The once-through steam generator is located within the reactor vessel in the annular space between the core support barrel and the reactor vessel inner wall. The secondary coolant is completely evaporated in a single pass through the steam generator. The steam generator tubes are divided into two groups that can be operated independently and the tubes in each group will be cross wound to reduce thermal twisting.

The steam generator consists of tube bundle, downcommer, two feed water and steam headers, shrouds to guide primary flow, and tube supporting structures. Approximately 1100 tubes are helically coiled in the effective heat transfer region and the effective coiling height is 3m. To assure equal steam quality from individual tubes, the length of tubes in the effective tube bundle is maintained as nearly equal as possible by varying the number of tube starts and helix angles in each tube column. The tube material is inconel 690 with 19 mm outer diameter through the whole tube length. The tube bundle is supported by eight perforated radial support plates, which transfer the load to the bottom support structure located on the supporting lug. Each tube can be accessed easily through the feed water and steam headers which are attached to the reactor vessel for in-service inspection and maintenance.