 Criticality is maintained as the fuel burns up by adding beryllium plates in a tray on top of the core.The reactor core sits in a pool of regular light-water, 2.5 m diameter by 6 m deep, which provides cooling via natural convection.In addition to passive cooling, the reactor has a high degree of inherent safety; that is, it can regulate itself through passive, natural means, such as the chain reaction slowing down if the water heats up or forms bubbles.