Fast breeder reactors are seldom used anymore because of safety concerns, as they have a higher potential for explosions. but this explosion hazard does not come from the nuclear fission reaction. what does it come from? explain your answer in just one or two sentences.

Nuclear reactors generate energy through fission, the process by which an atomic nucleus splits into two or more smaller nuclei. During fission, a small amount of mass is converted into energy, which can be used to power a generator to create electricity. In order to harness this energy, a controlled chain reaction is required for fission to take place. When a uranium nucleus in a reactor splits, it produces two or more neutrons that can then be absorbed by other nuclei, causing them to undergo fission as well. More neutrons are released in turn and continuous fission is achieved.

What's the yellow wallpaper?