MAJOR TECHNICAL PARAMETERS
Parameter Value
Technology developer, country of origin
Holtec International,United States of America (Holtec)
Reactor type PWR
Coolant/moderator Light water / light water Thermal/electrical capacity,
MW(t)/MW(e)
525 / 160
Primary circulation Natural circulation NSSS Operating Pressure
(primary/secondary), MPa
15.5 / 3.4 Core Inlet/Outlet Coolant
Temperature (oC)
229 / 321
Fuel type/assembly array UO2 pellet / square array Number of fuel assemblies in
the core
57
Fuel enrichment (%) 4.95 (maximum) Core Discharge Burnup
(GWd/ton)
45 (maximum, initial design) Refuelling Cycle (months) 24 nominal (flexible)
Reactivity control mechanism Control rods and soluble boron Approach to safety systems Fully Passive; utilize varied
phenomena and redundancy.
Design life (years) 80
Plant footprint (m2) 20 500 RPV height/diameter (m) 15 / 3
RPV weight (metric ton) 295 (with fuel and internals) Seismic Design (SSE) 0.3g, derived from the NRC
Regulatory Guide 1.60 Fuel cycle requirements /
Approach
Approximately 1/3 batch fraction removed each refuelling outage Distinguishing features Defence-in-Depth with passive safety cooling systems and active non-safety systems; critical components below grade.
Design status Development for a Preliminary Safety Analysis report. in support of commercial project and pre- licensing engagements.
Completed Phase 1 of vendor design review with CNSC in Canada.
1. Introduction
The SMR-160 has been developed by Holtec International as an advanced PWR small modular reactor producing 525 MW thermal power or 160 MW electric power. The plant design incorporates robust passive safety systems to achieve a highly reliable design that protects owner’s investment from all postulated accidents, sabotage, or inadvertent human actions. The SMR-160 design is ‘walk-away safe’ – no operator actions are necessary to cope with design basis accidents and safely reject decay heat. The plant is greatly simplified relative to conventional plants to improve its fabricability, constructability, and maintainability, in part, facilitated by incorporating entirely passive safety systems and a natural circulation primary loop. A modular construction plan for the SMR-160 involves fabrication of the largest shippable components prior to arrival at a site. A 24-month construction period is envisaged for each Nth-of-a-kind unit.
SMR-160 (Holtec International, United
2. Target Application
The primary application of SMR-160 is electricity production with optional cogeneration equipment (i.e., hydrogen generation, district heating, and seawater desalination). The design is readily configurable for siting in water scarce locations using Holtec International’s air-cooled condenser technology. The SMR-160 is capable of both “black-start” and isolated operation, rendering the plant ideal for destinations with unstable power grids or off-grid applications.
3. Main Design Features
Design PhilosophyThe SMR-160 design philosophy is driven by the principal criterion of achieving unparalleled safety without reliance on active systems or operator actions during design basis accidents, while ensuring the SMR-160 design remains inherently securable, fabricable, constructible, and economically competitive in world-wide markets.
Nuclear Steam Supply System
The SMR-160 is a pressurized water reactor with a naturally circulating reactor coolant system (RCS) primary loop. The RCS is comprised of the reactor pressure vessel (RPV) and a steam generator (SG) in an offset configuration with an integrated pressurizer flanged to the top of the steam generator. The RPV and the SG are connected by a single connection which contains both the hot leg and the cold leg in concentric ducts. Unique among integral PWRs, the offset configuration allows easy access to the core without moving the RPV or SG during refuelling. Due to the high SG superheat there is no need for a moisture separator reheater (MSR) or multiple trains of feedwater heaters. The secondary loop eliminates high-pressure turbine stages.
Reactor Core
The SMR-160 employs an efficient reactor core design that uses a traditional reload shuffle. The reactor core contains standard length 17x17 PWR fuel assemblies just like those currently available from several commercial suppliers, along with typical control rod assemblies. An owner can be assured of a diverse supply chain for critical reactor components like fuel, rod cluster control assemblies, and control rod drive mechanisms. The reactor vessel internals support the reactor core, the control rod assemblies, and the control rod drive shafts within the RPV. The core is designed for a nominal two-year cycle with flexibility for shorter or longer cycles depending upon utility requirements. The SMR-160 core is based on proven PWR technology and operational characteristics and is designed to ensure large margin to thermal-mechanical fuel limits.
Reactivity Control
Long term reactivity control is provided by burnable absorbers integral to the fuel which are designed to optimize 3D power distributions, cold shutdown margin, and hot excess reactivity. Short term changes in reactivity are controlled by adjusting soluble boron and movements of control rod assemblies (CRAs). CRAs are positioned by control rod drive mechanisms (CRDM) based on existing electro-mechanical technology.
The CRDMs are located outside the reactor coolant system on the RPV upper head.
Reactor Pressure Vessel and Internals
The RPV is an ASME Section III, Class 1, thick-walled cylindrical pressure vessel with an integrally welded bottom head and a removable top head. The upper extremity of the RPV shell is equipped with a tapered hub flange, which is bolted to a similar flange welded to the top head. The offset configuration of the SG and RPV enables the use of traditional external control rod drive mechanism and greatly simplifies refuelling operations relative to typical integral PWR designs. There are no penetrations to the RPV below the elevation of the safety injection lines. The reactor internal structures are designed to be supported from the bottom of the vessel and are completely replaceable.
