[en] Extended burnup of LWR fuels has been required recently. One of the most important factors limiting the extension of fuel burnup is foreseen to be waterside corrosion of fuel cladding. In this corrosion, major problems exist in nodular corrosion in BWR and irradiation-accelerated corrosion in PWR. Extensive studies on these problems have obtained a large amount of knowledge and some corrosion-resistant materials have been developed, while there is still significant amount of unknown factors of corrosion under irradiated condition. The present report reviews the current status of studies of cladding waterside corrosion, and discusses the direction and priorities of corrosion study. (author) 78 refs