Angra 1 steam generator replacement starts

23 January 2009

The Angra 1 nuclear power reactor in Brazil will tomorrow begin a maintenance outage lasting some four months, during which time the unit will be refuelled and have its steam generators replaced.

Angra 1 (Eletronuclear)
Angra 1 (Image: Eletronuclear)
Plant operator, Eletronuclear, began reducing power at the 626 MWe pressurized water reactor (PWR) on 20 January in preparation of the outage. Westinghouse has been contracted to carry out the actual steam generator (SG) replacement work. The unit is scheduled be restarted around 6 June, with full power being reached by 27 June.
Steam generators transform the heat produced in the reactor's core into steam that drives the electricity generation turbines. The new SGs for Angra 1 have been manufactured by Brazil's Nuclebras Heavy Equipment (Nuclep), with technical assistance from Areva of France. The new SGs are 21 m long and 4.5 m in diameter, and weigh in at 343 tons each.
Eletronuclear, operator of Brazil's only nuclear power plant, took the decision to replace the SGs in Angra 1 after it was discovered that alloys used in the tubes of the existing generators were showing some susceptibility to corrosion, necessitating frequent integrity tests. The new SGs, which the company says are made of more resistant materials, will help to improve the plant’s efficiency and performance, as well as helping to extend its life.
The company has invested some $724 million in the purchase and installation of the new steam generators. Eletronuclear officially received two new steam generators for Angra unit 1 in March 2008. The plant was at that time undergoing preparatory work in readiness for the installation of the new steam generators, which had previously been due to take place in September.
Replacement of SGs is a major undertaking, but Eletronuclear points out that similar work has been carried out at 89 other nuclear power reactors around the world and by 2011, a further 16 units will have undergone SG replacements.
In order to remove the existing steam generators and install the new ones, a hole will have to be cut in Angra 1's concrete and steel containment structure. The old SGs, once removed, will be stored on-site for later dismantling and disposal.
In November 2007, Eletronuclear placed an order with Mitsubishi Heavy Industries (MHI) of Japan for a new reactor vessel closure head for Angra 1. The reactor vessel closure head, another major plant component, will also help make operations at the Brazilian plant more reliable and economical.
Angra is home to two PWRs. Construction began on both plants in the 1970s but Brazil's economic problems meant that building work was interrupted. Angra 1 started up in 1985. In its early years it was beset by steam supply system problems, but it has performed well since 1999 although there is still room for improvement - its 2006 annual load factor of 52.9% was well below that of most of the world's nuclear power reactors which performed at load factors of 75% and above. Angra 2, which has a capacity of 1270 MWe, started up in 2000.