For a series of configurations of high-level waste (HLW) storage in a salt repository, gamma transport and deposition have been calculated together with the heating of the salt around waste containers. These time-dependent data were used to calculate colloid growth due to irradiation using a theory by Jain and Lidiard. The results show that by a proper choice of storage parameters the colloid fraction can be limited to a few percent. Overpacking by a few centimetres of steel will reduce the amount to <1%. With the methods described a safe and economic design of HLW containers for final disposal will be possible.