8 Sensitivity and Uncertainty of Criticality
227
(a) EE1 core
(b) E3 core
-5.0E-04
4.5E-03
9.5E-03
1.5E-02
2.0E-02
2.5E-02
3.0E-02
1.0E-04
1.0E-02
1.0E+00
1.0E+02
1.0E+04
1.0E+06
Sensitivity coefficient per lethargy [-]
Neutron energy [eV]
Al-27
B-10
B-11
C-12
H-1
O-16
U-234
U-235
U-236
U-238
U-235
Al-27
C-12
-5.0E-04
4.5E-03
9.5E-03
1.5E-02
2.0E-02
2.5E-02
3.0E-02
1.0E-04
1.0E-02
1.0E+00
1.0E+02
1.0E+04
1.0E+06
Sensitivity coefficient per lethargy [-]
Neutron energy [eV]
Al-27
B-10
B-11
C-12
H-1
O-16
U-234
U-235
U-236
U-238
C-12
Al-27
Fig. 8.5 Sensitivity coefficients for inelastic scattering reactions in excess reactivity (Ref. [1])
dominant over the sum of all contributions, including the capture and fission reactions
of
235 U; a large contribution [19] was attributable to the sensitivity coefficients of
235 U capture and fission reactions. For the worth of C1 control rod in E3 core, the
total uncertainty was 164.1 pcm, although the reaction-wise contribution was slight
in the boron isotopes, as shown in Table 8.7, demonstrating the same tendency of
excess reactivity as in EE1 core shown in Table 8.6. Finally, the uncertainty of k eff
in excess reactivity and control rod worth (C1, C2 and C3 rods) was summarized
around 150 pcm in the EE1 and E3 cores.
Furthermore, the effect of decreasing uncertainty induced by nuclear data on
calculated k eff was investigated by the cross-section adjustment method [20, 21], with
the use of uncertainty of k eff values. The result of this investigation demonstrated a
great improvement from around 150 to 3 pcm induced by nuclear data of JENDL4.0 in all excess reactivity and control rod worth in EE1 and E3 cores. Moreover, by