(Adds Petrobras comment)
By Jeb Blount
RIO DE JANEIRO, Aug 25 (Reuters) - Brazil's state-run oil company Petrobras confirmed on Monday a refinery in Rio de Janeiro sprang a leak in one of its only operating steam boiler units and that maintenance was being carried out on the unit.
Petroleo Brasileiro SA, as the firm is formally known, said units at the refinery were operating "normally" but would not specify whether output had been affected.
The president of the union responsible for workers at the plant had previously told Reuters of the leak on Monday morning.
The leak in a boiler linked to one of the units of the Duque de Caxias Refinery was discovered on Sunday. The boiler is part of a system that helps provide heat and other energy for the plant, said Simao Zanardi, president of the union, known as Sindipetro Caxias.
The refinery, commonly known as REDUC, is Brazil's fourth-largest and recently processed nearly 248,000 barrels of oil a day. With another boiler out of service for scheduled maintenance, the U-1320 system is one of the only major sources of heat energy for REDUC, the union said.
Union stewards said they planned to talk with Petrobras management and Brazilian labor-law prosecutors at REDUC about the leaks and are asking that the unit be shut while the leak is repaired, Zanardi said.
Union officials have been complaining about a series of accidents at Petrobras refineries as the Rio de Janeiro-based company struggles to boost domestic production of fuels such as gasoline and diesel in an effort to limit imports. Last week a worker died of burns suffered at a Petrobras refinery in Manaus.
On Sunday REDUC was also required to evacuate workers at the boiler undergoing maintenance, the union said. That boiler also provides energy to REDUC as well as helping treat the plant's carbon monoxide waste.
Brazil's labor-law prosecutors office in Brasilia was not immediately able to confirm if its officials were on site at REDUC, but said that no new cases had been formally launched either on Sunday or Monday.
Brazil's government, which controls Petrobras, requires the company to sell gasoline in Brazil at about 10 percent less than world prices and diesel at about 4 percent less. This has exacerbated losses on imports.
To limit the need for imports Petrobras has been running its refineries at about 98 percent of capacity and increasing the amount of fuel its 13 existing Brazilian refineries can process. This has put pressure on equipment and made some operations unsafe, the union says.
Petrobras preferred shares, the company's most-traded class of stock, rose 3.11 percent in early afternoon trading in Sao Paulo, to 21.57 reais, on track for its highest close in more than two years. (Reporting by Jeb Blount; Editing by David Gregorio, Bernard Orr)