Dr Anthonie Cilliers is a Nuclear Engineering specialist with a PhD Nuclear Engineering and M.Eng (Computer & Electronic) degree. He works at the North-West University as Programme Manager: Nuclear Engineering and as research lead on numerous projects.
Anthonie also specialises in Nuclear Knowledge Management where he is the initiator and coordinator of the national academic network, ‘South African Network for Nuclear Education, Science and Technology’ (SAN-NEST).
I can imagine a South Africa 20 years from now, a South Africa that has reindustrialised; a South Africa with opportunities for developing industries and above all, a South Africa that contributes to the world economy’s full potential.
For a developing country being able to maximise its capacity for developing value in its natural resources, the availability and combination of natural resources and available energy becomes essential. South Africa is rich in natural resources, but to provide energy to beneficiate it requires an intervention.
This intervention comes in the form of the IRP2010.
The Integrated Resource Plan 2010 (IRP2010) indicates that 9,600MW of nuclear power will be installed in the country by 2030. This is essential to continue providing clean stable baseload energy in South Africa with an aging coal plant fleet.
The Department of Energy is expected to release the Request for Proposals (RFP) very soon, and when they do, most of the uncertainty around the cost of these plants will be resolved.
The technologies available for the RFP will most likely be limited to Pressurised Water Reactor (PWR) plants, a similar design to that of the Koeberg plant, with additional passive safety systems. In this article the technologies available for the 9,600MW will be explored.
Nuclear power plant differences
It is always important to distinguish PWR power plants from the most often mentioned Chernobyl nuclear power plant, which suffered a catastrophic accident in 1986.
These technologies are vastly different and are subjected to vastly different safety considerations. The Chernobyl nuclear power plant consisted of a very large graphite block with pressure tubes and water as a coolant flowing through the graphite block.
The purpose of the graphite block is to slow down neutrons in order to sustain the nuclear chain reaction, the water on the other hand is cooling down the plant and these two systems are essentially separated. During an accident where coolant has reduced cooling effectiveness, the nuclear chain reaction is maintained, which caused the initial accident at Chernobyl.
In a PWR nuclear power plant, all the fuel is located inside a steel pressure vessel, with water acting as a coolant and neutron slowdown medium. During a scenario where the cooling capacity is reduced, the nuclear chain reaction is also automatically stopped and only 10% of the operating heat is still being produced. In order to ensure the plant is still being sufficiently cooled down, a number of diverse systems are employed to actively cool the core during the worst postulated accidents.
The probability of these systems being unable to effectively cool the plant due to failure is extremely low, lower than any other risk a person is exposed to on a daily basis. In a case that these systems do fail, the large concrete containment building is designed to contain and limit any radioactive releases.
This sounds good, but that is for the traditional Generation II plants, design and technology is still improving.
Generation III plants
The new plants under consideration for the 9,600MW nuclear fleet in South Africa will all be Generation III plants.
These plants not only fully comply with the Generation II plant specifications; they also include additional passive systems to ensure that all cooling systems will always function at full capacity, even without any power sources or interventions.
Most generation III plants were designed from the original Westinghouse PWR design.
The AP1000 is a nuclear power plant designed and sold by Westinghouse Electric Company, now majority owned by Toshiba. The plant is a pressurised water reactor with improved use of passive nuclear safety. The first AP1000 is expected to start operations in 2017 in China.
The AP1000 makes use of a water coolant system that absorbs all the generated heat during an accident condition. The water is then allowed to boil off inside the containment only to condense against the inner steel lining of the containment.
The condensed coolant then flows back into the coolant water tank to continually cool the reactor system. The steel lining inside the containment is cooled by coolant sprays being supplied from a water tank on top of the containment. This water tank only needs to be replenished every 72 hours.
In other words, during the worst postulated accident conditions, the plant will be maintained in a safe condition with the only operator interaction being the refilling of the containment coolant water tank after 72 hours.
The philosophy of the AP1000 design relies on that of simplicity, reduction of components susceptible to failure and the reliance on natural effects to keep the plant within the safe design limits during all conditions.
