Considering the urgent need for enhancing critical heat flux (CHF) on the outer surface of the reactor pressure vessel (RPV) by in-vessel retention (IVR) on Generation III pressurized water reactors (PWRs), we prepare a porous coating of 316 L stainless steel on the surface of SA508 Grade 3 (SA508–3) steel by flame spraying in this study. Using a small-scale pool boiling experimental setup, we first investigate boiling heat transfer characteristics on bare surfaces and flame-sprayed porous coating surfaces of SA508–3 steel in deionized water at atmospheric pressure, and obtain pool boiling curves and CHFs at different inclination angles. Furthermore, we carry out the IVR engineering verification tests for a full-height RPV bottom head on the REPEC-II test facility built at Shanghai Jiao Tong University. Our experimental results demonstrate that the flame-sprayed porous coatings can significantly enhance the CHF by 21–50 % at different inclination angles of the RPV bottom head. Our full-height facility tests demonstrate that the CHF in the high-inclination angle region, which normally has very high heat flux due to the focusing effect, exceeds 2 MW/m2 on the flame-sprayed porous coating surface. Therefore, our flame-sprayed porous coating has the potential to improve the safety margin of RPV.