This doesn't seem like a terribly great idea, for several reasons. Belgium is nearly bankrupt, with a government deficit that the EU is already giving us grief for, in spite of some of the highest tax rates in the world. That same government hasn't exactly managed any of its semi-public companies particularly well: the national telco is for shit, postal service is nearly bankrupt, railways are mismanaged and underfunded, etc.
The reactors in question have been shut down by virtue of being too old (1974, 1975, 1982, 1985). Some of them have cracks in the reactor vessels. Maintenance has been lacking. There was also a case of sabotage which was never resolved.
Meanwhile Belgium has a lot of off-shore wind power in the north sea, but lacks battery capacity and transmission lines. Spending money on that would likely be a much better investment.