Power plant design | Small and medium reactors

South Korea thinks small

6 November 2010

Preparations for a design licence application are under way for South Korea's home-grown 100MWe small reactor

The Korea Atomic Energy Research Institute (KAERI) launched a project to develop an SMR in 1997. Based on numerous preceding studies, the South Korean government decided to develop an integral type pressurized water reactor (PWR) with a rated thermal power of 330MWt (electric power of 100MWe). This reactor is called the System-Integrated Modular Advanced Reactor (SMART).

The SMART project was a part of the Republic of Korea's ambitious plan to foster the nuclear power industry as one of its new green growth engines. Recently, a consortium led by Korea Electric Power Corporation has been organised. Other participants are Pohang Iron and Steel Company (POSCO), STX Heavy Industry, Daewoo Shipbuilding & Marine Engineering, Daewoo Engineering & Construction, Iljin Energy, and Samchang Co, all of South Korea. The consortium has pledged to contribute KRW100 billion (about $83 million) to complete SMART design work. KEPCO group companies will take up a total of 51% equity participation in the consortium, with companies from the POSCO group taking up 28% and other companies taking smaller shares.

The SMART reactor is characterized by enhanced safety and its capability to undertake diverse functions—electricity generation, seawater desalination and district heating. One SMART reactor can supply power and water to a city with a population of 100,000.

Reactor design

The main data for the SMART reactor is shown in Table 1, below. A schematic of the nuclear steam supply system (NSSS) is shown below. One defining characteristic of SMART is its integral layout. The single reactor pressure vessel contains all primary components such as the reactor core, steam generators, reactor coolant pumps and a pressurizer. This integral arrangement of the reactor vessel assembly makes it possible to remove the large-size pipe connections between major components, thus essentially preventing the occurrence of large break loss of coolant accidents. The in-vessel pressurizer is designed to control the system pressure at a nearly constant level over the entire range of design basis events.

In addition, another important design feature in SMART is the introduction of simplified and improved safety systems. SMART employs passive safety systems such as a passive residual heat removal system (PRHRS) to accomplish the inherent safety functions and mitigate the consequences of postulated accidents. The PRHRS prevents overheating and over-pressurization of the primary system in case of emergency events by removing the core decay heat through only natural circulation.

The low power density design with a slightly enriched (less than 5 weight percent) UO2-fuelled core has proven to provide a thermal margin of higher than 15% to accommodate any anticipated transients with regard to the critical heat flux.

This feature ensures core thermal reliability under normal operation. Reactivity control during normal operation is achieved by soluble boron and control rods. Burnable poison rods are introduced for flat radial and axial power profiles, which results in an increased thermal margin of the core. The nearly constant reactor coolant average temperature programme in the reactor regulating system improves load follow operation performance in view of a stable pressure and water level within the pressurizer.

The once-through steam generator cassette consists of helically-coiled heat transfer tubes to produce superheated steam at 300 degrees Celsius in normal operating conditions. The small inventory of the steam generator secondary side water prohibits the water’s return-to-power following a steam line break accident.

Other improved design features include the canned motor reactor coolant pump, which has no pump seals, thus preventing loss of coolant associated with pump seal failure. Four channel control rod position indicators contribute to the simplification of the core protection system and to the enhancement of the system reliability.

Furthermore, an advanced man-machine interface system using digital techniques and equipment reduces human error factors and consequently improves plant reliability.

Engineered safety systems that are designed to function automatically on demand consist of a reactor shutdown system, a safety injection system, a passive residual heat removal system, a shutdown cooling system and a containment spray system. Additional safety systems include a reactor overpressure protection system and a severe-accident mitigation system. Under any circumstances, the reactor can be shut down by inserting control rods or injecting boron.

The core is maintained undamaged for 72 hours without any corrective actions by the operator. The reactor overpressure at any design basis event can be reduced through the opening of the pressurizer safety valve.

Preliminary safety analyses of the SMART show that the reactor remains in a safe condition for all design basis events. Detailed safety analyses are being carried out in the course of development of a standard design.

A small-sized reactor is known to be economically less competitive than a large-capacity commercial power reactor, but the aforementioned simplified features contribute to the reduction of construction costs.

International interest

At present, a pre-application review is being carried out. Preparations are under way to apply for the standard design approval from the South Korean licensing authority. In addition, developers are currently working on experimental verification of SMART technology. Their goal is to obtain design approval by the end of 2011. For this goal, they intend to complete documentation needed for the approval application by the end of 2010. To achieve this target, major players of the South Korean nuclear industry, including Korea Power Engineering Company, Korea Nuclear Fuel, and Doosan Heavy Industries are working together with KAERI.

Once they have the design approval, the promoters of the SMART project will enter the budding global small nuclear reactor market. Several countries have already expressed keen interest in SMART plants. For instance, Kazakhstan has agreed with the South Korean government to undertake a joint safety study on the SMART as part of its programme to introduce nuclear power generation. The country's electricity grids are divided into three regions, and the western and northern regions suffer from an electricity shortfall. International cooperative work is underway to produce mutual benefits and the SMART developers are sure that it is the best localization approach for the development of an advanced nuclear reactor system.

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Table 1: SMART main data

Reactor type: Integral PWR

Thermal power (MWt): 330

Electric power (MWe): 100

Desalination (ton/day): 40,000

Design life (years): 60

Fuel and reactor core:

Assembly type: 17x17 square FA

Fuel material: UO2

Maximum enrichment (wt%): 5%

Active core length (m): 2.0

Refuelling cycle (months): 36

Reactor coolant system

Design pressure (MPa): 17

Operating pressure (MPa): 15

Design temperature (C): 360

Core outlet temperature (C): 323

Core inlet temperature (C): 296

Minimum flow rate (kg/s): 2090

SMART reactor SMART reactor

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