European
Nuclear Society
e-news
Issue 17 Summer 2007
http://www.euronuclear.org/e-news/e-news-17/czech-young-gen.htm
On 1 April 2007, an overcast morning and bitingly cold wind has chased one’s hands into the safety of warm pockets. In spite of this ten intrepid Czech “youngsters” met at 8.30 at the entrance to the Škoda JS factory – at Bolevec near the famous Czech city of Pilsen. We were welcomed there by Dr. Václav Bláha, Vice President of the Czech Nuclear Society, who was our guide throughout the visit to Škoda JS that day.
First we were introduced to the history of the Bolevec area. At the turn of the 19th and 20th century it served as a testing ground for all kinds of weapons that the Škoda company manufacturzed. Even by now there are supposed to be unexploded munitions buried below several meters of ground somewhere in the area. It started being used for the nuclear industry in the second half of 20th Century. Škoda JS is in fact the successor of the company Power Plant Construction, which was founded in 1955 and has played a key role in the development and construction of the Czechoslovakian design heavy water moderated and gaseous CO2 cooled power plant, A1, in Jaslovské Bohunice (150 MWe, operational between 1972-1977 and closed due to an accident classed 4 on the INES scale). Later on it also played a significant role in the construction of Soviet-type light water reactors (WWER) that were used all over central Europe. At present, the main operations at Bolevec are concentrated in two buildings –the so called “Light Hall” and the Experimental Hall.
In the Light Hall we were greeted by the Head of Operations, Miroslav Hejda, who explained the origins of the Hall’s name – the word “light” refers to its manufacture of products weighing less than 5 tons. At present these are namely linear step drives for control organs for reactors WWER-440 and WWER-1000, pins for carrying the CASTOR spent fuel containers and the non-nuclear parts of the nuclear fuel for WWER-1000 (fuel assembly heads and bases) for Westinghouse. The Light Hall was built 15 years ago and it is a very modern factory. The construction material used for most of the products is austenitic steel precisely machined on numerical-controlled lathes. Machined parts are then welded on special workplaces. Pride of place in the factory goes not only to the Japanese NC-lathes “Mazak”, but also to a device for electron-beam welding. Surfaces of the welded metal joint are heated inside a vacuum chamber under bombardment by electrons that are accelerated by 60 kilovolts at currents reaching up to 250 milliamperes (the maximum input is, therefore, 15 kW). The process can be seen through a lead-glass partition to protect staff from fast electron induced X-rays. This clean way of welding without any additional welding components makes it possible to weld parts up to 4 cm in depth (from one side – welds from both sides allows welds of up to 8 cm deep). It masters the welding of most metals and is very useful for welding high carbon-content steels (max. 22 % C). However, it can not weld zinc as it quantitatively evaporates in the combined high temperature/low pressure conditions. After welding the products are transferred into the assemblage hall, where they are de-greased and tested for flaws – especially their welds. The employed testing techniques include¬ ultra-sound, X-ray and magnetic fluorescence analyses. At the end of the process the finished products are displayed on stands prepared for the customer.
Czech YG members assembled in front of the Škoda JS Reactor
Hall, around a symbolic model of a VVER-440 reactor vessel that was produced
there on many occasions.
Next Dr. Bláha showed us the Experimental Hall which was originally used for the gas cooled programme of the heavy water moderated A1 reactor. Because of its earlier function it is no less than 24 meters high to be able to house the long gas channels. However, the gas programme was cancelled (not only due to political reasons) in 1968 and, in connection with the light-water programme, a water-circuit adapted to the parameters of a WWER-1000 reactor was installed there. It has been used, e.g., for testing control rod drives under real operation thermo hydraulic conditions. In addition to the water loop, an independent sodium loop was installed in the Experimental Hall as part of the fast reactor research programme, but it never actually was operational. In the 1990s, hexagonal fuel assemblies made by Westinghouse for the Temelín NPP (2 x WWER-1000) were intensively tested, particularly for heat-transfer crisis – a phenomenon that causes rapid fall of heat-transfer from the over- heated fuel rod to the cooling medium due to the formation of a thin vapour film on the surface of the cladding. New tests are currently being planned in connection with the change of the Temelín NPP’s fuel supplier from Westinghouse to the Russian firm TVEL.
After visiting the Experimental Hall we headed south by car from the wooded Bolevec area into the factory-grounds of the originally jointly-owned Škoda company, which is located in the Pilsen city centre. Within the cluster of factory buildings the companies that took over from the old machinery-making giant are located. As we made our way through the labyrinth we passed the main factory of Škoda POWER, which manufactures turbines. However, we were also interested to visit Škoda JS’ second key manufacturing plant – the Reactor Hall. Head of Operations, Miroslav Nolc, explained that the building is 27 years old and its 40 meters tall and that the lifting-capacity of the strongest crane is 400 tons. In the past, the Hall produced WWER 440 and 1000 reactor vessels, but after the completion of Temelín NPP the nuclear programme slowed down and production was focused temporarily on reactor vessels for the chemical industry (with no lower requirements, one chemical reactor for ammonia production could run tests under a pressure about 50 MPa) and for CASTOR spent fuel containers.
As we passed through the Reactor Hall, we could see that production was devoted exclusively denoted to the nuclear power industry, because Škoda JS has been successful on the markets of Western Europe. IN addition to the production of CASTOR transport containers (the older type) for the Obrigheim NPP (Germany), we saw production linked to that “symbol of European nuclear renaissance” – the European Pressurized Reactor for Olkiluoto 3, in Finland.
