Decay heat is best described as the residual heat from radioactive decay after reactor shutdown that must be cooled.

Decay heat is best described as the residual heat from radioactive decay after reactor shutdown that must be cooled.

• A. The heat generated during normal operation.
• B. The residual heat from radioactive decay after shutdown that must be cooled.
• C. Heat produced by chemical reactions in the coolant.
• D. Heat generated by ambient temperature.

Answer: (D)

Decay heat is the residual energy released by radioactive decay of fission fragments in the fuel after the reactor is shut down, and it must be removed by cooling. Even though the fission reactions are stopped, the fragments left behind continue to decay and emit energy, so the fuel stays hot for hours to days. This ongoing heat production is what cooling systems must handle post-shutdown. This description matches the concept of decay heat precisely: it is not the heat produced during normal operation (that comes from sustained fission), it is not heat from chemical reactions in the coolant, and it’s not heat from ambient temperature. The reason the other ideas don’t fit is that they describe different sources of heat or conditions, whereas decay heat specifically refers to energy released by radioactive decay after shutdown that requires cooling.

Decay heat is the residual energy released by radioactive decay of fission fragments in the fuel after the reactor is shut down, and it must be removed by cooling. Even though the fission reactions are stopped, the fragments left behind continue to decay and emit energy, so the fuel stays hot for hours to days. This ongoing heat production is what cooling systems must handle post-shutdown.

This description matches the concept of decay heat precisely: it is not the heat produced during normal operation (that comes from sustained fission), it is not heat from chemical reactions in the coolant, and it’s not heat from ambient temperature. The reason the other ideas don’t fit is that they describe different sources of heat or conditions, whereas decay heat specifically refers to energy released by radioactive decay after shutdown that requires cooling.