Some of the metallurgical problems in the construction of nuclear reactors are discussed. Typical problems resulting from neutron bombardment encountered such as uranium growth, deterioration of fuel cans, thermal effects, and radiation effects, are presented in detail. Solutions to some of these problems found during the construction of the Calder Hall reactor in the United Kingdom are given as examples of the complex problems encountered. Some of the basic solid-state effects due to neutron irradiation are still not fully understood and are being investigated.