THERE have now been explosions at three reactors in the Fukushima nuclear power plant in Japan. The stated cause is the explosion of an air/hydrogen mix in buildings adjacent to the reactors.  The explosions are relatively small but what worries the public is that any explosion in such a vicinity conjures images of Chernobyl, and some people will not be convinced that these are not atomic  explosions. The physics of nuclear weapons is against small atomic  explosions: you either get a big atomic explosion or you don t.  The containment vessel of the reactor is of very thick steel, and designed against rupture. The reactor itself cannot behave like an atom bomb, but loss of cooling water is a heat hazard. If the reactor is not cooled the reactive elements will possibly melt.  This has to be made good in some way and it seems that sea water will be used. That will have the major effect of making the reactor unsalvageable. Sea water contains every known element, but apart from sodium and chlorine the concentrations are small. Nevertheless, some of these elements dissolved in the impure cooling water will become radioactive, although insignificant in quantity compared with the normal background radioactivity of the Earth s crust and the sea to which the contamination will be returned. The elements of steam, oxygen and hydrogen do not become radioactive and can be safely vented.  The Japanese reactors have been well designed in that radioactivity has been well isolated and contained. The incident will give ammunition to those opposed to nuclear energy, and it will be a difficult task for the Japanese to get new reactors built.  Chris Parton,  40 Bellshill Road, Uddingston.  as Japan faces the worst nuclear disaster since Chernobyl ( Meltdown fears grow in worst nuclear crisis since Chernobyl , The Herald, March 15) we must question whether a reliance on national grids and base load is the safest and most economical way of producing and supplying power.  Maybe we need to consider moving away from a national grid to a more localised Scottish grid, where power is more commonly generated at source.  Despite the Government s 80% emission reduction target and electrical tariff system, there is little incentive for utility companies to provide connections for smaller micro-generation. Connection charges can be prohibitive and even with the new Renewable Heat Incentive there may be insufficient profit in schemes that plan to sell power back to the grid.  Furthermore, the lack of regulation in the micro-generation market means there is no control over the type of generator chosen in a particular area or commitment to long-term maintenance. Utilities companies are therefore reluctant to reduce base load provision and this leads to calls for new expensive nuclear, gas or coal power plants.  Having attended a Scottish Enterprise workshop on micro-generation last week, I know there is an urgent need to stimulate innovatio