A. Introduction

A commercial nuclear power reactor essentially consists of heat-transfer systems for converting the energy of fissioning uranium to electricity via a conventional steam-turbine cycle. The predominant type of reactor is water-cooled, in which the fission heat generated in the fuel is removed by water and transferred to steam. Such use of water as coolant raises the possibility that the systems can become subject to several fouling phenomena. As described in this article, some of those phenomena are found only in nuclear systems because of their unique characteristics.

The reactors described here are of two types: indirect-cycle, comprising the pressurized water reactors (PWRs) and pressurized heavy water reactors (PHWRs - more specifically, those of the CANDU ^∗ ® design), and direct-cycle, comprising the boiling water reactors (BWRs). The indirect-cycle reactors have a primary coolant system to transfer heat from the reactor core to heat exchangers or steam generators where the secondary coolant boils to produce steam for the turbines, while the direct-cycle reactors have the water coolant boiling directly to steam in the core itself. Besides the primary and steam circuits, other water systems such as the condenser cooling, the various ancillary heat exchangers around the reactor and, in the CANDU alone, the separate moderator system, can experience fouling. The inexorable processes of corrosion are very much responsible.

B. Primary Heat Transport System

(a) Pressurized Water Reactors