New Safe Confinement
|This article is outdated. (April 2012)|
||This article may contain an excessive amount of intricate detail that may only interest a specific audience. (November 2012)|
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 complex from leaking radioactive material into the environment. Originally planned to be in place by 2005, as of 2011[update] the confinement is expected to be completed by the French consortium Novarka in 2015.
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 by Chernobyl liquidators 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.
- 1 The existing shelter
- 2 Design and construction
- 2.1 International competition
- 3 Waste storage
- 4 Project status
- 5 Responsible organizations
- 6 Safety
- 7 See also
- 8 References
- 9 External links
The existing shelter
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 15 degrees from 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[when?] 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.
Design and construction
In 1992, Ukraine's Government held an international competition for proposals to replace the hastily constructed sarcophagus.
Of the 394 entries, only the British submission proposed a sliding arch approach.
Subsequently, a pan-European study (the TACIS programme) re-examined the proposals of the top three finalists of the competition. The study selected the 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 harmful dose of radiation.
Currently the containment arch for the damaged nuclear power station at Chernobyl is under construction. This has led to more articles and papers about the arch in addition to those already described in this feature. However, in all cases no mention is made about the origin of the sliding arch concept, although some do allude to the international competition of 1992/1993.
The sliding arch concept has been described as a very elegant solution to a difficult problem so its origin is worth recording.
In the autumn of 1992, Design Group Partnership (DGP) of Manchester was invited to assist the Atomic Energy Authority (AEA) for the U.K.’s submission for the international competition organized by the Ukrainian Government.
D.G.P’s senior management were assembled to generate a solution. David Haslewood suggested an arch, built off site, and then slid over the existing Soviet built ‘sarcophagus’ because:-
1. Off site construction would limit the radiation doses of the construction workers to a minimum. 2. An arch fitted snugly over the damaged reactor (minus its chimney). 3. An arch would be easier to slide rather than a square box.
There were 394 entries to the competition of which 19 were examined in detail and of these only one was a sliding arch. The outcome of the competition was no overall winner, but the French submission came 2nd with the UK and German proposals coming joint 3rd.
However since the competition the world has adopted the sliding arch concept but it now has members supporting a dismantling crane which was not a requirement for the 1992 competition. As of 2013, the arch is being assembled in preparation for sliding over the Soviet ‘sarcophagus’ thereby providing a safe secondary confinement as originally envisaged.
The New Safe Confinement (NSC) was designed with several design goals in mind:
- Convert the destroyed ChNPP Unit 4 into an environmentally safe system (i.e. contain the radioactive materials at the site to prevent further environmental contamination)
- Reduce corrosion and weathering of the existing shelter and the Unit 4 reactor building
- Mitigate the consequences of a potential collapse of either the existing shelter or the Unit 4 reactor building, particularly in terms of containing the radioactive dust that would be produced by such a collapse.
- Enable safe deconstruction of unstable structures (such as the roof of the existing shelter) by providing remotely operated equipment for their deconstruction.
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 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 Chornobyl New Safe Confinement — an Overview.
The foundations of the NSC must meet the primary design 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 Unit 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 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 3.28 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:
- Stabilization of the Object Shelter in order to prevent collapse during construction.
- Excavation and construction of foundation.
- Assembly of first and second arches to form Bay 1, installation of east wall on arch 1.
- Bay 1 will be 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 Unit 4.
- Construction of the fragmentation, decontamination, and auxiliary buildings
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.
Deconstruction of existing structures
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 deconstruction 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 deconstruction.
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.
Elements to be deconstructed
The following elements of the Object Shelter are planned for deconstruction:
|Element||Quantity||Mass of each
|Length of each
|Length of each
|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|
|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|
|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|
Types of materials to be deconstructed
The elements that are to be deconstructed fall into several broad material types:
- Flat (roof panels)
- Three dimensional (pipes, trusses, beams)
- Reinforced concrete
- Cast in place
- Fragments of steel structures and equipment
- Fragments of reinforced concrete structures
- Materials added after the Chernobyl accident to mitigate its consequences.
Near to the Chernobyl site, the Vektor 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 which is a subsidiary of the Russian Atomstroyexport. This storage is reported to be able to contain 75000 cubic meters. The storage is both for (temporal) high level waste as well as 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. As of April 2011, the estimated completion date has been updated to Summer 2015. The project has involved workers and specialists from at least 24 countries in addition to Ukraine.
