| 摘要 |
PURPOSE:To improve the safety of a reactor core operation by providing neutron moderating layers into the upper part of the metal fuel elements in fuel rods in a part of a fuel assembly. CONSTITUTION:The neutron moderating layers are provided on the upper part of a part of the fuel rods sealed therein with the metal fuel elements 3 by disposing a material 4 contg. a neutron moderating material such as beryllium to said upper part. The neutron spectra in the upper part of the reactor core where a fuel temp. is high and a Doppler effect is large are thereby softened and the impression of the negative reactivity by the Doppler effect is enhanced. The negative feedback effect in isothermal coefft. and output coefft. is, therefore, intensified and the safety with the reactor core operation is improved.
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