Small and micro

19 May 2020

The potential benefits of small and micro nuclear power plants continue to attract increasing attention worldwide.

Above Image: Artist’s impresssion of Rolls-Royce SMR


The US Department of Defense has recently awarded contracts to BWXT, Westinghouse and X-energy (USD13.5m, USD11.95m and USD14.31m, respectively) to work on mobile nuclear reactor technology under a Strategic Capabilities Office initiative called Project Pele.

Project Pele “involves the development of a safe, mobile and advanced nuclear microreactor to support a variety of Department of Defense missions, such as generating power for remote operating bases,” the DoD says. “After a two-year design-maturation period, one of the three companies may be selected to build and demonstrate a prototype.”

The project’s uniqueness “lies in the reactor’s mobility and safety”, said Dr Jeff Waksman, Project Pele program manager. “We will leverage our industry partners to develop a system that can be safely and rapidly moved by road, rail, sea or air and for quick set up and shut down, with a design which is inherently safe.”

In January 2019, SCO issued a request for information to industry for the development of Project Pele technology. The three companies were chosen from the ensuing competition to develop engineering designs. Critical to the Pele programme is co-ordination with the Department of Energy, the Nuclear Regulatory Commission, and industry partners, which “allows the rapid development of workable prototype designs that support evaluation, safety analysis, and, ultimately, construction and testing.”

DOD says it uses about 30 TWh of electricity per year and more than 10 million gallons of fuel per day – levels that are expected to increase. “A safe, small, mobile nuclear reactor would enable units to carry a nearly endless clean power supply, enabling expansion and sustainment of operations for extended periods of time anywhere on the planet.”

“The United States risks ceding nuclear energy technology leadership to Russia and China,” said Jay Dryer, SCO director. “By retaking technological leadership, the United States will be able to supply the most innovative advanced nuclear energy technologies.”

Micro reactors would significantly reduce the need for investments in costly power infrastructure, while in civilian applications, they could be easily relocated to support disaster response work and provide temporary or long-term support to critical infrastructure like hospitals, as well as remote civilian locations where delivery of electricity and power is difficult, the DOD notes.

The Department of Defense has also published in the Federal Register a notice of intent to conduct an environmental impact statement process for the project, as required under the National Environmental Policy Act of 1969 (NEPA), which includes giving the public the opportunity to review and comment on proposed actions, alternatives and the environmental analysis.

Westinghouse said the DoD funding would be used to finalise the design for a prototype of a mobile, “defense” version of its eVinci design, which it calls DeVinci. This expands upon the transportability capabilities of the eVinci micro reactor by allowing use to be made of “standard military transportation.”

The eVinci micro reactor, designed to be suitable for both power and heat supply, employs a solid core with channels for both heat pipes and fuel. Each fuel channel in the core is adjacent to at least two heat pipes for efficiency and redundancy, with the relatively large number of in-core heat pipes intended to increase system reliability and safety. Decay heat also can be removed by the heat pipes via the decay heat exchanger.

The use of heat pipes in nuclear reactors is new to the commercial nuclear industry, says Westinghouse, “but liquid metal heat pipe technology is mature and robust with a large experimental test database to support implementation of the technology.”

Use of heat pipes “addresses some of the most difficult reactor safety issues and reliability concerns present in current Generation II and III commercial nuclear reactors (and, to some extent, Generation IV concepts) – in particular, loss of primary coolant”, Westinghouse believes.

Heat pipes operate in a passive mode at relatively low pressures, less than an atmosphere. Each individual heat pipe contains only a small amount of working fluid, which is fully encapsulated in a sealed metallic pipe. There is no primary cooling loop, hence no mechanical pumps, valves, or large-diameter primary loop piping typically found in all commercial reactors today. Heat pipes simply transport heat from the in-core evaporator section to the ex-core condenser in continuous isothermal vapour/ liquid internal flow.

The eVinci micro reactor design uses a primary heat exchanger in the form of annular tubes around the ex-core condenser section of the heat pipes, with inlet and outlet plenums at the condenser section ends. Depending on the application, the reactor core can “easily run for up to 10 years without the need for refuelling.”



