Barakah Nuclear Energy Plant Plant Cooling Water System Development

Emirates Nuclear Energy Corporation (ENEC)

World Nuclear Performance Report 2017 Case Study

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Barakah Nuclear Energy Plant (Photo:Enec)

Construction of the UAE’s first nuclear energy plant is underway at Barakah, approximately 300km west of Abu Dhabi city. The Barakah Nuclear Energy Plant consists of four nuclear power generating units with a combined capacity of approximately 5,600 MW, and their associated facilities. The four units are Generation III+ reactors of the APR1400 design. Construction of the power plant commenced in July 2012, following the receipt of the Construction License from the Federal Authority for Nuclear Regulation (FANR) and a ‘No Objection Certificate’ from Abu Dhabi’s environmental regulator, the Environment Agency – Abu Dhabi (EAD). EAD regulates ENEC and the Barakah project in terms of environment and sustainability. 

One of the earliest and most critical tasks for the Barakah project was the conceptual and final design for the tertiary plant cooling water system. This task was initiated even before ENEC awarded the Prime Contract to the Korea Electric Power Corporation (KEPCO) for the design, construction and commissioning of the Barakah plant. 

The tertiary plant cooling water system provides for the removal of thermal heat generated from power generation sources such as the turbine-generator condenser steam exhaust and a host of energy plant support system heat exchangers, as well as other sources. The unique climate conditions of the Arabian Gulf and the UAE required specific parameters and criteria to be set up in order to ensure that the cooling system was able to operate at optimal efficiency. 

Some of the unique aspects that required consideration for the development of the cooling water system for the Barakah plant included: 

  • Assessment of cooling water options, including natural draft cooling towers and once-through cooling with water intake and discharge from the adjacent Arabian Gulf.
  • Environmental impact assessment requirements mandated by government agencies such as EAD for protection of aquatic and biological species in the Arabian Gulf region.  This included limitations for water intake flow velocities and discharge effluent temperature rises.
  • Evaluation of Arabian Gulf ambient water and air temperature histories and flow patterns coupled with wave patterns to minimize thermal recirculation from discharge plume to cooling water intake in order to maintain optimum power generation and shutdown safety functions.
  • Optimization of the plant cooling water system to support project schedule and budget while maintaining the highest standards of safety and quality.

Prior to awarding of the Prime Contract in 2009, a number of studies were conducted in support of the Environmental Impact Assessment for various cooling water options. It was concluded that a once-through cooling arrangement was a better option than the cooling tower option due to extreme ambient air characteristics, among other considerations.

After the awarding of the Prime Contract, ENEC worked collaboratively with KEPCO and subcontractors to complete two separate cooling water conceptual design thermal modeling analyses between 2010 and 2014.  Several complex datasets were collected and evaluated for inputs into the computer models.  They included:

  1. Cooling system design information specific to the Korean APR1400 technology.
  2. Meteorological and oceanographic data specific to the local region of the Arabian Gulf.
  3. Bathymetric survey data for the shallow characteristics of the local Arabian Gulf region.
  4. Series of alternative intake and discharge channel configurations including assumed channel depths post-dredging operations.
  5. Several scenarios to take into account the possibility of potentially constructing between 2 and 8 nuclear units at the Barakah site, and variation in intake bypass flow rate from an integrated seawater bypass pump-house uniquely added to limit discharge plume temperature.

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Aerial Intake Channel (Photo:Enec)

During the initial thermal modeling effort, cooling water computer analyses outputs were completed for more than 12 candidate layouts. They all comprised of breakwater structures to be constructed for cooling water system intake and discharge channels. Layouts were initially considered with combined total breakwater length of more than 46 kilometers. Model output results were then used to produce assessment documents and reports such as:

  • Thermal plume distribution graphs
  • Environmental study reports
  • Sediment transport studies
  • Construction and operations/maintenance studies

A final plant cooling water breakwater and dredging arrangement was agreed at the end of December 2010 to allow for construction to begin and to support the overall project schedule.  The initial thermal modeling results for this configuration provided confidence that environmental and operational requirements would be met for the planned four units once they are operational.  The breakwater layout was optimized, resulting in a combined total length of 15 kilometers, making it one of the longest breakwaters in the global nuclear energy industry. By comparison, the breakwater of Shin Kori, the reference plant for Barakah, is only 1 kilometer long.

