The new developed on-line monitoring method which is based on a temperature difference between an instrumented fuel element and the pool water below a research reactor in practice, as known power measuring by thermal balance is as following. The reactor core is cooled by natural convection of demineralized light water in the reactor pool. Heat is removed from the reactor pool and released into the atmosphere through the primary cooling loop, the secondary cooling loop and the cooling tower. Pool temperature depends on reactor power, as well as external temperature, because the latter affects heat dissipation in the cooling tower. The total power is determined by the thermal balance of cooling water flowing through the primary and secondary loops added to the calculated heat losses. These losses represent a very small fraction of the total power (about 1.5% of total). The inlet and outlet temperatures are measured by four platinum resistance thermometers (PT-100) positioned at the inlet and at the outlet pipes of the primary and secondary cooling loops. The flow rate in the primary loop is measured by an orifice plate and a differential pressure transmitter. The flow in the secondary loop is measured by a flow-meter. The pressure transmitter and the temperature measuring lines were calibrated and an adjusted equation was added to the data acquisition system. The steady-state is reached after some hours of reactor operation, so that the power dissipated in the cooling system added with the losses should be equal to the core power. The thermal power dissipated in the primary and secondary loops were given by:

Чсооі = m. Cp. AT (10)

where qC00{ is the thermal power dissipated in each loop (kW), m is the flow rate of the coolant water in the loop (kg. s-1), cP is the specific heat of the coolant (kJ kg-1 °C-1), and ДТ is the difference between the temperatures at loop the inlet and outlet (°C). Figure 21 shows the power evolution in the primary and secondary loops during one reactor operation.

8. Acknowledgement

The authors are thankful InTech publication for their scientific effort to develop the sciences. We also, thank Mrs. M. Mohammadi for her effort to preparing the manuscript.

9. Conclusion

Power monitoring channels play a major role in retaining a safe reliable operation of nuclear reactors and nuclear power plants. Accurate power monitoring using advanced developed channels could make nuclear reactors a more reliable energy source and change public mind about this major energy resource. Regarding harsh accidents such as Chernobyl, Three-Mile Island and the recent accidents in Fukushima nuclear power plants and their dangerous effects on the environment and human life, the importance of developing reactor safety system like power monitoring channels are more attended. New generations of nuclear power plants are much safer than their predecessors because of their new accurate safety systems and more reliable monitoring channels. They produce energy from nuclear fission and are the cleanest, safe and environment-friendly source of energy among many investigated power resources (Javidkia et al., 2011).

There is no doubt that nuclear power is the only feasible green and economic solution for today’s increasing energy demand. Therefore, studying, researches and more investments on the power monitoring systems and channel in nuclear reactors will help to create an inexhaustible source of safe and clean energy.