Ex-vessel cooling is an important concept for ensuring safety in a nuclear power plant. Many researchers have focused on critical heat flux (CHF) enhancement using reactor pressure vessels. Previous studies mainly focused on other types of enhancement methods, and few investigated the use of radiation to improve boiling heat transfer. In this study, gamma-ray radiation and electron-beam radiation are used to increase the boiling heat transfer for CHF. Initially, droplet tests are performed to check the hydrophilicity after irradiation. The results show that the contact angle decreases sharply in the irradiated materials. Then, pool boiling experiments are performed using bare and honeycomb surfaces. Gamma-ray irradiation and electron-beam irradiation of the bare surfaces cause CHF enhancements of similar to 60% and 50%, respectively. However, no improvement is observed for the honeycomb surface after irradiation. The coolant amount supplied by the honeycomb to the boiling surface is believed to affect the CHF. After irradiation, the coolant amount supplied to the boiling surface does not increase. Thus, the coolant supply reaches a limit, and no further CHF enhancement is observed from the irradiated honeycomb surface. It is also observed that the irradiation source had no effect on CHF enhancement. (C) 2017 Elsevier Ltd. All rights reserved.