(a) Given a collection of n thermal neutrons in a natural uranium reactor, how m

Question

(a) Given a collection of n thermal neutrons in a natural uranium reactor, how many 235U atoms (of N total fuel atoms) disappear following the absorption of these neutrons?

(b) How many 239Pu atoms appear? Consider the production of 239U from absorption of the original thermal neutrons and also the secondary fast fission neutrons, taking p=0.9 and =1.0.

(c) The ratio between the numbers found in (b) and (a) is called the conversion ratio and represents a measure of whether a converter reactor will function as a breeder, that is, produce more fuel than it consumes. Evaluate the conversion ratio and comment.

(d) Repeat the calculation for a reactor fueled with a 1% fissile 233U (f=530 b, a=47.7 b, v=2.49) and 99% fissile 232Th (f=0, a=7.4 b).

Explanation / Answer

Solution a)

235U disappears because of the below mentioned two processes,

a) First one is the fission process and

b) Second one is the non-fission capture of neutron. T

We know that the rate of non-fission capture is almost 1/4 * rate of fission.

So total rate at which 235U willl disappears is 1.25*1.06*1020 atoms/s = 1.33*1020 atoms/s.

If we have to convert it into kg/day then the conversion is as follows:-

1.33*1020 atoms/s* 235 u/atom*1.661*10-27 kg/u

= 5.19*10-5 kg/s

= 4.5 kg/day (approximately)

Hence the total number of 235 U atoms that disappears will be 1.33*1020 atoms/s.

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