Small modular reactor

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https://en.wikipedia.org/wiki/Small_modular_reactor 

 

Illustration of a light water small modular nuclear reactor (SMR)

Small modular reactors (SMRs) are a type of nuclear fission reactor which are smaller than conventional reactors. This allows them to be manufactured at a plant and brought to a site to be assembled. Modular reactors allow for less on-site construction, increased containment efficiency, and enhanced safety due to passive nuclear safety features. SMRs have been proposed as a way to bypass financial and safety barriers that have inhibited the construction of large conventional nuclear reactors in recent decades.

Several designs exist for SMR, ranging from scaled down versions of existing nuclear reactor designs, to entirely new generation IV designs. Both thermal-neutron reactors and fast-neutron reactors have been proposed, as well as molten salt and gas cooled reactor models.

A main hindrance to the commercial application of SMRs as of 2015 is licensing, since current regulatory regimes are adapted to conventional nuclear power plants and have not been adapted to SMRs in terms of staffing, security etc. Time, cost and risk of the licensing process are critical elements for the construction of SMRs.

Advantages and potential uses

The main advantage of small modular reactors is that they could be manufactured and assembled at a central factory location. They can then be sent to their new location where smaller SMRs can be installed with little difficulty. However, SMR module transportation is critical and needs further studies.

Another advantage of the small reactor is that a user can install their first unit, instantly generating revenue and cash flows, then later add as many other smaller reactors as necessary — cutting back on financing times and saving on long, drawn out construction processes.  

Some larger SMRs require more significant on-site construction, such as the 440 MWe 3-loop Rolls-Royce SMR, which targets a 500-day construction time.

SMRs are particularly useful in remote locations where there is usually a deficiency of trained workers and a higher cost of shipping. Containment is more efficient, and proliferation concerns could be lowered. SMRs are also more flexible in that they do not necessarily need to be hooked into a large power grid, and can generally be attached to other modules to provide increased power supplies if necessary.

The electricity needs in remote locations are usually small and highly variable. Large nuclear power plants are generally rather inflexible in their power generation capabilities. SMRs have a load-following design so that when electricity demands are low they will produce a lower amount of electricity.

Many SMRs are designed to use new fuel ideas that allow for higher burnup and longer fuel cycles. Longer refueling intervals can decrease proliferation risks and lower chances of radiation escaping containment. For reactors in remote areas, accessibility can be troublesome, so longer fuel life can be very helpful.

SMRs could be used to power significant users of energy, such as large vessels or production facilities (e.g. water treatment/purification, or mines). Remote locations often have difficulty finding economically efficient, reliable energy sources. Small nuclear reactors have been considered as solutions to many energy problems in these hard-to-reach places. Cogeneration options are also possible.

Because of the lack of trained personnel available in remote areas, SMRs have to be inherently safe. Many larger plants have active safety features that require "intelligent input", or human controls. Many of these SMRs are being made using passive or inherent safety features. Passive safety features are engineered, but do not require outside input to work. A pressure release valve may have a spring that can be pushed back when the pressure gets too high. Inherent safety features require no engineered moving parts to work. They only depend on physical laws.

Rolls-Royce aims to sell nuclear reactors for the production of synfuel for aircraft.

Operation

A nuclear fission chain is required to generate nuclear power.

There are a variety of different types of SMR. Some are simplified versions of current reactors, others involve entirely new technologies. All current small modular reactors use nuclear fission. When an unstable nucleus (such as ²³⁵
U) absorbs an extra neutron, the atom will split, releasing large quantities of energy in the form of heat and radiation. The split atom will also release neutrons, which can then be absorbed by other unstable nuclei, causing a chain reaction. A sustained fission chain is necessary to generate nuclear power. SMR designs include thermal-neutron reactors and fast-neutron reactors.

