Source multiplication measurements and neutron correlation analyses for a highly enriched uranium subcritical core driven by an inherent source in Kyoto University Critical Assembly

Figures & data

Figure 1. Description of 1/8”P60EUEU fuel assembly.

Figure 2. Top view of core configuration and neutron detector location.

Table 1. Experimental patterns of control rods and central fuel loading.

Subcritical	Axial position of contral and safety rods						Central	Subcriticality*
Pattern	C1	C2	C3	S4	S5	S6	Loading	[%k/k]
Critical	U.L.	678.98 mm	U.L.	U.L.	U.L.	U.L.	C.I.	—
S	U.L.	629.99 mm	U.L.	U.L.	U.L.	U.L.	C.I.	0.102 ± 0.003
A	U.L.	L.L.	U.L.	U.L.	U.L.	U.L.	C.I.	0.307 ± 0.008
B	L.L.	U.L.	U.L.	U.L.	U.L.	U.L.	C.I.	0.725 ± 0.018
C	L.L.	L.L.	L.L.	U.L.	U.L.	U.L.	C.I.	1.483 ± 0.040
D	L.L.	L.L.	L.L.	U.L.	U.L.	L.L.	C.I.	2.056 ± 0.054
E	L.L.	L.L.	L.L.	L.L.	L.L.	L.L.	C.I.	3.189 ± 0.083
F	L.L.	L.L.	L.L.	L.L.	L.L.	L.L.	C.W.	13.604 ± 0.381

L.L.: Lower Limit [0 mm], U.L.: Upper Limit [1200 mm], C.I.: Completely Inserted, C.W.: Completely Withdrawn, *Calculated by MVP3 code.

Table 2. Isotopic properties of uranium used in the present calculation.

Isotope	^234 U	^235 U	^236 U	^238 U
Abundance of the fuel [wt%]	0.95	93.15	0.42	5.47
Half life [y]	2.450E+05	7.040E+08	2.348E+07	4.468E+09
Q-value of α decay [MeV]	4.858	4.678	4.572	4.270
Spontaneous fission fraction per α decay* [%]	1.64E-09	7.00E-09	9.40E-08	5.45E-05
Number of neurons emitted from a spontaneous fission**	1.81	1.86	1.91	2.01
Neutron yield from (α,n) reaction per α particle*** [n/α]	1.94E-07	1.27E-07	9.69E-08	4.17E-08

The above spontaneous fraction*, neutron number**, and neutron yield*** were quoted from references [22,23] and [24], respectively.

Table 3. Inherent neutron source strength per enriched fuel plate [n/s/plate].

Isotope	^234 U	^235 U	^236 U	^238 U	Total
Spontaneous fission	2.055E-04	3.038E-05	5.5721E-05	2.330E-03	2.622E-03
(α,n) reaction	1.340E+00	2.954E-02	3.007E-03	8.871E-05	1.340E+00
Total	1.340E+00	2.957E-02	3.063E-03	2.419E-03	1.375E+00

Table 4. Total inherent neutron source strength of the present core.

Pattern	Number of fuel (1/8”P60EUEU)	Number of EU plates	Total inherent source strength [n/s/core]
S, A ~ E	26	3120	4289
F	23	2760	3794

Figure 3. Subcriticality dependence of neutron count rate measured for subcritical systems driven by inherent source.

Figure 4. Subcriticality dependence of neutron count rate measured for subcritical systems driven by Am-Be source.

Figure 5. Subcriticality obtained by neutron source multiplication method for subcritical systems driven by inherent source.

Figure 6. Subcriticality obtained by neutron source multiplication method for subcritical systems driven by Am-Be source.

Figure 7. Subcriticality dependence of Y obtained by Feynman-α analysis under reactor drive by inherent source.

Figure 8. Non-physical behavior of correlation amplitude Y of counter B4.

Figure 9. Prompt-neutron decay constant obtained from Feynman-α analysis for subcritical systems driven by inherent source.

Figure 10. Prompt-neutron decay constant obtained from Feynman-α analysis for subcritical systems driven by Am-Be source.

Figure 11. Subcriticality dependence of conditional counting probability obtained by Rossi-α analysis under reactor drive by inherent source.

Figure 12. Comparison of Rossi-α conditional counting probability under respective drives by inherent and Am-Be source.

Figure 13. Prompt-neutron decay constant obtained by Rossi-α analysis under reactor drive by inherent source.

Figure 14. Prompt-neutron decay constant obtained by Rossi-α analysis under reactor drive by Am-Be source.

Figure 15. Ratio of standard deviation to mean of prompt-neutron decay constants obtained by Feynman-α analysis for three neutron counters.

Figure 16. Subcriticality derived from prompt-neutron decay constant by using Simmons & King method.

Figure 17. Subcriticality dependence of kinetic parameters calculated by MVP3.

Figure 18. Subcriticality obtained from prompt-neutron decay constant by using the inhour method.

Figure 19. S/N ratio of Rossi-α analysis under respective reactor drives by inherent and Am-Be sources.

Figure 20. Effective inherent source strength derived from Rossi-α analysis.

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