There are no nuclear reactors in Ireland.
And even if there were, how on earth could a current from the Irish sea possibly 'well up' off the coast of India, for heaven's sake?! Show us a link to this claim of yours.
This looks like another product of the wonderful world of half-knowledge. There are word-wide currents that redistribute water around the planet. The oceans are not isolated pools but part of one global system. The part of the global current system called the Gulf Stream plunges into the depths after losing most of its heat near Iceland (and therefore also near Ireland) and then does indeed wend all the way around Africa before coming to the surface again in the Gulf of Arabia, near India.
This in itself is interesting, but the "alternative thinkers" can use anything to extend their paranoid world-views. Show one of them that the thermohaline circulation exists, and instantly it gets woven into the universal conspiracy dream-world. Reactors will appear anywhere they are needed to dump contamination into the current that can then spread it around the world. (Note: Japan is not near any of the major world ocean currents, only local currents.)
Building a 'narrative' with verisimilitude requires at least some real-world facts. When the core of the narrative is complete fantasy, the facts drawn in to provide the real-world links can come from very far afield. :)