JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
- pin pitch : 1.265 cm,
-
-
fuel pellet radius : 0.412 cm,
outer radius of cladding region : 0.476 cm.
Fuel depletion calculations are performed with a
linear heat rating of 179 W/cm till 45 GWd/t and are
followed by a cooling time of five years.
Resonance self-shielded cross sections are
generated with the equivalence theory using a
107-group library based on JENDL-4.0. With the
region-wise 107-group cross sections, eigenvalue
calculations are performed with the collision probability method. White boundary conditions are
assigned to reduce a computational cost. The above resonance and eigenvalue calculations are
performed at depletion steps, 0, 0.1, 1, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, 35,
37.5, 40, 42.5 and 45 GWd/t. Depletion calculations are carried out by the Pade method with
twenty depletion sub-steps for each depletion step. Figure 1 shows a burn-up chain for heavy
nuclides utilized in the present study. This chain is almost the same as that of the SRAC code.
Table 1 Initial number densities of fuel
Fig. 1 Burn-up chain for heavy nuclides
Sensitivity calculations are performed with the depletion perturbation theory for the neutron
flux and nuclide density coupled field. The target of the sensitivity calculations is
concentrations of curium isotopes after 45 GWd/t burn-up and 5-year cooling time. The
sensitivities of the concentrations are calculated to fission and capture cross sections and
half-lives of heavy nuclides. While we obtain energy group-wise sensitivities, we show
one-group-integrated sensitivities in order to ease a comparison.
4. Numerical results
Figure 2 shows one-group sensitivities to fission and capture cross sections of major actinides.
The following are observed in this figure:
- Negative sensitivities to fission cross sections are observed. When a fission cross section
increases, the neutron flux level decreases since the heat rating is constant. That results in