One of the most important considerations in the design of electronic systems for post-accident monitoring in a nuclear power plant is how to deal with the complex and uncertain radiation environments. Without using special design methodologies and adequate protection, nonradiation-hardened commercial-off-the-shelf (COTS) electronic components can easily be damaged. In this paper, a new design methodology is proposed so that COTS components can be used in building post-accident monitoring systems (PAMSs). To validate the effectiveness of the methodology, a prototype wireless post-accident monitoring system has been designed, implemented, and evaluated in a 60Co gamma radiation environment. It has been concluded that even at a dose rate of 20 krad (Si)/h, the prototype system operates satisfactorily even after being irradiated for 21 h. The system also operates satisfactorily at a low dose rate of 200 rad (Si)/h. It can be concluded that, even with COTS components, the proposed design can effectively extend the lifespan of post-accident monitoring systems in different radiation environments. Based on the experimental results, it can be said with confidence that the developed radiation-tolerant wireless monitoring system can operate for at least 8 h under the highest observed dose rate (530 Sv/h) encountered during the Fukushima Daiichi nuclear disaster and would have been able to provide crucial information to first responders following the accident.