A cylindrical uranium fuel rod of radius 5 mm in a nuclear reactor is generating heat at the rate of 4 ´ 107 W/m3. The rod is cooled by a liquid (convective heat transfer coefficient 1000W/m2-K) at 250 C. at steady state, the surface temperature (in K) of the rod is
(a) 308 (b) 398
(c) 418 (d) 448