Traditional underwater lighting systems in nuclear power plants utilize halogen-tungsten lamps, which suffer from low luminous efficiency and short service life, leading to inefficiencies and maintenance challenges. Light-emitting diode (LED) technology offers significant advantages in terms of higher luminous efficiency and longer lifespan, making it a promising alternative. However, LED implementation requires dedicated driver circuits, and their radiation tolerance becomes a critical factor limiting their application in nuclear environments. Although radiation-hardened components designed for aerospace applications could enhance radiation tolerance, their high cost makes them economically unfeasible. This paper presents a 300W radiation-hardened AC-DC power supply using exclusively commercial-off-the-shelf (COTS) components for LED driving applications. The proposed design employs a three-phase rectification input stage, eliminating the need for electrolytic capacitors which typically have limited lifespan and poor radiation tolerance. A non-isolated linear constant current topology is adopted, ensuring flicker-free LED operation. To improve radiation hardness, the system incorporates wide bandgap Silicon Carbide (SiC) MOSFETs, which inherently demonstrate superior radiation tolerance compared to conventional silicon devices. The minimal capacitance design achieves a high power factor. Although the use of linear circuit topology results in lower efficiency compared to traditional switching topologies, the driver still maintains efficiency above 85%. Experimental results demonstrate that this cost-effective LED driver achieves a Total Ionizing Dose (TID) tolerance of 5 Mrad, making it suitable for nuclear power plant applications.