Unit 4 of Belgium’s Doel nuclear power plant will stay offline for the remainder of 2014, after an oil leak caused by employee sabotage significantly damaged the turbine.

The 1090 MW Doel 4 pressurised water reactor was shut down automatically on Tuesday 5 August, following a loss of lubricating oil in the steam turbine.

Inspections conducted by the Belgian nuclear regulator, FANC, concluded that the oil leak "probably resulted from a voluntary manual intervention." A GDF Suez spokesman later told Reuters that somebody had tampered with the system used for emptying oil from the Alstom-made turbine.

Initial investigations suggest "significant damage" has been caused to the HP turbine.

"Based on this partial analysis, it appears that Doel 4 will definitely not return to operations before December 31, 2014," Electrabel said.

Once the low-pressure parts of the turbogenerator have been opened and investigated, the operator says it will have a clearer picture of the time needed for repair.

Nuclear power plants account for almost 40% of Belgium’s 15 GW installed capacity. With two additional nuclear units – Doel 3 and Tihange 2 expected to be out of action until at least the autumn after unexpected results from tests on the reactor pressure vessels – this means Belgium is without a 20 per cent of its capacity.

The government has announced that it will expand new demand reduction measures being implemented this winter to take into account the unplanned outage at Doel 4. It has already expanded its strategic reserve to 1.2 GW to prepare for the potential prolonged outage at Doel 3 and Tihange 2.