The following schedule was released in June 2003:
- 12 February 2004 - complete the NSC conceptual design
- 13 March 2004 - Government of Ukraine to approve the conceptual design
- 13 June 2004 through 13 September 2004 - conduct a tender and sign a contract with the winner to proceed with relevant engineering and construction work
- 16 April 2006 through 20 May 2007 - lay foundations for the NSC
- 16 April 2006 through 22 October 2007 - fabricate steel arch segments, assemble, move in contact and secure arch sections
- 23 October 2007 through 19 February 2008 - install cranes, piping and lighting fixtures under the arch
- 20 February through 29 February 2008 - slide the arch structure in place over the existing Shelter
- 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.
- 17 September 2007, 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 five years. 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. 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.
- February 2010, The Director-General of the plant's facility administration projected completion of the NSC in 2013; Novarka began construction in September 2010.
- 8 April 2011, Updates from the European Bank for Reconstruction and Development (EBRD) state the NSC will be assembled by "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.
- April 2011, Some project milestones, including infrastructure and preparatory work such as the NSC pilings, have been completed.
- April 2012, Steel erection begins.
- May 24th 2013, The metal arch structure of the second raising group was near completion. The interior systems including duct work and dismantling cranes were under construction. The exterior paneling was also being added to the second section and was at 79% completion.
- June 13th 2013, the second lifting operation was performed.
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.
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 cancelled. The annual limit (20 millisieverts) may be reached by spending 12 minutes above the sarcophagus roof or a few hours around the chimney.
- "NOVARKA and Chernobyl Project Management Unit confirm cost and time schedule for Chernobyl New Safe Confinement". European Bank for Reconstruction and Development. 08 Apr 2011. Retrieved 2011-08-16.
- International Competition, 1992 - Ukraine Government
- "A Second Shelter for Chernobyl" - Proceedings of the Institution of Civil Engineers - February, 1997 - Paper 11133
- Excell, John (11 February 2013). "Building Chernobyl's New Safe Confinement". TheEngineer.co.uk.
- http://www.delukr.ec.europa.eu/press_releases.html?id=47113[dead link]
- Nukem, project description for the INDUSTRIAL COMPLEX FOR SOLID RADWASTE MANAGEMENT (ICSRM) AT CHERNOBYL NUCLEAR POWERPLANT, access date 31-07-2008[dead link]
- Chernobyl Receives Nuclear Waste Processing Complex. Gabriel Gache, April 25, 2008.
- http://www.eubusiness.com/news-eu/1208978222.51/[dead link]
- "Chernobyl New Safe Confinement - New Completion Date Announced". Chernobyl and Eastern Europe. February 15, 2010. Retrieved 2011-03-16.
- Meo, Nick (26 November 2013). "Chernobyl's arch: Sealing off a radioactive sarcophagus". BBC News.
- "Ukraine may hold new tenders on Chernobyl safety facility". BBC Monitoring International Reports. 27 September 2006.
- "Chernobyl to be covered in steel". BBC News. 18 September 2007. Retrieved 20 May 2010.
- "VINCI AND BOUYGUES SIGN CONTRACT TO BUILD CONTAINMENT SHELTER FOR THE CHERNOBYL SARCOPHAGUS". Retrieved 2011-04-19.
- "Work begins on new sarcophagus for Chernobyl reactor". Nuclear Power Daily. September 24, 2010. Retrieved 2011-03-16.
- Hankinson, Andrew (3 January 2013). "Containing Chernobyl: the mission to defuse the world's worst nuclear disaster site". Wired.co.uk.
- "Workers raise first section of new Chernobyl shelter". 3 News. Associated Press. November 28, 2012.
- Heintz, Jim (2012-11-27). "Workers raise 1st section of new Chernobyl shelter". Associated Press. "Workers have raised the first section of a colossal arch-shaped structure that eventually will cover the exploded nuclear reactor at the Chernobyl power station."
- Conceptual Design of the Chornobyl New Safe Confinement— An Overview (2004) by Charles Hogg—Bechtel Corp., Matthew Wrona—Bechtel National, Inc., Philippe Convert, Yuriy Nemchinov, Pascal Belicard, Valery Kulishenko, Eric Schmieman, Michael Durst published by Pacific Basin Nuclear Conference
- Chornobyl: Five-Year Schedule set for New Safe Confinement Over Wrecked Unit (June 9, 2003)
- Project Implementation Phase 2 from Chernobyl Nuclear Power Plant
- SIP Project Summary Document from The European Bank for Reconstruction and Development
- Description of the New Safe Confinement. Design of the new protective shield under Sarcophagus.
- PDF. European Bank for Reconstruction & Development
- Computer rendered video of the construction process, Novarka, October 2009