MAJOR TECHNICAL PARAMETERS
Parameter Value
Technology developer, country of origin
Mitsubishi Heavy Industries, Ltd. (MHI), Japan
Reactor type Integral PWR
Coolant/moderator Light water / light water Thermal/electrical capacity,
MW(t)/MW(e)
1000 / 350 Primary circulation Natural circulation NSSS Operating Pressure
(primary/secondary), MPa
15.5 / 5.0 Core Inlet/Outlet Coolant
Temperature (oC)
329 / 345
Fuel type/assembly array UO2 pellet / 21x21 square Number of fuel assemblies
in the core
97
Fuel enrichment (%) 4.8
Core Discharge Burnup (GWd/ton) > 40 Refuelling Cycle (months) 26
Reactivity control mechanism Control rods drive mechanism Approach to safety systems Hybrid (Passive + Active)
system
Design life (years) 60
Plant footprint (m2) 4900 RPV height/diameter (m) 17 / 6 RPV weight (metric ton) --
Seismic Design (SSE) 0.3g
Fuel cycle requirements / Approach Similar to existing PWR plants Distinguishing features Integral PWR with natural
circulation; employs two types of in-vessel steam generator
Design status Conceptual design completed
1. Introduction
The Integrated Modular Water Reactor (IMR) is a medium sized power reactor with a reference thermal output of 1000 MW(t) producing an electrical output of 350 MW(e). The IMR is developed for potential deployment after 2025. IMR employs the hybrid heat transport system (HHTS), a natural circulation system for the primary heat transport. The in-vessel control rod drive mechanism (CRDM) is the primary means of reactivity control.
These design features allow the elimination of the emergency core cooling system (ECCS).
2. Target Application
The IMR is primarily designed as a land-based modular power station to generate electricity. Because of its modular characteristics, it is suitable for large-scale power stations consisting of several modules and also for small distributed-power stations, especially for small grids. IMR can also be used for cogeneration of electricity and district heating, seawater desalination, process steam production and so forth. IMR adopts structures, systems and components that require no large-scale infrastructure. This facilitates regulatory authority’s approval for the construction and operation of power plant.
3. Main Design Features
Design PhilosophyThe IMR is an integral PWR where the primary system components are installed within the reactor pressure vessel (RPV). Main coolant piping and primary coolant pumps are eliminated by adopting natural circulation
system. Pressurizer is eliminated by adopting the self-pressurization system. There are two types of steam generator (SG) inside the RPV; The first type is located in the vapour/upper region of the RPV and the other is located in the liquid/lower region of the RPV. These SGs are also used as decay heat removal heat exchangers during normal startup and shutdown operations and in accidents. Hence to eliminate the need of ECCS, the SGs serve as a passive safety system that do not require any external power. The IMR has a moderation ratio similar to the operating PWRs. Thus, its properties of fresh and spent fuel are similar. This allows for conventional safeguards measures and PWR management practices for new and spent fuel. Support systems, such as the component cooling water system, the essential service water system and the emergency AC power system, are designed as non-safety grade systems, made possible by use of a stand-alone diesel generator.
Nuclear Steam Supply System
The HHTS is employed to transport the fission energy released in the fuel to the SGs by both vapour formation and liquid temperature rise. The energy transported by vapour produces secondary steam in SGV, and the energy transported by liquid temperature rise produces secondary steam in SGL. The SGV also has a function of primary system pressure control, and the SGL has the function of core power control through the core inlet temperature by controlling the feedwater flow rate.
Reactor Core
The IMR core consists of 97 fuel assemblies in 21×21 array with an average enrichment of 4.95 % and produces an output of 1000 MW(t). The refuelling interval is 26 effective full-power months. The power density is about 40% of current PWRs but the fuel lifetime is 6.5 years longer, so that an average discharged burnup of 46 GWd/ton can be attained, which is approximately the same as in current PWRs. The cladding material is Zr–
Nb alloy to assure integrity at a temperature of 345°C and over the long reactor lifetime. To maintain the core thermal margin and to achieve a long fuel cycle, the core power density is reduced to one-third of that conventional PWRs. The design-refuelling interval is three (3) years in three (3) batches of fuel replacement.
The fuel rod design is the same as that for a conventional PWR.
Reactivity Control
The chemical shim reactivity control is not used in the IMR, rather both control rods that contain enriched 10B and burnable absorbers control the whole reactivity. Control rods with 90 wt% enriched B4C neutron absorber perform the reactivity control, and a soluble acid boron system is used for the backup reactor shutdown to avoid corrosion of structural materials by boric acid. The hydrogen to uranium ratio (H:U) is set to five, which is larger than in conventional PWRs, to reduce the pressure drop in the primary circuit. The coolant boils in the upper part of the core and the core outlet void fraction is less than 20% locally and less than 40% in the core to keep bubbly flow conditions. To reduce axial power peaking caused by coolant boiling, the fuel consists of two parts: the upper part with higher enrichment and the lower part with lower enrichment. Additionally, hollow annular pellets are used in the upper part of the fuel to reduce axial differences in burnup rate. Two types of in-vessel CRDMs are adopted. One is motor driven CRDM for the control bank. This CRDM has the function of controlling reactivity during operation by finely stepping the control rod position. The other is the hydraulic type CRDM. This CRDM has the scram function and applies to the shut-down bank. The control rods connected to this CRDM are moved by hydraulic force from the bottom position to the top, and then held by electro-magnetic force. When the scram signal is initiated, the control rods are released and inserted into the core by gravity by turning off the power to the CRDM.
