against criticality accidents are important requirements for the modified STACY:
for example, limitation of the core configuration together with the safety plates
inserted so as to keep a subcritical state during submersion.
A schedule of the STACY modification is shown in Fig. 22.4. The first criticality
experiment in the modified STACY is scheduled for 2018. The modified STACY
will provide benchmark data on criticality safety for fuel debris to validate the
criticality control measures applicable to the Fukushima Daiichi NPS. The new
criticality control measures need to be established by the time the fuel debris begins
to be retrieved from each reactor unit of the Fukushima Daiichi NPS. According to
the governmental council, retrieval of the fuel debris is scheduled to start as early as
2020, depending on the progress in the decommissioning of each reactor unit [2].
22.4 Concluding Summary
For the decommissioning of the Fukushima Daiichi Nuclear Power Station Units
1, 2, and 3, research and development activities have been pursued to retrieve fuel
debris from the pressure and containment vessels of each reactor unit. In preparation for the retrieval, however, there remain serious problems concerning the
cooling water of fuel debris from the aspect of criticality safety.
To study the new criticality control measures for the fuel debris, the Japan
Atomic Energy Agency has carried forward a project to modify the Static Experiment Critical Facility (STACY) and to pursue critical experiments regarding the
fuel debris. STACY, a facility using solution fuel, is to be converted into a thermal
critical assembly using fuel rods and a light water moderator. A series of critical
experiments will be conducted in the modified STACY using simulated fuel debris
samples. These samples are to be manufactured by mixing UO 2 and reactor
structural materials with various chemical compositions.
Fuel Debris
Retrieval
Critical Experiments
Licensing Procedure
Sample
taking
Sample
taking
Water-Filling in CV
Decontamination
and Shielding
Water-Leak
Investigation
Inspection from
Outside of CV
First
Criticality
Construction
Fig. 22.4 Schedule of the STACY modification. CV containment vessel
22 Modification of the STACY Critical Facility for Experimental Study on Fuel. . .
267
for example, limitation of the core configuration together with the safety plates
inserted so as to keep a subcritical state during submersion.
A schedule of the STACY modification is shown in Fig. 22.4. The first criticality
experiment in the modified STACY is scheduled for 2018. The modified STACY
will provide benchmark data on criticality safety for fuel debris to validate the
criticality control measures applicable to the Fukushima Daiichi NPS. The new
criticality control measures need to be established by the time the fuel debris begins
to be retrieved from each reactor unit of the Fukushima Daiichi NPS. According to
the governmental council, retrieval of the fuel debris is scheduled to start as early as
2020, depending on the progress in the decommissioning of each reactor unit [2].
22.4 Concluding Summary
For the decommissioning of the Fukushima Daiichi Nuclear Power Station Units
1, 2, and 3, research and development activities have been pursued to retrieve fuel
debris from the pressure and containment vessels of each reactor unit. In preparation for the retrieval, however, there remain serious problems concerning the
cooling water of fuel debris from the aspect of criticality safety.
To study the new criticality control measures for the fuel debris, the Japan
Atomic Energy Agency has carried forward a project to modify the Static Experiment Critical Facility (STACY) and to pursue critical experiments regarding the
fuel debris. STACY, a facility using solution fuel, is to be converted into a thermal
critical assembly using fuel rods and a light water moderator. A series of critical
experiments will be conducted in the modified STACY using simulated fuel debris
samples. These samples are to be manufactured by mixing UO 2 and reactor
structural materials with various chemical compositions.
Fuel Debris
Retrieval
Critical Experiments
Licensing Procedure
Sample
taking
Sample
taking
Water-Filling in CV
Decontamination
and Shielding
Water-Leak
Investigation
Inspection from
Outside of CV
First
Criticality
Construction
Fig. 22.4 Schedule of the STACY modification. CV containment vessel
22 Modification of the STACY Critical Facility for Experimental Study on Fuel. . .
267