Legal provisions for mandatory referendums at national level

Belgium
Answer
No
Source
Constitution 1831 (with amendments through2012)
https://www.constituteproject.org/search/topics#?key=referen&cons_id=Belgium_2012
Constitution 1831 (with amendments through2012)
https://www.constituteproject.org/search/topics#?key=referen&cons_id=Belgium_2012