A pulsed steam relief safety device (IPU PG – Impulsnoe Predokhranitelnoe Ustroistvo Sbrosa Para) has been developed by St Petersburg-based engineering company OKAN specifically for units 1-4 of the Akkuyu NPP under construction in Türkiye. The design can also be used on newly constructed VVER-1000 and VVER-1200 power units, including during modernisation.
The IPU PG is an element of the system for protecting the main pipeline from excess pressure. It is part of a steam valve block and is installed in the steam chambers of VVER-1200 reactor plants. Each steam chamber is equipped with two PG IPUs – main and reserve.
The product is designed to quickly release steam into the atmosphere in emergency situations. Its design ensures opening and closing of valves in no more than one second, releasing superheated steam with a design temperature of up to 350°C. Pressure and temperature operating conditions require the device to be highly reliable, instantaneous and resistant to extreme loads, including seismic ones.
“Development of the IPU PG took about three years, and the production of the prototype was carried out in parallel with the design work,” said Nikolai Buravsky, General Director of OKAN. “The tests lasted about a year, and during this time the device confirmed its reliability and compliance with the high requirements of the nuclear industry. To date, we have supplied eight such devices to unit 1 of the Akkuyu NPP and plan to supply another 24 units for units 2-4 in the near future. This is an important step towards large-scale import substitution, ensuring the technological independence of the industry.”
Design of the IPU PG took into account: new requirements of JSC Atomenergoproekt for digitalisation and control systems; increased loads associated with increased turbine power; experience in operating similar systems at the Leningrad, Novovoronezh and Belarusian NPPs; typical operational problems (blockages, maintenance complexity, maintainability).
Key technical solutions included an electrically actuated valve actuator (DN32) that could open at full speed in 0.3 seconds. This was used for the first time in the design of an IPU PG instead of classical solenoid valves. This showed reliable operation of the device at an emergency temperature of more than 180 ° C in the steam chamber. The complete modularity of the design made it possible to avoid welded joints. The control elements are located on the rear wall of the main safety valve, the structure is easily disassembled and maintained on site without dismantling.
Minimising surfacing and welding was critical for improving maintainability and reliability. The new approach allowed for easy recovery and diagnostics. OKAN’s own filter elements were used for in a PG IPU. The filters are quickly replaced according to the cartridge principle, without disassembling the device. An adjustable throttle on the reset line made it possible to adjust the opening and closing times of the valve without changing the design. The setting is done with a key.
The device uses more than 15 reed switches (limit switches) to control the positions of the valves. The reed switches were designed and manufactured by OKAN specifically to meet the requirements of the IPU PG for Akkuyu NPP.
More than 20 contractors from Russia and Belarus participated in the project, each of which was involved taking into account its technological features, profile and experience. All structural elements were produced with subsequent 100% input control at the OKAN site, which ensured not only quality control of all parts and preventing defects from entering the final product, but also ensured absolute traceability of each component from the raw material to the final product. This approach ultimately allowed each IPU PG to pass acceptance tests the first time.
As a result, localisation of more than 90% was achieved. The housing elements, pipeline fittings, position sensors, control units and filter elements were entirely Russian-made. The reed sensors (limit switches) specially developed for NPP use replaced imported analogues. The only remaining component of foreign origin is one of the electric drives, but in the next stage OKAN plans to replace it with a completely Russian version.
OKAN conducted an extensive testing programme of each valve and assembly as well as seismic tests and vibration resistance on a full-scale bench. The electric drive exceeded the calculated service life by more than twice without repair. Comprehensive acceptance took about a year. The device showed stable operation in all specified modes, including emergency and unstable ones.
“In the first phase, separate tests were carried out on key components of the system, including the electrically operated pulse valve and control units,” said Dmitry Kravchenko, head of the company’s testing department. “Particular attention was paid to the speed of their operation and the accuracy of control signals, as well as checking their operation under high temperature loads and modelling emergency situations. These measures made it possible to assess the reliability and stability of the system in conditions close to real ones.”
The IPU PG is designed to be versatile. It can be adapted for use on any power units of the VVER-1200 generation, both during construction and during modernisation. OKAN is ready for mass production and is considering the potential for export.
