◎ Purpose and outline of the facility

  FCA (Fast Critical Assembly) is the country’s only critical assembly for the study of the neutronic characteristics of fast reactors.
FCA is a horizontal, split-table type reactor, which consists of a pair of half-assemblies composed of a matrix tube structure. The half-assemblies remain separated in the shutdown state and are brought together in the operating state.
A FCA experimental core is constructed by inserting plate-type or block-type fuels (U and Pu) and core materials (Na, Stainless Steel, etc.) into each of the half-assembly fuel drawers. FCA has a great deal of flexibility for fuel composition and core geometry, which can facilitate experiments for a wide variety of mock-up cores.

◎ R&D activities

  Taking advantage of the FCA’s described core configuration flexibility and simulation capability of a wide range of neutron spectra, various types of experiments have been conducted to develop experimental and analytical techniques in reactor physics, and provide basic data for nuclear data evaluation.
For technological development related to the safe handling of melted fuels (i.e., fuel debris), which are generated in severe nuclear reactor facility accidents, a new series of experiments are being proposed for FCA to obtain experimental data for the verification of analytical methods that can deal with complex geometries, simulating the possible piling-up of fuel debris.

◎ Contributions

  The FCA experiments have made significant contributions to the development of fast reactors by providing experimental data, which has been requested for the evaluation of nuclear design, and safety review of the experimental fast reactor “JOYO” and prototype fast breeder reactor “MONJU.”

A diagram of the FCA core
A diagram of the FCA core

External view of the core (a cross-section of the half-assembly)
External view of the core (a cross-section of the half-assembly)

◎ A brief history of FCA

1967.4 First criticality  
1970~ Mock-up experiments for the experimental fast reactor “JOYO”
1974 Enlargement of the FCA core
1975~ Mock-up experiments for the prototype fast breeder reactor “MONJU”
1983~ Experiments to study neutronic characteristics for large fast breeder reactor cores, etc.

◎ Major specifications

Name Fast Critical Assembly (FCA)
Type A horizontal, split-table type
First Criticality April 29, 1967
Number of Operations More than five thousand
Dimensions of half-assembly Approximately 2.8 m2 in cross-section and 1.3 m long
Fuel Enriched U and Pu
Maximum thermal power 2 kW
Copyright(C) Japan Atomic Energy Agency. All Rights Reserved.