Here is an explanation of a cooling and cleanup system

http://www.nrc.gov/docs/ML1125/ML11258A385.pdf

11.7.1 Introduction
Nuclear power plants are on 18 to 24 month operating cycles. At the end of an
operating cycle, a nuclear power reactor is shut down for refueling. One-quarter to one third of the fuel bundles in the reactor core are permanently discharged as spent fuel. New fuel bundles are loaded into the core as replacements. Spent fuel bundles continue to produce heat and radiation as unstable fission byproducts decay. Rev 09/11 11.7-2 USNRC HRTD
The Fuel Pool Cooling and Cleanup (FPCC) System maintains the fuel storage pool and separator storage pool at an acceptable temperature. The FPCC system also removes dissolved and suspended solids. Removal of these solids is required to maintain the pools within acceptable activity limits. It also maintains the necessary water quality and clarity to store, transfer, and service the reactor internals and fuel bundles.

The fuel storage racks maintain fuel bundles in a subcritical configuration. The fuel storage racks may hold new fuel bundles waiting to be placed into the reactor core as well as spent fuel bundles.
The functional classification of the FPCC system is that of a safety related system.
The purposes of the FPCC system are:
• To remove decay heat released from spent fuel bundles.
• To maintain water quality for refueling activities and storage of spent fuel bundles.
• To provide shielding to reduce radiation levels on the refueling floor.
• To maintain fuel bundles in a subcritical configuration.
The FPCC system consists of:
• pumps
• heat exchangers
• filters
• demineralizer
• diffusers
• storage pools

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Note added at 3 days21 hrs (2016-06-21 15:58:37 GMT) Post-grading
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Glad to have helped