Adding 250 MWe at Oskarshamn 3

1 September 2007

Manufacture of the blading and of the three LP rotors is now underway for the new 1450 MWe steam turbine to be installed at the Oskarshamn 3 BWR, owned by E.On/Fortum company OKG. The new machine will be a direct replacement for the existing 1200 MWe turbine, and will have the same configuration (1HP (double flow) + 3LP (double flow)) and speed (1500 rpm), but with a total LP exhaust area increased to 155 m2. The new turbine in fact features the largest last stage blades yet made by Alstom, each 1.7m long and weighing over 100 kg (the same blades that will be used in the 1750 MW steam turbine being supplied to Flamanville).

LP rotor during welding at Alstom's Belfort facility

The new steam turbine layout will be similar to the original machine but will require modified bearings, lube and jacking oil systems and other associated subsystems. The new turbine and generator will be mounted in-line on a common 72 m long shaft.

The Oskarshamn 3 turbine is being replaced as part of a major upgrade programme called PULS (Power Uprate with Licensed Safety), which will increase the reactor thermal output rating from 3020 MWt to 3900 MWt.

Under a 180 million euro contract with OKG, Alstom is supplying the turbine, generator (rated at 1670 MVA with a power factor of 0.9), upgraded balance-of-plant (including replacement moisture separator reheaters) and electrical equipment (including new transformers). Westinghouse is the contractor on the reactor systems side.

The uprated plant is due to resume commercial operation in late 2008.

Oskarshamn 3 last stage blade during forging

3D model of the HP casing produced by Alstom China, Wuhan. The casing itself is being manufactured by Voestalpine

Live steam will be supplied to the HP turbine from the reactor at 2115 kg/s through four steam lines via four new steam inlet valves of bigger size to reduce pressure drop. The feedwater temperature will remain at 218°C. With these boundary conditions, plant performance has been optimised using Alstom's ALPRO suite. Most of the turbine parameters except the inlet and outlet flow to the reactor have been tuned to achieve best performance, eg all pressures and temperatures at the different HP and LP extractions.

Upper section of HP inner casing during production at Voestalpine

Pressure drop over the HP module was set to provide a suitable pressure at the exhaust, with optimisation of flow and moisture content.

Dimensioning of the last stage LP blade is dependent on condenser behaviour. As part of the project, the two outer rows of tube bundles in the turbine condenser are being replaced with tubes of modern corrosion-resistant material, to reduce pitting. To achieve the increased output, with approximately the same temperature increase, the main cooling water flow is being increased by about 20% to around 55 m3/s.

"3D" high-efficiency-profile last stage blade, as being used for the new Oskarshamn 3 steam turbine

Valve body for one of the new HP steam inlet valves at Alstom's Elblag foundry in Poland

The existing turbine protection is being replaced by a modern digital system, modified to meet the 'two out of three' fault-trip requirement common to the turbine plant as a whole.

Although dating from the 1980s, the original instrumentation and control systems related to the operation of the reactor systems are being retained, eliminating the need to renew formal licensing for the I&C "1E" systems.

While employing the same basic operational and supervisory I&C control room technology, new operating parameters such as increased water and steam flow-rates, higher steam conditions and higher output power levels from the uprated plant, will require significant modifications.

See also article by Amel Akhtar in Nuclear Engineering International (sister title to MPS), June 2007, pp 16-17

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