The uranium fuel inside the reactor will gradually be used
up while the reactor is at power. As such, a refuelling
outage, which is usually conducted annually or in every
18 months depending on the enrichment of U-235 in the
fuel,
will be carried out at the end of a fuel cycle. About one-third
of the fuel assemblies will be replaced with new ones
during
each refuelling outage. The used fuel assemblies (spent
fuel) contain highly radioactive nuclides and
generate a considerable amount of heat due to radioactive
decay. Hence, it would be transported for storage in a "spent
fuel pool" inside
the Fuel Building situated adjacent to the Containment Building.
The process, carried out under water, includes unloading
of fuel assemblies from the reactor core and its transportation
to the spent fuel pool. The spent fuel pool is filled up
with borated cooling water to
shield the radiation. In addition, it is equipped with a
cooling system to extract the decay heat from the spent
fuel by circulation of the pool water. The bottom of the
spent fuel pool has over 700 storage cells and allows storage
of all spent fuels taken out from the reactor unit up to
ten years.
