Nuclear rod upper end plug

The invention belongs to the technical field of fuel element, and more specifically relates to a nuclear rod upper end plug. The nuclear rod upper end plug is of a structure with upper diameter smaller than lower diameter; the middle part of the structure is provided with a through hole; the upper end is an upper end plug conical boss; an upper end plug small cylindrical structure is arranged under the upper end plug conical boss; an upper end plug large cylindrical structure is arranged under the upper end plug small cylindrical structure; from the upper end plug small cylindrical structure to the upper end plug large cylindrical structure, transition is realized through a small conical surface and a large conical surface from up to down; a groove is formed at the connection part of the small conical surface and the large conical surface; between the groove and the external surface of the small cylindrical structure, a conical structure is adopted for transition; the bottom of the upper end plug large cylind