Photograph: Construction in lower strength sedimentary clay rock © Steve Barlow

development of the safety case

The disposal safety case will need to demonstrate that a GDF if implemented at a particular site can be constructed safely, can be operated without harm to workers, members of the public and the environment, and following closure, will continue to be safe in the long-term.  The disposal safety case is the responsibility of the delivery body and will be subject to independent scrutiny by safety and environmental regulators.  The safety case will be developed over a number of years and will increase in its level of detail, as understanding of the site increases and as the design progresses from concept stage to detail.

The safety case and design will progress through a number of hold-points and regulators will not permit progression to the next stage if the safety case arguments and evidence are not sufficient for the stage.

Regulators have published guidance regarding their expectations for the scope and coverage of a safety case. 

• Guidance from the Environment Agency - Guidance on Requirements for Authorisation

• Guidance from the Office for Nuclear Regulation is too extensive to list here, but their Technical Assessment Guide on Purpose, Scope and Content of Safety Cases is a good start

• In addition it should be expected that any disposal safety cases developed by Radioactive Waste Management will be compliant with international safety requirements as published by the International Atomic Energy Agency - e.g. Specific Safety Requirements SSR-5 

characteristics of a safety case

IAEA SSR-5 Requirement 13 describes a safety case as follows:

The safety case for a disposal facility shall describe all safety relevant aspects of the site, the design of the facility and the managerial control measures and regulatory controls. The safety case and supporting safety assessment shall demonstrate the level of protection of people and the environment provided and shall provide assurance to the regulatory body and other interested parties that safety requirements will be met.

In practical steps this means that the developer should understand the hazards involved in handling and disposing of radioactive waste, identify who may be harmed and how, and then should evaluate risks and put in place necessary precautions. This is in essence the same process as should be applied for any industrial or work-place activity and is summarised as the HSE Five-Step process. In the case of a geological disposal facility:

understand the hazards

• What are the radiological and physical/chemical characteristics of the waste packages

• What are the fault situations that may be expected during the handling and emplacement of waste packages

• How will the waste packages behave if subjected to fault conditions

• How will the waste packages and GDF evolve in the long-term

• How might the waste packages evolve if the environmental conditions deviate from the 'as planned' scenario

• What are the transport mechanisms by which radioactivity may return to the surface environment after closure, or during the operational phase

identify who may be harmed and how

• Understand where workers will be working e.g. construction workers, operators, maintenance crews, admin staff

• Identify where members of the public may be relative to the site

• Understand how workers, members of the public or the environment may be exposed to radiation or other impacts (e.g. pollution) 

evaluate the risks and decide on precautions

• Identify and implement a safe operating envelope through engineered safety measures and procedures

• Design-out faults where possible, apply the 'hierarchy of control'

• Develop the Engineering schedule and the Maintenance, Inspection and Testing schedule

• Based on understanding of the safety functions provided by the geology, decide on the safety functions required from the engineered system 

record the findings and implement

• Record the outcome of the safety analyses, capturing the safety arguments and evidence-base in the safety case

review the risk assessment

• As new information becomes available review the safety case and iterate with the GDF design team

  • Can risks be reduced further

  • Is the GDF being constructed and operated in line to deliver the design target set for the post-closure phase