Approximate concentration distributions of point defects around a dislocation in irradiated material are obtained by dividing the region near the dislocation into two parts in which some definite approximations are used. Then dislocation biasfactor for interstitials is determined, the value of the factor is less than the previous one by 20-50%. As a result, a formula of swelling due to void growth in irradiated materials is obtained, it agrees with experimental data reasonably.