On ballooning-free feature of a dual cooled fuel under LOCA

• Dual cooled fuel (DCF) free from a ballooning rupture under LOCA is designed.
• Increase of cycle length or coolant area of DCF is possible by present design.
• A tube thickness resistant to a collapse never causes a ballooning failure.

The basic design of a dual cooled fuel (DCF) for an OPR-1000 nuclear power plant has been recently developed. It was shown that the DCF can enhance the fuel safety by considerably reducing the fuel temperature. This paper shows another safety feature of the DCF under a loss of coolant accident (LOCA), which is obtained from a dual tube structure of a fuel rod. A ballooning rupture, which may occur in a conventional fuel rod with a single tube when the LOCA takes place, can be prevented by designing the thickness of an inner cladding tube of the DCF properly. The idea is to make the inner cladding be collapsed before the outer cladding is ballooned during the LOCA transient. This is applied to the currently designed DCF for the OPR-1000. The result shows that, if the inner cladding thickness is within the range of 0.19–0.42 mm, it will be collapsed when the LOCA occurs but will not be ballooned during normal operation, while the outer cladding will remain intact at both conditions.