Crud:

Further to the corrosion film, corrosion products within the form of lastly divided; insoluble oxide particles known as crud become suspended within the reactor loosely or coolant adheres to metal surfaces.  It has various undesirable features.  It could be transported throughout a reactor coolant system. Conclude, it could accumulate and foul heat-transfer surfaces or clog flow passages. The most undesirable features of crud, therefore, are in which it becomes activated while exposed to radiation. Since crud could be transported throughout the reactor coolant system, it could collect outside the reactor core, causing radiation hot spots which increase ambient radiation levels. Hot spots caused through collections of crud might occur at the entrance to the purification heat exchanger and other areas of low flow velocity.  Crud which is loosely adhered to metal surfaces could suddenly become suspended within the reactor coolant.

The crud release could result from an increased oxygen concentration, a decreased (or significantly changed) pH, a huge temperature change (cooldown or heatup), or a physical shock to the system. Physical shocks involve starting, stopping, or changing pump speeds or other evolutions such as a reactor scram or a relief valve lift.  The output is a sudden increase within reactor coolant activity.  The release of crud within this fashion is termed a crud burst.  Crud bursts frequently lead to the removal of protective corrosion films and make the freshly exposed metal more susceptible to additional corrosion.  Further to the corrosion crud and film, a few of the corrosion products are soluble and are simply transported throughout the system.

High crud concentrations within the system could also complicate disposal of primary coolant.  Several of the corrosion products have associatively long half-lives and represent important biological hazards.  If, thus, primary coolant is drained or leaks from the plant soon after a crud burst, further procedures might required to be utilized to minimize the effects of this condition.

Thus, if the conditions mentioned previously (O₂, pH) are changed, the solubility of these corrosion products will change, and they could then be transported to and deposited anywhere within the reactor coolant system.

Corrosion through product is scale that is made up of deposits on surfaces from the formation of insoluble compounds from generally soluble salts.  Most general is calcium or magnesium carbonates (CaCO₃ or MgCO₃).