Heavy water tank

The invention belongs to the technical field of nuclear reactors and particularly relates to a heavy water tank. The heavy water tank comprises an upper flange, a main cylinder, a lower flange and a lower seal head assembly, wherein the upper end of the main cylinder is welded with the upper flange; the lower end of the main cylinder is connected with the lower seal head assembly; an overflow cofferdam assembly is fixedly arranged on an inner wall of the main cylinder through bolts; a lower grid plate assembly is arranged on the lower seal head assembly, comprises a lower grid plate and further comprises a vertical hole-path support member, cold source and hot source vertical hole-path support members and a safe rod guide tube support member which are fixed on the lower grid plate throughbolts; and the lower grid plate is arranged on a short link through bolts. The lower grid plate assembly further comprises a support short cylinder on which the lower grid plate is fixed, and the support short cylinder is fix