Reactor Pressure Vessel and Internals
The upper part of the RPV inside diameter is about 6 m in order to accommodate the in-vessel SGs. The inside diameter of the lower part of the RPV is reduced to about 4 m in order to minimize the cold-side water volume.
In order to eliminate the necessity for the consideration of LOCA, the largest diameter nozzle connected to the RPV is reduced to less than 10 mm. In addition, the lowest location of the nozzle is above the core to improve the reliability of the RPV. The core is located in the bottom of the RPV and the SGs are located in the upper part of the RPV. Control rod guide assemblies are located above the core and a riser is set above the control rod guide assemblies to enhance the natural circulation.
Reactor Coolant System
In the HHTS, IMR employs natural circulation and a self-pressurized primary coolant system, altogether resulting in a simple primary system design without reactor coolant pumps and pressurizer, it also reduces maintenance requirements. The HHTS reduces the size of RPV. The coolant starts boiling in the upper part of the core, and two-phase coolant in bubbly flow flows up in the riser and condenses in the SGs. This design approach increases coolant flow rate and thus reduces the height of RPV to transport the heat from the core.
The IMR primary cooling system design under bubbly flow makes it easy to employ PWR design technologies.
Steam Generator
The IMR adopts two types of SG. The first one is the SG in vapour region (SGV) located above the water level in the RPV. The energy transported by vapour formation generates secondary steam through SGV. As the vapour in the RPV is condensed by SGV, controlling the feedwater flow rate to SGV controls the RPV pressure. The other is the steam generator in liquid region (SGL) of the RPV. The energy transported by liquid
temperature rise generates secondary steam through SGL. Because the core inlet temperature can be controlled by the amount of heat removal through SGL, the core power can be controlled by feedwater flow rate to SGL.
By this method, the movement of the control rods for controlling reactor power will be minimized. For SGL, a U-type tube bundle is adopted, since it is necessary to minimize pressure drops on both the primary and secondary sides to maintain good natural circulation performance. A C-type steam generator is adopted for SGV to optimize space utilization in the vapour part of the RPV.
Pressurizer
The physical pressurizer vessel is eliminated by adopting the self-pressurization system.
4. Safety Features
Engineered Safety System Approach and Configuration
By adopting an integral type primary system, accidents that may cause fuel failure, such as loss of coolant accidents (LOCA), rod ejection (R/E), loss-of-flow (LOF) and locked rotor (L/R), are eliminated in IMR. Since the diameter of the pipes connected to the RPV is limited to less than 10 mm, the water level in the RPV can be maintained at normal levels by water injection from the charging pumps. There are two trains of the SDHS.
If a malfunction such as SG tube leakage occurs, system functions are maintained. The capacity of chemical and volume control system (CVCS) is provided via eight 3-inch pipes connected to the RPV. No ECCS and containment cooling/spray systems are required in IMR. Safety injection systems are eliminated by adopting the SDHS and by limiting the nozzle diameter connected to the primary system. Hence, containment spray system is also eliminated. The auxiliary feedwater system is used for startup and shutdown procedures during normal operation. The auxiliary feedwater system is not a safety system. When the auxiliary feedwater system becomes unavailable, the SDHS is actuated. The IMR adopts simplified support systems, such as the component cooling water system (CCWS), the essential service water system (ESWS) and the emergency AC power system. These are designed as non-safety grade systems powered by a stand-alone diesel generator.
Decay Heat Removal System
The SDHS is activated to remove the decay heat from the RPV to the atmosphere. Even if water leakage occurs and the charging pumps fails to operate, water leakage would be terminated automatically when the pressures inside and outside the RPV are equalized. In the passive steam generator cooler (PSGC), decay heat is removed by water-cooling in the early stage of the accident and then, the heat transfer mode is gradually replaced by air-cooling. Therefore, water, power and operators are not necessary for maintaining the plant safety.
Containment System
A compact containment vessel (CV) is made possible due to the integrated primary system and simplified auxiliary systems. The IMR uses reinforced concrete containment. A higher design pressure of the containment is to meet the safety requirement that water leakage from RPV shall be terminated automatically. Since this
CV is about one size larger than the RPV, it is expected to resist high pressure. The reactor containment facility is part of the engineered safety systems, which include SDHS. The containment system is designed to suppress or prevent the possible dispersion of large quantities of radioactive materials.
