not build then. Reports in recent years that, other States have worked secretfy to acquire nuclear weapons are a cause for concern, but devel-opnents have not so far borne out the early fears of a very rapid. horizontal nuclear proli feration, l+26. The main reason is that a State vilf not develop nuclear weapons sin4>ly because it has the capability to do so. Such a fundamental d.ecision nil-1 be based on other factors, as has been discussed in paragraphs 368-383 above, Nevertheless, general techno.logical developnent as 1,re11 as the increasing reliance internationally on nuclear por+er for generation of electricity is leading to a rise in the number of countries which potentially wou,ld have the capability to develop nuc],ear lreapons. This does not nean that operation of a cortrmercia.l nuclear pover reactor autonaticaLly gives a State the capability to construct a nuclear weapon. The recent Internationa-L Nuclear luel Cycle Evaluation (INFCE) study concludes that fuel cycle facilities are not the nost efficient Toute to acquire materials for the manufacture of nuclear \reapons, ilowever, a State vith a small nuclear industry including an active but not necessarily l"arge research coraponent wil-l- have a reserve of knor'ledge which, if so applied, could be utilized in a programme to deve.lop nuclear weapons . \27. fhe spread of nuclear power has al-so been accompanied by the gradual spread of the sensitive technologies through which fissionable material usable in weapons is obtained - uranium enrichment and reprocessing. With tirne, the ability to make weapon-grad.e nateriaf is probably within the reach of some 15 to 2! cormtries. \28. In response to international requirements for energ:y, '"rorld nuclear por,re" capacity rose from about 1l+,oOO M,fe to more than ?8,000 M^Ie betffeen a97o and 1976. INFCE quotes a figure of 131 ,000 lff,Ie at the end of 1979, and a figure of alnost