I. Introduction
Currently, damaged reactors and melted nuclear fuel at the Fukushima Daiichi nuclear power plant emit intense gamma radiation persistently. The maximum radiation intensity is reported to be 1000 Sv/h. Therefore, devices that are more radiation-hardened than space-grade VLSIs are necessary for the decommissioning of reactors and for the moving of melted nuclear fuel at the Fukushima Daiichi nuclear power plant [1],[2J. The total-ionizing-dose tolerances of currently available radiation-hardened VLSIs are insufficient for decommissioning and dismantlement operations [3]– [6]. In fact, the working durations of current radiation-hardened devices are limited to 10 hr.