[en] Chemical precipitates formed in the recovery water following a Loss of Coolant Accident (LOCA) have the potential to increase head loss across the Emergency Core Cooling System (ECCS) strainer, and could lead to cavitation of the ECCS pumps, pump failure and loss of core cooling. Atomic Energy of Canada Limited (AECL) has been involved in the investigation of chemical effects on head loss for its CANDU® and PWR (Pressurized Water Reactor) customers. The chemical constituents of the recovery sump water depend on the combination of chemistry control additives, fission products, radiolysis products (e.g., nitric acid), and the corrosion and dissolution products from metals, concrete, and insulation materials. Some of these dissolution and corrosion products (e.g., aluminum and calcium) may form significant quantities of precipitates. The presence of chemistry control additives such as lithium and sodium hydroxide, trisodium phosphate (TSP) and boric acid can significantly influence the precipitates formed. While a number of compounds may be shown to be thermodynamically possible under the conditions assumed for precipitation, kinetic factors play a large role in the type and morphology of precipitates observed. Precipitation is also influenced by insulation debris, which can trap precipitates and act as nucleation sites for heterogeneous precipitation. This paper outlines the AECL approach to resolving the issue of chemical effects on ECCS strainer head loss, which includes modeling, bench top testing and reduced-scale testing; the latter conducted using a temperature-controlled variable-flow closed-loop test rig that includes an AECL Finned Strainer® test section equipped with a differential pressure transmitter. Models of corrosion product release and the types of precipitates expected in post-LOCA sumps are discussed. Finally, this paper discusses reduced-scale test results and presents a possible method for chemical effects head loss modeling. (author)