Thermal-neutron reactors rely on a moderator to slow neutrons and generally use ²³⁵
U as fissile material. Most currently operating nuclear reactors are of this type. Fast reactors don't use moderators to slow down the neutrons, therefore they rely on the nuclear fuel being able to absorb neutrons travelling at higher speeds. This usually means changing the fuel arrangement within the core, or using different fuel types. ²³⁹
Pu is more likely to absorb a high-speed neutron than ²³⁵
U.

A benefit of fast reactors is that they can be designed to be breeder reactors. As these reactors produce energy, they also let off enough neutrons to transmute non-fissionable elements into fissionable ones. A very common use for a breeder reactor is to surround the core in a "blanket" of ²³⁸

U, which is the most easily found isotope of uranium. Once the ²³⁸
U undergoes a neutron absorption reaction, it becomes ²³⁹
Pu, which can be removed from the reactor once it is time to refuel, and used as more fuel once it has been cleaned.

Cooling

Currently, most reactors use water as a coolant. New reactor designs are experimenting with different coolant types. Liquid metal cooled reactors have been used both in the United States and other countries for some time. Gas cooled reactors and molten salt reactors are also being looked at as an option for very high temperature operation.

Thermal/electrical generation

Traditionally, nuclear reactors use a coolant loop to heat water into steam, and use that steam to run turbines to generate electricity. Some new gas-cooled reactor designs are meant to drive a gas-powered turbine, rather than using a secondary water system. Thermal energy from nuclear reactors can also be used directly, without conversion to electricity. Nuclear reactor heat can be used in hydrogen production and other commercial operations, such as water desalination and the production of petroleum products (extracting oil from tar sands, creating synthetic oil from coal, etc.).

Staffing

Several SMR developers are claiming that their designs will require fewer staff members to run the reactors because of the increased inherent and passive safety systems. Fewer staff members is also a safety risk if plant owners decide to cut corners by assigning even fewer support staff to each reactor. Some of the reactors, like the Toshiba 4S, are reportedly designed to run with little supervision.

Load following

Nuclear power plants have been historically deployed to cover the base load of the electricity demand.

Some nuclear power plants might perform daily load cycling operation (i.e. load following) between 50% and 100% of their rated power. With respect to the insertion of control rods or comparable action to reduce the nuclear power generation, a more efficient alternative might be the “Load Following by Cogeneration”, i.e. diverting the excess of power, respect to the electricity demand, to an auxiliary system. A suitable cogeneration system needs:

1. to have a demand of electricity and/or heat in the region of 500 MWe–1.5 GWt;
2. to meet a significant market demand;
3. to have access to adequate input to process;
4. to be flexible: cogeneration might operate at full load during the night when the request of electricity is low, and be turned off during the daytime.

From the economic standpoint, it is essential that the investment in the auxiliary system is profitable. District heating, desalination and hydrogen have been proposed as technically and economically feasible options. SMR can be ideal to do load following being used for desalination over the night.

Waste reduction

Many SMRs are fast reactors that are designed to have higher fuel burnup rates, reducing the amount of waste produced. At higher neutron energy more fission products can be usually tolerated. As mentioned before, some SMRs are also breeder reactors, which not only "burn" fuels like ²³⁵
U, but will also convert fertile materials like ²³⁸
U (which occurs naturally at a much higher concentration than ²³⁵
U) into usable fuels.

Some reactors are designed to run on the alternative thorium fuel cycle, which offers significantly reduced long-term waste radiotoxicity compared to the uranium cycle.

There has been some interest in the concept of a traveling wave reactor, a new type of breeder reactor that uses the fuel it breeds. The idea would eliminate the need to remove the spent fuel and "clean" it before reusing any newly bred fuel.

Safety

Since there are several different ideas for SMRs, there are many different safety features that can be involved. Coolant systems can use natural circulation – convection – so there are no pumps, no moving parts that could break down, and they keep removing decay heat after the reactor shuts down, so that the core doesn't overheat and melt. Negative temperature coefficients in the moderators and the fuels keep the fission reactions under control, causing the fission reactions to slow down as temperature increases. While passive control is a key selling point, a functioning reactor may also need an active cooling system in case the passive system fails. This addition is expected to increase the cost of implementation. Additionally, SMR designs call for weaker containment structures.

