TRS435_web

adioactive that it would not be suitable for the construction of a nuclear
weapon. Similar observations have already been made for the IFR fuel cycle
[18], in which the material is considered to be self-protecting for the reasons
mentioned above. The arguments put forward in Section 3.4.3 on the lack of
‘attractiveness’ of the product (isotopic quality, chemical purity, heat output
and radiation) also apply.
3.5.4.1. Safeguardability of pyroprocessing
According to the present safeguards inspection system, effective
safeguarding of pyroprocessing plants would be more difficult than is the case
for conventional plants, since it is more difficult to measure and keep track of
the fissile material in the process. The ITU and CRIEPI have been working on
methods for the quantitative analysis of plutonium and MAs in salt and
cadmium matrices.
In order to establish a material inventory, a bulk measurement (volume
or mass) must be taken, followed by a sample from the bulk and a
measurement of the compound concentration in the sample. Whereas the
fissile material inventory can be determined by bulk measurement of the initial
metal alloy mass of spent fuel, sampling of the solidified electrolyte or of the
metal cathode is much more difficult than in aqueous processes. At this early
stage of process development it has been observed that the material sometimes
suffers from lack of homogeneity, hence a higher number of samples have to be
taken for analysis. Effective safeguards verification of fissile material at new
types of pyroprocessing plant has to be developed.
With respect to analytical methods, well established chemical methods
such as isotope dilution mass spectrometry (IDMS) or inductively coupled
plasma mass spectrometry (ICP–MS) can be applied for the assay of plutonium
and MAs. Chemical sample preparation will be required, whichever of the two
analytical methods is applied. It is, however, relatively labour intensive and
requires a careful study of the chemical recoveries of the critical elements.
IDMS cannot be applied to neptunium, due to the lack of an appropriate
spike isotope. Americium and curium can be measured by IDMS using 243 Am
and 248 Cm as spikes. ICP–MS can be applied to all MA elements. However,
separation chemistry (e.g. ion exchange, extraction chromatography or high
performance liquid chromatography) is still required to avoid isobaric interferences.
Better radiometric methods can be used for the assay of MAs in
samples from pyroprocessing. The efforts required for sample preparation
can be reduced to a minimum. Development work in this context is being
33