The iodine pills, which help reduce radiation build-up in the thyroid, would be given to children under 18 and pregnant women living within a 100-kilometre (62-mile) radius of a plant, health ministry spokeswoman Edith Schippers told AFP.
Until now, the tablets have been available within 20 kilometres of a plant, to everyone aged 40 and under.
The Netherlands has only one nuclear power plant -- at Borssele in the southwest -- but the expansion will also see pills given to people living in border areas near Germany's Emsland plant and two Belgian facilities, Doel and Tihange.
Dutch authorities said they would "follow how (the Belgians) carry out the distribution of these pills and where they will be available -- whether people will have to go and find them at a pharmacy or at a local health service," Schippers said.
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Once tablets were distributed to children and pregnant women, the rest of the supply of 15 million could be made available to everyone caught up in a potential accident, including "tourists, visitors and workers".
Security fears have also risen after investigators last year discovered surveillance footage of a Belgian nuclear official in the apartment of a suspect linked to the Brussels and Paris attacks.