It can be difficult to think of nuclear energy as a sustainable resource. Unlike other alternative resources, nuclear energy has long been an abomination to environmentalists, mainly because of the storage of radioactive waste. However, nuclear reactors are also a source of efficient electricity and do not emit Any polluting gas, and, for certain types of reactors, its design minimizes waste and basically prevents the reactor from melting. Regarding this text, what is wrong with the following understanding? ['Nuclear energy can hardly be seen as a sustainable resource.', 'Some types of reactors can basically prevent the reactor from melting.', 'The nuclear reactor does not emit any contaminated waste and gases.', 'Nuclear reactors are a source of efficient electricity, and some reactor designs have been improved.']