atw - International Journal for Nuclear Power | 05.2020

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atw Vol. 65 (2020) | Issue 5 ı May 294 NEWS | Inside the plasma vessel: The previous cladding with carbon tiles has been abandoned; the vessel is ready for installation of the new water-cooled wall protection. Photo: IPP, Torsten Bräuer Greifswald is in full swing. Watercooled inner cladding of the plasma vessel will make the facility suitable for higher heating power and longer plasma pulses. Production of the new cladding’s centrepiece, the so-called divertor, was taken over by the institute’s Garching branch. For tomorrow, final delivery to Greifswald is scheduled, where the preparations for installation of the components have been completed. The installation work will last until well into next year. Wendelstein 7-X, the world's largest stellarator fusion device, is to investigate the suitability of such devices for power plants. At the end of 2018, the experiments on Wendelstein 7-X were temporarily terminated after two successful work phases (see PI 11/18). Upgrading of the plasma vessel has been ongoing since then. “First of all, most of the old components had to be taken out. Installation of the new ones can now begin,” says Prof. Dr. Hans- Stephan Bosch, whose division is responsible for technical operation of the device. Whereas most of the wall protection components were previously operated uncooled, large sections of the wall will be watercooled starting with the next round of experiments: “This will then enable Wendelstein 7-X to generate plasma pulses lasting up to 30 minutes”, states Professor Bosch. Centrepiece of the new wall cladding is the so-called divertor, the most heavily loaded component of the plasma vessel. In ten double strips on the inner wall of the plasma vessel, the divertor tiles follow the curved contour of the plasma edge. They protect those wall areas to which particles from the edge of the plasma are magnetically directed. A pump behind a gap in the middle of each double strip removes the impinging plasma and impurity particles. In this way, the divertor can be used to control the purity and density of the plasma. Demanding manifacture In the high-performance experiments planned, the new water-cooled divertor plates, which replace the previous uncooled ones, are designed to withstand a load of up to ten megawatts per square metre – like a space shuttle re-entering the Earth’s atmosphere. Without water cooling, however, the heat-resistant divertor tiles made of carbon-fibre-reinforced carbon could not withstand this load for the intended 30-minute plasma pulses. They are therefore welded onto water-cooled plates made of a copper-chromium-zirconium alloy. The coolant, supplied by small steel tubes, ensures that the heat energy is removed. Each of the ten curved divertor strips consists of twelve of these plates, which in turn are composed of individual elements. In total, these 890 elements comprise almost half a million individual parts, from the heat-resistant surfaces to the special screws. The high-performance components are the result of a long development, manufacturing and testing process carried out by the Integrated Technical Centre (ITZ) and the “Components in the Plasma Vessel” work group at IPP in Garching in cooperation with industrial com panies. “The complex geometry of the components was particularly challenging, given the high level of accuracy and reliability required,” explains IPP engineer Dr. Jean Boscary, who headed production and assembly of the “big puzzle”: “There should be no water leakage later in Wendelstein 7-X”. Accordingly, already the preparatory work was extensive: In 2003, the development and production contract for the divertor elements was concluded with an industrial company. After four preseries and more than 60 prototypes, five years of series production could start in 2009. To complete a divertor element, 82 manufacturing steps and 44 tests were necessary. The surface of each of the 16,000 carbon tiles had to be milled three-dimensionally into shape – with tolerances of sometimes only 0.1 millimetres to avoid any overheating of protruding edges. The joining technique between carbon and copper alloy was specially developed for Wendelstein 7-X. At IPP in Garching, the divertor elements were then joined together on steel frames to form plates. Cooling pipes and cooling water distributors were joined by means of a special welding technique developed at the ITZ: “Among the 2,000 welded joints, the subsequent tests were only able to detect two leaks,” says Dr. Boscary. In other respects, too, there were always quality assurance tests between the individual work steps. For production control, for example, the load capacity of the parts was examined in Garching's GLADIS heat test rig. The experience gained in this “largest heat protection project in fusion research to date” is unique worldwide, Jean Boscary emphasizes. All ten divertor strips have now been completed. A major part has already been delivered to IPP at Greifswald; the last transport is scheduled for tomorrow. Challenging assembly At Greifswald, everything is prepared for installation of the high- performance components: In particular, the water pipes are installed in the plasma vessel, a total of 4.5 kilometres. “In the meantime, we have started laying the complex water pipes that bridge the last 40 centimetres between the vessel wall and the divertor plates,” explains assembly head Dr. Lutz Wegener. Later on, the plates must fit exactly to these connections. Although the extremely tricky work had previously been practised in a one-to-one model – “virtually a double assembly,” says Dr. Wegener – there are surprises when installing the 240 fitting pipes. The great tightness between the components makes welding a challenge, for which a special precision technique is used anyway. Often new designs and new manufacturing are necessary. In the narrow space also many screws are News