Although the number of CASTOR containers being manufactured was high (in total 15), all the production process steps were demonstrated at each individual work-station. The 120 ton steel-iron cast in the form of a hollow cylinder that is closed at the bottom is supplied by the steel foundry of the Škoda Steel company. It is machined by first cutting inner steps for two hermetical lids. Vertical sample-drills are then made through the container walls (to test the metal’s homogeneity). If the analysis yields positive results, the whole diameter of the container is drilled with long vertical holes, in which special polyethylene rods will be inserted to slow down the fast neutrons arising from the spontaneous fission of higher transuranic elements contained in the spent fuel. After preparing the places where the carrying-pins are inserted, the flat surface of the cylinder is machined into characteristic ribbing to allow better heat-removal. Once all the mechanical adjustments have been made, the vessel is then galvanised with a 3-millimeter thick layer of nickel (during this process the vessel is filled with an electrochemical nickel-solution) for 7 days. After the internal nickel coating, the external surfaces are shot-blasted in a special container with an abrasive powder stream (and, therefore, de-greased) in order to make the protective varnish paint - which was blue in this case - stick better to the surface. Apart from the CASTOR containers, CONSTOR containers for the Lithuanian NPP Ignalina are also made in the Reactor Hall. These containers are different insofar as they are not just metal - the hollow space inside the metal double wall is filled with concrete.
The Hall has a variety of giant milling cutters and drilling machines for machining the metal products. We were primarily told that the boring mill schies capable of work with up to 10 meters large objects and about a giant automated welding machine (using welding flux). The machining modifications create mechanical stresses that have to be removed by heating – which is done inside one of the two giant electrical furnaces that reach temperatures of up to 800°C.
AREVA has chosen Škoda JS as a supplier for the internal parts of the EPR reactor vessel (European Pressurized Reactor, 4500 MWt, 1600 MWe). In the Reactor Hall we had, therefore, a chance to stand inside the steel neutron reflector of the squared reactor core – at that time it contained stacked, un-welded rings. We saw the inner reactor barrel and we observed the very slow circular precision grinding process carried out by one of the control rod stabilizing grids. In addition, we were also shown the welding of the reactor-supporting ring. The reactor pressure vessel itself is being manufactured in Japan, because the stringent requirements for low number of metal welds of such a great vessel increases the minimum metal ingot weight to levels that can be met only by the steel-works of Mitsubishi Heavy Industries.
We would like to give a special vote of thanks for the successful organization of the trip to Dr. Bláha and the Škoda JS company as the last part of our excursion in Pilsen was not to the Škoda factory but to the world-famous Plzenský Prazdroj a.s. brewery (although its name is more popular in its German version - Pilsner Urquell - that can be roughly translated into English as "The Headspring of Pilsen."). In the brewery, founded in 1842 as “The Citizens’ Brewery of Pilsen”, a professional guide – Mr. Hála – gave us a tour around the brewery and showed us roughly how Pilsner Urquell beer is brewed. He led us from a very nice Info center through a small gate into the factory itself. There a small mini-bus took us to the most modern part of the factory that was finished only this year – a bottling plant with a surface area of 2000 square meters! In this great hall, which cost over 1 billion Czech Crowns (35 million €) to build, there are lines for the control & removal, washing and filling of glass bottles (plus an extra one for filling alluminium cans, of course). The glass bottles are removed and re-melted after 3 or 4 cycles between the brewery and its customers. The bottling plant can produce over 60 thousand bottles a day, even though more than half of its space is no longer used and is awaiting possible expansion. In fact, only some of the bottles are filled with Pilsner Urquell beer. The plant also bottles other beer brands produced by breweries belonging to the Pilsner Urquell group (Gambrinus, Radegast and Velkopopovický Kozel).
Next we passed by an array of tall vertical cylindro-conical fermenting tanks, where the beer maturing process takes place, and the historical 46 meters tall water tower. Then we visited the newly-built brewery where the giant copper and stainless-steel kettles contain the “mash” (mixture of water and crushed barley malt) that then forms a fermentable liquid called “wort” (a water mixture of simple sugars generated by boiling off the starch from the barley grains). This is that is then mixed and boiled with hops, which give the beer its characteristic taste.
Finally, we visited the underground part of the brewery, which is not used nowadays except for a very small part where the company has preserved the historical way of maturing beer in cold cellars in wooden tubs and barrels. Under the brewery are large underground cellars that were mined out during the 19th Century. They once housed around 6 000 wooden barrels containing up to 30 or 40 hectoliters. The fresh (so called “green”) beer produced by 1 week of fermentation in opened tubs at temperatures slowly rising from 5 to 9 °C had been transferred into the great barrels, where it slowly matures into its final form over several months. When the maturing process is over, the beer was transferred into small beer barrels and distributed all around the country to the local pubs. At present, the brewery has 13 fermentation vats and 90 oak barrels – we were invited to test a specimen of this historical beer, which is different from the contemporary beers by its significant content of beer yeast. All presently mass-produced beers are filtered from the yeast (since the beginning of 20th century) and pasteurized (since the end of the Second World War). So, it was a memorable ending to a long day.
© European Nuclear Society, 2007