Besides nuclear waste incineration, there is interest in this type reactor because it is perceived as inherently safe, unlike a conventional reactor. In most types of critical reactors, there exist circumstances in which the rate of fission can increase rapidly, damaging or destroying the reactor and allowing the escape of radioactive material (see SL-1 or Chernobyl disaster). With a subcritical reactor, the reaction will cease unless continually fed neutrons from an outside source. However, the problem of heat generation even after ending the chain reaction remains, so that continuous cooling of such a reactor for a considerable period after shut-down remains vital in order to avoid overheating. However, even the issue of decay heat can be minimized as a subcritical reactor needn't assemble a critical mass of fissile material and can thus be built (nearly) arbitrarily small and thus reduce the required thermal mass of an emergency coolant system capable of absorbing all heat generated in the hours to days after a scram.