436
6 Applications: Two-Region Pebble Beds
Fig. 6.32 Detention zone of initial loading pebbles
6.3.5.2 Average Retention Time
Excessive residence time could result in severe irradiation and thermal damage to
pebbles and even possible fission product leakage. By tracking the flow of each
pebble, the flow trajectory and residence time can be obtained. As for initial loading
pebbles, average retention time is defined as follows:
T ret =
N
i=1
t re
n ini
(6.10)
where t re is the residence time of initial loading pebble i, and n ini is the number of
initial loading pebbles (N ).