2 Subcriticality
37
Fig. 2.20 Subcriticality
dependence of f R C 1 /C 2
(Ref. [21])
can be observed and these ratios are considered to be the asymptotic value, i.e., the
Degweker’s factor. Averaging the ratios over the subcritical range from Pattern C
to F, we obtained the second term, i.e., the Degweker’s factor of 0.082 ± 0.021.
This value is consistent with 0.067 ± 0.011 determined from the previous Rossi-α
analysis [1].
2.3 Beam Trip and Restart Methods
2.3.1 Experimental Settings
2.3.1.1 Core Configurations
A series of accelerator-beam trip and restart experiments is carried out to determine
the subcriticality of a reactor system driven by a pulsed 14 MeV neutron source
[28]. This core configuration is shown in Fig. 2.21. The core was composed of 20
regular fuel assemblies and one partial fuel assembly, which were loaded on the grid
plate. The fuel and moderator elements of each assembly were set in a 1.5-mm-thick
aluminum sheath and the cross section of the elements within the assembly was the
square of 2”. The regular fuel assembly was composed of 36 unit cells of one (1/16”
thick) uranium plate with Al clad and two (1/8” and 1/4” thick) polyethylene plates,
while the partial fuel assembly was composed of 12 unit cells of these plates. The
partial fuel assembly was employed to adjust the excessive reactivity of the core.
37
Fig. 2.20 Subcriticality
dependence of f R C 1 /C 2
(Ref. [21])
can be observed and these ratios are considered to be the asymptotic value, i.e., the
Degweker’s factor. Averaging the ratios over the subcritical range from Pattern C
to F, we obtained the second term, i.e., the Degweker’s factor of 0.082 ± 0.021.
This value is consistent with 0.067 ± 0.011 determined from the previous Rossi-α
analysis [1].
2.3 Beam Trip and Restart Methods
2.3.1 Experimental Settings
2.3.1.1 Core Configurations
A series of accelerator-beam trip and restart experiments is carried out to determine
the subcriticality of a reactor system driven by a pulsed 14 MeV neutron source
[28]. This core configuration is shown in Fig. 2.21. The core was composed of 20
regular fuel assemblies and one partial fuel assembly, which were loaded on the grid
plate. The fuel and moderator elements of each assembly were set in a 1.5-mm-thick
aluminum sheath and the cross section of the elements within the assembly was the
square of 2”. The regular fuel assembly was composed of 36 unit cells of one (1/16”
thick) uranium plate with Al clad and two (1/8” and 1/4” thick) polyethylene plates,
while the partial fuel assembly was composed of 12 unit cells of these plates. The
partial fuel assembly was employed to adjust the excessive reactivity of the core.