Comparisons of nuclear characteristics between circular core cell and rectangular core cell as material engineering test reactor

The comparisons of nuclear characteristics were made between the circular cell (BR-2 type core unit cell), and the rectangular cell (ETR type core unit cell) in the Material Engineering Test Reactor. The uranium weight ratio of U-Al alloy for the meat of fuel plates is taken as a parameter. Design parameters such as critical mass, average flux of the loop per unit power, allowable maximum flux of the loop, mass coefficient and void coefficient were examined as criterions for the comparisons. In view of co-existence of beryllium and light water in the circular cell, the advantage of beryllium was studied. In the calculation, the thermal utilization of the circular cell was estimated as exactly as possible, solving the space dependent thermalization formula. The conclusions obtained by this study include, (1) We can load the fuels in the rectangular cell more tightly than in the circular cell. But we can not find the essential difference in each case if we can adjust the weight ratio parameter easily. (2) When we desire high allowable flux of the loop or high flux of the loop per unit power, we may adjust the uranium weight ratio in accordance with the requirement. (3) If we fill up the gap of the tightly loaded circular cells with beryllium which has smaller absorption cross section than light water, and if we can adjust the uranium weight ratio easily according to the requirement, it might be said that the circular cell has some advantage because of the improved thermal utilization. (4) We can take the negative void coefficient in the circular cell more easily than the rectangular one. (author)