International nuclear

Urenco, Bruce Power and AMEC NSS Limited recently announced that they had signed an MOU to cooperate in the design, licensing and development of Urenco’s U-Battery micro nuclear system for the Canadian electricity and heat market.

The U-Battery contains a 10 MWth nuclear heat source that can be configured to produce either 4 MWe plus useful heat in a cogeneration mode or process heat at a delivery temperature of 750 C.

Under the MOU, the three companies will conduct a feasibility study for the potential deployment of micro nuclear reactors across Canada, including Bruce Power as the owner and/or operator of a fleet of U-Battery units.

They will also investigate the suitability of a Bruce Power site for the deployment of a U-Battery demonstration reactor.

Steve Threlfall, the General Manage of U-Battery, provided background information on the discussions that led to the MOU.

Threlfall said that Urenco and Bruce Power began talking about the possibility of cooperation at an advanced and small modular reactor conference sponsored by Canadian Nuclear Labs in March of last year.

When Bruce Power’s Frank Saunders said during a presentation that he did not see how small reactors could ever be viable, Threlfall saw an opportunity.

He knew his company would benefit from a partnership with an experienced nuclear plant operator.

Since the inception of the U-Battery development project Urenco had recognized its small electricity and heat generation design was particularly well suited for the Canadian market of industrial, mining and remote community applications.

As an enrichment company, Urenco is not a major presence in Canada’s natural uranium-based nuclear power market. It could benefit from joining with a strong Canadian partner like Bruce Power.

With that concept of win-win in mind, Threlfall told Saunders about U-Battery’s design and its operational concept, including the potential for remote operation with a small local footprint.

He explained that the safety case for the U-Battery is not dependent on maintaining a coolant pressure boundary. It does not require redundant systems capable of suppling large volumes of make up coolant during accident conditions.

Instead, it depends on a fuel form that is engineered, manufactured and tested to be capable of retaining fission products at any temperature below 1600 C.

Triso coated fuel particles are tiny spheres of uranium dioxide (UO2), uranium oxycarbide (UCO) or even uranium metal coated with three layers of material. There is a low density layer of pyrolytic graphite, a tight layer of silicon carbine and a final layer of high density pyrolytic graphite.

The first layer provides space for gas expansion. The SiC layer is impervious to penetration from fission products and the final layer of pyrolytic graphite protects the SiC layer from damage.

Triso particles are mixed with graphite and pressed into a fuel pellet. The pellets are stacked into fuel channels in large graphite blocks that also contain channels that provide space for gas flow and control rods.

Graphite moderated, gas-cooled reactors have a strong negative temperature coefficient of reactivity that ensures fission stops if the reactor gets too hot.

The reactor size, shape and power capacity are chosen to assure that even under worst case conditions, its decay heat is not sufficient to exceed fuel temperature limits even if there is no coolant flow and no coolant pressure.

Fission product retention doesn’t require a supply of electrical power. It does not require a high degree of assurance of coolant pressure boundary integrity. It does not depend on redundant sources of water or numerous methods of forcing the coolant into a damaged system.

Over the course of the past year, Bruce Power listened and apparently did enough verifying research to agree to participate in the system development.

Supply Chain Progress

Urenco, an enrichment company, is well positioned to supply itself with the high assay, low enriched uranium (HALEU) – defined to be uranium containing more than 5% but less than 20% U-235 – that will be used in the U-Battery’s five year fuel cycle.

The initial fuel load will include roughly 200 kilograms of slightly less than 20% enriched uranium in Triso coated fuel form.

The reactor will contain about 20-30 times as much reactor grade graphite. The graphite prismatic moderator blocks will be similar to those used at the Ft. St. Vrain gas cooled reactor that operated in Colorado for a little more than a decade.

Urenco is working with BWXT as a supplier for the Triso coated fuel.

BWXT developed the repeatable processes and pilot scale manufacturing capability used in the Department of Energy’s Triso fuel development and testing program. That program is one of the surviving components of what began as the Next Generation Nuclear Plant (NGNP) project.

Threlfall indicated that Urenco is talking to at least two potential suppliers for the graphite moderator blocks, but he was not at liberty to share any details.

The partnership has begun working on submitting a vendor design review package to the Canadian Nuclear Safety Commission.

That is the first step in a process that will take several years. It expects to have its first unit operating in the mid 2020s.

A version of the above was first published by Fuel Cycle Week. It is republished here with permission.