Depending on the type of reactor, refueling may be done on-line or may require the plant to be shutdown. The fuel must be replaced because some of the fuel assemblies can no longer generate the full power expected. Usually the fuel assembly is in the reactor for 3 to 5 years. Also during a refueling, fuel assemblies may be relocated to optimize the power generation across the reactor so that no areas of the reactor generate undesired levels or non-uniform conditions.

CANDU and RBMK reactors allow on-line refuelings. On-line refueling may replace 1 to 3 fuel assemblies per day depending on the type and size of the reactor and the number of fuel assemblies.

The photo to the left shows the refueling machine used to remove fuel assemblies from the reactor.

Boiling and Pressurized water reactors must be shutdown to perform the refueling. During a refueling shutdown, 25 to 40% of the fuel assemblies may be replaced. The number replaced depends on the cycle length and number of fuel assemblies in the reactor.

Courtesy Ignalina NPP

Courtesy Leibstadt NPP

The photo to the right shows the reactor as seen under water for all refuelings. The characteristic blue glow is Cerenkov radiation - attributed to radioactive particles moving faster than the speed of light in water. With time the blue glow diminishes.

Photos illustrating the process:

More on refueling outages and what events occur.

Copyright 1996-2005.  Joseph Gonyeau. All rights reserved. Revised: March 15, 2001.