Spent fuel pool

The fuel bundles fresh from the core are normally segregated for several months for initial cooling before being sorted into other parts of the pool to wait for final disposal.

High-density racks also incorporate boron-10, often as boron carbide (Metamic,[1][2] Boraflex,[2] Boral,[3] Tetrabor and Carborundum[4])[5][6][2] or other neutron-absorbing material to ensure subcriticality.

[9] Other research envisions a similar low-power reactor using spent fuel where instead of limiting the production of hydrogen by radiolysis, it is encouraged by the addition of catalysts and ion scavengers to the cooling water.

[10] The neutron absorbing materials in spent fuel pools have been observed to degrade severely over time, reducing the safety margins of maintaining subcriticality;[4][5][11][2][6] in addition, it has been shown that the in-site measurement technique used to evaluate these neutron absorbers (Boron Areal Density Gauge for Evaluating Racks, or BADGER) has an unknown degree of uncertainty.

[6] If there is a prolonged interruption of cooling due to emergency situations, the water in the spent fuel pools may boil off, possibly resulting in radioactive elements being released into the atmosphere.

[12] In the magnitude 9 earthquake that struck the Fukushima nuclear plants in March 2011, three of the spent fuel pools were in buildings which had been damaged and were seen to be emitting water vapour.

The US NRC wrongly stated that the pool at reactor 4 had boiled dry[13]—this was denied at the time by the Government of Japan and found to be incorrect in subsequent inspection and data examination.

[15][16][17] According to Dr. Kevin Crowley of the Nuclear and Radiation Studies Board, "successful terrorist attacks on spent fuel pools, though difficult, are possible.