Calculating Mass Percent in UO2 Nuclear Fuel

1. Feb 20, 2017

Goldberg

1. The problem statement, all variables and given/known data
Hello guys, I was using mcnp code SERPENT, and while defining materials i encountered a problem. The problem is that for example: if i'm given that i have a 3.5 percent enriched U-235. how do i find the rest of the mass percents of U-234, U-238, O2. Now since i know mass percent of U-235 i can use the equation given below to calculate the mass percent of U-234 in Uranium of that UO2 fuel, and the rest of the uranium would be U-238. But now what would be the weight percent of the Uranium in UO2 fuel?
From research i have found that O2 should be around 66 percent. but i have no way to calculate it. Can you please help. Thank you.

2. Relevant equations

3. The attempt at a solution

2. Feb 21, 2017

Staff: Mentor

You can calculate the average mass of an uranium atom with your isotopic mixture. You can look up the average mass of an oxygen atom. With both, you can calculate the average mass of the UO2 group, that should help to get the final answer.

3. Feb 27, 2017

Goldberg

I got that what do i do after that

4. Feb 28, 2017

Staff: Mentor

After getting the final answer?

Can you show what you got?

5. Feb 28, 2017

Goldberg

The thing is that since its UO2, somehow in the answer im given, U and O and O are divivded out of 100. So O2 is equal to ~66 percent. and as i increase the U-235 content Uranium mass percent increases from the basic ~33.33 percent, and the penalty of that is received by O2 mass percent.
The method you told me to calculate from gives me Uranium of UO2 as ~88 mass percent of the compound which is incorrect. It has to be about 66 percent.

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6. Feb 28, 2017

Staff: Mentor

I don't understand that part.

Oxygen has 67% of the atoms, but its mass fraction is much smaller.
Uranium has about 88% of the mass fraction of UO2, the other 12% are oxygen.

7. Feb 28, 2017

Goldberg

ok lets try to find the atom percent because the answer is given as ~66 percent oxygen, so that might be an option. because it's definitely not 88 % one.
So how do i get that?

8. Feb 28, 2017

Staff: Mentor

UO2 - two out of three atoms are oxygen. 2/3 or 66.7%.

9. Mar 1, 2017

Goldberg

I tried but wasnt able to do it . This is basically the table i want. if i take the number density of O2 and divide by the total i get 66 %. so basically i can either get the number density or this percentage.http://imgur.com/a/2M4HH

10. Mar 1, 2017

Goldberg

Picture

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11. Mar 1, 2017

Staff: Mentor

I don't understand the problem.

By number of atoms, you have 66.7% oxygen, the result of a trivial calculation as shown above.
By mass, you have 12% oxygen, the result of the calculation you did above.
Those two numbers are not expected to be the same.

Where is the problem now?

12. Apr 10, 2017

Goldberg

Ok, The manual for this software is stupid. I know that the table is right so it might be from the number of atoms. Can you tell me how would i go about doing that

13. Apr 11, 2017

Doing what?