The Partial Defect Detector (PDET) is an instrument under development at Lawrence Livermore National Laboratory.  PDET is associated with a new measurement methodology that uses multiple tiny neutron and gamma detectors in a form of cluster and high precision driving system to obtain underwater radiation measurements inside a Pressurized Water Reactor (PWR) spent fuel assembly. The method takes advantage of the PWR fuel design which contains multiple guide tubes which can be accessed from the top. The data obtained in such a manner can provide spatial distribution of neutron and gamma flux within a spent fuel assembly.

(Source: LLNL-CONF-413954)