The western German city of Aachen has started issuing free iodine tablets to some 500,000 residents and people living nearby because an ageing Belgian nuclear plant is seen as a risk.
People can register on the city website to receive coupons exchangeable at pharmacies stocking the pills.
Iodine can reduce the risk of thyroid cancer after a release of radiation.
There have been German protests over Belgium's Tihange nuclear plant, some 70km (43 miles) from Aachen.
Reactors there and at Belgium's other nuclear plant, at Doel near Antwerp, have been shut down repeatedly for safety reasons. There are seven reactors in total.
Belgium's federal nuclear agency (AFCN) says scientific checks on the micro-cracks, involving international experts, did not suggest that radiation could leak out, according to media reports.