CRUD AND GALVANIC CORROSIONDOE-HDBK-1015/1-93CorrosionCH-02Rev. 0Page 22CRUD AND GALVANIC CORROSIONA major potential problem is crud. Crud can cause an increase inbackground radiation levels. When two dissimilar metals are in closevicinity, the opportunity for ion transfer is high. The result is a perfectenvironment for galvanic corrosion. Because of the numerous types ofmaterials used in nuclear facilities, galvanic corrosion is a major concern.EO 1.13DEFINE the following terms:a.Crudb.Scalec.Galvanic corrosionEO 1.14IDENTIFY the five problems associated with the presence orrelease of crud into reactor coolant.EO 1.15STATE the four causes of crud bursts.EO 1.16STATE the two conditions that can cause galvanic corrosion.EO 1.17EXPLAIN the mechanism for galvanic corrosion.EO 1.18IDENTIFY the two locations that are susceptible to galvaniccorrosion.EO 1.19STATE the five control measures used to minimize galvaniccorrosion.CrudIn addition to the corrosion film, corrosion products in the form of finely divided, insoluble oxideparticles called crudbecome suspended in the reactor coolant or loosely adhere to metalsurfaces. Crud has several undesirable characteristics. It can be transported throughout thereactor coolant system. As a result, it can accumulate and foul heat-transfer surfaces or clogflow passages. The most undesirable characteristic of crud, however, is that it becomesactivated when exposed to radiation. Because crud can be transported throughout the reactorcoolant system, it can collect outside the reactor core, causing radiation hot spots that increaseambient radiation levels. Hot spots caused by collections of crud may occur at the entrance tothe purification heat exchanger and other areas of low flow velocity. Crud that is looselyadhered to metal surfaces can suddenly become suspended in the reactor coolant.
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