A spherical reactor fuel element ( =20 W/(m K), r=0.05 m) is encased in a thin metal cladding with negligible thermal resistance. The radioactive decay in the element can be described by the constant heat source density = 5. 107 W/m3. The heat transfer coefficient to the surrounding coolant of temperature T = 40C is = 4000 W/(m2K). (a) Describe the temperature field T(r) in the fuel element. (b) What is the temperature TW at the surface of the fuel element? (c) What is the temperature T0 at the center of the fuel assembly? (d) What is the heat flux density w at the surface of the fuel element