Helical steam generator passes test

27 February 2014

Testing activities have been successfully completed for a first-of-a-kind helical coil steam generator (HCSG) for use in NuScale Power's small modular reactor (SMR) design.

NuScale's helical coil steam generator (Image: NuScale)

The component, which will convert nuclear heat into process steam in the integral pressurised water reactor, has been tested at SIET SpA's facilities in Piacenza, Italy.

The tests, aimed to help design and test a steam generator stabilisation system, provide data on the full range of operation to benchmark computer codes and models for the HCSG, and to measure steam generator outlet conditions as a function of primary and secondary systems and tube geometry. The performance of the HCSG was tested over the expected range of reactor operating conditions.

Pressurised water reactors use steam generators to transfer the heat from the reactor coolant – the primary circuit – to heat water in a secondary circuit to make steam to power the electricity generation turbines. They do this by circulating the reactor coolant through thousands of tubes, typically about 2cm in diameter, which are surrounded by the water of the secondary circuit. In conventional nuclear power plants, steam generators are huge components, typically weighing up to 800 tonnes, with the tubes in either a vertical or horizontal configuration and relying on pumps to keep the coolant circulating.

NuScale's self-contained SMR design houses the reactor core, pressuriser and steam generator inside a single containment vessel. It relies on gravity, not pumps, to circulate the water in the primary circuit up through a riser above the core and down through the HCSG, which as its name suggests contains tubes in a spiral configuration. After passing through the HCSG, the cooled water is pulled down by gravity to the bottom of the reactor pressure vessel where it is drawn through the core again. A single module can generate up to 45 MWe of electricity and is just under 25m in length, 4.6m in diameter and weighing around 450 tonnes.

In December 2013, the US Department of Energy selected NuScale's SMR to receive federal funding for up to half of the cost of developing, licensing and commercialising the reactor, and Nuclear Regulatory Commission (NRC) is currently undertaking pre-application activities in anticipation of a design certification application around the third quarter of 2015.

During the testing process, the commission carried out a quality assurance inspection of NuScale's testing activities at the Italian facilities, which it found to be fully compliant with the relevant federal regulations. The NRC inspection identified no findings of significance, observations, violations, recommendations or non-conformances, a result described as a "rare outcome" by NuScale.

Researched and written
by World Nuclear News