# Homework Help: Homework Nuclear Physics

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1. Nov 22, 2015

### Rath123

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

What initial mass of 23592U is required to operate a 350 MW reactor for 3 yrs? Assume 46% efficiency.

2. Relevant equations

I used Mass* C* efficiency as a decimal= power (e^-6) * time (in seconds)
and got 800 as the mass, however, this was incorrect
3. The attempt at a solution
(M)*(3e8)^2* .46= 350e6* 9.14 i think it was (whatever 3 years in seconds is) and i was getting 800 as the mass, or 799Kg specifically however, this is incorrect . Where am i going wrong?

2. Nov 22, 2015

### Rath123

the three years in seconds was : 9.461e+7

3. Nov 22, 2015

### SteamKing

Staff Emeritus

You should try to lay them out in some logical fashion, so others can follow.

In a nuclear reactor, only a small amount of the mass of uranium is converted to energy. The rest winds up as nuclear waste.

The fission of U-235 in the reactor is governed by the reaction discussed in this article:

https://en.wikipedia.org/wiki/Uranium-235

4. Nov 23, 2015

### andrevdh

Last edited: Nov 23, 2015
5. Nov 23, 2015

### SteamKing

Staff Emeritus
I think the efficiency is for the conversion of the energy released by the fission into the electric power which comes out of the plant. There is a limit to the amount of energy which can be extracted from the steam turbines, generators, etc. which are all used with the nuclear reactor to turn the energy of fission into electricity.

6. Nov 23, 2015

### andrevdh

Yes. I realized it and edited my post.