The Slovak Nuclear Regulatory Authority (ÚJD) has issued the final authorisation for commissioning of unit 3 of the Mochovce nuclear power plant. Operator Slovenské elektrárne expects soon to start loading fuel into the reactor's core ahead of its commissioning.

Mochovce units 3 and 4 (Image: Slovenské electrárne)

Construction of the first two 471 MWe VVER units at the four-unit Mochovce plant started in 1982. Work began on units 3 and 4 in 1986, but stalled in 1992. The first two reactors were completed and came into operation in 1998 and 1999 with a project to complete units 3 and 4 beginning ten years later. The final design includes many upgrades to safety and security, including increased aircraft impact protection and emergency management measures based on lessons from the Fukushima accident which were incorporated during the project.

In December 2016, Slovenské elektráne applied for licences to commission Mochovce 3 and 4, to receive the fresh nuclear fuel they would need to start and to operate radioactive waste storage facilities as 'early use' commissioning activities.

However, ÚJD said that there were shortcomings in those submissions "caused by the state of readiness of the Mochovce 3 and 4 nuclear facility to perform the required tests and to document their results". Slovenské elektráne had addressed these issues by February 2018.

Meanwhile, ÚJD received an appeal against its decisions so far from Austrian anti-nuclear group Global 2000, and the regulator raised this with its 'second instance' authority, the president of ÚJD. The contested decisions were "examined in their entirety", said ÚJD, and the appeals were rejected in two separate decisions.

In February 2020, ÚJD published a positive draft decision on commissioning Mochovce 3 and again Global 2000 responded in the public comment period. This resulted in extensive inspections of Mochovce 3's piping. In May 2021, ÚJD decided to issue the commissioning permits for that unit, which again was appealed by Global 2000.

In January this year, ÚJD announced its draft decision to uphold the May 2021 decision to issue the commissioning permits, with all avenues for appeal exhausted.

ÚJD on 25 August issued a second-instance decision in which it rejected an appeal against the unit's launch and confirmed the first-instance decision permitting Mochovce 3 to begin operating.

Slovenské elektráne noted the decision was preceded by a number of technical inspections and tests of all systems and equipment, which demonstrated readiness for putting the nuclear facility into operation.

"Readiness of the reactor for the first fuel assembly loading and the beginning of active tests had to be demonstrated comprehensively by the investor in all areas considered, from the completion of construction objects, through the completion of the installation of technological systems, successful verification of project functions by the series of inactive system and integral tests, removal of identified deficiencies and shortcomings, securing fire and radiation protection, environmental protection up to preparedness staff and operational documentations," the regulator said.

Commissioning process

The ÚJD's decision will enter into force after 15 days. "From the legislative point of view, the loading of fuel, which begins the commissioning of nuclear installation, is possible on the day of the entry into force of the issued decision," ÚJD said.

"The launch of the nuclear block is an important milestone, it is great news for our company and for Slovakia. Especially now, at the time of the energy crisis," said Slovenské elektráne CEO Branislav Strýček. "The third block of Mochovce and our people are ready for launch. We will start loading the fuel into the reactor immediately after this permit becomes valid."

The physical launch of the reactor will begin once fuel loading has been completed, Mochovce plant director Martin Mráz noted. "After its completion, the stage of energy start-up follows, when the power of the reactor is gradually increased. We need roughly 18 weeks to achieve 100% performance," he said.

The commissioning phase ends after all physical and energy start-up tests have been carried out, with a 144-hour demonstration run at full power. The reactor will start supplying electricity to the grid after synchronisation with the grid, which will happen at 20% nominal power.

Generation from Mochovce 3 will cover about 13% of Slovakia's total electricity consumption, increasing the share of nuclear energy in the total electricity mix from 52% to 65%, according to Slovenské elektráne. The annual production of the reactor will save 2.6 million tonnes of carbon dioxide emissions annually, it added. "After the start of production, Slovakia will become self-sufficient in supplying the country with electricity."

The Ministry of Economy added, "The start-up of the fourth unit of the Mochovce nuclear power plant could be put into operation in approximately 21 months, i.e. in the spring of 2024."

Researched and written by World Nuclear News