I doubt if the contributions are using 'act' and 'law' indiscriminately.
the name of an act is generally given using the term 'act'.
the Nuclear Energy Act, to use your example.
the definitions are typically ambiguous.http://dictionary.cambridge.org/define.asp?ke...
has the following for 'act':
a law or formal decision made by a parliament or other group of elected law-makers
so that two conditions are necessary for something to be an ACT in the sense given above:
1/ it is in the form of a law or formal decision
2/ it is enacted by parliament or other group of *elected* lawmakers
a rule, usually made by a government, that is used to order the way in which a society behaves, or the whole system of such rules
so that we can conclude the following from the definitions above:
an ACT need not be a law, it can also be a formal decision.
an ACT need not be a rule used to order the way in which a society behaves
a LAW need not be made by government
a LAW brought into being by a nonparliamentary, or non-elected governing body, is *not* an ACT.
using both words in one sentence can indicate their usage:
" The LAWs governing nuclear power plants are covered by the Nuclear Energy ACT"
Reversing the words, and the meaning is lost, the sentence nonsense:
" the ACTs governing nuclear power plants are covered by the Nuclear Energy LAW"