaluate the effects of a Class F-3.0 tornado upon the structure.
The NSC will be assembled in the following steps:
This process of assembly is advantageous because it takes advantage of the designed mobility of the structure to maximize the distance between workers and the reactor building, thereby minimizing their uptake dosage of radiation.
As each bay is completed infrastructure equipment including that for ventilation systems, radiation monitoring, plumbing, and electrical will be installed.
The NSC is to be constructed 180 metres (590 ft) west of unit four and slid into place. The actual sliding of the structure along foundation rails is a difficult process. The system to be used in construction of the NSC is derived from civilian bridge launching and bridge cantilever methods.
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. However, the first option would require the relocation of the hydraulic jacks after each push. This relocation process would necessitate more worker interaction with the system and a greater worker exposure to radiation. The second option was chosen because it would expose workers to a lower radiation dose, and would move the structure into its final position in just less than 24 hours.
The final phase of construction of the NSC involves the deconstruction of the unstable structures associated with the original Object Shelter. The goal of deconstruction 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 deconstruction, but also the loads of those cranes.
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:
The cranes' carriage interchangeability allows the rotation of the largest members to be deconstructed, reducing the overall size of the NSC by approximately one arch bay.
After the members to be deconstructed are removed by crane they must be fragmented into pieces small enough to decontaminate. It is expected that the primary contamination of most deconstructed elements will be loose surface contamination (mostly dust) and can largely 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 deconstruction process were selected upon the basis of 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 deconstruction process have not yet 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. At this time no policy has been made as to the disposal and processing of fuel containing materials.
The following elements of the Object Shelter are planned for deconstruction:
| Element | Quantity | Mass of each (metric tons) |
Length of each (meters) |
Length of each (feet) |
| Southern roof flat panels | 6 | 31 | 28.7 | 94.2 |
| Southern roof flat panels | 6 | 16 | 28.7 | 94.2 |
| Southern hockey stick panels | 12 | 38 | 25.5 | 83.7 |
| Mammoth beam | 1 | 127 | 70 | 229.7 |
| Northern beam B1 | 1 | 65 | 55 | 180.4 |
| Southern beam B1 | 1 | 65 | 55 | 180.4 |
| Northern hockey stick panels | 18 | 9 | 18 | 59.1 |
| Eastern hockey stick panels | 1 | 7.25 | 7 | 23.0 |
| Light roof | 6 | 21 | 36 | 118.1 |
| Piping roof | 27 | 20 | 36 | 118.1 |
| Northern beam B2 | 1 | 57 | 40 | 131.2 |
| Southern beam B2 | 1 | 57 | 40 | 131.2 |
| TOTALS: | 85 elements | 2024 tons | N/A | N/A |
The elements that are to be deconstructed fall into several broad material types:
Near to the Chernobyl site, the Vektor Radioactive Waste Storage Facility[4] is being built, consisting of the Industrial Complex for Solid Radwaste Management (ICSRM),[5] a nuclear waste storage site. It is being constructed by Nukem Technologies, a German nuclear decommissioning company which is a subsidiary of the Russian Atomstroyexport. This storage is reported to be able to contain 75000 cubic meters.[6][7] The storage is both for (temporal) high level waste, and low and intermediate level waste storage.
The New Safe Confinement (NSC) was originally intended to be completed in 2005, but the project has gone through several delays. In June 2003 the projected completion date was slated for February 2008. In 2009, planned completion was projected for 2012; the same year, progress was made with stabilization of the existing Sarcophagus, which was then considered stable enough for another 15 years. On February 2010 the reported completion date of the NSC was pushed back to 2013.[8] As of April 2011, the estimated completion date has been updated to Summer 2015.[1]
The following schedule was released in June 2003:
In 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.[9]
On 17 September 2007, BBC News reported that the project contract was finally signed, with French consortium Novarka (consisting of Vinci Construction Grands Projets and Bouygues Construction as 50/50 partners) constructing the 190 by 200 meter arch structure. Construction costs were estimated as $1.4bn with a project time of 5 years.[10]
The constructing consortium itself reported slightly different numbers, mentioning a contract of 432 million euros, and dimensions of 150 meters length, 257 meters span and 105 meter height. Estimated time for completion was given as 53 months, including 18 months of planning and design studies, with a projected completion in mid-2012.[11]
In February 2010, the Director-General of the plant's facility administration projected completion of the NSC in 2013;[8] Novarka began construction in September 2010.[12]
Continued updates from the European Bank for Reconstruction and Development (EBRD) state an assembly date of the NSC in "summer 2015 and subsequently be slid over the present shelter", with an updated cost of completion estimated at €1.54bn, and a funding shortfall of €600m.[1] Necessary project landmarks, including important infrastructure and preparatory works such as the NSC pilings, have been completed as of April, 2011.[1]
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. The EBRD assigned the Shelter Implementation Plan to project number 4807 in the country of Ukraine.