The reliability challenge for nuclear energy

Nuclear power is an established and reliable way to generate electricity. In normal operating conditions, 75% of UK nuclear capacity can be assumed available to meet peak demand.

The challenge

Eight of the nine existing UK nuclear power stations are scheduled to close by 2028. Some may continue to operate for longer than currently scheduled, if EDF Energy and the Office for Nuclear Regulation (ONR) is satisfied this is safe, but eventually they will need to be replaced.

No nuclear power station generates electricity all of the time. There are periods when it will operate at reduced levels or will be shut down for refuelling and maintenance. Most shutdowns are planned, and because of this can happen when demand is expected to be lower. Some reactors continue to operate at 20–40% of capacity while being refuelled, which typically takes three to four days, about every six weeks.

Unplanned shutdowns occur when the power station is forced to shut down either by its control system (automatic shutdown) or by the plant operator (manual shutdown) due to a suspected fault. A precautionary approach is used for the shutdown systems and operating regimes of all nuclear power stations. 

The solution

Nuclear power stations are designed to deliver a reliable level of electricity for long periods of time. The new plants proposed for the UK are expected to generate electricity as much as 90% of the time during normal operation.

In 1990, only a quarter of the world's nuclear plants had load factors of over 75% – that is, they generated more than 75% of their theoretical maximum electrical output. Today, almost two thirds of nuclear plants have load factors of over 75%, and a quarter have load factors higher than 90%.

The proposed new generation of nuclear power stations in the UK aims to set a new standard, with shorter outage periods and reduced fuel consumption per kilowatt-hour (kWh) of electricity generated. This means they will use less fuel and will need to refuel less often.