Some SMR designs have underground placement of the reactors and spent-fuel storage pools, which provides more security. Smaller reactors would be easier to upgrade quickly, require a permanent workforce, and have better passive quality controls.

Economics

A key driver of SMRs are the alleged improved economies of scale, compared to larger reactors, that stem from the ability to prefabricate them in a manufacturing plant/factory. Yet, according to some studies, the capital cost of SMRs and larger reactors are practically equivalent. A key disadvantage is that the improved affordability can only be realised if the factory is built in the first place, and this is likely to require initial orders for 40–70 units, which some experts think unlikely.

Another economic advantage of SMR is that the initial cost of building a power plant using SMR is much less than that of constructing a much more complex, non-modular, large nuclear plant. This makes SMR a smaller-risk venture for power companies than other nuclear power plants. However, modularisation and modularity influence the economic competitiveness of SMRs. Financial and economic issues can hinder SMR construction.

However operational staffing costs per unit output increase as reactor size decreases, due to some staffing costs being fixed and lesser economies of scale. For example, a similar number of technical and security staff to a large reactor may be required. For small SMRs staff costs per unit output can be as much as 190% higher than the fixed operating cost of large reactors.

In 2017 an Energy Innovation Reform Project study of eight selected companies looked at reactor models with reactor capacity between 47.5 MWe and 1,648 MWe in development. The study found the advanced reactors had an average capital cost total of $3,782/kW, average operating cost total of $21/MWh and levelized cost of electricity of $60/MWh. However there is no standardized approach to evaluate the economic and financial performance of the latest reactors in development, so it’s difficult to make any comparisons between models and existing infrastructure.

Founder of The Energy Impact Center, Bret Kugelmass, believes thousands of SMRs could be built in parallel, "thus reducing costs associated with long borrowing times for prolonged construction schedules and reducing risk premiums currently linked to large projects." Executive Vice President at GE Hitachi Nuclear Energy, Jon Ball, agreed, saying the modular elements of SMRs will also help reduce costs associated with extended construction times.

Licensing

A major barrier is the licensing process, historically developed for large reactors, preventing the simple deployment of several identical units in different countries. In particular the US Nuclear Regulatory Commission process for licensing has focused mainly on large commercial reactors. The design and safety specifications, staffing requirements and licensing fees have all been geared toward reactors with an electrical output of more than 700MWe.

Licensing for SMRs has been an ongoing discussion. There was a workshop in October 2009 about licensing difficulties and another in June 2010, with a US congressional hearing in May 2010. With growing worries about climate change and greenhouse gas emissions, added to problems with hydrocarbon supplies from foreign countries and accidents like the BP oil rig explosion in the Gulf of Mexico, many US government agencies are working to push the development of different licensing for SMRs. However, some argue that weakening safety regulations to push the development of SMRs may cancel out their enhanced safety characteristics.

The U.S. Advanced Reactor Demonstration Program will help license and build two prototype SMRs during the 2020s, with up to $4 billion of government funding support.

Non-proliferation

Nuclear proliferation, or the use of nuclear materials to create weapons, is a concern for small modular reactors. As SMRs have lower generation capacity and are physically small, they are intended to be deployed in many more locations than existing nuclear plants. This means both at more sites in existing nuclear power states, and in more countries that previously did not have nuclear plants. It is also intended that SMR sites have much lower staffing levels than current nuclear plants. Because of the increased number of sites, with fewer staff, physical protection and security becomes an increased challenge which could increase proliferation risks.

Many SMRs are designed to lessen the danger of materials being stolen or misplaced. Nuclear reactor fuel can be low-enriched uranium, with a concentration of less than 20% of fissile ²³⁵
U. This low quantity, non-weapons-grade uranium makes the fuel less desirable for weapons production. Once the fuel has been irradiated, the fission products mixed with the fissile materials are highly radioactive and require special handling to remove safely, another non-proliferation feature.

