"We are not reassured because we did not get answers to all of our questions and so there is still a security gap," said environment ministry advisor Olaf Munichsdorfer.
"We are not totally convinced that all has been done to establish the origin of the cracks," he said, referring to fissures found in two Belgian reactors.
"We also said Luxembourg is exposed to this risk," added Munichsdorfer, who visited Belgium with Luxembourg Development Minister Camille Gira.
Tihange is about an hour's drive south of Brussels and the same distance from Luxembourg, which has become increasingly concerned, along with Germany, about the safety record of Belgium's nuclear plants.
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The authorities found tiny pressure vessel cracks in 2012 in Tihange 2 and also in the Doel 3 reactor just north of Belgian's commercial hub and major port, Antwerp.
Closed down for repairs, they were both restarted late last year, with Doel 3 halted again after a water leak.
"We resumed service following an audit from a US research firm, an international firm that guaranteed the structural integrity of the vessels," Electrabel spokeswoman Florence Coppenolle said earlier this month.
Munichsdorfer said Jambon has invited Luxembourg to send an official at an unspecified date to inspect the Tihange plant, just as a Dutch minister will tour the Doel plant on Wednesday.
A German official is also due to visit the Tihange plant, he added.
He said the two neighbours also agreed to "reinforce the exchange of information on the nuclear (issue)."
"We listened to their questions and replied to them. We have explained the security measures," Mouligneaux said, confirming that the two sides agreed on a visit to Tihange and to boost communication.
"We stressed that security, particularly nuclear security, is a priority," she said.