TRS435_web

(h)
(i)
Connection to HLW vitrification.
A high and medium level alpha waste treatment plant.
Americium and curium targets contain significant amounts of 238 Pu,
244 Cm and fission products; because of this combination, the irradiated capsules
are very difficult to handle and reprocess. One alternative to spent target
reprocessing consists of carrying out a once through irradiation in a thermal
island of an FR MOX reactor until 200 dpa (limit of capsule/target pin
cladding) in order to eliminate further processing [9].
According to this scenario, 98% of a given americium inventory could be
eliminated by neutron irradiation over ~20 years. The irradiated capsules from
such a test, if they resist the intense radiation and the high helium pressure,
may have to be overpacked before their long term storage to avoid leakage
inside the storage facilities. The transformation of the americium target into a
mixture of 80% fission products and 20% TRUs is possible in a target type
capsule but cannot be extrapolated to industrial quantities, since in this case the
global impact of the americium depletion in the target and the americium
generation in the driver fuel has to be taken into account.
Transmutation of americium and curium is a technical challenge in its
operational phase, but the radiological impact is slightly positive (i.e. an
actinide reduction factor of 10–20 can be expected) and its influence on waste
management is rather limited. Once an inventory has been transformed
(almost) completely in a fission product mixture, the management of it is
identical to the management of actinide free vitrified HLW. The main long term
benefit is the elimination of 241 Am, which is the parent of the very long lived
and slightly mobile 237 Np, but its partial (~12%) transformation into some long
lived plutonium ( 238,239,240 Pu) and curium isotopes is a drawback that limits its
usefulness for long term waste management.
It is obvious that ADS systems could be more efficient at providing the
necessary neutrons to transmute a fertile 241 Am– 243 Am mixture than critical
FRs, in which the driver fuel will itself be a generator of americium and curium.
From the safety point of view, the loading of the ADS reactor is more flexible,
since the void reactivity coefficient remains negative even with very high TRU
loadings. It is beyond the scope of this report to discuss the reactor safety
implications of this new type of transmutation facility [2].
2.4.5. Transuranic element processing and transmutation issues
The presence of plutonium together with MAs determines the
throughput and criticality requirements of the processing facility. The mass of
the separated TRUs is roughly 10–15 times higher than the mass of the
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