The tests took 24 hours to complete and were conducted at pressure of 24.5 MPa, the statement said.
Cold testing verifies that welds, joints, pipes and components in the primary circuit are able to withstand pressures higher than those during normal operation.
Testing of the secondary circuit of the Belarusian-1 unit is scheduled to be carried out by the end of the month, Atomstroyexport said.
There are two 1,109-MW Russian VVER-1200 pressurised water reactor units under construction at the Belarusian site. Construction of Unit 1 began in November 2013 and of Unit 2 in April 2014.