An improved method for Monte Carlo simulation is described to calculate the neutral-particle transport in a divertor throat and to evaluate the helium removal efficiency from a burning plasma. The required pumping speed for the helium removal is discussed with special emphasis placed on the efferts of long exhausting duct and of scrape-off plasma variables. The analysis for International Tokamak Reactor (INTOR) single null divertor suggests a possibility that the pumping requirement for INTOR could be drastically eased—e.g., <104 l/s, for the high scrape-off plasma density of the order of 1013 cm-3.