Reference core design of the experimental multi-purpose very high temperature reactor

At the start of reference core design of the Experimental Multi-Purpose Very High Temperature Reactor (VHTR), nuclear and thermo-hydraulic characteristics were studied extensively to search for optimum values of the VHTR core parameters. Described in this report are the procedures and the results of core nuclear studies, especially concerning core nuclear characteristics in radial and axial fuel zoning. Main results are the following. (1) In radial direction uniform fuel zoning is the best. (2) In axial direction suitable fuel zoning is necessary; i.e. in blockwise zoning from core top to bottom, 8, 8, 8, 6, 4, 2 w/o enriched fuel (average 6 w/o of 6 blocks) for Mark-I, and 7, 7, 5, 5, 5, 3, 3 w/o (average 5 w/o of 7 blocks) for Mark-II. (3) There is no essential difference in fuel temperature between hollow and annular fuel rods, because of low power density of the Experimental VHTR core. (4) 85 and 73 fuel columns are proposed for Mark-I and Mark-II core respectively. (author)