Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
TABLE 1. MAXIMUM ACTIVITY OF THE MAIN FISSION PRODUCTS.
Core, 2 h after
shutdown
Spent fuel Primary system Gaseous effluents
Rare grases 10 7 TBq 10 6 TBq 3 10 2 TBq 2 10 2 TBq
Iodine 2 10 7 TBq 10 6 TBq 20 TBq
Caesium 10 7 TBq 2 10 4 TBq
It should be pointed out that:
Under normal operating conditions, a nuclear reactor has no “natural” power level.
In order to be able to operate for at least a year without refuelling and
counterbalance various power‐related effects, the core has to contain a quantity of
fissile material far exceeding the critical mass at cold shutdown. The power level
produced by this material consequently results from combining various parameters
which must be controlled from outside.
Under particular operating conditions, the energy released in a nuclear reactor can
increase extremely quickly, in an uncontrolled manner and can then only be limited
by neutron feedback effects related to temperature rises or fuel dispersal.
Energy released in fuel that was part of a chain reaction cannot afterwards be
annulled, even when the reaction is over. In fact, radioactive products deriving
from fission must themselves release a certain amount of energy in order to reach
a stable state. They do this with a decay period specific to each element which can
be very short (less than 1 second), or average (months or years) or very long
(hundreds or thousands of years). Although decreasing, the power produced will
for a long time be greater than one‐thousandth of the rated power and this calls for
continuous cooling (Table 1.3).
Prevention of specific risks therefore requires:
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