Nuclear energy to go

Three US Laboratories are aiming to develop a small, sealed, transportable, autonomous nuclear reactor in a tamper-resistant container.

Three US Laboratories are aiming to develop a conceptual design of a reactor that would deliver nuclear energy to developing countries and significantly reduce the proliferation concern associated with expanded use of nuclear power.

Lawrence Livermore, which leads the collaboration, is researching materials and coolants for the reactor and evaluating how it can be deployed. Argonne National Labs is designing the reactor, and Los Alamos is contributing its expertise on coolant and fuel technologies.

The SSTAR, as the reactor is called, is designed as a lead-cooled fast reactor (LFR) that can supply 10 to 100 MWe with a reactor system that can be transported in a shipping cask.

According to project leader Craig Smith, a nuclear engineer in Livermore’s Energy and Environment Directorate, the reactor will be about 15 metres tall by 3 metres wide and will not weigh more than 500 tons – small and lightweight enough to be transported on a ship and by a heavy-haul transport truck.

‘With SSTAR, countries won’t need a large nuclear reactor industry to benefit from nuclear energy,’ says Smith. ‘Because the supplier nation will provide both the reactor and the associated fuel-cycle services, the host nation can produce electricity without needing an independent supply of uranium or other fuel at the front end of the cycle.’

The host nation also won’t have to dispose of the nuclear waste at the back end of the cycle as it would be returned to the supplier for recycling.

SSTAR addresses proliferation concerns with other features as well. No refueling is necessary during the reactor’s operation, which eliminates access to and long-term storage of nuclear materials on-site. The design also includes detection and signalling systems to identify actions that threaten the security of the reactor.

And because of the reactor’s small size and its thermal and nuclear characteristics, the design can include a passive method to shut down and cool the reactor in response to hardware or control failures.

SSTAR also offers potential cost reductions over conventional nuclear reactors. Using lead or lead-bismuth as a cooling material instead of water eliminates the large, high-pressure vessels and piping needed to contain the reactor coolant.

The low pressure of the lead coolant also allows for a more compact reactor because the steam generator can be incorporated into the reactor vessel. Plus with no refuelling downtime and no spent fuel rods to be managed, the reactor can produce energy continuously and with fewer personnel.

Several challenges must be addressed before the SSTAR design is ready for prototype testing, however.

The Livermore team must develop materials for the fuel and coolant boundary that are compatible with the coolant. Lead, especially when alloyed with bismuth, tends to corrode the fuel cladding and structural steel. Controlling the oxygen in the coolant will help reduce corrosion. In addition, the team must identify materials that would best withstand the damaging effects of long-term exposure to fast neutrons. Structural damage could include material swelling and ductility loss, both of which may limit the life of the reactor.

In 2003, the Laboratory’s SSTAR team participated in a feasibility study with a team from the Central Research Institute for Electric Power Industry (CRIEPI) in Japan. In this study, the two teams evaluated a modified design, developed by the Japanese team, for a small liquid metal-cooled reactor using sodium as a coolant. A scientist from CRIEPI is now working at Livermore, and the teams are sharing the results from their respective projects.

Passive safety features also will be developed to ensure that any failure in the control system will shut down the reactor and initiate a natural convection system to cool the reactor core and reactor vessel. The characteristics of these features will depend on the geometry and mechanical support system provided for the nuclear reactor. In addition, the prototype will test the performance of the passive safety features and the system designed to monitor them.

Because the spent reactor will be radioactive, the research team must develop packaging and transportation systems so the reactor can be removed safely. The team also must design a process to cool the reactor while it is being shipped to the recycling facility. The design criteria for meeting these challenges may affect the maximum power level that can be achieved.

But the tri-laboratory collaboration has more work to do before an SSTAR demonstration. According to Smith, the team plans to refine the SSTAR design and then develop a prototype reactor, which could be ready for testing as early as 2015. The Livermore team feels confident that SSTAR will provide a new-generation reactor- one that is safe, proliferation-resistant, and able to operate anywhere in the world.