The already-cloudy future of the giant Sellafield nuclear complex has been further complicated by news that some 3,500 workers are to be balloted over strike action to protect pension rights.

Traditionally nuclear workers have enjoyed lucrative pension deals, but the impending transfer of the Sellafield decommissioning contract to the private sector – which is now in doubt also – has led to a dispute over the kind of benefits hundreds of the site’s workers will receive.

The Daily Telegraph newspaper reports that some 300 staff want to transfer their pensions from the scheme provided by current Sellafield operator BNFL across to a scheme provided by the site’s new owners, the Nuclear Decommissioning Authority (NDA). Trade union officials claim that the NDA’s scheme is superior and that the body has a duty to transfer all the workers involved in decommissioning Sellafield to the new fund.

An NDA spokesman was quoted as saying by the newspaper: We have been working closely with the trade unions to develop pension arrangements which deliver our obligations under the [UK government’s 2004] Energy Act and we believe we have done so.

The ballot on strike action has been compounded by the apparent collapse of plans to sell British Nuclear Group, an arm of BNFL, which has a five year contract to decommission Sellafield. It had been expected that the company would have been bought by a US engineering major, but a squabble erupted between BNFL and the NDA, which supervises the decommissioning of all UK nuclear sites, as to how the sale should be achieved.