Determining Fissile Content in PWR Spent Fuel Assemblies Using a Passive Neutron Albedo Reactivity with Fission Chambers Technique

State regulatory bodies and organizations such as the IAEA that are concerned with prevent- ing the proliferation of nuclear weapons are interested in a means of quantifying the amount of plutonium in a given spent fuel assembly. The complexity of spent nuclear fuel makes the mea- surement of plutonium content challenging. There are a variety of techniques that can measure various properties of spent nuclear fuel including burnup, and mass of ?ssile content. No single technique can provide all desired information, necessitating an approach using multiple detector systems and types. This paper presents our analysis of the Passive Neutron Albedo Reactivity- Fission Chamber (PNAR-FC) detector system. PNAR-FC is a simpli?ed version of the PNAR technique originally developed in 1997. This earlier research was performed with a high ef?- ciency, 3 He-based system (PNAR-3He) with which multiplicty analysis was performed. With the PNAR technique a portion of the spent fuel assembly is wrapped in a 1 mm thick cadmium liner. Neutron count rates are measured both with and without the cadmium liner present. The ratio of the count rate with the cadmium liner to the count rate without the cadmium liner is calculated and called the cadmium ratio. In the PNAR-3He technique, multiplicity measurements were made and the cadmium ratio was shown to scale with the ?ssile content of the material being measured. PNAR-FC simpli?es the PNAR technique by using only a few ?ssion chambers instead of many 3 He tubes. Using a simpli?ed PNAR-FC technique provides for a cheaper, lighter, and thus more portable detector system than was possible with the PNAR-3He system. The challenge with the PNAR-FC system are two-fold: 1) the change in the cadmium ratio is weaker as a afunction of the changing ?ssile content relative to multiplicity count rates, and 2) the ef?ciency for the ?ssion chamber based system are poorer than for the 3 He based detectors. In this paper, we present our research on using the PNAR-FC detector system to quantify the ?ssile content of a spent nuclear fuel assembly.