A spent fuel pool is a holding area for spent nuclear fuel to allow it to cool before being moved to more appropriate long-term storage. As fuel is used up in the reactor, it can be transferred to the pool where it remains submerged to create radiation shielding and give it an opportunity to cool down. The pool may be operated with an automatic system so workers don’t come into direct contact with components except for servicing needs. In other cases, workers need to manually manipulate fuel rods and other components to place fuel in storage.
Typically, spent fuel pools are located close to the reactor for convenience. They are composed of giant concrete tanks lined with stainless steel and equipped with racks to hold individual fuel rods. Insulating boron may be added to reduce the risk of a chain reaction. The depth of the pool dictates how many rods it can hold; legal requirements may stipulate a certain amount of coverage and facilities could make a spent fuel pool even deeper for increased safety.
As the rods sit in the spent fuel pool, the temperature of the water increases. Nuclear facilities need to constantly circulate the water through cooling equipment and back into the pool to keep temperatures low. They also monitor it for signs of reactions that might be causing large levels of hydrogen to build up around the spent fuel pool. This requires ongoing supervision from skilled technicians familiar with common issues surrounding spent fuel pools so they can act quickly if problems begin to develop.
Facilities may maintain an initial pool for immediate cooling, followed by a larger pool for older fuel. As it starts to fill up, technicians need to transfer old fuel rods to dry cask storage. In this technique, rods are removed from the pool and placed in specially-designed containers which prevent radiation leakage. The stored fuel can be transported to a long-term storage facility, where it breaks down slowly over time.
Significant safety concerns surround spent fuel pool design. If the pool is not properly designed and maintained, there is a risk of a nuclear chain reaction that could cause serious environmental harm. Pools are also at risk of becoming too full, leading to a situation where a power plant has no space to store spent fuel rods. Engineers responsible for the design and maintenance of nuclear facilities need to provide evidence that they are planning ahead to accommodate fuel, and can meet regulatory standards for nuclear fuel safety.