atw Vol. 65 (2020) | Issue 5 ı May Operating Results January 2020 Plant name Country Nominal capacity Type gross [MW] net [MW] Operating time generator [h] Energy generated, gross [MWh] Month Year Since commissioning Time availability [%] Energy availability [%] *) Energy utilisation [%] *) Month Year Month Year Month Year 295 OL1 Olkiluoto BWR FI 910 880 744 690 053 690 053 270 155 522 100.00 100.00 100.00 100.00 100.81 100.81 OL2 Olkiluoto BWR FI 910 880 744 689 116 689 116 260 053 202 100.00 100.00 99.93 99.93 100.68 100.68 KCB Borssele PWR NL 512 484 744 380 431 380 431 168 361 865 99.58 99.58 99.57 99.57 100.16 100.16 KKB 1 Beznau 7) PWR CH 380 365 744 286 929 286 929 130 595 749 100.00 100.00 100.00 100.00 101.56 101.56 KKB 2 Beznau 7) PWR CH 380 365 744 285 111 285 111 137 581 894 100.00 100.00 100.00 100.00 100.94 100.94 KKG Gösgen 7) PWR CH 1060 1010 744 792 734 792 734 322 908 969 100.00 100.00 99.80 99.80 100.52 100.52 CNT-I Trillo PWR ES 1066 1003 744 786 250 786 250 256 534 276 100.00 100.00 100.00 100.00 98.69 98.69 Dukovany B1 PWR CZ 500 473 744 374 399 374 399 116 258 583 100.00 100.00 100.00 100.00 100.64 100.64 Dukovany B2 PWR CZ 500 473 744 371 137 371 137 111 414 455 100.00 100.00 99.81 99.81 99.77 99.77 Dukovany B3 PWR CZ 500 473 580 284 866 284 866 110 536 602 77.96 77.96 76.86 76.86 76.58 76.58 Dukovany B4 2) PWR CZ 500 473 0 0 0 110 706 957 0 0 0 0 0 0 Temelin B1 4) PWR CZ 1080 1030 664 712 309 712 309 122 627 122 89.25 89.25 88.38 88.38 88.48 88.48 Temelin B2 PWR CZ 1080 1030 744 815 233 815 233 118 297 851 100.00 100.00 100.00 100.00 101.27 101.27 Doel 1 2) PWR BE 454 433 0 0 0 137 736 060 0 0 0 0 0 0 Doel 2 2) PWR BE 454 433 0 0 0 136 335 470 0 0 0 0 0 0 Doel 3 PWR BE 1056 1006 744 805 963 805 963 263 917 613 100.00 100.00 100.00 100.00 102.00 102.00 Doel 4 PWR BE 1084 1033 744 817 807 817 807 270 456 082 100.00 100.00 100.00 100.00 99.92 99.92 Tihange 1 2) PWR BE 1009 962 0 0 0 307 547 424 0 0 0 0 0 0 Tihange 2 PWR BE 1055 1008 744 781 306 781 306 258 835 824 100.00 100.00 99.99 99.99 100.50 100.50 Tihange 3 PWR BE 1089 1038 744 806 745 806 745 281 369 321 100.00 100.00 100.00 100.00 100.18 100.18 NEWS Plant name Type Nominal capacity gross [MW] net [MW] Operating time generator [h] Energy generated, gross [MWh] Time availability [%] Energy availability [%] *) Energy utilisation [%] *) Month Year Since Month Year Month Year Month Year commissioning KBR Brokdorf DWR 1480 1410 744 947 448 947 448 361 668 470 100.00 100.00 94.14 94.14 85.65 85.65 KKE Emsland DWR 1406 1335 744 1 046 514 1 046 514 358 646 715 100.00 100.00 100.00 100.00 100.13 100.13 KWG Grohnde DWR 1430 1360 744 994 849 994 849 389 269 695 100.00 100.00 99.97 99.97 92.91 92.90 KRB C Gundremmingen SWR 1344 1288 744 1 004 133 1 004 133 342 327 685 100.00 100.00 100.00 100.00 99.94 99.94 KKI-2 Isar DWR 1485 1410 744 1 102 078 1 102 078 366 864 547 100.00 100.00 99.98 99.98 99.52 99.52 GKN-II Neckarwestheim DWR 1400 1310 744 1 042 000 1 042 000 341 280 244 100.00 100.00 100.00 100.00 100.28 100.28 difficult to access for tools and a solution has to be found on a case- bycase basis: “Welded or screwed – the connections should remain tight for the next twenty years”. Compared with these tasks, subsequent installation of the divertor plates should be easier. “We have already developed special tools for this purpose – for example to lift and move the 70-kilogram plates,” says Lutz Wegener. Even the kick plate, on which the technicians in the vessel walk over the sensitive divertor and wall protection tiles, was a separate development project: it had to guarantee safe standing in a very confined space and be adapted to the unusual shape of the plasma vessel. On the other hand, it must not damage the wall structures or lead to any impurities that could later perturb the plasma. Plasma operation is expected to resume at the end of 2021. It is planned to begin with low water cooling, low heating power and short plasma pulses in order to allow testing of all installations in operation after the long break in experiments. With full cooling, longer pulses with plasma energies of up to one gigajoule should be possible – a target that will be slowly approached. Instead of the previous hundred-second pulses with heating powers of two megawatts and plasma energies of 200 megajoules, the cooled high-performance divertor should later allow pulses lasting up to 30 minutes at full heating power. Wendelstein 7-X will then be able to demonstrate the essential advantage of stellarators, namely their ability to operate continuously. | www.ipp.mpg.de (201121501) Reactors Finland, Hanhikivi-1: Fennovoima announces details of progress with basic design review (fennovoima, nucnet) The company building the Hanhikivi-1 nuclear power plant in Finland has received 222 documents from the Russian plant supplier, of which 134 have been conditionally accepted, 54 rejected and 34 remain under review. At the end of 2019, Fennovoima was still waiting for the delivery from Raos Project Oy, a subsidiary of Russian state nuclear corporation Rosatom, of the basic design packages of the turbine island and buildings, of which the basic design documents for buildings are – except for the control room building – almost complete. *) Net-based values (Czech and Swiss nuclear power plants gross-based) 1) Refueling 2) Inspection 3) Repair 4) Stretch-outoperation 5) Stretch-inoperation 6) Hereof traction supply 7) Incl. steam supply BWR: Boiling Water Reactor PWR: Pressurised Water Reactor Source: VGB News
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atw - International Journal for Nuclear Power | 05.2020

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