130
C. H. Pyeon
Table 5.2 Subcritical multiplication factor k s in Eq. (5.2) deduced from 115 In(n, γ) 116m In reaction
rates in subcriticality 2,900 pcm (Ref. [3])
Target
Calculation
Experiment
C/E value
W
0.42033 ± 0.00100
0.45874 ± 0.01003
0.92 ± 0.02
W–Be
0.56355 ± 0.00100
0.57662 ± 0.01510
0.98 ± 0.03
Pb–Bi
0.48830 ± 0.00100
0.48488 ± 0.01335
1.01 ± 0.03
(15, H) in Fig. A2.1). Moreover, the results demonstrated that the Pb–Bi target was
confirmed fairly well for an upcoming target in actual ADS, as predicted in several
experimental and numerical analyses, by its comparison with the W target, although
its static core characteristics were almost the same as those of the W target.
5.1.3 Effects of Neutron Spectrum
5.1.3.1 Core Configuration
Starting from the reference core (Fig. A2.11) that reached a criticality, reaction rate
experiments [9] (Cases II-1 to II-4 in Fig. 2A.16) in ADS were carried out in the
KUCA A-core by varying subcriticality ranging from 2,483 to 11,556 pcm, as shown
in Figs. A2.16a through A2.16d. The ADS cores comprise normal fuel assembly “F,”
partial fuel assembly “16”, Pb–Bi-zoned fuel assembly “f,” polyethylene moderator
“p” and reflector rods. Normal fuel assembly “F” is composed of 36 cells of a highlyenriched uranium (HEU) fuel plate 1/16
thick, polyethylene (p) plates 3/8
thick,
and upper and lower polyethylene blocks about 25
and 20
long, respectively, in an
aluminum (Al) sheath 2.1 × 2.1 × 60
, as shown in Fig. A2.12. The numeral “16”
corresponds to the number of unit cells in the partial fuel assemblies for reaching
criticality in the core shown in Fig. A2.14. The Pb–Bi-zoned fuel assembly “f” is
composed of 30 unit cells with two HEU plates 1/8
thick, Pb–Bi plate 1/8
thick, 30
unit cells of two HEU plates 1/8
thick and polyethylene plates 1/8
thick, as shown
in Fig. A2.13.
The subcriticality in the pcm units was experimentally obtained with the combined
use of control rod worth and its calibration curve measured by the rod drop method
and the positive period method, respectively, in Case II-1 (Fig. A2.16a). For the
deduction of subcriticality in Case II-1, the effective delayed neutron fraction β eff
and the neutron generation time were obtained with 783 pcm and 4.64E-05 s,
respectively, with MCNP6.1 and JENDL-4.0. In Cases II-2 to II-4 (Figs. A2.16b–d),
the reference of subcriticality in the pcm units was attained with MCNP6.1 eigenvalue
calculations and the JENDL-4.0 library, because the reactivity of control and safety
rods was made by the substitution of fuel assembly rods for the polyethylene ones.
C. H. Pyeon
Table 5.2 Subcritical multiplication factor k s in Eq. (5.2) deduced from 115 In(n, γ) 116m In reaction
rates in subcriticality 2,900 pcm (Ref. [3])
Target
Calculation
Experiment
C/E value
W
0.42033 ± 0.00100
0.45874 ± 0.01003
0.92 ± 0.02
W–Be
0.56355 ± 0.00100
0.57662 ± 0.01510
0.98 ± 0.03
Pb–Bi
0.48830 ± 0.00100
0.48488 ± 0.01335
1.01 ± 0.03
(15, H) in Fig. A2.1). Moreover, the results demonstrated that the Pb–Bi target was
confirmed fairly well for an upcoming target in actual ADS, as predicted in several
experimental and numerical analyses, by its comparison with the W target, although
its static core characteristics were almost the same as those of the W target.
5.1.3 Effects of Neutron Spectrum
5.1.3.1 Core Configuration
Starting from the reference core (Fig. A2.11) that reached a criticality, reaction rate
experiments [9] (Cases II-1 to II-4 in Fig. 2A.16) in ADS were carried out in the
KUCA A-core by varying subcriticality ranging from 2,483 to 11,556 pcm, as shown
in Figs. A2.16a through A2.16d. The ADS cores comprise normal fuel assembly “F,”
partial fuel assembly “16”, Pb–Bi-zoned fuel assembly “f,” polyethylene moderator
“p” and reflector rods. Normal fuel assembly “F” is composed of 36 cells of a highlyenriched uranium (HEU) fuel plate 1/16
thick, polyethylene (p) plates 3/8
thick,
and upper and lower polyethylene blocks about 25
and 20
long, respectively, in an
aluminum (Al) sheath 2.1 × 2.1 × 60
, as shown in Fig. A2.12. The numeral “16”
corresponds to the number of unit cells in the partial fuel assemblies for reaching
criticality in the core shown in Fig. A2.14. The Pb–Bi-zoned fuel assembly “f” is
composed of 30 unit cells with two HEU plates 1/8
thick, Pb–Bi plate 1/8
thick, 30
unit cells of two HEU plates 1/8
thick and polyethylene plates 1/8
thick, as shown
in Fig. A2.13.
The subcriticality in the pcm units was experimentally obtained with the combined
use of control rod worth and its calibration curve measured by the rod drop method
and the positive period method, respectively, in Case II-1 (Fig. A2.16a). For the
deduction of subcriticality in Case II-1, the effective delayed neutron fraction β eff
and the neutron generation time were obtained with 783 pcm and 4.64E-05 s,
respectively, with MCNP6.1 and JENDL-4.0. In Cases II-2 to II-4 (Figs. A2.16b–d),
the reference of subcriticality in the pcm units was attained with MCNP6.1 eigenvalue
calculations and the JENDL-4.0 library, because the reactivity of control and safety
rods was made by the substitution of fuel assembly rods for the polyethylene ones.