Swedish Small Nuclear Reactor Funded

SEALER (Swedish Advanced Lead Reactor) is a passively safe lead-cooled reactor designed for commercial power production in a highly compact format. Its fuel is never replaced during operation, which minimizes costs related to fuel management. The integrity of steel surfaces exposed to liquid lead is ensured by use of alumina forming alloys, containing 3-4 wt% aluminium.

The future cost for purchasing a SEALER-Arctic unit is estimated at CAD 100 M. The owner’s cost of a factory assembled SEALER-55 unit (as part of a multi-unit plant) is estimated at € 200 M. These values include the cost of the fuel.

For Arctic applications, the fuel is 2.4 tons of 19.9% enriched uranium oxide, and the rate of electricity production may vary between 3 to 10 MW, leading to a core-life between 10 and 30 years (at 90% availability).

For on-grid applications, the fuel is 21 tons of 12% enriched uranium nitride and the rated power is 55 MWe, leading to an equivalent full power core-life of 25 years.

The Swedish Energy Agency has now awarded the partners SEK99 million to put towards building an electrically powered non-nuclear prototype SEALER at Oskarshamn for testing and verifying materials and technology in an environment of molten lead at high temperatures. The 1:56 scale prototype will be operated for five years starting in 2024.

An academic network based at KTH is connected to the project. The Sunrise (Sustainable Nuclear Research In Sweden) project – whose partners include KTH, Luleå University and Uppsala University – has already received SEK50 million (USD6 million) in funding.

Lead coolant
The most important advantage of using liquid lead as coolant for a nuclear reactor is that it allows designing the reactor in a highly compact format, with an outstanding set of safety features, including:

• No violent exothermic reaction with water
• A very high boiling temperature, reducing the risk for loss of coolant
• An excellent potential for decay heat removal by natural convection
• Chemical retention of iodine and caesium, should a fuel failure occur
• Inherent shielding of gamma radiation from fission products

Lead Crystal Glass

Moreover, the use of lead as coolant results in a so called “fast” neutron spectrum, which facilitates production of fissile fuel from U-238 with a conversion ratio larger than unity. Hence, fuel resources increase by two orders of magnitude, making nuclear power sustainable for thousands of years. Moreover, the fast neutron spectrum makes it possible to efficiently transmute the long-lived waste, such as americium and curium, into stable or short-lived fission products, with a minimum of negative side-effects on the safety of reactor and fuel-cycle facilities.

Break-through innovation
A major disadvantage of using lead coolants is the risk for corrosion attack on fuel cladding and steam generator tubes. The high solubility of nickel in lead makes it necessary to form and maintain a protective oxide film on the surfaces of structural materials. However, chromium oxide scales forming on conventional stainless steels grow too thick after a year of full-power operation in a lead-cooled reactor, making them mechanically unstable. Silicon or aluminium alloyed steels form thinner films of silicon and aluminium oxides, respectively, rendering the steels corrosion proof over longer exposure times. In Russia, a silicon alloyed steel has been developed for use in the SVBR-100 and BEST-300 reactors, whereas in Germany, a technique for surface alloying of steels with FeCrAlY has allowed to improve corrosion and fretting performance significantly.

In collaboration with Swedish steel industry, LeadCold materials experts have developed an aluminium alloyed steel (Fe-10Cr-4Al-RE) which exhibits perfect corrosion resistance during exposure to lead for more than two years at T = 550°C, and for more than 10 weeks at 850°C. The addition of reactive elements (RE) reduces the risk for formation of chromium carbides that may be detrimental for corrosion resistance, and allows to keep the aluminium concentration at a level low enough to ensure weldability of the material. Based on this break-through innovation, LeadCold has designed the SEALER reactor for commercial power production.

Written By Brian Wang, Nextbigfuture.com