CRUD AND GALVANIC CORROSION

CRUD AND GALVANIC CORROSION DOE-HDBK-1015/1-93 Corrosion CH-02 Rev. 0 Page 22 CRUD AND GALVANIC CORROSION A major potential problem is crud. Crud can cause an increase in background radiation levels. When two dissimilar metals are in close vicinity, the opportunity for ion transfer is high. The result is a perfect environment for galvanic corrosion. Because of the numerous types of materials used in nuclear facilities, galvanic corrosion is a major concern. EO 1.13 DEFINE the following terms: a. Crud b. Scale c. Galvanic corrosion EO 1.14 IDENTIFY the five problems associated with the presence or release of crud into reactor coolant. EO 1.15 STATE the four causes of crud bursts. EO 1.16 STATE the two conditions that can cause galvanic corrosion. EO 1.17 EXPLAIN the mechanism for galvanic corrosion. EO 1.18 IDENTIFY the two locations that are susceptible to galvanic corrosion. EO 1.19 STATE the five control measures used to minimize galvanic corrosion. Crud In addition to the corrosion film, corrosion products in the form of finely divided, insoluble oxide particles called crud become suspended in the reactor coolant or loosely adhere to metal surfaces. Crud has several undesirable characteristics. It can be transported throughout the reactor coolant system. As a result, it can accumulate and foul heat-transfer surfaces or clog flow passages. The most undesirable characteristic of crud, however, is that it becomes activated when exposed to radiation. Because crud can be transported throughout the reactor coolant system, it can collect outside the reactor core, causing radiation hot spots that increase ambient radiation levels. Hot spots caused by collections of crud may occur at the entrance to the purification heat exchanger and other areas of low flow velocity. Crud that is loosely adhered to metal surfaces can suddenly become suspended in the reactor coolant.