Efficient Water Management and Selection of Cooling System for Future NPP in Bangladesh

Water withdrawal today presents a vital issue for Bangladesh to build a new nuclear power plant (NPP) as the country has a deficit in its water resources. It is an issue that may create conflict among the socio-economic activities that require and depend on the water like agriculture that mostly depends on river and ground water. Very recently nuclear power has come into focus during debates on energy generation, often in relation to wider issues such as global warming and climate change. According to Power System Master Plan (PSMP) 2016 of the Government of Bangladesh, it is estimated that a capacity of 7200 MWe of electricity may be generated from nuclear power by 2041 (PSMP, 2016). The government of Bangladesh has already started the construction work of 2400 MWe Rooppur NPP and planning to construct more units of NPPs in the future to fulfill the planning of PSMP 2016. Usually, water is used as a coolant for most of the commercial NPP designed in the present world. In this paper, a study has been performed about the estimation of both the needs for cooling water and other essential systems for a future NPP in Bangladesh using IAEA’s Water Management Program (WAMP). Moreover, the selection of cooling systems by evaluating three different criteria: water resource, environment, and economics, has also been performed during this study. Keyword: Cooling system of NPP, IAEA, Water Management Program (WAMP), NPP, and Bangladesh. INTRODUCTION: Water management is an important topic for countries like Bangladesh considering building new NPPs. Good water management addresses the issue of securing water for NPPs at various stages: construction and flushing, cold and hot testing, the condenser cooling operation including the primary coolant makeup system, as well as the safety inventory and release from radioactive liquid waste treatment structure (Moss et al., 1998). In all stages of construction, operation and maintenance of any NPP, efficient water management is needed. Water use involves two processes that can occur separately or simultaneously: water consumption and water withdrawal. Water consumption occurs when water either ceases to exist as a liquid, through evaporation (direct evaporation in a cooling tower or increased surface evaporation from the source due to the elevated temperature) or when water is degraded through International Journal of Material and Mathematical Sciences, 2(6), 93-98, 2020 Publisher homepage: www.universepg.com, ISSN: 2707-4625 (Online) & 2707-4617 (Print) https://doi.org/10.34104/ijmms.020.093098 International Journal of Material and Mathematical Sciences Journal homepage: www.universepg.com/journal/ijmms Hasan et al., / International Journal of Material and Mathematical Sciences, 2(6), 93-98, 2020 UniversePG l www.universepg.com 94 contamination so that it is not fit to be returned directly to its original source. Withdrawal water means water is removed from a source. It may have consumed and not returned to its origin. The difference between water consumption and water withdrawal is important to any discussion about water use. Normally open loop cooling systems may withdraw significantly more water than recirculating cooling towers, but consume substantially less (Baker, 1988). Other systems may withdraw no water at all, but still consume water, as in reservoir evaporation at a hydroelectric power plant. However, when making such comparisons, differences in cooling water temperature as well as the thermal efficiency of the power plant must be kept in mind. Water requirements for NPPs may vary, based on the cooling system they involve, the thermal efficiency of the NPP, the need for service water, safety and nonsafety system designs, as well as the waste disposal techniques (Hasan et al., 2020; Mathey, 1990). Selection of site is also a very important parameter in terms of availability of cooling water as well as appropriate atmospheric conditions. These parameters will higher plant efficiencies at lower water withdrawal rates. Water is required mainly for cooling of NPPs. It is compulsory to carefully choose and design cooling system for NPP. There is a number of cooling processes that can reduce the water consumption rapidly. Cooling water requirements of NPPs exceed the conventional fossil fuel power stations on an average by 20-25 percent (Khamis and Kavvadias, 2012). Most of the existing NPPs have lower thermal efficiency which is responsible for this as they operate with lower steam pressures and temperatures. These parameters can be varied very slightly as of the limits forced by the common use of zircaloy as a material for fuel cladding and thermal hydraulic considerations [6]. Another limiting condition is the manufacturing capabilities of the main reactor heavy components. Different methods of cooling used for NPP/Technologies available for cooling systems Power plants require dependable access to large amounts of water, mainly for cooling. Normally NPPs use water for cooling in two ways: 1) convey heat to the steam turbines from the reactor core 2) remove and reject excess heat from the internal steam circuit. If the power plant is next to a large natural water body (Like sea, big river or large inland water body) then the cooling may be achieved simply with a oncethrough cooling system, where large amounts of water are circulated through the condensers and discharged back into water body with less amount of withdrawn. If such water body does not exist nearby, the cooling may have carried out by passing water throughout the condenser unit and then through a cooling tower, where an up breeze of air through water droplets cools the water. Normally an on-site water body may be good enough for this. Fig 1: WAMP user interface. Hasan et al., / International Journal of Material and Mathematical Sciences, 2(6), 93-98, 2020 UniversePG l www.universepg.com 95 Table 1: Distribution of cooling systems in current operating NPPs Once-through cooling Closed cycle Sea/Lake/ River water Cooling tower 45% 15% 14% 26% METHODOLOGY: Water Management Program (WAMP) is used for this study. The IAEA has developed and released the WAMP, which is freely available to all Member States which may be used for the estimation of water needs in NPPs especially for water cooled NPPs. The program estimates both the needs for cooling water and other essential systems. Following flow chart shows a brief idea about different cooling types available presently Fig 2: Different types of cooling system. Study of cooling system for the proposed site For the proposed site, the following NPP parameters have been chosen, considering that Bangladesh is going to construct large size NPP in future. Parameters chosen are shown on Table 2. Table 2: Assumed Power Plant Specifications and Site conditions Power Plant Specifications Type Light Water Reactor Reactor electric capacity 1199 MWe Reactor thermal capacity 3600 MWth Reference efficiency 33% Rejected heat 2380 MWth Coolant flow rate through reactor 23.88 m 3 /s Hasan et al., / International Journal of Material and Mathematical Sciences, 2(6), 93-98, 2020 UniversePG l www.universepg.com 96 Site conditions Location River/Inland Dry bulb temperature 28 °C Wet bulb Temperature 23.6 °C Relative Humidity 70% Surface water temperature 25 °C River flow 95 m3/s Average wind velocity 3.05 m3/s After considering the above mentioned specification, the cooling water requirements were calculated using WAMP software. The results are tabulated below: Table 3: Simulation result for water withdrawal and water consumption for different cooling systems Cooling System Type Water Withdrawal (m 3 /s) Water Consumption (m 3 /s) Once Through 58.12 0.79 Once Through (Cooling Pond) 58.12 0.79 Close Loop with Cooling Pond 0.67 0.45 Wet Cooling (Mechanical Draft) 1.54 1.05 Wet Cooling (Natural Draft) 1.58 1.13 Hybrid Plume Abatement 1.57 1.07 Fig 3: Close Loop cooling system with cooling Pond simulation result. Air Temperature 30 °C 94 °C 66.87 °C MW 67 °C 23 m3/s Area needed: 0.3 km 2 2624 Cooling pond Steam turbine

