Cleaning inside high-temperature radioactive underwater environment is a dangerous, hazardous and time consuming task. There is currently a lack of systematic research on ROVs (Remotely Operated Vehicles) for cleaning operations in radioactive environments. This paper proposes a novel cleaning ROV targeting the cleaning of bottom and walls of the underwater facility, as well as object retrieving. Firstly, a modular structure for the ROV is designed, which includes an electronic control cabin with radiation shielding and heat dissipation architecture, an adsorption moving chassis equipped with cleaning tools, and an object retrieving manipulator. Secondly, structural analysis of the key components is performed, and a hydrodynamic simulation of the cleaning ROV is conducted to analyze its underwater performance. Thermodynamic simulations of the electronic control cabin are carried out, and its heat dissipation performance is verified through experiments. Finally, a prototype ROV is constructed and tested in a pool cleaning experiment. The results indicate that the developed ROV meets the operational requirements.