Slovak utility Slovenske Elektrarne (SE) said on 12 September that it does not expect technical corrections required by the Slovak Nuclear Regulatory Authority (UJD) to further delay the planned launch of new units at its Mochovce NPP. 

However, following the completion of hot testing, UJD said a number of deficiencies on first of two new 470MWe units must be remedied before fuel loading can begin.

During the tests, which included heating and pressurising the reactor and assessed the cooling circuit and safety systems for reactor core cooling, UJD identified a large number of seemingly unrelated minor deficiencies that could have a synergic effect, potentially causing complications during commissioning of the unit.

SE said the modifications would not have a significant impact on the schedule and the budget, currently estimated at €5.4 billion ($5.91 billion). Mochovce 3 is now expected to be technically ready for fuel loading in autumn 2019, with fuel loading beginning in February 2020. Mochovce 4 will follow a year later.

The expansion of Mochovce nuclear plant was originally planned for launch in 2012 at a cost of €2.8 billion. The Slovak state owns 34% of SE, while Slovak Power Holding, a joint venture between Italy’s Enel and Czech energy group EPH, owns the remainder. EPH has the option to buy out Enel once Mochovce 3&4 are complete.

SE spokesman Miroslav Šarišský, commenting on the modifications required by UJD, said: "The extended revision included a thorough inspection of the reactor and other components of the primary circuit, especially the reactor internal structures, main circulation pumps, piping, volume compensator and others."

He said SE conducted visual, leak-proof, pressure, ultrasonic and other tests to check the integrity and quality of primary circuit components and to detect impurities or foreign objects. "The extended revision also included the complete dismantling and subsequent assembly of the internal reactor parts," he noted. The revision will be finally completed following an assessment of the required additional tests and a repeat pressure test of the primary circuit as a condition for authorisation to load fuel into the reactor.

SE identified a number of problems during the takeover of equipment from suppliers. These were duly recorded and the deadline for their remediation was specified by UJD. Their number was initially relatively large – in the order of thousands. However, UJD said it is gradually decreasing. "In order to confirm the readiness of the block for heating it is necessary to remove 86 deficiencies," the UJD noted.

Some experts question whether the current schedule will be met. "Probably the most time-consuming will be to repeat the pressure test, which I think is usually planned for approximately two months," said Jozef Mišák from the Czech technology company ÚJV Řež, who previously served as the chairman of ÚJD.

"I assume that minimising the impact on the schedule of work is primarily a matter of good organisation. However, in no case should the time demands for additional activities have a negative impact on their quality," he added.

Mišák said UJD’s findings reflect the responsible work of his inspectors. "At the same time, it is also a notice for SE to increase the requirements for the quality of work of its suppliers and also for the performance of their own quality control ," he said.

According to Misak, tests during the preparation for the loading of nuclear fuel are carried out precisely in order to detect any shortcomings that would affect the safety and fluency of future operation. "It goes without saying that all deficiencies must be corrected before the fuel is charged."

Hot testing took place between December 2018 and March  "The vast majority of the tests were successful. For some tests, the Office requested additional analysis by Slovenské elektrárne," UJD said. It was necessary to demonstrate, through non-standard measurements, the correct operation of the regulation of voltage and power of diesel generators under load, UJD said. "From this point of view, the findings are serious and forced the tests to be repeated." There were also problems with ventilation and coolant flow as well as electrical faults.