Construction
Construction can only start when a preferred site for the geological disposal facility has been agreed with the local community and Government, following appropriate site investigations. [ How will we find a site? ]
Part of this work will involve the Nuclear Decommissioning Authority's (NDA's) delivery organisation undertaking underground investigations. The aim of this work will be to confirm a site's suitability to host a geological disposal facility that complies with safety and environmental regulatory requirements. This process will be subject to regulatory scrutiny and the NDA's delivery organisation will have to submit specific assessments for review at agreed hold-points. If the site meets the regulatory requirements, the regulators would permit construction of a geological disposal facility to proceed at the preferred site. Planning permission will be required for underground investigative work and construction of the geological disposal facility. The investigations and demonstrations will provide information to help increase the understanding of how the geological disposal facility will interact with the surrounding rock. The information gained will help improve the geological disposal facility design and safety cases, and will be used in updating regulatory submissions.
Fig 1: Part of the geological disposal facility under construction in Finland (courtesy Posiva)
Several buildings will be built in preparation for the receipt, inspection and emplacement of radioactive waste underground. These will include:
- a waste handling and transfer building, and
- a transport container maintenance and storage building.
In addition, prior to emplacement buffer/backfill handling facilities will be constructed. A Visitor's Centre may also be constructed.
The selection and final design of the most appropriate form of access depend on several factors which include waste package throughput, the depth of the vaults, the geology to be accessed and the views of stakeholders, which includes the public. It is expected that access underground will be by an inclined tunnel (known as a "drift"), with possibly three vertical shafts also being constructed for ventilation and spoil removal.
The underground facilities will be developed in stages to enable waste emplacement operations to begin as soon as possible, once relevant approvals have been received. Key underground facilities that will be constructed include inlet cells to receive the waste packages, disposal vaults for intermediate and low level waste (ILW/LLW), disposal tunnels for high level waste (HLW) and spent fuel and an inlet cell and buffer/backfill handling facilities. It is envisaged that the facility will be able to safely start receiving waste shipments with just one or two disposal areas constructed and fitted out. Construction of the remainder of the facility is planned to proceed in parallel with waste receipts and operation.
Proven technology
The geological disposal facility will be constructed using a combination of tried and tested techniques, such as drilling, blasting, and tunnel boring machines. These engineering techniques and the methods used to employ them safely will be tailored to suit the geological environment. Much of the necessary equipment is already used extensively in the tunnelling, civil engineering and mining industry in various geological environments. For example a tunnel boring machine has been used to excavate a seven-mile tunnel in volcanic rock in the USA and the Channel Tunnel in chalk in the UK and France.
Excavations can also be carried out using a combination of smaller excavation machines and explosives. This is the construction technique currently being used at the site chosen for the geological disposal facility for spent nuclear fuel in Finland.
Rock supports and tunnel lining will be used where necessary to provide a safe working environment and long-term stability of the underground excavations for a repository. If necessary, underground openings can be redesigned as excavations progress. Inflow of water will be controlled in line with operational requirements for safety and environmental protection.
Ease of construction
Ease of construction in various geological environments will be an important issue in the precise siting of the geological disposal facility. Technical factors such as rock strength, stress state, groundwater flow conditions, and increasing temperature with depth, will all need to be considered in evaluating potential locations and depths for the disposal facility.
All construction activities will be closely regulated and scrutinised by the Health and Safety Executive's Mining Inspectorate and Construction Division.
Operation
During the operation phase, major work will include the transport of waste to the geological disposal facility, inspection of wastes and emplacement underground.
Fig 3: Underground transport facilities at a disposal facility in Sweden (courtesy SKB)
Transport operations associated with a geological disposal facility include the transport of radioactive waste, construction materials, excavation spoil and personnel. The transport system could involve any combination of road, rail or sea transport. An important consideration in gaining the necessary approval for any transport operation will be to demonstrate that it is safe and efficient and has as low an environmental impact as possible.
During operation, additional disposal vaults (for ILW/LLW) and emplacement tunnels and deposition holes (for HLW and spent fuel) will be constructed, equipped and commissioned as required. Construction and waste emplacement activities will be managed to ensure the two activities are kept separate.
The facility will receive consignments of radioactive waste. The waste packages will be lifted from the delivery vehicle using an overhead crane and transferred to a wagon that will take them to the underground vaults. The duration of the emplacement phase will be determined by a number of technical and economic factors, including the lifetime of the interim surface stores and the rate of emptying, as well as factors such as the decommissioning strategies for nuclear power stations and any new nuclear programme [ link to section Wastes from new nuclear power stations ].
During this operational period (probably lasting decades) the waste packages will be monitored and for ILW will be readily retrievable. The NDA's delivery organisation will continue to work in partnership with the local community to ensure their issues and concerns are addressed.
Fig 4: Transport cask in the reception area of the Swedish central interim storage facility for spent nuclear fuel (courtesy SKB)
Further information
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