X-energy is focused on high temperature gas-cooled reactor (HTGR) development and TRISO fuel for use in the HTGR, while BWXT says it has shipped 400 nuclear reactor cores to the US Naval Nuclear Propulsion Program and has led and/or supported the design of more than 40 nuclear reactor systems. “We believe this experience will provide us a solid platform from which to complete a robust and innovative approach that will support the Defense Department’s front-line power needs for its service members”, said Ken Camplin, president of BWXT’s Nuclear Services Group.

BWXT is restarting the TRISO production line at its Lynchburg, Virginia, site and has recently announced the award of a contract from the USDOE’s Oak Ridge National Laboratory (ORNL) to manufacture TRISO nuclear fuel “to support the continued development of the Transformational Challenge Reactor (TCR).”

The TCR concept aims to make use of innovative technologies, notably additive manufacturing, to “explore solutions to the high costs and lengthy deployment timelines that threaten the future of nuclear energy” says BWXT.

SMR developments in Turkey, Estonia and Finland

Turkey’s EUAS International ICC and Rolls-Royce have signed an MoU with the aim of studying the “technical, economic and legal applicability” of small modular reactors (SMRs) and also the possibility of their joint production, with Rolls-Royce representing a design consortium consisting of: Assystem; Atkins; BAM Nuttall; Laing O’Rourke; National Nuclear Laboratory (NNL); Rolls-Royce; Jacobs; TWI (The Welding Institute); and UK Nuclear AMRC.

Fermi Energia of Estonia is working with Fortum, Vattenfall, Tractebel and Orano on SMR permitting, construction times, identification of suitable sites in Estonia and the spent fuel management, with conclusions to be published in January 2021. Estonian electricity production is largely based on oil shale and extremely carbon intensive.

In Finland, VTT has launched a project to develop an SMR tailored to district heat production. The focus is on technologies
suited to the heating networks of Finnish cities, with the objective of “creating a new Finnish industrial sector around the technology that would be capable of manufacturing most of the components needed for the plant.”

Nuclear energy is the single largest source of electricity in Finland, currently covering about one third of the domestic production. But, even though the carbon footprint of power production is therefore small in Finland, achieving carbon neutrality at the national level requires major emission reductions in other sectors, in particular heating. Decarbonising heat production is one of the most significant climate challenges faced by Finnish municipalities, with the country committed to phasing out coal in energy production by 2029. “The schedule is challenging, and the low- cost alternatives are few. To reach the target... innovations...are required. Nuclear district heating could provide major emission reductions,” says Ville Tulkki, research team leader at VTT.

VTT notes that internationally, many SMR projects have advanced to the licencing phase, but most of them are intended for power production or as energy sources for high-temperature industrial processes. District heating, requiring a water temperature of about 100°C, enabling the use of simplified and potentially less costly solutions.

As well as being a cost-effective solution for heating Finnish homes in cities and densely populated areas, VTT points out that district heating is also widely used in for example central and eastern Europe, and that too requires a low-emission energy source.

Many of the current plans for replacing the fossil fuels used for district heat production are largely based on biomass. However, in the future, VTT cautions, this could become a valuable raw material, replacing oil in, for example, industrial applications and in the production of transport fuels. “Nuclear energy offers an alternative that liberates biomass from heat production for other uses.”

In the development of its district heating SMR, VTT, which has about 200 researchers in nuclear energy and related fields, says it can draw upon in-house calculation tools and multidisciplinary expertise. “For example, in the modelling of the reactor core, we are able to apply high-fidelity numerical simulation methods that have become feasible due to advances in high-performance parallel computing”, said Jaakko Leppa¨nen, research professor, reactor safety, VTT. The Serpent software developed by Leppa¨nen has been applied to reactor modelling and radiation transport applications in 250 universities and research organisation in 44 countries.

Over the last five years or so, VTT has been involved in a number of SMR-related activities. At the EU level, it is for example co-ordinating the ELSMOR (towards European Licencing of Small MOdular Reactors) project, launched last year, and is leading one of the work packages of the new McSAFER project, which is developing next generation calculation tools for the modelling of SMR physics.

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