“The passive heat removal system (PHRS) utilizes steam generators to remove residual heat and cool the reactor core in beyond design basis accidents that cause electricity cut-offs or a total loss of feedwater,” explains Vitaly Shutikov, Head of the Reactor Department at Leningrad II, which is now under construction. “The system is unique for its ability to operate independently. It is designed to ensure sustainable removal of residual heat from the reactor core through three of four independent channels for at least 24 hours. As for now, all of the four loop channels have passed quality tests and are ready for use. They will be kept in standby mode as long as the unit is in operation.” The PHRS is one of the most important components of a nuclear power plant as it ensures safety of nuclear reactor operation in emergencies. Passive heat removal systems have been installed at Kudankulam (India) and Novovoronezh II (Russia), and are provided for in the design of Akkuyu (Turkey).
PHRS tests were carried out as part of hot functional tests meant to ensure that the core equipment as well as auxiliary and safety systems of Leningrad II are functioning as designed. Hot testing is the last major step before the start-up of the unit. “The loop channel ensures coolant circulation through the steam generator and the multi-sectional heat exchanger, which is placed inside the emergency heat removal tank and connected to the steam generator through inlet and outlet pipes. The emergency heat removal tanks are located at Level +59.850 m in the dome section of the reactor building. As they are positioned well above the steam generators, the coolant circulation in the loop is induced by gravity. “The tests have proved that the system is fully operational and capable of removing residual heat and cooling the reactor core in case of a total blackout at the plant,” said Alexander Nakonechny, a shift supervisor at the Reactor Department of Leningrad II.
Hot functional tests are conducted to check the core equipment and systems for compliance with design specifications and prove their readiness for commissioning and fuel loading. Successful hot tests will therefore mean that Unit 1 of Leningrad II is ready for fuel loading. The nuclear station has already passed almost a half of 78 functional tests.
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Leningrad NPP operates four 1000 MW reactor units. The plans are to replace this capacity with two VVER-1200-based units of Leningrad II, which is now under construction. VVER-1200 is Rosatom’s flagship reactor based on the AES-2006 design featuring a number of definitive advantages over the VVER-1000 reactor. In particular, it offers a 20% higher power capacity and a doubled service life (60 vs. 30 years) of its core components, reactor vessel and steam generator body. More important is that the new design is fully compliant with the post-Fukushima safety requirements.
The Russian AES-2006 design features an array of unparalleled safety systems. One of them is a core catcher, a unique safety device designed by Russian nuclear engineers to mitigate effects of a nuclear meltdown. In case of an accident, the core catcher medium mixes with the molten core materials and distributes them evenly inside the catcher body. The catcher can hold the molten core for an unlimited period of time, preventing nuclear materials from getting outside. The first ever core catcher was installed at the Russian-designed Tianwan Nuclear Power Plant in China. Passive heat removal is another unparalleled safety feature of the AES-2006 design. This technology allows for cooling of the reactor core in case of power outage without human involvement.
The world’s first Generation 3+ reactor has been commissioned at Novovoronezh II. New safety systems, increased service life of the primary equipment and improved automation solutions significantly reducing the need for manpower will almost double the cost efficiency of Novovoronezh II.
