8 Sensitivity and Uncertainty of Criticality
219
Table 8.1 Experimental
uncertainties of HEU fuel
plate (Refs. [1, 2])
Cause of uncertainty
Error (%)
Composition
3.0
Length of both sides (one side: 0.2%)
0.3
Thickness
3.1
Table 8.2 Measured results
[pcm] of excess reactivity and
control rod worth with
standard deviation obtained
from experimental data in
EE1 and E3 cores (Refs. [1,
2])
Reactivity
EE1 (error: %)
E3 (error: %)
Excess
210 ± 6 (3.1)
264 ± 2 (0.8)
C1 rod
838 ± 11 (1.4)
551 ± 6 (1.2)
C2 rod
144 ± 3 (2.4)
429 ± 4 (1.0)
C3 rod
521 ± 8 (1.7)
329 ± 4 (1.4)
EE1: β eff : 831 pcm and : 3.027E-05 s by MCNP6.1 with JENDL4.0
E3: β eff : 805 pcm and : 4.771E-05 s by MCNP6.1 with JENDL4.0
temperature, delayed neutron parameters induced by numerical analyses, fuel composition uncertainty caused by heterogeneity distribution and deformation inside the
Al sheath. Among these factors, the mechanical reproducibility of control rod position, in this study, was considered of great impact caused by tolerance and instability
of control rod inside the Al sheath in a horizontal direction than the experimental
uncertainty of excess reactivity and control rod worth, because the other uncertainties are relatively minor. Furthermore, heterogeneous arrangement of fuel plates in
an axial direction was attributable to random selection of fuel plates for making fuel
cells with a record number of fuel plates. Therefore, the experimental uncertainty
of excess reactivity and control rod worth was finally determined to be about 3%
at most by averaging the experimental data, and estimating its standard deviation,
as observed in operations of the previous decade in the KUCA A-core, as shown in
Table 8.2.
8.2 Criticality
8.2.1 Numerical Simulations
8.2.1.1 Stochastic Calculations
Excess reactivity was numerically deduced by the MCNP6.1 code [4] with the
JENDL-4.0 [5] and the ENDF/B-VII.0 [6] libraries through the difference between
the critical and super-critical states in the core; control rod worth was numerically
obtained by the difference between critical and subcritical states. For the evaluation
219
Table 8.1 Experimental
uncertainties of HEU fuel
plate (Refs. [1, 2])
Cause of uncertainty
Error (%)
Composition
3.0
Length of both sides (one side: 0.2%)
0.3
Thickness
3.1
Table 8.2 Measured results
[pcm] of excess reactivity and
control rod worth with
standard deviation obtained
from experimental data in
EE1 and E3 cores (Refs. [1,
2])
Reactivity
EE1 (error: %)
E3 (error: %)
Excess
210 ± 6 (3.1)
264 ± 2 (0.8)
C1 rod
838 ± 11 (1.4)
551 ± 6 (1.2)
C2 rod
144 ± 3 (2.4)
429 ± 4 (1.0)
C3 rod
521 ± 8 (1.7)
329 ± 4 (1.4)
EE1: β eff : 831 pcm and : 3.027E-05 s by MCNP6.1 with JENDL4.0
E3: β eff : 805 pcm and : 4.771E-05 s by MCNP6.1 with JENDL4.0
temperature, delayed neutron parameters induced by numerical analyses, fuel composition uncertainty caused by heterogeneity distribution and deformation inside the
Al sheath. Among these factors, the mechanical reproducibility of control rod position, in this study, was considered of great impact caused by tolerance and instability
of control rod inside the Al sheath in a horizontal direction than the experimental
uncertainty of excess reactivity and control rod worth, because the other uncertainties are relatively minor. Furthermore, heterogeneous arrangement of fuel plates in
an axial direction was attributable to random selection of fuel plates for making fuel
cells with a record number of fuel plates. Therefore, the experimental uncertainty
of excess reactivity and control rod worth was finally determined to be about 3%
at most by averaging the experimental data, and estimating its standard deviation,
as observed in operations of the previous decade in the KUCA A-core, as shown in
Table 8.2.
8.2 Criticality
8.2.1 Numerical Simulations
8.2.1.1 Stochastic Calculations
Excess reactivity was numerically deduced by the MCNP6.1 code [4] with the
JENDL-4.0 [5] and the ENDF/B-VII.0 [6] libraries through the difference between
the critical and super-critical states in the core; control rod worth was numerically
obtained by the difference between critical and subcritical states. For the evaluation