Sir, - On two recent occasions - September 11th and 22nd - thermonuclear fusion has had extremely favourable notice in your columns; unfortunately, the considerable downsides of both the fusion process and programme were omitted.Contrary to your reports, the process of fusion is not non-polluting - how can it be when it uses radioactive tritium as one of its fuels? Tritium, being a form of hydrogen, is extremely difficult to contain and is liable, as HTO, to penetrate any biocycle - i.e., it can enter the human body with a potential to cause cancer or genetic damage.There is also a major problem of radioactive waste arising from the surrounding structures of a fusion reactor, but this is a problem that the fusioneers seem to ignore in their extraordinarily gung-ho publicity. Indeed, it would be good to hear some pronouncements on this issue from Mr Frank Turvey or any other of the Irish participants in the fusion programme. Come on out lads, you've been hiding your lights under a bushel for altogether too long.The fusion programme has been in existence of roughly half-a-century and is still not in realistic sight of lift-off. Its major success has been in securing the lion's share of energy research funding, thus diverting much needed cash from renewables and energy efficiency, the two areas vital for combating global climate change. It is time we turned away from the discredited nuclear dreams of the mid-century, dreams of which fusion is the sole, increasingly quaint and increasingly beleaguered survivor. - Yours, etc.,From Jim WoolridgeEarthwatch, Bantry, Co Cork.