The AP1000 is a perfect example of a PWR with a passive safety system.
The EPR is a third generation PWR design. It has been designed and developed mainly by Frematome now Areva and Électrictité de France (EDF) in France, and Siemens in Germany.
In Europe this reactor design was called European Pressurised Reactor, and the internationalised name was Evolutionary Power Reactor, but it is now simply named EPR.
The EPR design philosophy revolves around the evolution of conventional PWR plants, having the most operating experience of any plant. In addition to that, the EPR includes additional redundant and diverse systems to ensure that during any postulated accidents and multiple failures, the plant will be effectively cooled, and maintained in a safe state.
The EPR also includes a so called “core catcher” or corium spreading and cooling area inside the containment.
This system is designed to operate only under the worst accident scenarios and will maintain the core in a safe geometry while being able to safely cool the core with no radioactive releases to the atmosphere.
The APR-1400 (for Advanced Power Reactor 1400 [MWe]) is an advanced pressurised water nuclear reactor designed by the Korea Electric Power Corporation (KEPCO).
Originally known as the Korean Next Generation Reactor, this Generation III reactor was developed from the earlier OPR-1000 design and also incorporates features from the US Combustion Engineering (C-E) System 80+ design.
Currently there is one unit in operation (Shin Kori unit 3) and seven units under construction, four in the United Arab Emirates at Barakah and three in South Korea: one at Shin Kori and two at Shin Hanul. Two more units are planned with construction yet to commence at Shin Kori.
The APR1400 is an evolutionary plant developed from the same base as the original Westinghouse PWR design.
It includes safety systems similar to that of the AP1000 plant with a slightly larger power output of 1,400MW electrical.
China has officially adopted the AP1000 as a standard for inland nuclear projects. The National Development and Reform Commission (NDRC) has already approved several nuclear projects, including the Dafan plant in Hubei province, Taohuajiang in Hunan, and Pengze in Jiangxi.
The NDRC is studying additional projects in Anhui, Jilin and Gansu provinces. China wants to have 100 units under construction and operating by 2020, according to Aris Candris, Westinghouse’s previous CEO.
In 2008 and 2009, Westinghouse made agreements to work with the State Nuclear Power Technology Corporation (SNPTC) and other institutes to develop a larger design, the CAP1400 of 1,400MWe capacity, possibly followed by a 1,700MWe design.
China will own the intellectual property rights for these larger designs. Exporting the new larger units may be possible with Westinghouse’s cooperation. In September 2014, the Chinese nuclear regulator approved the design safety analysis following a 17-month review.
The VVER-TOI is a Russian design for a two-unit nuclear power plant. The Russian abbreviation VVER stands for ‘water-water energy reactor’ (i.e. water-cooled water-moderated energy reactor) referring to a typical PWR design.
The Russian PWR however is the only design that was not designed from the original Westinghouse PWR design. For this reason, it includes a few unique distinguishing features. The main distinguishing features of the VVER compared to other PWRs are:
- Horizontal steam generators
- Hexagonal fuel assemblies
- No bottom penetrations in the pressure vessel
- High-capacity pressurisers providing a large reactor coolant inventory
The TOI version of the VVER plant also includes the latest advancements in passive safety systems similar to that of the AP1000 reactor. Here a distinguishing feature is the use of an air-cooled radiator system located around the containment vessel in place of the refillable water tank.
This increases the 72-hour operator intervention time indefinitely. The VVER-TOI plant also includes a “core catcher” similar to that of the EPR design.
The technology for South Africa
When comparing the above technologies in order to determine a preferred ‘technical’ design, the result is inconclusive. All these plants conform to the highest standards of design, operating and safety features with very little to choose between the vendors.
South Africa is truly spoiled for choice and the final decision may just come down to the cost of the plants.
Whichever plant South Africa eventually decides on; I am very excited about the prospects of unlocking our country’s industrial potential with an abundance of stable baseload energy to support our development plans and dreams.