Some SMR designs are intended to have lifetime cores so the SMRs do not need refuelling. This improves proliferation resistance by not requiring any on-site nuclear fuel handling. But it also means that there will be large inventories of fissile material within the SMRs to sustain a long lifetime, which could make it a more attractive proliferation target. A 200 MWe 30-year core life light water SMR could contain about 2.5 tonnes of plutonium toward the end of its working life.

Light-water reactors designed to run on the thorium fuel cycle offer increased proliferation resistance compared to conventional uranium cycle, though molten salt reactors have a substantial risk.

The modular construction of SMRs is another useful feature. Because the reactor core is often constructed completely inside a central manufacturing facility, fewer people have access to the fuel before and after irradiation.

Reactor designs

Numerous new reactor designs have been proposed across the world. A small selection of the most notable current SMR designs is listed below.

  Design   Licensing   Under construction   Operational   Cancelled   Retired

List of small nuclear reactor designs

Name	Gross power (MWe)	Type	Producer	Country	Status
4S	10–50	SFR	Toshiba	Japan	Detailed design
ABV-6	6–9	PWR	OKBM Afrikantov	Russia	Detailed design
ACP100	125	PWR	China National Nuclear Corporation	China	Design complete
ARC-100	100	SFR	ARC Nuclear	Canada	Design: Vendor design review. One unit approved for construction at Point Lepreau Nuclear Generating Station in December 2019.
ANGSTREM	6	LFR	OKB Gidropress	Russia	Conceptual design
B&W mPower	195	PWR	Babcock & Wilcox	United States	Cancelled in March 2017
BANDI-60	60	PWR (floating)	KEPCO	South Korea	Detailed design
BREST-OD-300	300	LFR	Atomenergoprom	Russia	Under construction
BWRX-300	300	ABWR	GE Hitachi Nuclear Energy	United States	Licensing stage
CAREM	27–30	PWR	CNEA	Argentina	Under construction
Copenhagen Atomics Waste Burner	50	MSR	Copenhagen Atomics	Denmark	Conceptual design
CMSR	100	MSR	Seaborg Technologies	Denmark	Conceptual design
EGP-6	11	RBMK	IPPE & Teploelektroproekt Design	Russia	Operating (not actively marketed due to legacy design, will be taken out of operation permanently in 2021)
ELENA	0.068	PWR	Kurchatov Institute	Russia	Conceptual design
Energy Well	8.4	MSR	cs:Centrum výzkumu Řež	Czechia	Conceptual design
Flexblue	160	PWR	Areva TA / DCNS group	France	Conceptual design
Fuji MSR	200	MSR	International Thorium Molten Salt Forum (ITMSF)	Japan	Conceptual design
GT-MHR	285	HTGR	OKBM Afrikantov	Russia	Conceptual design completed
G4M	25	LFR	Gen4 Energy	United States	Conceptual design
IMSR400	185–192	MSR	Terrestrial Energy	Canada	Conceptual design
TMSR-500	500	MSR	ThorCon	Indonesia	Conceptual design
IRIS	335	PWR	Westinghouse-led	international	Design (Basic)
KLT-40S	35	PWR	OKBM Afrikantov	Russia	Operating
MHR-100	25–87	HTGR	OKBM Afrikantov	Russia	Conceptual design
MHR-T	205.5x4	HTGR	OKBM Afrikantov	Russia	Conceptual design
MRX	30–100	PWR	JAERI	Japan	Conceptual design
NP-300	100–300	PWR	Areva TA	France	Conceptual design
NuScale	60	PWR	NuScale Power LLC	United States	Licensing stage
Nuward	300–400	PWR	consortium	France	Conceptual design, construction anticipated in 2030
PBMR-400	165	HTGR	Eskom	South Africa	Cancelled. Postponed indefinitely
RITM-200	50	PWR	OKBM Afrikantov	Russia	Operational since October 2019
Rolls-Royce SMR	440	PWR	Rolls-Royce	United Kingdom	Design stage
SMART	100	PWR	KAERI	South Korea	Licensed
SMR-160	160	PWR	Holtec International	United States	Conceptual design
SVBR-100[65][66]	100	LFR	OKB Gidropress	Russia	Detailed design
SSR-W	300–1000	MSR	Moltex Energy	United Kingdom	Conceptual design
S-PRISM	311	FBR	GE Hitachi Nuclear Energy	United States/Japan	Detailed design
TerraPower	10	TWR	Intellectual Ventures	United States	Conceptual design
U-Battery	4	HTGR	U-Battery consortium[c]	United Kingdom	Design and development work
VBER-300	325	PWR	OKBM Afrikantov	Russia	Licensing stage
VK-300	250	BWR	Atomstroyexport	Russia	Detailed design
VVER-300	300	BWR	OKB Gidropress	Russia	Conceptual design
Westinghouse SMR	225	PWR	Westinghouse Electric Company	United States	Cancelled. Preliminary design completed.
Xe-100	80	HTGR	X-energy	United States	Conceptual design development
Updated as of 2014. Some reactors are not included in IAEA Report. Not all IAEA reactors are listed yet.

