A spherical tank with a radius of 40cm is filled with a homogeneous mixtire of U-235 and light water. The mixture has a moderator-to-fuel ratio N(water)/N(235) of 800.
a) What is keff of the mixture?
b) What is keff for this bare core?
What should the radius of the tank in the problem be to produce a critical configuration? What is the critical mass of U-235 needed?