U-Pu InSpector: A Dedicated Instrument for Assessing the Isotopic Composition of Uranium and Plutonium

Application

Fast and accurate determination of the isotopic composition of uranium and plutonium is essential for many applications. The worldwide trend towards nuclear disarmament, as well as growing concerns about the possible diversion of fissile material to non-peaceful use, has increased the importance of these measurements for nuclear safeguards verification and border controls. Nuclear fuel facilities require such measurements for input control, output control and process measurements. These applications require fast and accurate measurements, fool-proof system operation, and, in many cases, physical portability of the measurement apparatus.

The determination of the enrichment of uranium has historically been a most difficult task. In the non-destructive analysis (NDA) technique, the 185 keV line from the decay of 235 U and/or the 1001 keV line from 238 U are monitored with a HPGe or NaI detector. The interpretation of these data depends on a careful calibration and on the assumption that the conditions under which the calibration has been done are identically reproduced during the measurement. Large errors can be introduced when the detector-sample geometry is only slightly altered, when the performance of the NaI or HPGe detector changes or when the homogeneity, chemical composition or the filling height of the sample differ from the calibration standard.

The determination of the isotopic composition of plutonium has historically been less of a problem. In particular, the NDA technique based on high resolution gamma spectroscopy with a low energy germanium (LEGe) detector and the Multi-Group Analysis (MGA) code [1] has proven to be very successful for measuring the isotopic concentration of plutonium. But this technique required skilled and highly qualified inspectors to set up the instruments correctly (energy calibration, pole zero setting, ...) and to interpret the spectra and messages that appear on the MGA output report. Equipment was transportable but far from portable because the analyzer and associated shielding could not easily be handled by one person.

Destructive analysis (DA) techniques are usually more precise. However, they cannot give immediate answers since a small sample must be selected and transported to a laboratory for chemical treatment and analysis. Furthermore, there is always the question of homogeneity and whether or not the sample is truly representative.

The U-Pu InSpector discussed in this note overcomes the numerous problems described above. It makes use of new developments in detector and shielding technology, the InSpector™ 2000 portable analyzer, Genie™ 2000 software, and improved MGA and MGAU codes for plutonium and uranium, respectively.