Impurity characteristics have been investigated in high power (20 MW) NB heated discharges of outer and lower X-point configurations with TiC coated molybdenum or graphite first walls. The light impurity concentrations and Zeff had the lowest values in the outer X-point discharges with TiC coated molybdenum first walls. In high density discharges, the heat load on the divertor plate was suppressed by radiative cooling originating from carbon and hydrogen in the divertor region. To simulate the behaviour of the helium ash in a fusion reactor, helium particles were fuelled by a 30 keV helium beam or gas puffing in NB heated hydrogen plasmas. The neutral pressures of helium and hydrogen in the divertor region were proportional to n̄e3. For the helium transport in the main plasma, the inward flow pinch of helium ions was slightly more pronounced than that of the hydrogen ions.