Spent fuel vessel manufacturer Holtec International has revealed a few details of its small reactor design, called HI-SMUR (Hotec inherently safe modular underground reactor).
The 446 MWt reactor (postulated to have an electrical power of 145 MWe) consists of a single 140ft (42.7m)-long vertical vessel with integral steam generator and reactor core. The reactor core holds 32 assemblies of conventional PWR fuel arranged in a single, seismically-qualified freestanding frame. Reactor coolant circulation would rely only on gravity, according to a presentation by president and CEO Kris Singh.
The secondary side steam, which will be superheated in the reactor vessel, will power a single train of high-pressure and low-pressure steam generators.
The entire reactor is buried up to a closure head at grade. Surrounding and supporting the reactor is reinforced concrete.
The reactor vessel is constructed of ductile stainless steel. The primary system uses no boric acid; consequently there is no continuous water purification system. Cleanup would be carried out during an outage.
A fuel cycle would last 3-4 years. Spent fuel would be moved underwater to fuel storage pool, and then to a ventilated dry cask storage area underground.
The reactor has strong negative reactivity coefficient with increasing temperature. Normal reactor shutdown is not powered. Residual heat removal during shutdown is carried out by natural circulation.
Holtec claims construction would take 18 months after the first unit has been built. It estimates construction costs as $5000/kW for a single-unit site; $4500/kW for a 10-unit site. All equipment is shop-fabricated, and almost all made in the USA. Site work would consist of civil engineering and assembly, with 'minimal' welding and consequent non-destructive examination.
Holtec says that proof-of-principle calculations have been completed; detailed design is expected to be finished by May 2012, with a licence submittal by December 2012. Construction would begin on a full-size prototype in the June 2012-14 timeframe.
