Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Kowata, Yasuki; Fukumura, Nobuo
PNC TN9410 96-131, 35 Pages, 1996/05
Plutonium fuel could be utilized in the entire core of heavy water moderated, boiling light water cooled pressure-tube-type reactor (HWR). The void reactivity, however, depends on the various parameters of the lattice. It is especially significant to clarify the influence of plutonium nuclides on the void reactivity. The void reactivities in the infinite HWR lattices have been parametrically analyzed to clarify the influences of changes in the lattice parameters on the void reactivity using the WIMS-D4 code with the JENDL-3.1 nuclear data. In this lattice calculation, it has been known that the behavior of the void reactivity can be made clear by separating the components for fuel nuclides, neutron cross sections, energy group and regions in lattice cell from the void reactivity using the important reaction rates. If the macroscopic 2200m/s neutron absorption cross section of fuel is identical each other, it has been shown that the void reactivity of the HWR lattice shifts further to the negative side in the narrower pitch lattice, and in the plutonium lattice than in the uranium lattice. The effect reducing the void reactivity to the negative by plutonium is caused mainly by the presence of the resonance cross section at around 0.3eV of 
Pu. Because the higher the content of Pu is, the less the recovery effect of neutron density within the resonance energy due to decrease in the thermal neutron scattering of hydrogen is with increase in coolant void fraction, so that the decreased resonance fission rate for Pu contributes to the more negative side for the void reactivity.
Kowata, Yasuki
PNC TN9410 91-285, 27 Pages, 1991/08
The effect of the gadolinia-poison on coolant void reactivity in a pressure-tube-type heavy water reactor has been clarified by critical experiments and analyses. Experiments were carried out in the 25 cm lattice pitch DCA (Deuterium Critical Assembly) core in which few gadolinia-poisoned fuels were loaded in the central region. Four or three gadolinia-poisoned UO
fuel rods were used in the middle layer of 28 rod or 36 rod fuel cluster as the gadolinia-poisoned fuel respectivity. The concentration of gadolinia in gadolinia-poisoned fuel pellets was changed from 0.0 to 0.1, 0.5 and 1.0 wt% in order. Void reactivity calculated by the lattice code WIMS-D using the collision probability method and the diffusion code CITATION were compared with experimental ones. Calculated values for cores with gadolinia-poisoned fuels agree with experimental ones within 
0.2$. The void reactivity tends to shift toward positive side with adding gadolinia-poison, but it soon saturates around the 0.5wt% gadolinia concentration. These tendencies are remarkable as an increase in loading ratio of gadolinia-poisoned fuels in the core or as a location to the outer layer of gadolinia-poisoned fuel rods in the cluster. However, this tendency is relieved when fuel material of reference fuel without gadolinia-poisoned fuel rods changed from UO to PuO-UO mixed oxide. The reason why the coolant void reactivity shifts to the positive side with the addition of gadolinia to the fuel is that an increase in the neutron absorption of gadolinium due to voiding make an increase in the neutron importance at the reference fuel region to promote, so that it tone up the fission yield component of the void reactivity.
Kowata, Yasuki*; Fukumura, Nobuo
Nuclear Science and Engineering, 99(4), p.299 - 312, 1988/08
None
