Mochovce: Hot hydro tests start at Unit 3

Mochovce: Hot hydro tests start at Unit 3
On 21 Dec 2018 Slovenské elektrárne began the hot hydrotest at Mochovce nuclear power plant Unit 3.

The test comprises several stages, during which pressure and tightness tests of the primary circuit and Mochovce NPP Unit 3 reactor are progressively performed, together with functional tests of equipment in the primary and secondary circuit, as well as safety systems, air conditioning, electrics and instrumentation and control systems.

The hot hydrotest was preceded by a minor inspection of primary circuit equipment, aimed at verifying the state of equipment following the cold hydrotest, to ascertain and remove failures on equipment that could arise during the cold hydrotest and assess the state of metal of the equipment and piping, including welds on selected equipment.

The minor inspection began essentially immediately after the end of the cold hydrotest. During the minor inspection, more than 5000 control checks were made, involving approximately 300 workers from Slovenské elektrárne year and the contractor organisations: Nuclear Power Research Institute (VUJE), Enseco and Škoda were involved.

The minor inspection comprised three main sub-stages:

  1. Preparation, during which it was necessary to de-pressurise the primary circuit, and tighten the reactor and dismantle the reactor shaft from the reactor pressure vessel.
  2. The inspection of the primary circuit equipment on which the pre-operational inspections were performed: the reactor pressure vessel, reactor shaft, steam generators, main circulation pumps, volume compensator, piping, tanks, exchanges, etc.
  3. Assembly of the reactor with all internal reactor parts and imitator fuel cassettes (for now without nuclear fuel) and completion of works on the primary circuit.

Only qualified and experienced specialists worked on the inspection, in clean conditions – in a dust-free environment, as under real operation, or a shutdown of the equipment, and in strict compliance with FME (foreign material exclusion) principles, in order to prevent any foreign objects from entering the equipment. Over the course of the inspection, the results were recorded in measurement and control check logs with attachments (photographs, diagrams maps, sub logs), including a description of all defects, their removal, and repeated control checks.

Following completion of the hot hydrotest programme, a major inspection will follow, and after that there will come the physical start-up, which will begin with the introduction of nuclear fuel into the reactor.