ABSTRACT
A number of operating U.S. power generating facilities with closed-cycle cooling systems (CCS), and also those plants with open-cycle (once-through) cooling (OCS), are considering modifications to either modify or utilize closed-cycle cooling in the future. Some of the characteristics common to these plants include:

• Aging equipment and materials resulting in cooling system performance and reliability deterioration.
• Increased cost and lessened availability of raw cooling water leading to new closed-cycle systems to utilize higher cycles of concentration (COC).
• Decreasing quality of available water supplies.
• Compliance requirements associated with §316(a) and §316(b) of the Clean Water Act.
• Cooling system performance problems from legacy issues such as initial under-sizing.
• Power generating owner and operator desires for; Power uprates (typically for nuclear units), Unit life extension & Need for improved operating cost competitiveness.

This paper addresses vital considerations that need to be addressed to help ensure that the wisest approach is used for evaluating or modifying existing open- or closed -cycle cooling systems.