A nuclear power station is well prepared for possible emergencies. In case of a reactor shutdown, it will still produce some residual heat and need cooling water to lower its temperature. To ensure effective cooling, a modern nuclear power station like Daya Bay is supported by multiple main and back-up power sources such as the Guangdong grid, CLP power grid and on-site diesel generators. In case of a complete power outage, the reactor can make use of steam-driven and mobile water pumps to maintain cooling.