Proposed sites

Canada

In 2018, the Canadian province of New Brunswick announced it would invest $10 million to attract SMR research to New Brunswick with a potential site for a demonstration project at the Point Lepreau Nuclear Generating Station. It was later announced that SMR proponents Advanced Reactor Concepts and Moltex would open offices in New Brunswick with the potential of developing sites at Lepreau.

On 1 December 2019, the Premiers of Ontario, New Brunswick and Saskatchewan signed a memorandum of understanding  "committing to collaborate on the development and deployment of innovative, versatile and scalable nuclear reactors, known as Small Modular Reactors (SMRs)." They were later joined by Alberta in August 2020.

China

In July 2019 China National Nuclear Corporation announced it would start building a demonstration ACP100 SMR on the north-west side of the existing Changjiang Nuclear Power Plant by the end of the year.

Poland

Polish chemical company Synthos declared plans to deploy a Hitachi BWRX-300 reactor (300 MW) in Poland by 2030. A feasibility study for the project was completed in December 2020 and licensing process started with Polish National Atomic Energy Agency.

United Kingdom

In 2016 it was reported that the UK Government was assessing sites for deploying SMRs in Wales - including the former Trawsfynydd nuclear power station - and on the site of former nuclear or coal-fired power stations in Northern England. Existing nuclear sites including Bradwell, Hartlepool, Heysham, Oldbury, Sizewell, Sellafield and Wylfa are thought to be possibilities. The target cost for a 440 MWe Rolls-Royce SMR unit is £1.8 billion for the fifth unit built. In 2020 it was reported that Rolls-Royce has plans to construct up to 16 SMR's in the UK. In 2019, the company received £18 million to begin designing the modular system, and the BBC claims that the government will provide an additional £200 million for the project as a part of its green plan for economic recovery.

United States

In December 2019 the Tennessee Valley Authority was authorized to receive an Early Site Permit (ESP) by the Nuclear Regulatory Commission for potentially siting an SMR at its Clinch River Site in Tennessee. This ESP will be valid for up to 20 years, and addresses site safety, environmental protection and emergency preparedness associated. TVA has not made a technology selection so this ESP is applicable for any of the light-water reactor SMR designs under development in the United States.

The Utah Associated Municipal Power Systems (UAMPS) announced a teaming partnership with Energy Northwest to explore siting a NuScale Power reactor in Idaho, possibly on the Department of Energy's Idaho National Laboratory.

The Galena Nuclear Power Plant in Galena, Alaska was a proposed micro nuclear reactor installation intended to reduce the costs and environmental pollution required to power the town. It was a potential deployment for the Toshiba 4S reactor.