* Operator GDF Suez says reactor reopening delayed
* Belgium should still have enough power, ministry spokeswoman (Adds background, comments from GDF unit, energy ministry)
BRUSSELS, Sept 13 (Reuters) - A second nuclear reactor in Belgium has indications of cracks in its core tank, the nuclear regulator said on Thursday, putting further strain on the country's energy supply as it heads into winter.
Preliminary results of tests being carried out at Tihange 2, a reactor operated by GDF Suez unit Electrabel, showed that there were indications of cracks on the core tank, Belgium's nuclear regulator FANC said in a statement.
The 1,008 megawatt reactor in the south of the country was to reopen from a scheduled shutdown in October, but that will now be delayed while experts analyse the results.
Last month, Belgium halted the 1,006 megawatt Doel 3 reactor near Antwerp after the discovery of suspected cracks in the core tank and the site will not reopen this year.
"We have found the same indications as we found at the Doel 3 power plant, and now we will analyse and constitute a file to hand over to the FANC," said a spokeswoman for Electrabel.
It means that two out of Belgium's seven nuclear reactors will be offline.
A report prepared for the Belgian government this year showed the country was at risk of electricity shortages if the three oldest reactors were taken off the grid as planned in 2015.
However, a spokeswoman for Melchior Wathelet, state secretary in charge of energy, said that Belgium would still have enough energy even without the two reactors.
"When we heard about the defaults at Doel 3 and the potential defaults at Tihange 2 we conducted simulations ... and that shows that there won't be a problem of supply," she said.
Belgium is trying to decrease its reliance on nuclear power, which accounted for 57 percent of its electricity in 2011.
In July Belgium's cabinet postponed the planned closure of one of its oldest nuclear reactors by a decade over concerns the country may not be able to generate enough alternative energy.
The component in question was built by now defunct Dutch company Rotterdamsche Droogdok Maatschappij, which also constructed parts for nuclear plants throughout Europe and in the Americas.
Beyond Belgium, Rotterdamsche Droogdok was responsible for two units in Germany that are no longer operating, two in the Netherlands, two in Spain, one in Sweden, two in Switzerland, 10 in the United States and one in Argentina, the Paris-based Nuclear Energy Agency said. (Reporting By Ben Deighton; Editing by David Cowell)