A key component of the additional (passive) safety system - the melt localisation device (melt trap) – has been installed at unit 3 the Akkuyu NPP under construction in Turkey, according to Rosatom. It was unloaded at the Vostochny cargo terminal and transported to the construction site before being installed in the design position in the reactor shaft. The height of the body of the trap is 6.14 metres and the diameter is 5.83 metres. The melt trap is a container in the form of a steel cone weighing 144 tons, which, in the event of an emergency, holds fragments of the melted core. During NPP operation, it is filled with special materials, upon interaction with which the core melt loses some of the accumulated heat. The chemical processes arising from this interaction make it possible to retain and cool the melt. The device was manufactured at the Russia’s Tyazhmash plant, which specialises in the production of such equipment.
At the same time, the Volgodonsk branch of AEM-Technologies (part of Rosatom’s Atomenergomash) completed a complex technological operation to unbend a pipe billet for the bottom of the nuclear reactor for unit 4 of the Akkuyu NPP. The work was carried out in several stages using a thermal press. A forged steel billet in the form of a pipe weighing more than 80 tons with a diameter of 2.5 metres was preheated in a furnace for about two hours at a temperature of 800 degrees. The temperature was then increased to 1040 degrees for another four hours. A crane was used to transfer the red-hot billet to the press, where it was partially unbent with the help of two dies using a force is 10,000 tons. During this process the temperature of the workpiece must not fall below 800 degrees.
Next, the billet is heated for another two hours before being sent to another press where it finally becomes a square sheet using a press force of up to15,000 tons. A circle will then be cut out of the sheet to form the bottom of the nuclear reactor. Unbending makes it possible to obtain a seamless workpiece six by six metres for the reactor bottom. Sheet forgings of such dimensions are not transportable, and the manufacturing technology does not allow welded joints on the product.
Meanwhile, the Petrozavodsk branch of JSC AEM-Technologies tested the pressure compensator for Akkuyu unit 1. This is a welded thick-walled vessel consisting of four cylindrical thick-walled shells and two elliptical bottoms. The entire inner surface of the body of the product is covered with a layer of anti-corrosion cladding. Also, devices are installed in the body to ensure operation and maintenance: an inner shell to which electric heater blocks are attached, a collector, pipelines, stairs and decking. The pressure compensator is part of the key equipment of the NPP reactor hall and is designed to create and maintain pressure in the primary circuit of the reactor.
Rosatom is building four VVER-1200 reactors at the Akkuyu site, under a build-own-operate model. Construction of the first unit began in 2018, with start-up planned for 2023.
The All Russian Scientific & Research Institute for Nuclear Power Plant Operation (VNIIAES - part Russian nuclear utility Rosenergoatom) said on 29 June it had begun training control operators for the Akkuyu NPP using full-scale and analytical simulators. Until mid-August, seven groups of engineers will take part in training at the VNIIAES test site, who will later manage the Akkuyu units. They include both Russian nuclear scientists with extensive NPP experience and Turkish specialists who previously studied at Russian universities. The instructors are from the Rosatom Technical Academy, which is responsible for training the personnel of Russian NPPs built abroad.
The full-scale simulator (FMT) is designed for training, licensing and maintaining the qualifications of the operating personnel of the NPP unit control panel. The analytical simulator (AT) is a software and hardware modelling complex designed to train and maintain the qualifications of operational personnel. Both were developed by VNIIAES without using any foreign codes for modelling. Later this year, both simulators will be dismantled and shipped to the Akkuyu NPP site in Turkey.
Image: Core melt trap installation at Akkuyu unit 3 (photo courtesy of Akkuyu Nuklear)