5. Plant Safety and Operational Performances
The IMR is designed to operate automatically within the range of 20 to 100 % of rated output power by the reactor control system. Even in the low output range below 20%, the control system can control the reactor automatically in the low power-operating mode. The primary system pressure and reactor power are controlled by feedwater and control rods.
6. Instrumentation and Control Systems
The instrumentation and control (I&C) systems provide the capability to control and regulate the plant systems manually and automatically during normal plant operation and provide reactor protection against unsafe plant operation. Fully digitalized I&C system including computerized control board for plant operator are provided with the required conventional system.
7. Plant Layout Arrangement
The IMR concepts of building layout are reducing the bill of quantity for construction material, shortening the construction period and standardizing the plant design. Utilizing the steel plate reinforced concrete and simplify the shape of building and structures achieve the construction cost and period reduction.
Reactor Building
Ground level is assumed to be flat land above sea level. The bedrock is assumed to be less than 40 m below ground to enable the use of pile foundations. The integrated reactor building can house two units. Exclusion of waste disposal facilities in another building.
Balance of Plant
The advanced BOP system allows the utilization of produced heat for non-electrical applications such as process heat, mining (oil sand extraction) and desalination. The turbine generator, turbine, condenser, moisture separator and reheater (MSR) and their auxiliary equipment are installed in the turbine building. The turbine generator is arranged with its axis in line with the reactor.
8. Design and Licensing Status
The IMR conceptual design study was initiated in 1999 by MHI. A group led by MHI including Kyoto University, the Central Research Institute of the Electric Power Industry and the Japan Atomic Power Company developed related key technologies through two projects, funded by the Japanese Ministry of Economy, Trade and Industry (2001–2004 and 2005–2007). Validation testing, research and development for components and design methods, and basic design development are required before licensing.
9. Fuel Cycle Approach
The IMR fuel cycle approach including spent fuel management is in line with the approach for the existing PWR plants. It leads the minor design modification for existing fuel cycle facilities, and the IMR approach is accepted by public without discomfort.
10. Waste Management and Disposal Plan
The IMR waste management and disposal plan is in line with the existing PWR plants concept. The IMR approach is accepted by public without discomfort.
11. Development Milestones
1999 MHI started conceptual design study for IMR.
2001-2004 An industry-university group led by MHI, including Kyoto University, Central Research Institute of Electric Power Industries (CRIEPI), the Japan Atomic Power Company (JAPC), and MHI were developing related key technologies through two projects, funded by the Japan Ministry of Economy, Trade and Industry. In the first project, the feasibility of the HHTS concept was tested through experiments.
2005-2007 In the second project, the thermal-hydraulic data under natural circulation conditions for the HHTS design were obtained by four series of simulation tests using alternate fluids.
2009-2011 Startup transient tests to verify the startup flow instability were studied
2019 MHI is developing a new Small Reactor based on the IMR experiences with funding support by the Ministry of Economy, Trade and Industry.
MAJOR TECHNICAL PARAMETERS
Parameter Value
Technology developer, country of origin)
KAERI, Republic of Korea and K.A.CARE, Kingdom of Saudi Arabia
Reactor type Integral PWR
Coolant/moderator Light water / light water Thermal/electrical capacity,
MW(t)/MW(e)
365 / 107 Primary circulation Forced circulation NSSS Operating Pressure
(primary/secondary), MPa
15 / 5.8 Core Inlet/Outlet Coolant
Temperature (oC)
296 / 322
Fuel type/assembly array UO2 pellet / 17x17 square Number of fuel assemblies
in the core
57 Fuel enrichment (%) < 5 Core Discharge Burnup
(GWd/ton)
< 54 Refuelling Cycle (months) 30
Reactivity control mechanism Control rod driving mechanisms and soluble boron
Approach to safety systems Passive
Design life (years) 60
Plant footprint (m2) 90 000 RPV height/diameter (m) 18.5 / 6.5
RPV weight (metric ton) 1070 (including coolant) Seismic Design (SSE) > 0.3g with 0.18g of automatic
shutdown Fuel cycle requirements /
Approach
Conventional LWR requirements applied (spent fuel capacity: 30 years) Distinguishing features Coupling with desalination and
process heat application, integrated primary system
Design status Licensed/certified (standard design approval)
1. Introduction
The System-integrated modular advanced reactor (SMART) is an integral PWR with a rated electrical power of 107 MW(e) from 365 MW(t). SMART adopts advanced design features to enhance safety, reliability and economics. The advanced design features and technologies implemented in SMART were verified and validated during the standard design approval review. To enhance safety and reliability, the design configuration incorporates inherent safety features and passive safety systems. The design aim is to achieve improvement in economics through system simplification, component modularization, reduction of construction time and high plant availability.
2. Target Application
SMART is a multi-purpose application reactor for electricity production, sea water desalination, district heating, process heat for industries and suitable for small or isolated grids. SMART has a unit output large enough to meet the demands of electricity and fresh water for a city population of 100 000.