In the world of nuclear reactor science and safety, the ductile-brittle transition temperature, which is used to measure the strength of the inner wall of a reactor pressure vessel, is a critical factor.
The steel walls of a reactor vessel wear out through years of direct exposure to neutron irradiation, and when they are weakened they can become brittle with sudden temperature drops.
A high DBTT means the walls can shatter at a relatively high temperature when the vessel is going through the cooling process, similar to pouring ice-cold water into a hot glass, causing it to shatter.