The latest results of B2-Eirene modelling of ITER divertor operation are presented. The operational window is further explored with an improved model of the neutral transport, the effect of gas leaks between the divertor cassettes is assessed, and the sensitivity of the results to features of the divertor geometry and to the gas puffing arrangement is analysed. The presence of neutral-neutral collisions in the model makes the results rather insensitive to the detail of the divertor shape. The

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... alysis shows that the effect of the gas leak on the divertor performance in ITER is weak and therefore inter-cassette sealing may be not critical.