Ultimately, the heat removed from the reactor must be transferred to another location outside of the reactor facility. The choice of secondary heat sink is highly dependent on the available cooling resources and location of the reactor facility. Facilities may remove the reactor heat to cooling towers, city water supply, ground water or facility chill water. In case of ground water, it is pumped from a ground water well or pond near the reactor site through pipes into the basement of the institute. A typical design (for a 250 kW facility) is shown in Figure 3. One or more ground water pumps are available with a typical flow capacity of 15 m³/h and an average temperature of about 12 °C. A flow meter monitors the consumption or volumetric flow rate after entering the building and then the water is pumped into a tank system to increase the pressure if necessary. The additional tank may not be necessary for pumps of sufficient flow rate and discharge pressure. The water is piped through the heat exchanger and then returns to the environment. Two pressure sensors (p_in, p_out) measure the pressure drop before and after the heat exchanger.

The water activity should be monitored before being discharged to the environment (i.e. with a very sensitive NaI detector or periodic samples). This is to assure that no radioactivity is released to the environment and to provide a record of that fact. The radioactive material concentration signal should be transmitted to the control room for on-line monitoring. Risk of a release to the environment is minimized by maintaining the integrity of the secondary system and insuring the secondary coolant system pressure is always maintained higher than primary coolant pressures. Some facilities monitor the pressure differential between the primary to secondary and alarm or cause action if the system pressures are too close for reasonable protection of leakage.