Reactor Coolant System
The SMR-160 RCS operates purely by natural circulation, as reactor coolant circulates entirely as a result of the density difference in the primary water and the height of the RPV and steam generator. This ability to circulate is present as long as the fuel assemblies in the core produce heat. There are no reactor coolant pumps in the system. The RCS consists of three major components as shown in the figure above, a Reactor Pressure Vessel (RPV), a Steam Generator (SG), and an integral Pressurizer.
Steam Generator
The SMR-160 includes a single, vertically oriented, once through straight tube SG with the reactor coolant SMR-160 Containment Internals
flowing inside thermally treated Inconel 690 tubes. The use of straight tubes ensures easy access for in-service inspection. The SG uses sub-cooled feedwater to produce superheated steam on the shell side. The SG features a large inventory of secondary water on the shell side which provides substantial margin to dry-out.
Pressurizer
The pressurizer is integral to the steam generator and uses heaters and cold-water spray nozzles to perform the functions of a typical pressurizer. Integrating the pressurizer with the steam generator eliminates significant primary piping, along with the typical supporting structures normally connecting the primary external loop of a PWR to an external pressurizer and reactor coolant pumps. The large relative size of the Pressurizer eliminates any need for Power Operated Relief Valves (PORVs).
4. Safety Features
The SMR-160 safety basis incorporates defence-in-depth via multiple and varied pathways for rejection of decay heat. All safety systems are located inside the robust containment enclosure structure, rendering them secure and safe from external threats. All makeup water needed for a postulated loss of coolant accident (LOCA) is inside containment making the containment isolable during a LOCA reducing possible dose to the public and effects on the environment. Another large inventory of water within a reservoir between the containment enclosure structure and the containment structure provides long-term post-accident coping and allows the decay heat removal function to transition to air cooling for an unlimited coping period after a design basis accident.
Engineered Safety System Approach and Configuration
SMR-160 relies on passive and redundant safety systems that also operate by natural circulation. The passive safety systems ensure safe shutdown can be maintained and decay heat removal occurs for an unlimited period without the need for power, make-up water, or operator actions. If available, active non-safety systems can be used by operators to mitigate events and preclude the need for using the engineered safety systems. This approach ensures that the plant achieves ultimate safety while simultaneously ensuring recovery of the plant after an event.
Passive Core Cooling System (PCCS)
The PCCS is designed to provide emergency core cooling and makeup to the RCS during postulated accidents.
The system uses passive means such as natural circulation for core cooling and compressed gas expansion and gravity injection for core makeup without the use of active components such as pumps. The PCCS is comprised of four major subsystems:
- Primary decay heat removal system (PDHR) - Secondary decay heat removal system (SDHR) - Automatic depressurization system (ADS) - Passive core make-up water system (PCMWS)
The PDHR directly cools the primary coolant by re-routing the reactor coolant through a heat exchanger and rejecting the heat to a second loop full of water. The second loop rejects its heat to the large annular reservoir (AR) around containment. The SDHR provides an alternative passive means to reject decay heat. The SDHR is a closed loop system that relies on buoyancy driven flow to route steam from the SG to a heat exchanger in the AR, where the steam then condenses and rejects its latent heat. Condensate is then returned to the shell side of the SG. The ADS is a depressurization system designed to safely let down RCS pressure to the sealed containment to permit staged safety injection by the PCMWS and permit long-term recirculation within the containment vessel.
Containment and the Passive Containment Heat Removal System (PCHR)
The SMR-160 containment system consists of a steel containment structure (CS), enclosed within a reinforced concrete containment enclosure structure (CES). The CES provides shielding and protection from external events. The CES walls are constructed of extremely robust steel-concrete modules designed to withstand an impact from large commercial aircraft and other potential hazards. In addition to preventing the release of radioactive fission products to the environment, the containment system acts as a large passive heat exchanger.
The containment system is partially embedded, with approximately half of the total height located below grade to maximize protection against external hazards and dampen seismic effects for critical components.
The PCHR passively cools the containment volume, without any required actuations. During a postulated high energy release, steam rejects heat to the inner wall of the containment, condensing as heat is transported to the AR. The large heat transfer area and high conductance of the metal containment wall results in near- instantaneous heat rejection to the AR. The AR then rejects heat to the environment.
5. Plant Safety and Operational Performances
The SMR-160 natural convection-driven reactor coolant loop is coupled with an optimized simple steam cycle and is well adapted to load following. Refuelling operations take advantage of industry operational experience to limit the required number of heavy lifts, use traditional core shuffling techniques, and incorporate all necessary inspections and maintenance.
6. Instrumentation and Control Systems
SMR-160 utilizes the Mitsubishi Electric Total Advanced Controller (MELTAC) platform for the plant I&C/HSI design. MELTAC is a proven technology, with over 300 reactor-years of operating experience.
