Information on the Course of the Hot Hydrotest and the Next Steps in the Process of Preparing Unit 3 of NPP Mochovce 3 & 4 for Commissioning

Hot Hydrotest:

From December 21, 2018 to March 15, 2019, hot hydrotest was carried out at Unit 3 of NPP Mochovce 3 & 4 (EMO 3 & 4). Hot hydrotest is the last comprehensive test of unit equipment prior to its commissioning. During the hot hydrotest, the most important technological equipment of the Unit was tested:

• Reactor (without nuclear fuel, with fuel assembly imitators loaded);
• Cooling circuit of the reactor (main circulation pumps, steam generators, pressurizer and other);
• Safety systems for cooling the reactor core (hydro-accumulators, pumps supplying water for the reactor core cooling);
• Important secondary circuit equipment to safely cool down the reactor.

A large number of tests have been carried out during the hot hydrotest according to the pre-approved program. In the course of the hot hydrotest, the reactor and its cooling circuits were heated to an operating temperature of 260 degrees C and pressurized to 12.2 MPa. At the end of the test, the entire primary circuit was cooled and depressurized.

The subject of the hot hydrotest was also the strength pressure test of the reactor and of the primary circuit to a pressure of 19.2 MPa. Such a test is performed only once during the entire lifetime of the nuclear Unit, in the following operation the testing pressure to verify the strength is 16.8 MPa, and the normal operating pressure is 12.2 MPa.

The hot hydrotest was interrupted twice (from 18 January until 7 February, and from 21 February until 25 February) due to reasons not directly related to the equipment under test. In both cases, the cause of the interruption was the collision of completion construction work with the tests of hot hydrotest.

The ÚJD SR inspectors checked continuously during the entire hot hydrotest the performance of tests on equipment and systems, and fulfilment of their success criteria. In this respect, the ÚJD SR inspectors highly evaluated the workload and expertise of the staff of the commissioning unit of EMO 3 & 4 and the contractors.

ÚJD SR requested from Slovenske Elektrárne, a. s., a detailed analysis of the activities of tested systems and equipment for review. The analysis should demonstrate whether the tested systems worked in accordance with the design during the test.

Although preliminary results suggest a successful test run, ÚJD SR will only issue the final assessment of the hot hydrotest on the basis of an evaluation of the results of inspection activity during the hot hydrotest, and based on the assessment of the submitted documentation. According to the results of the submitted analyses, ÚJD SR accepts the hot hydrotest, or decides about repeating some tests.

Integral Tightness and Strength Test of the Hermetic Zone:

From March 15 to March 23, 2019, the integral tightness and strength test was carried out in the hermetic areas. This is a test of rooms located around the reactor and its basic equipment (hermetic zone). The purpose of the hermetic zone is to capture radioactive substances that may be released from the cooling circuit of the reactors in the event of leakage, and their reliable separation from the environment. During the test, the hermetic zone was pressurized with air up to 250 kPa (cca 2.5 atm., absolute pressure), leaks (tightness) and deflections of selected walls (strength) were measured. The measurement results (tightness and strength) are significantly better than the required criteria.

Extended Revision of the Primary Circuit:

Extended revision of the primary circuit after the hot hydrotest started on 23 March 2019 and is still ongoing. The purpose of the extended revision is to carry out all necessary inspections of systems and equipment, to assess their status after the hot hydrotest and before the fuel is loaded to the reactor.