Some microreactor variants are smaller and containerized, potentially allowing for frequent transportability and could have similar characteristics to diesel gensets. These transportable or mobile microreactors introduce challenges regarding shielding, environmental impact assessments, and security. Even so, nuclear gensets are now being pursued by both miliary and civilian vendors. USNC led the push for containerized micro-reactor in 2017 with the Pylon, which is a nuclear platform for use on Earth and in space. These are designed to be drop-in replacements for diesel or gas generators.
Nomenclature: the industry has given many names to theses types of reactors including transportable, microreactor, containerized, fission battery, nuclear battery, nuclear genset, etc. The underlying theme is that these reactor systems can be transported in a few containers. Long term, many of these designs aim to achieve a diesel gensets performance and public acceptance.
As described in the academic literature, core tenets of the nuclear gensets (aka fission batteries, microreactors, etc) are shown below.
- Economic – Cost competitive with other distributed energy sources (electricity and heat) used for a particular application in a particular domain. This will enable flexible deployment across many applications, integration with other energy sources, and use as distributed energy resources.
- Standardized – Developed in standardized sizes, power outputs, and manufacturing processes that enable universal use and factory production, thereby enabling low-cost and reliable systems with faster qualification and lower uncertainty for deployment.
- Installed – Readily and easily installed for application-specific use and removal after use. After use, fission batteries can be recycled by recharging with fresh fuel or responsibly dispositioned.
- Unattended – Operated securely and safely in an unattended manner to provide demand-driven power.
- Reliable – Equipped with systems and technologies that have a high level of reliability to support the mission life and enable deployment for all required applications. They must be robust, resilient, fault tolerant, and durable to achieve fail-safe operation.
On-site nuclear reactors offer several advantages compared to off-site options. They eliminate the need for extensive transmission infrastructure and reduce the burden of fuel transport. Distributed and transportable microreactors allow for adjustments in capacity assets at each site depending on demand which could change on a year to a year basis. Like the current genset and turbine solution, on-site reactors provide the possibility for on-site process heat, which is more efficient compared to using electrical heaters.
On-site power solutions will take one of two forms depending on the site power needs and transportability requirements: transportable microreactors or fixed microreactors and SMRs. Nuclear vendors would have to develop a range of power plants that produce the required power with sufficient N+1 redundancy.
Temporary sites, either with changing demand or moving location, could be serviced by transportable microreactors on month to year-long time scales. Transportable microreactors could be containerized reactor and power conversion systems with surface or rig mounting features, or they could be configured into dedicated power barges. For the containerized approach, the goal would be a drop-in genset replacement.
Cost, Redundancy, and Fuel Challenges
While transportability provides advantages, transportable microreactors pose cost challenges due to economies of scale, redundancy needs, and lower utilization of nuclear fuel.
First, to be transportable, the reactor must be small. Typical sizes for these reactors are around 1.5 MWe, typically limited by core and shielding capabilities. In general, the smaller the size, the lower the economy of scale. However, this may be offset by economies of mass manufacture if there is a sufficient production volume to drive costs down. Second, redundancy requirements (typical N+1 configurations are 2x100%, 3x50%, or 4x33%) necessitate a considerable overcapacity of nuclear assets with backup diesel gensets, leading to CAPEX costs exceeding the current power delivery model. Finally, small, containerized reactors can have relatively higher fuel costs and lower fuel utilization which drives up the leveled cost of energy.
Another challenge to utilizing transportable reactors is regulatory uncertainty. In the use case of a transportable reactor, the reactor would be shipped with fuel to an intended site for use. Once operations are complete, the reactor would then be shipped to another site. This raises questions of transporting a reactor with used fuel, site permitting, and site security for widely dispersed small scale nuclear power systems. Some technological approaches can reduce the need for site-specific environmental impact assessments. For example, transportable microreactors can be designed for a high degree of seismic isolation or be able to deterministically tolerate beyond design basis accidents across all considered sites. While it is being considered in the U.S., it is unclear at this point whether transportability of reactors will become a viable option in the next several decades.
HTGR is most widely pursued microreactor technology
HTGRs are one technology that demonstrate a strong potential for success in these applications. In particular, helium cooled HTGRs utilizing prismatic TRISO-based fuels show particular promise in meeting the demanding requirements for onsite upstream O&G applications. These reactors can withstand complete loss of coolant accidents and potentially even explosive and fire damage around the reactor with minimal fission product release.
This assessment is consistent with that made by the US DOD as part of Project Pele. This project is developing HTGR technology to provide carbon free and resilient energy to US military bases, and aims for reactor demonstration in 2025. Military bases, like upstream O&G sites, are distributed in remote and off grid areas and require power levels with similar capacity factors and load following ability. These reactors would likewise be replacing diesel gensets which have high fuel cost, particularly in off-grid locations. The designs are to be transportable by a C-17 aircraft, requiring compact packages that fit within a 20 or 40-foot ISO 688 container and weigh less than 40-tons. The reactors should have capability for 72-hour startup and disassembly as well as black start capabilities.
There are several heat-pipe cooled microreactors in development including Westinghouse eVinci , KRUSTY, and MARVEL. Some of these reactors may use TRISO or TRIGA fuel elements with graphite or metal hydride moderators and reflectors. Instead of helium, the designs intend to use sodium heat pipes to transport heat from the core to the balance of plant.