Berkeley Power Station

Friday 30 April 2010

The Client
Berkeley power station in Gloucestershire, is the first commercial nuclear power station in the UK to be decommissioned. It came into service in 1962 and after 27 years of successful operation - generating enough electricity on a typical day to serve an urban area the size of Bristol - the twin reactor station closed in 1989. The station is now proceeding through a measured and calculated programme of work to decommission the site and Magnox Electric Ltd is working on behalf of the NDA to manage and progress the work plan on site safely, efficiently and with due care for the environment.

Challenge
To provide geotechnical information that will enable the design of foundations for a proposed intermediate level waste storage Facility (ILW store)

Benefits

• Integrated geotechnical resources and expertise for an array of investigation, testing and monitoring techniques from one contractor
• High degree of communication and efficient co-ordination of different elements of the investigation
• Less risk and uncertainty on foundation design choices
• Flexible approach to the management of resources during a highly intensive investigation

Background
Berkeley Power Station ceased operating in 1992. The focus is very much on managing the decommissioning of the site and the safe future storage of waste. The site's history meant a number of obstructions were present, including a backfilled former turbine hall, petrol and diesel tanks, a back filled water supply reservoir and foundations for tunnels which formerly contained 132kV cables. These past uses have resulted in nonradioactive contamination of the site (mainly construction wastes, hydrocarbons and PCBs).

Natural geology
The general geology in the low lying area to the north of the Radiation Controlled Area of Berkeley Power Station comprises Mercia Mudstone overlying Thornbury Beds. Drift deposits, including Alluvium and Head, are also present nearby.

Objective
A key objective for the investigation was to enable Arup the consulting engineers to decide the type of foundation that could be adopted for a new heavily loaded shielded vault in which to store intermediate level waste from the power station. It would need to be secure in terms of its structural integrity and indifferent to any anticipated settlement. Understanding the potential occurrence of ground movements (particularly differential settlement) was critical to the design process.

Choices
Significant amounts of geotechnical data had to be gathered to enable Arup to assess whether a shallow foundation for the proposed ILW store would be suitable, or whether a deeper piled option would be necessary.

Solution

• Specific project requirements for Soil Mechanics to achieve this objective, included:
• Confirmation of site stratigraphy
• Determination of the nature and extent of backfilled excavations associated with buried obstacles
• Determination of the low-strain shear modulus for the assessment of soil structure interaction
• Ground stiffness parameters to enable the assessment of settlement and differential settlement of the proposed store
• An assessment of the state of contamination of the ground

Conclusion
A primary goal for the project was to provide factual data to enable decisions on foundations to be made on economic grounds without compromising another key driver – the crucial need by Magnox Electric Ltd for risk management in regard to the storage of waste associated with the nuclear fuel industry.

"Key to the success of the investigation was the fact that Soil Mechanics could integrate its services and offer group wide support. They responded quickly with a high degree of communication and efficient co-ordination of a wide array of data requirements and use of different techniques" Senior Engineer Magnox

Project Date May 2007 to Nov 2007

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