One of the problems which may be encountered in the operation of NPR, or of any similar pressurized-water reactor, is the deposition of crud in the reactor core, particularly on the surfaces of the fuel elements. This crud consists primarily of iron oxides resulting from the corrosion of the piping. It has generally been found to deposit preferentially in a radiation field such as is present in the reactor core. Such deposition is undesirable for two reasons. First, the crud will become activated, and on subsequent release may create radioactivity levels in the ex-reactor components of the primary loop high enough to be a hazard to maintenance and operating personnel. Secondly, the crud deposit is a poor conductor of heat, and even a rather thin film can raise the cladding temperature by 100 -- 200{degree}C and result in accelerated corrosion of the cladding.