Characteristics of storage in pools

Once unloaded from the nuclear reactor, the spent fuel must be kept in storage in pools for it to cool down.

The choice of water as a medium for this immediate storage is due to its high heat transfer coefficient, its good properties as a shielding medium, its transparency, the ease with which it is handled and its low cost.

The nuclear power plant pools are normally of reinforced concrete with an inner stainless steel cladding. These structures are resistant to design basis earthquakes and are normally rectangular in shape.

The fuel is located at a depth of between 10 and 13 metres in order to ensure that the fuel rods, which measure up to some 4.5 metres in length and which are placed vertically, remain covered by several metres of water (this being necessary to guarantee shielding). Furthermore, the pools are equipped with the following:

• Leak detectors, which alert the control room in the event of any leakage being detected.
• Cooling systems, based on heat exchangers, which must guarantee that the fuel remains submerged and that the water temperature is adequate.
• Water purification systems.

All the Spanish nuclear power plants have changed the storage racks in their pools, thus delaying their saturation and providing time for decision-making regarding the temporary dry storage of spent fuel in Spain.