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Nuclear Safeguards Education Portal

Spent Fuel Signatures

Radiation from spent nuclear fuel, along with other observations, can be used as signatures for spent fuel operational and isotopic characteristics.  Signatures are signals (alone or in combination) and other characteristics that can be used to identify specific phenomena. Because spent fuel is not destructively analyzed (DA) until it is reprocessed, spent fuel signatures must rely on non-destructive analysis (NDA)  of spent fuel radiation.  

Signatures that depend on only one characteristic can be used directly as a measure for that characteristic.  For example, the concentration of Nd-144, illustrated in Figure 3 (a), can be used as a signature to measure burnup.  Signatures that depend on multiple spent fuel characteristics can still be useful for checking the consistency of the facility operator's report.  For example, the concentration of Sm-147, illustrated in Figure 3 (b) depends on the fuel assembly irradiation history and cooling time.  The single signature cannot uniquely resolve those characteristics, but the irradiation history and cooling time from the facility operator's report can be used to computationally simulate a value of Sm-147.  If the measured value of Sm-147 does not reasonably match the simulated value, then there may be an inconsistency with the facility operator's report for that fuel assembly, and it should be further investigated.  

Isotopic -char -fig2 

Isotopic -char -fig 2b

Reproduction of Figure 3. Concentration in atoms/barn-cm of fission products (a) Nd-144 and (b) Sm-147 (from Ref. 5) for the 5 fuel assembly irradiation case histories of Figure 2.

While the Nd-144 and Sm-147 examples provide good visual explanations of how signatures can be used as measures for spent fuel characteristics, unfortunately, both are stable isotopes and cannot be measured with NDA techniques. The following pages will examine the various spent nuclear fuel signatures that can be derived using NDA techniques.

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