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> 133<br />
3. Comparison <strong>of</strong> Calculated and Measured<br />
Decay Powers<br />
Decay powers <strong>of</strong> fission products were calculated by the DCHAIN 15 ^ code using the<br />
<strong>JNDC</strong> nuclear data library <strong>of</strong> fission products described in Section 2, the library evaluated by<br />
Tasaka 20 > and the ENDF/B-IV library for the thermal neutron fission <strong>of</strong> 233 U, 235 U, 239 Pu<br />
and 241 Pu, and for the fast neutron fission <strong>of</strong> 23S U. The results are compared with the latest<br />
decay power experiments at ORNL 3 " 6) , LANL 7>8) and University <strong>of</strong> Tokyo 12 " 14 >.<br />
3.1 Comparison with ORIML Experiment<br />
Dickens et al. 3 ' 6 ^ at ORNL measured the decay power <strong>of</strong> fission products for thermal<br />
neutron fission <strong>of</strong> 23S U, 239 Pu and 241 Pu. Samples <strong>of</strong> mass 1 to 10 ptg were irradiated for 1<br />
to 100 s using the fast pneumatic-tube facility at the Oak Ridge Research Reactor. The resulting<br />
beta- and gamma-rays emitted by the samples were counted for times-after-fission <strong>of</strong> 2<br />
to 14000 s. The. data were obtained for beta- and gamma-rays separately as spectral distributions,<br />
N(Er) versus ET and N(Ep) versus Ep. For gamma ray, the spectra were obtained using<br />
an Nal detector; and for beta ray, the spectra were obtained using an NE-110 detector with<br />
an anticoincidence mantle. The raw data were unfolded to provide spectral distributions with<br />
modest resolution. These distributions were integrated over Er and Ep to provide total yield<br />
and energy integrals as a function <strong>of</strong> time after fission.<br />
The rate <strong>of</strong> energy release after t seconds following an instantaneous pulse <strong>of</strong> fission<br />
can be estimated by dividing the energy integrals by the counting time tcount . The cooling<br />
time t is taken as<br />
I— t wait ' U. D ^ tirr ad ' I count )><br />
where, twail = waiting time before counting after irradiation,<br />
tirrad - irradiation time,<br />
tcount = counting time.<br />
The difference between the estimate and an "exact" value is very small for most measurements<br />
since twail is greater than {tirrad + tcount )• It becomes large for short waiting times<br />
compared with the irradiation and counting times and reaches a maximum at t = 2.7 s which<br />
are approximately 4% and 2% for 239 Pu and 241 Pu, respectively, for both beta- and gamma-ray<br />
energy-release data. For most <strong>of</strong> integrals, the uncertainties (la) are less than 4%, 4% and<br />
5% for the fissions <strong>of</strong> 235 U, 239 Pu and 241 Pu, respectively.<br />
Figures 3.1.1 (a) through 3.1.9 (a) show the comparisons <strong>of</strong> calculated and measured<br />
decay heat powers <strong>of</strong> beta, gamma, and beta + gamma rays by thermal neutron fissions <strong>of</strong><br />
235 U, 239 Pu and 241 Pu. The abscissa is the time t after burst fission and the ordinate is the<br />
decay power multipled by the time t. The ratios <strong>of</strong> the calculated decay powers to the measured<br />
ones are also shown in the figures (b) for evaluating easily the percent discrepancies<br />
between calculated and measured decay powers.<br />
As seen from these figures the beta decay powers calculated by the present <strong>JNDC</strong> library<br />
agree with the measured results within the accuracy <strong>of</strong> ± 7% for the fissions <strong>of</strong> the all three<br />
nuclides 235 U, 239 Pu and 241 Pu. The accuracy has been much improved compared to the<br />
accuracies <strong>of</strong> ± 20% and ± 28% attained by the Tasaka library and the ENDF/B-IV library,