| 摘要 |
PURPOSE:To enable safe and stable operation by increasing the number of the partially long fuel rods of a mixed type fuel assembly to the number larger than the number of the partially long fuel rods of an uranium fuel assembly. CONSTITUTION:The number of the partially long fuel rods 2B of the mixed type fuel assembly for a boiling water reactor using uranium fuel and mixed type fuel is increased to the number larger than the number of the partially long fuel rods of the uranium fuel assembly, by which no fuel rods 2A are made to exist and water is made to exist in the four corners in the upper part of the fuel assembly; therefore, the water to fuel ratio in the upper part increases. The neutron spectra of the mixed type fuel assembly are, therefore, equalized to the neutron spectra of the uranium fuel assembly and since the value of control rods and the difference between the reaction at the time of a low temp. and the reaction at the time of operation are equalized to those of the uranium fuel assembly, the safe and stable operation is enabled even if the uranium fuel assembly and the mixed type fuel assembly are used in combination.
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