234
M. Yamanaka
Table 8.11 Comparison between measured and calculated reactivity at critical experiments in E3
core (Ref. [2])
Reactivity
Experiment[pcm]
MCNP6.1 [pcm]
SCALE-6.2/KENO-VI [pcm]
Excess
252 ± 2
242 ± 11
(0.96 ± 0.04)
229 ± 13
(0.91 ± 0.05)
C1 rod
526 ± 6
536 ± 11
(1.02 ± 0.02)
502 ± 13
(0.95 ± 0.03)
C2 rod
410 ± 4
377 ± 11
(0.92 ± 0.03)
410 ± 13
(1.00 ± 0.03)
C3 rod
314 ± 4
315 ± 11
(1.04 ± 0.04)
312 ± 13
(0.99 ± 0.04)
(): C/E (calculation/experiment) value
8.3.2.2 Core Components
The impact of
235 U was observed about a significant 900 pcm in both EE1 and E3
cores, as shown in Tables 8.12 and 8.13, respectively. Especially, in the EE1 core,
the uncertainty was mostly composed of the values of χ, ν and (n, γ ) (capture cross
section) reactions of
235 U that are related to the infinite multiplication factor. In fact,
sensitivity profiles of the χ value of
235 U shown in Fig. 8.8 were large with a large
number of standard deviations. A marked difference was observed in the ν value of
235 U shown in Fig. 8.9 between EE1 and E3 cores at thermal neutron and resonance
regions in sensitivity profiles; also, core spectrum dependence on sensitivity was
effectively canceled by constant standard deviation at these regions.
The uncertainty of capture reactions of polyethylene with the consideration of the
thermal scattering law S(α, β) (termed *
1 H in Tables 8.12 and 8.13) was effective in
E3 core more than scattering (*
1 H (n, n)) reactions caused by the soft spectrum core
with a large number of moderators as indicated by sensitivity profiles in Figs. 8.10
and 8.11.
Furthermore, the core spectrum was found to be dependent on the uncertainty of
aluminum (Al) in the HEU plate (U-Al alloy) and aluminum in the core component
(Al sheath) at KUCA indicated by “
27 Al” and “*
27 Al,” respectively, as shown in
Figs. 8.12 and 8.13. In the EE1 core, elastic scattering and inelastic scattering (
27 Al
(n, n
)) reactions in HEU plates affected the uncertainty because of the large sensitivity
at the fast neutron region as shown in Figs. 8.14 and 8.15, respectively. Also, at the
hard spectrum core, elastic scattering reactions of the Al sheath indicated higher
value than that of
27 Al in HEU plates. Here, uncertainty that is not varied by control
rod insertion should be emphasized, because the impact of nuclear reactions related
to boron are very small and not shown in Tables 8.12 and 8.13. Accordingly, the
calculated results of excess reactivity and control rod worth were considered in good
agreement with the measured ones within a 10% difference because the uncertainty
of boron is not induced by control rod insertions.
M. Yamanaka
Table 8.11 Comparison between measured and calculated reactivity at critical experiments in E3
core (Ref. [2])
Reactivity
Experiment[pcm]
MCNP6.1 [pcm]
SCALE-6.2/KENO-VI [pcm]
Excess
252 ± 2
242 ± 11
(0.96 ± 0.04)
229 ± 13
(0.91 ± 0.05)
C1 rod
526 ± 6
536 ± 11
(1.02 ± 0.02)
502 ± 13
(0.95 ± 0.03)
C2 rod
410 ± 4
377 ± 11
(0.92 ± 0.03)
410 ± 13
(1.00 ± 0.03)
C3 rod
314 ± 4
315 ± 11
(1.04 ± 0.04)
312 ± 13
(0.99 ± 0.04)
(): C/E (calculation/experiment) value
8.3.2.2 Core Components
The impact of
235 U was observed about a significant 900 pcm in both EE1 and E3
cores, as shown in Tables 8.12 and 8.13, respectively. Especially, in the EE1 core,
the uncertainty was mostly composed of the values of χ, ν and (n, γ ) (capture cross
section) reactions of
235 U that are related to the infinite multiplication factor. In fact,
sensitivity profiles of the χ value of
235 U shown in Fig. 8.8 were large with a large
number of standard deviations. A marked difference was observed in the ν value of
235 U shown in Fig. 8.9 between EE1 and E3 cores at thermal neutron and resonance
regions in sensitivity profiles; also, core spectrum dependence on sensitivity was
effectively canceled by constant standard deviation at these regions.
The uncertainty of capture reactions of polyethylene with the consideration of the
thermal scattering law S(α, β) (termed *
1 H in Tables 8.12 and 8.13) was effective in
E3 core more than scattering (*
1 H (n, n)) reactions caused by the soft spectrum core
with a large number of moderators as indicated by sensitivity profiles in Figs. 8.10
and 8.11.
Furthermore, the core spectrum was found to be dependent on the uncertainty of
aluminum (Al) in the HEU plate (U-Al alloy) and aluminum in the core component
(Al sheath) at KUCA indicated by “
27 Al” and “*
27 Al,” respectively, as shown in
Figs. 8.12 and 8.13. In the EE1 core, elastic scattering and inelastic scattering (
27 Al
(n, n
)) reactions in HEU plates affected the uncertainty because of the large sensitivity
at the fast neutron region as shown in Figs. 8.14 and 8.15, respectively. Also, at the
hard spectrum core, elastic scattering reactions of the Al sheath indicated higher
value than that of
27 Al in HEU plates. Here, uncertainty that is not varied by control
rod insertion should be emphasized, because the impact of nuclear reactions related
to boron are very small and not shown in Tables 8.12 and 8.13. Accordingly, the
calculated results of excess reactivity and control rod worth were considered in good
agreement with the measured ones within a 10% difference because the uncertainty
of boron is not induced by control rod insertions.