Calder Hall

Calder Hall is the oldest Station in the fleet of the 11 Magnox Power Stations. It was first commissioned between 1956 and 1958. It is situated in the North West of England in the county of Cumbria. The plant is located within the boundaries of the Sellafield Nuclear site. Calder Hall consists of four gas cooled reactors and two turbine halls. At full power the electrical output of the Station, to the grid, was 200 megawatts.

Location of Calder Hall

Calder Hall was the first commercial Nuclear Power Station in the UK and its four reactors are of a Magnox design – the term comes from the Magnesium Alloy that is used to encase the nuclear fuel.

In June 2002 a decision was made to shut the Station ahead of its planned closure date. The decision was made entirely on economic grounds since maintenance work required to continue generation was considered to be too costly to be viable. The Station ceased generation in March 2003, after celebrating 46 years of successful, safe, electricity generation.

Before decommissioning could begin an Environmental Statement needed to be prepared and submitted to the Nuclear Installations Inspectorate (NII), and formal consent to decommission obtained from the NII. Prior to this the NII put the Environmental Statement out for public consultation. Consent to decommission was granted in June 2005.

The decommissioning project at Calder Hall is considered in three phases:

The exact duration of each decommissioning phase may be shorter than those stated.

Calder Hall at present is in the Care and Maintenance Preparation phase which, in general terms means, we have to place the site into a state where although maintenance will be needed, human intervention is minimised. All buildings and machinery, except the reactor buildings will be dismantled. Some partial dismantling of the reactor buildings such as removal of machinery will take place but large items such as the reactors, the concrete biological shields and the main gas ducts will not be removed until final site clearance. The boilers, which are very large items located externally to the reactor buildings, will be laid down close to the reactor buildings. The cooling towers, turbine halls, workshops and stores will all be demolished.

Most of the structures will be demolished using conventional methods but it is intended to demolish the cooling towers by a controlled explosion known as RIM (rapid implosion method). This is much safer than having people working at height for a long period of time. Local people will be informed when this is going to happen.

At the end of the Care and Maintenance Preparation phase the only significant structure remaining on site will be the four reactor buildings in the form of ‘Safestores’ (modified to ensure that they remain safe, secure and weatherproof) and the laid down boilers. The site will then move into Care and Maintenance, which could extend for around 85 to 100 years. The objective of this phase is to allow natural radioactive decay within the reactors to simplify the process of final reactor dismantling.