# Homework Help: Mass of Fuel Rods

1. Aug 14, 2011

### kraigandrews

1. The problem statement, all variables and given/known data

The electric power generated by a single average size nuclear reactor block is between 400 and 800 MW. The fission of one 235U nucleus generates 185 MeV energy on average. What is the total mass of the fuel rods loaded into a 760 MW reactor for a one year period, if the fuel rods contain 3.50 percent of 235U? Assume that the overall thermodynamic efficiency of converting heat to electric energy is 33.0 percent.

3. The attempt at a solution
So to start out I multiply the 185MeV by 3.5% then from there I am lost.
Help in any way is appreciated, thanks.

2. Aug 14, 2011

### SteamKing

Staff Emeritus
You are starting at the wrong end of the process. You know the rated power output of the plant in MW. You know the efficiency of the conversion of heat energy into electric power output. You know the reactor is loaded with enough 235U to supply one year of electric power at the rated output of 760 MW. Find out how much energy the fuel rods in the reactor are required to produce for a year. Then apply the energy equivalent of a single fission to determine the amount of 235U, factoring in the ratio of 235U to the rest of the fuel rod material.

3. Aug 14, 2011

### kraigandrews

So i multiplied 760MW by 31536000s to get the Energy output for one year, then do I take the energy of one fission and divide by that and multiply by 0.035 and then 0.33?

Last edited: Aug 14, 2011
4. Aug 15, 2011

### SteamKing

Staff Emeritus
This is basically a unit conversion problem. You are not thinking it through clearly.