We are developing superconducting ultrahigh resolution gamma-detectors for non-destructive analysis (NDA) of nuclear materials,
and specifically for spent fuel characterization in nuclear safeguards. The detectors offer an energy resolution below 100 eV
FWHM at 100 keV, and can therefore significantly increase the precision of NDA at low energies where line overlap affects
the errors of the measurement when using germanium detectors. They also increase the peak-to-background ratio and thus improve
the detection limits for weak gamma emissions from the fissile Pu and U isotopes at low energy in the presence of an intense
Compton background from the fission products in spent fuel. Here we demonstrate high energy resolution and high peak-to-background
ratio of our superconducting Gamma detectors, and discuss their relevance for measuring actinides in spent nuclear fuel.