Implementation of the emergency depressurization system – an important safety element of the Rovno NPP
18. 12. 2020
Assembly works within the project "Implementation of the Containment Emergency Depressurization System" are being carried out at the currently shut down units No. 3, 4 of the Rovno Nuclear Power Plant.
World experience in the operation of nuclear power plants regarding the possible risks of environmental pollution in the event of serious accidents (including those from the Fukushima NPP) has enabled the development of filtered emission removal technology.
The emergency depressurization system is designed for highly efficient cleaning of the steam-gas mixture formed in the containment during emergency ventilation, serves to protect the containment and it is the last safety barrier preventing the loss of integrity.
Based on a tender, ŠKODA JS a.s. was selected as the manufacturer of the equipment for the emergency depressurization system at the Rovno NPP. Based on the statement of the chief engineer (for reconstruction and renewal) of Unit No. 2, Volodymyr Sus, this emergency depressurization system combines two filtration methods - "wet" (stage 1) and "dry" (stage 2).
“Thanks to the two-stage cleaning, a high efficiency of aerosol capture is ensured, and furthermore the risk of clogging and spreading of aerosols in the metal fiber filter is eliminated. The effectiveness of this technology has been proven in many researches and tests, including independent international tests, where it achieved a filtration coefficient of 99.9% for coarse and fine aerosols and 99.5% for iodine particles. Furthermore, the system allows release of all radioactive substances accumulated in the scrubber into the containment via the drainage pipeline. The emergency depressurization system is a passive system that will only be triggered in the event of a severe accident, and it serves as another additional system, however it is an important safety element” said V. Sus.
The basic work during the installation of the device is carried out in the period between outages, the actual connection to the operated safety systems is possible only during the planned service outage. At present, the installation of a part of the emergency depressurization system - the "Scrubber Venturi" gas cleaning unit - is being completed at Unit 3 of the Rovno NPP. With regard to its external dimensions, which are 3.4 x 5.5 m, and the weight of 24 tons, it is necessary to mount the scrubber by parts. The work is performed by specialists of the subcontracting organization Atomremont, s.r.o. (city of Yuzhnoukrainin) under the supervision of representatives of ŠKODA JS a.s. Work also continues on the assembly of support structures for the gas cleaning unit, and the fittings and equipment of the chemical reagent tank are being prepared. The piping system is already 80% assembled. As for the work on Unit 4, the specialists of "JUTEM Engineering" (city of Kiev) are currently assembling the system of internal parts of the scrubber, the metal fiber filters will be instaled in the near future.
In accordance with the project, the manufacturer's representatives participate in performing tests of various levels in the nuclear power plant premises before putting the system into trial and industrial operation, they provide special training for power plant personnel and warranty service of the equipment throughout the warranty period
“The scrubber test will be performed in a few days. Tests of the entire emergency depressurization system are already scheduled before the end of the planned service outage at Unit 3 of the Rovno NPP. One of the conditions for the approval of the technical solution of the instaled system by the State Nuclear Regulatory Authority is the emission of air mixture from the containment during the performance of strength tests of the reactor containment. These tests can be performed only after the end of the planned service outage. All necessary test programs were prepared by Rovno NPP specialists and approved by the supervisory body”, concludes Volodymyr Sus.
In the following year, after comprehensive and acceptance tests of the emergency depressurization system equipment, both VVER 1000 reactors of the Rovno NPP will be equipped with new, highly efficient global technologies that will increase the level of safety in the operation of the nuclear units.
For information: The project "Commissioning of the emergency depressurization system" is implemented within the Comprehensive NPP Safety Improvement Program, which is financed from EBRD / EURATOM funds.