Abstract: The sampling method by coupling criticality source direction biasing and the exponential transform is established for duct shielding calculation.In sample problem studying,the optimal source direction biasing parameter p₁、exponential transform parameter p₂ are supposed and the variance of duct calculating results by using this method is shown to reduce efficiently.Correction calculation for the duct of Nuclear Power Institute of China (NPIC) pulsed reactor shows the results are more close to the measured ones.

Key words: Monte Carlo method, criticality source direction biasing, exponential transform