Water management is an important topic for countries like Bangladesh considering building new NPPs. Good water management addresses the issue of securing water for NPPs at various stages: construction and flushing, cold and hot testing, the condenser cooling operation including the primary coolant makeup system, as well as the safety inventory and release from radioactive liquid waste treatment structure (Moss et al., 1998). In all stages of construction, operation and maintenance of any NPP, efficient water management is needed. Water use involves two processes that can occur separately or simultaneously: water consumption and water withdrawal.
Water consumption occurs when water either ceases to exist as a liquid, through evaporation (direct evaporation in a cooling tower or increased surface evaporation from the source due to the elevated temperature) or when water is degraded through contamination so that it is not fit to be returned directly to its original source.
Withdrawal water means water is removed from a source. It may have consumed and not returned to its origin. The difference between water consumption and water withdrawal is important to any discussion about water use. Normally open loop cooling systems may withdraw significantly more water than recirculating cooling towers, but consume substantially less (Baker, 1988). Other systems may withdraw no water at all, but still consume water, as in reservoir evaporation at a hydroelectric power plant. However, when making such comparisons, differences in cooling water temperature as well as the thermal efficiency of the power plant must be kept in mind.
Water requirements for NPPs may vary, based on the cooling system they involve, the thermal efficiency of the NPP, the need for service water, safety and nonsafety system designs, as well as the waste disposal techniques (Hasan et al., 2020;Mathey, 1990). Selection of site is also a very important parameter in terms of availability of cooling water as well as appropriate atmospheric conditions. These parameters will higher plant efficiencies at lower water withdrawal rates.
Water is required mainly for cooling of NPPs. It is compulsory to carefully choose and design cooling system for NPP. There is a number of cooling processes that can reduce the water consumption rapidly. Cooling water requirements of NPPs exceed the conventional fossil fuel power stations on an average by 20-25 percent (Khamis and Kavvadias, 2012). Most of the existing NPPs have lower thermal efficiency which is responsible for this as they operate with lower steam pressures and temperatures. These parameters can be varied very slightly as of the limits forced by the common use of zircaloy as a material for fuel cladding and thermal hydraulic considerations [6]. Another limiting condition is the manufacturing capabilities of the main reactor heavy components.

Different methods of cooling used for NPP/Technologies available for cooling systems
Power plants require dependable access to large amounts of water, mainly for cooling. Normally NPPs use water for cooling in two ways: 1) convey heat to the steam turbines from the reactor core 2) remove and reject excess heat from the internal steam circuit.
If the power plant is next to a large natural water body (Like sea, big river or large inland water body) then the cooling may be achieved simply with a oncethrough cooling system, where large amounts of water are circulated through the condensers and discharged back into water body with less amount of withdrawn.
If such water body does not exist nearby, the cooling may have carried out by passing water throughout the condenser unit and then through a cooling tower, where an up breeze of air through water droplets cools the water. Normally an on-site water body may be good enough for this.

METHODOLOGY:
Water Management Program (WAMP) is used for this study. The IAEA has developed and released the WAMP, which is freely available to all Member States which may be used for the estimation of water needs in NPPs especially for water cooled NPPs. The program estimates both the needs for cooling water and other essential systems.
Following flow chart shows a brief idea about different cooling types available presently -

Study of cooling system for the proposed site
For the proposed site, the following NPP parameters have been chosen, considering that Bangladesh is going to construct large size NPP in future. Parameters chosen are shown on Table 2. After considering the above mentioned specification, the cooling water requirements were calculated using WAMP software. The results are tabulated below: It is found that once through cooling system required highest amount of water for cooling and close loop with cooling pond required lowest amount of water.   Table 4 shows the capital and operation cost of different cooling system analyzed by WAMP software. This system has a higher establishment cost in compare with wet cool system but it has no operating cost at all (only base cost). The system has almost no environmental impact and very much favorable for a country like Bangladesh. So; close loop cooling system with cooling pond may be a good option for future NPP in Bangladesh with respect to the selected site conditions.

CONCLUSION:
As a new comer country in the field of nuclear power plant, Bangladesh need to consider the environmental impact as well as the cost effectiveness of the cooling system for NPPs. By considering both criteria it can be said that close loop cooling system with cooling pond can be a good option for future NPP in Bangladesh.

ACKNOWLEDGEMENT:
Sincere acknowledgement to the colleagues of Center for Research Reactor, AERE to support for the successful completion of the present study.