JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
where f g and f t1
, g are self-shielding factors for elastic scattering cross sections and
current-weighted total cross sections, respectively. Since a multi-group library does not include
self-shielding factors for higher order Legendre components of elastic scattering cross sections,
self-shielding factors for current-weighted total cross sections are used instead.
The revised library effect for HEU-MET-FAST-021 is shown in Table 2. In comparison with
the results before the revision, library effects become much smaller since shielded cross sections
are generally smaller than infinite dilution cross sections. Even after the revision, however,
non-negligible library effects due to the difference in higher order Legendre coefficients are still
observed. Figure 2 shows an energy group-wise library effect of iron-56 to the criticality of
HEU-MET-FAST-021 between JENDL-4.0 and JEFF-3.1.
In order to confirm the validity of the above treatment, a difference in the criticality of
HEU-MET-FAST-021 between JENDL-4.0 and JEFF-3.1 is directly calculated by the
perturbation theory. This perturbation calculation shows that differences in criticality due to the
difference in the first and second Legendre components of elastic scattering matrices are -0.0058
and +0.0025, respectively. Since this perturbation calculation focuses on differences in the
Legendre scattering cross sections, not in the Legendre coefficients, library effects of the
Legendre components of elastic scattering matrices between JEFF-3.1 and JENDL-4.0 are also
calculated. The library effects due to the first and second Legendre scattering cross section
differences are evaluated at -0.0047 and +0.0023, respectively. This result is consistent with the
former direct perturbation calculation.
5. Conclusion
A sensitivity analysis has been carried out focusing on higher order Legendre coefficients of
elastic scattering matrices. Non-negligible library effects have been observed in higher order
Legendre coefficients of elastic scattering matrices of uranium-238 and iron-56 between
JENDL-4.0 and the other modern nuclear data files. It has been also found that an attention
should be paid to the type of multi-group cross sections used for the library effect calculations. It is
concluded that the higher order Legendre coefficients should be accounted for if accurate library
effect evaluation is required.
Acknowledgment
The author wishes to express his deep gratitude to M. Ishikawa of Japan Atomic Energy
Agency for providing useful comments on this manuscript.
References
[1] J. Blair Briggs (ed.): International handbook of evaluated criticality safety benchmark
experiments, NEA/NSC/DOC(95)03/I, Nuclear Energy Agency, Paris (2009 Edition).
[2] T. Hazama, et al.: “Development of SLAROM-UF : a lattice calculation code with fine and
ultra-fine energy group cross sections,” J. Nucl. Sci. Technol., 43, p.908 (2006).