Experimental

• Fast Critical Assembly
• Reaction Rate Measurement
• Reactivity Worth Measurement
• Doppler Effects Measurement
• Brief History

Fast Critical Assembly

FCA is designed for studying physics characteristics of fast breeder reactor cores. Experiments are carried out to provide integral data for core design of a fast reactor by building various simulating assemblies. The reactor assembly is divided into two halves (Fig.2 and Fig.3), which are separated for fuel loading, then brought together for operation.

Fig. 1: Building of FCA



Fig. 2: Whole view of FCA



Fig. 3: Cross section of fixed half assembly (51 by 51 tubes)

Experimental cores are built in FCA by hand-loading plates of reactor materials (uranium, plutonium, sodium, stainless steel, etc.) into drawers (Fig.4), which are then put in the desired patten into each half of the assembly, a honey-comb of square tubes. The facility offers a large flexibility for fuel composition and core geometry.

Fig. 4: Drawers

Reaction Rate Measurement

Reaction rate, reaction rate ratio and power distribution are measured by foil irradiation, fission counter and ganma-counting methods (Fig.5).

Fig. 5: Micro fiision counters (left) and irradiation foils (right)

Reactivity Worth Measurement

Sample reactivity worth (See Fig.6), sodium void worth, and control rod worth are measured by critical balance and source multiplication methods.

Fig. 6: Schematic drawing of the experimental holefor sample worth measurement

Doppler Effects Measurement

Doppler reactivity worths of fuel and structure material are measured by heated sample oscillation technique.

Fig. 7: Spectrum dependence of natural UO₂ Doppler effects

Brief History

1967	First criticality on 29 April
1967	First criticality on 29 April
1967 - 1969	Experiments for the uranium cores
1969	Experiments for the k-infinity = 1 cores
1970 - 1972	Mockup experiments for “JOYO”
1972 - 1974	Mockup experiments for “MONJU”
1974 - 1975	Enlargement of the FCA matrix (51×51)
1975 - 1980	Mockup experiments for “MONJU”
1980 - 1982	Integral experiments for MA cross section
1982 - 1983	Mockup experiments for “JOYO MK-II”
1983 - 1986	Experiments for large FBR cores
1986 - 1989	Experiments for HCLWR cores
1990 - 1994	Experiments for advanced fuel FBR cores
1994 - 1995	Experiments for Moderator-Added FBR cores
1995 - 1998	International benchmark experiments for delayed neutron
1998 - 1999	“GEM:Gas Expansion Module” critical experiments
2000 - 2001	Basic experimental study for ADS
2002 - 2004	Experiments for RMWR cores
2004 - 2006	Mockup Experiments for 4S reactor
2006 - 2007	Experiments for PPP core concept
2007 -	Doppler effect measurement for MOX fueled LWR safety