Based on the contract concluded between companies Slovenské elektrárne, a.s. and VUJE, a.s. within the project “Completion of Mochovce NPP Units 3&4”, the “Team of Scientific and Technical Support of Commissioning” (TSTCS) was formed in VUJE, a.s. TSTCS is a group of experts highly experienced in the field of NPP commissioning and operation. The role of the group is to act as an independent supervisor over the nuclear safety principles to be observed during the preparation and performance of Mochovce NPP Units 3&4 commissioning. One of the important tasks of TSTCS is an independent evaluation of inactive tests of the safety systems. These systems are important in realtion to safety and to the systems for mitigating the severe accidents consequences.

The key part of inactive tests of Mochovce NPP Unit 3 was the 1st  hydro-test (cold hydro) and the 2nd hydro-test (hot hydro). Cold hydro at Unit 3 was performed according to the approved 3P201 program in the period from December 2017 to August 2018. The cold hydro was divided into five sub-stages: I. primary circuit cold tests, II. heating and tightness test of the primary circuit at 120 °C, III. circulation flushing of the primary circuit, III. strength and tightness test of the secondary side of steam generators, IV. ECCS tests and primary circuit drainage tests. The preliminary tightness test of the containment was also performed within the cold hydro.

 After the cold hydro finishing, a short inspection of the primary circuit was carried out according to the approved 3P202 program. Within this short inspection, pre-operational inspections of the primary circuit equipment was carried out, and the defects detected during the cold hydro were eliminated. The short inspection was followed by the hot hydro-test. The hot hydro was  performed according to the approved 3P203 program from December 2018 to April 2019. The hot hydro was divided into five sub-stages: I. primary circuit cold tests, II. primary circuit heating to 120 °C, tightness and strength test of the primary circuit at 120 °C, III. heating of the primary circuit to 260 °C, IV. primary circuit hot tests, V. primary circuit cooling tests and electric power supply loss test (black-out). The official tightness and strength test of the hermetic zone was also carried out within the hot hydro.

After the hot hydro finishing, the extended inspection of the primary circuit was carried out according to the approved 3P204 program. As part of the extended inspection, pre-operational inspections of the primary circuit equipment was carried out, and the defects detected during the hot hydro were rectified. In compliance with NRA SR request, TSTCS effected an independent evaluation of the cold hydro and hot hydro for Slovenské elektrárne, a. s. This time TSTCS follows with administrative proceeding for obtaining the licence for Mochovce NPP Unit 3 commissioning, to be issued by NRA SR.