JAERI 1287 JNDC Nuclear Data Library of Fission Products Fir
JAERI 1287 JNDC Nuclear Data Library of Fission Products Fir
JAERI 1287 JNDC Nuclear Data Library of Fission Products Fir
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<strong>JAERI</strong> <strong>1287</strong> 151<br />
4. Calculation <strong>of</strong> Decay Power <strong>of</strong> <strong>Fission</strong><br />
<strong>Products</strong><br />
The decay power <strong>of</strong> fission products has been calculated by the DCHAIN code using<br />
the <strong>JNDC</strong> nuclear data library described in Sec. 2 for the instantaneous fission pulse, a year's<br />
irradiation and the infinite irradiation. A year's irradiation is considered to be a typical irradiation<br />
time in a light water reactor operation. Thermal neutron fission <strong>of</strong> 235 U, 239 Pu, 241 Pu,<br />
233 U, fast neutron fission <strong>of</strong> 235 U, 238 U, 239 Pu, 232 Th, and 14 MeV neutron fission <strong>of</strong> 235 U,<br />
238 U were considered in the analysis. Neutron capture transformations <strong>of</strong> fission products<br />
during operation were neglected in the calculation. The cooling time after irradiation ranged<br />
from 0 to 10 13 s.<br />
The calculations <strong>of</strong> decay power in this section aim at comparison <strong>of</strong> the present results<br />
with other evaluations and, furthermore, at application for the best-estimate calculation <strong>of</strong><br />
LOCA. In order to compare the present library with others and to study the sensitivities <strong>of</strong><br />
fission products, contributions <strong>of</strong> important nuclides to the decay power are evaluated for<br />
the thermal neutron fission <strong>of</strong> 23S U.<br />
The calculated results have been fitted to an analytical function with thirty-one exponential<br />
terms to apply the present results conveniently to a LOCA analysis and other<br />
applications.<br />
4.1 Tables <strong>of</strong> Calculated Results<br />
Calculations <strong>of</strong> decay powers for the instantaneous burst fission, a year's irradiation, and<br />
the infinite irradiation are given in Tables 4.1.1, 4.1.2, and 4.1.3, respectively. Contribution<br />
<strong>of</strong> each fission-product nuclide to the decay power is shown for the thermal neutron fission<br />
<strong>of</strong> 235 U in Tables 4.1.4, 4.1.5, and 4.1.6, respectively, for the instantaneous fission, a year's<br />
irradiation, and the infinite irradiation.<br />
Methods are given subsequently for obtaining the decay power Pit, T) for an arbitrary<br />
reactor power history without neutron capture by fission products. Neutron capture in fission<br />
products has only a small effect upon the decay power for the cooling time less than 10 3<br />
s s9) . However, the direct summation calculation is necessary for the accurate evaluation <strong>of</strong><br />
the decay power, especially for long cooling times after long-term and high-neutron flux<br />
irradiation.<br />
The decay power Pit, T) for an arbitrary irradiation history PoiT) can be obtained<br />
either from fit) for the instantaneous fission, or Fit) for the infinite irradiation. From<br />
fit) , the decay power Pit, T) can be calculated as<br />
D ( r X^ / \<br />
Pit,T) = fJ^Q—f(t + T-T')dr (4.1.1)<br />
where<br />
t = cooling time after irradiation (s)<br />
T = total irradiation time (s)<br />
Pa = reactor power (MeV/s)<br />
Q = fission energy (MeV/fission)<br />
fit) = decay power after one fission [(MeV/s)/fission].<br />
From Fit) ,Pit,T) can be calculated as