Title:

Multirecycling of plutonium in advanced PWRs


Author(s):



Published by:

Publication date:

ECN
NUCLEAIR

1998


ECN report number:

Document type:

ECNR98007

Other


Number of pages:

Full text:

85

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Abstract:
The influence of the moderatortofuel ratio of MOX fueled PWRs on themoderator void coefficient, the fuel temperature coefficient, the moderator
temperature coefficient, the boron reactivity worth, the critical boron
concentration, the mean neutron generation time and the effective delayed
neutron fraction has been assessed. Increasing the moderatortofuel ratio to
values larger than three, gives a moderator void coefficient sufficiently
large to recycle the plutonium at least four times. Also the values of other
parameters like the boron reactivity worth, the fuel temperature coefficient,
the moderator temperature coefficient and the mean neutron generation time
improve with increasing moderatortofuel ratio. The effective delayed
neutron fraction is rather independent of the moderatortofuel ratio.
According to a pointkinetics model, a MOX fueled reactor with a
moderatortofuel ratio of four responds similarly to a moderator temperature
decrease as an UO_{2} fueled reactor with a moderatortofuel ratio of two.
This conclusion holds for both the instantaneous power increase and for the
deposited energy during a specific time interval. Scenario studies show that
four times recycling of plutonium in PWRs reduces the plutonium production
with a factor of three compared with a reference oncethrough scenario, but
that the americium and curium production triple. If the remaining plutonium
after four times recycling is disposed of, the reduction of the radiotoxicity
reaches only a factor of two. This factor increases to five at the maximum
when the plutonium is further recycled. Recycling of americium and curium is
needed to reduce the radiotoxicity of the spent fuel to lower values. In
general, the plutonium mass reduction increases and the minor actinides
production decreases with increasing moderatortofuel ratio of the MOX fuel.
Enlarging the moderatortofuel ratio can be achieved by increasing the rod
pitch or by reducing the fuel pin diameter. In both cases, the economic
penalty is about the same. 11 refs.
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