Information from the Nuclear Regulatory Authority on the next steps in the preparation of Mochovce Unit 3 for commissioning

Hot hydrotest

Hot hydraulic testing was carried out in Unit 3 of the Mochovce 3, 4 Nuclear Power Plant (EMO 3, 4) from 21/12/2018 to 15/03/2019. The hot hydrotest is the last comprehensive test of the unit equipment before its commissioning.

The hot hydrotest tested the pressure resistance of the reactor and the primary circuit at a pressure of 19.2 MPa. This test is conducted only once during the life of a nuclear unit; in subsequent operation, a pressure of 16.8 MPa is used for resistance tests and the normal working pressure is 12.2 MPa. The hot hydrotest was interrupted twice (from 18/01 to 07/02 and from 21/02 to 25/02) for reasons not directly related to the equipment being tested. In both cases the cause was a collision between the completion of building work and hot hydrotest tests. Inspectors from the Nuclear Regulatory Authority – ÚJD – monitored the performance of equipment and system tests and the fulfilment of success criteria throughout the hot hydrotest. In this context, the ÚJD inspectors greatly appreciate the hard work and professional approach of the staff of the unit for EMO 3, 4 commissioning and the contractors.

ÚJD asked Slovenské elektrárne to supply a detailed analysis of the activity of the tested systems and equipment for ÚJD to assess. The analysis should show whether the tested systems worked as designed during testing.

Although the preliminary results indicate that the tests were successful, ÚJD will issue the final evaluation of the hot hydrotest based on the findings of inspection during the hot hydrotest and an assessment of the submitted documentation. Based on the results of the submitted analyses, ÚJD will accept the hot hydrotests or decide that certain tests should be repeated.

Integrated test of the strength and tightness of hermetically sealed spaces

The integrated test of the strength and tightness of hermetically sealed spaces took place from 15/03 to 23/03/2019. This test focuses on the spaces around the reactor and its basic equipment (the hermetic zone, the containment). The hermetic zone is used to contain any radioactive substances that may be released from the reactor cooling circuit if it is breached, reliably keeping them from contact with the environment. During testing, the air pressure in the hermetic zone was raised to 250 kPa (around 2.5 atmospheres, absolute pressure value) and measurements were taken of leakage (tightness) and the movement of selected walls (strength). The results for both strength and tightness were significantly better than the required criteria.

Expanded inspection of the primary circuit

The expanded inspection of the primary circuit following the hot hydrotest began on 23/03/2019 and is currently still in progress. The purpose of the expanded inspection is to check the required checking of systems and equipment and assess their condition after the hot hydrotest prior to loading fuel into the reactor.

Source: ÚJD Press Report, 02 May 2019, abridged