MELTAC provides unique nuclear specific I/O and configuration flexibility to perform all nuclear safety and non-safety functions using the same digital platform.
7. Plant Layout Arrangement
Containment Enclosure StructureThe SMR-160 reactor is housed within a containment structure (CS) protected by a containment enclosure structure (CES). Nearly half of the CS and CES is embedded underground. These structures house all safety systems and the spent fuel pool and share a common basemat with the reactor auxiliary building.
Reactor Auxiliary Building
The reactor auxiliary building houses many of the plant auxiliary systems. It contains the new fuel and dry fuel storage handling facilities as well as the control room complex. This building is designed to process spent fuel for dry interim on-site storage within Holtec International HI STORM UMAX modules (an underground dry cask storage technology), without any modification to the standard plant design.
Balance of Plant
The steam turbine and associated systems are housed within the turbine building structure at grade level. The SMR 160 features an axial/side exhaust steam turbine, optionally configured for air cooled condensation.
SMR-160 is also adaptable to process applications such as desalination and district heating. The SMR-160 electric power system consists of the main generator, main transformer, auxiliary transformers, non-safety diesel generators and Class 1E batteries. The power supply to the plant AC power system during normal plant operation is provided from the main generator. The electrical system is designed to permit isolated operation in “island-mode” as well as start-up operations independent of the grid or “black-start.”
8. Design and Licensing Status
Pre-application activities for the SMR-160 have commenced with multiple international regulators in parallel with development of commercial project opportunities. The project execution plan projects initial operation of the first deployed reactors by the mid-2020s.
9. Fuel Cycle Approach
The SMR-160 fuel cycle is designed to discharge approximately one third of the fuel assemblies in the core each refuelling cycle, along with shuffling of a portion of the remaining fuel assemblies. The spent fuel is stored briefly in the spent fuel pool, which is uniquely protected within the same containment as the reactor.
New fuel assemblies are delivered using Holtec International’s HI-STORM system, which has decades of operating experience throughout the global light water reactor fleet. This allows the SMR-160 to eliminate significant complex handling equipment. The HI-STORM system has received multiple licensing approvals from the U.S. Nuclear Regulatory Commission.
10. Waste Management and Disposal Plan
High level waste management and disposal for the SMR-160 uniquely benefits from the integration of Holtec International’s dry storage technologies. After removal of spent fuel from the spent fuel pool within a Multi- Purpose Canister called an MPC-37, all spent fuel for the life of the plant can be stored on-site within an array of HI-STORM UMAX modules (an underground vertical storage cask design). The MPC-37 is a dual-purpose canister licensed for transportation off-site within the HI-STAR 190 transportation overpack.
11. Development Milestones
2012 Conceptual design of SMR-160 commencement 2015 Conceptual design completed for SMR-160 2020 Preliminary design completed for SMR-160
2021 Ready for commercialization using a construction permit based process
Plant Layout of SMR-160
MAJOR TECHNICAL PARAMETERS
Parameter Value
Technology developer, country of origin
Westinghouse Electric Company LLC, USA
Reactor type Integral PWR
Coolant/moderator Light water Thermal/electrical capacity,
MW(t)/MW(e)
800 / >225 Primary circulation Forced circulation NSSS Operating Pressure
(primary/secondary), MPa
15.5 Core Inlet/Outlet Coolant
Temperature (oC)
294 / 324
Fuel type/assembly array UO2 pellet/17x17 square Number of fuel assemblies in
the core
89 Fuel enrichment (%) < 5 Core Discharge Burnup
(GWd/ton)
> 62 Refuelling Cycle (months) 24
Reactivity control mechanism CRDM, boron Approach to safety systems Passive
Design life (years) 60
Plant footprint (m2) 65 000 RPV height/diameter (m) 28 / 3.7
Seismic Design (SSE) Based on CEUS sites Distinguishing features Incorporates passive safety
systems and proven components of the AP1000 plant and earlier Westinghouse designs
Design status Concept design completed
1. Introduction
The Westinghouse small modular reactor (SMR) is an integral pressurized water reactor (PWR) design that builds upon the concepts of simplicity and advanced passive safety demonstrated in the AP1000® plant. The power station delivers a thermal output of 800 MW(t) and a net electrical output of greater than 225 MW(e) as a standalone unit, completely self-contained within a compact plant site. The entire plant is designed for modular construction with all components shippable by rail, truck, or barge.
2. Target Application
The target application is the clean and safe generation of electricity; however, the Westinghouse SMR can also be used to provide process heat, district heat, and off-grid applications, including the generation of power necessary to produce liquid transportation fuel from oil sands, oil shale, and coal-to-liquid applications.
3. Main Design Features
Design PhilosophyDesign of the Westinghouse SMR utilizes passive safety systems and proven components – realized in the AP1000 plant reactor design and earlier Westinghouse designs – to achieve the highest level of safety, resiliency, and certainty in licensing, construction, and operations. The Westinghouse SMR is designed to be 100 percent modular and limits the size of primary components in order to enable unrestricted transportation, which reduces the need for costly infrastructure and increases the number of possible sites.