Subsequent second plant cooling water thermal modeling effort was then initiated using an independent consultant and different modeling software. This culminated in the completion of detailed analyses and reporting in September 2014.

Through the course of these two extensive studies and numerous meetings, it was concluded that the thermal discharge environmental limit of no more than 5oC at outfall could be achieved, with final agreed breakwater arrangements. The complete elimination of thermal recirculation was unavoidable when considering worst-case prevailing wind, although final arrangements would limit intake temperature increases to less than +1oC which has been deemed acceptable for plant operations.

Furthermore, as part of the obligation to meet the regulations of EAD, ENEC had to implement several design modifications to adapt to the UAE’s climate conditions. The Arabian Gulf generally, has higher temperatures than the waters off the coast of South Korea, for which the original APR1400 design was prepared. These changes include:

  • Larger pumps, heat exchangers and pipes to increase the water flow rate of the cooling systems to deal with higher seawater temperatures in the Gulf.
  • Each unit’s condenser has 85,000 titanium and super stainless steel tubes that will have a volume of 6000 m3 of sea water per minute passing through them. The amount of water withdrawn from and returned to the Arabian Gulf during operations for cooling is estimated at 105 m3/second per Unit.
  • A modified breakwater to ensure that the discharge and intake structures are at an increased distance from each other to avoid re-circulation of warmer water. As explained above, a limited intake temperature increase of less than +1oC was deemed to be acceptable.
  • Seawater intake and plant cooling systems designed to ensure compliance with EAD standards for changes in Gulf water temperature near the plants.
  • A refined intake screen design to help protect local fish populations during operations.
  • A seawater bypass system not in the original design mixes seawater with cooling water to reduce the effects of discharging warm water to the Arabian Gulf.

ENEC is working closely with Nawah Energy Company, the subsidiary mandated to operate and maintain the Barakah Nuclear Energy Plant, and will be implementing monitoring programs as Units 1 through 4 enter into commercial operation. These programs will be phased in to ensure environmental and operational commitments to regulatory authorities are met regarding cooling water thermal limits.

Interview

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Ricky Rice, Senior Civil Engineering Manager, ENEC 

Why is this cooling system being used at Barakah? 

Other cooling options such as cooling towers were considered during the Environmental Impact Assessment (EIA). Due to extreme ambient air and seawater temperatures, the cooling capability of those systems would be less effective for removing plant system heat loads.  The use of cooling towers (natural draft or mechanical draft) would still require a make-up water facility near the shoreline and a large overall facility footprint.  The combined effects of system efficiency, complexity, environmental impact and system maintenance made a once-through cooling option more desirable.

Have there been any challenges during development and construction of the system and how were they overcome? 

During the investigation and subsequent conceptual and final design of the cooling system, many challenges were encountered and overcome.  One specific challenge was the validation of design for breakwaters to withstand extreme waves characterized for the site due to historical peak winds, postulated cyclones and tsunamis.  To support the computer modeling and analytical calculations, scale model prototypes of various breakwater cross-sections were built in European test facilities and extreme design waves were applied to demonstrate structural integrity.  In addition, analyses were performed to confirm breakwater structural integrity for a postulated distant seismic event creating a tsunami that may propagate to the Barakah site.  These activities along with design studies for postulated oil spills, biofouling due to sea grass or jellyfish and sediment transport were necessary to demonstrate to regulatory agencies that the Ultimate Heat Sink cooling source from Arabian Gulf would remain reliable.

From construction standpoint, a major challenge included the need to obtain large quantities of rock materials to construct the breakwaters. The effect of this issue was minimized by the use of a portion of the dredged sand (from the intake/discharge channels) to build the inner core for parts of the breakwater.  Rock materials were then placed around the sand core for protection and construction time and material supply was optimized.  

Could this technology have applications at other nuclear power plants? 

This technology could be beneficial and applicable at other nuclear power plants located near large bodies of water used as cooling sources.  The careful consideration of thermal heat load and local site characterization, such as water source bathymetry, currents, temperatures, wind patterns and air temperatures is critical to ensure that the safety and efficiency of the plant facility is maintained.  The

Barakah site is somewhat unique due to the more shallow water and extreme temperature characteristics, which had implications on the time needed for the design of the breakwater and its subsequent construction.


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