J. Plasma Fusion Res. SERIES, Vol. 9 (2010) Lessons Learned from KSTAR Construction and Commissioning J. S. Bak, H. L. Yang, Y. K. Oh, Y. S. Kim, Y. M. Park, K. R. Park, W. C. Kim, M. K. Park, Y. S. Bae, I. S. Whang, K. W. Cho, Y. J. Kim, M. Kwon, G. S. Lee and the KSTAR Team National Fusion Research Institute (Received: 15 October 2009 / Accepted: 9 March 2010) KSTAR is an advanced tokamak with fully superconducting coils for the steady state research, which began in December 1995 and was completed in July 2008. As a single science project, it has been marked as the largest construction project in the history of Korea. During the construction period, we encountered several challenges, such as technical issues, cost overrun and schedule slippage. Nevertheless, we managed to overcome the difficulties through the devotion of all the participants under a strong leadership, and we finally succeeded in the first plasma discharge of 133kA/865ms in July 2008. Therefore, KSTAR, the first Nb3Sn based fully superconducting tokamak, has been recorded as the device that passed its commissioning without failure at its first trial. And as we speak, KSTAR is sustaining its momentum for the next campaign: it is getting ready for its operation of the toroidal magnetic field of 3 Tesla. At this presentation, we focus on the actual applications and resolutions applied to surmount the difficulties we faced during the KSTAR construction, as well as the events that occurred behind the scenes. Despite the scale difference between KSTAR and ITER, we strongly believe that the presentation will provide a great insight to the construction of the ITER device, which is very similar to KSTAR in terms of design and characteristics. Keywords: tokamak construction, performance, cost, schedule, preparation, leadership 1. Introduction KSTAR, the Korea Superconducting Advanced Research, is a tokamak construction project, which began in December 1995 (Fig. 1) and was completed in July 2008 (Fig.2). There are similarities and differences between KSTAR and ITER. But, one thing we should recognize is that they are both Nb3Sn based fully superconducting tokamak devices[1]. In the course of the KSTAR construction, we were excited from our achievements but also disappointed from our mistakes. At this presentation, we are going to Fig.2 Ceremony for KSTAR first plasma (15, Jul., 2008) highlight how much effort we made, how many trials and construction, hoping that our presentation will be of a errors we experienced in order to overcome the good service to you. We begin with actual cases of eight difficulties we faced during the construction. In critical sub-systems of KSTAR[2]. addition, we will share with you untold stories of the 2. Main Structure Following the completion of the concept design in 1998, we started the engineering design in 1999 and finished in 2001. During this period, we managed to identify many engineering issues by manufacturing a real size 62 ° vacuum vessel sector. From 2001, the negotiation for the procurement contract was put in place with Hyundai Heavy Industries (HHI), and we signed the contract in May 2002. And for the next two years, we completed the fabrication of the cryostat, vacuum vessel Fig.1 KSTAR project launch (29, Dec., 1995). and support structure[3,4]. author’s e-mail : [email protected] ©2010 by The Japan Society of Plasma Science and Nuclear Fusion Research 658 J.S. Bak et al., Lessons Learned from KSTAR Construction and Commissioning So, what really happened during this period? The assembling the last thermal shield of the vacuum vessel first obstacle of the main structure construction was that it followed by the assembly of the cryostat thermal shields consumed too much time to conclude the actual (CTS) in 2007. And the soundness of the CTS piping procurement contract. What was the principal reason? An system was verified at the time of the vacuum engineering design that was too idealistic and thus, lacked commissioning for the entire cryostat[5]. feasibility. Accordingly, we had to reassess the In the beginning, we failed to make any substantial engineering design in full measure, taking into advances in spite of long R&D hours. Therefore, we were consideration actual conditions, such as manufacturer’s left with insufficient time for the real design and its capacity, material supply schedule, and the feasibility of manufacture. In its manufacture stage, the poor required specifications. Then, we also decided to performance of Air Liquide, which was contracted to rearrange excessive design margins, which had been supply thermal and structural analyses on top of the reflected in the existing construction, to reduce the cost. concept design, resulted in an unstable management of Still, the tolerances remained unreachable as they were schedule. Another difficulty we faced was to develop a initially set too high. All of the industries argued that it procedure of assembly and assembling jig & fixtures for was impossible to maintain the welding distortion within a the vacuum vessel and vacuum vessel thermal shields permitted limit due to an excessive load of welding. And (VVTS), because these two have different dimensions. the complexity of the structure made it difficult to conduct Moreover, it was not easy to find out how surface the non destructive test (NDT) as well as the formation of condition of the plated thermal shields would affect the its shape. Furthermore, it was still too early to expect the emissivity, and how the development of one of the core industries to have a solid grasp of knowledge on the technologies, the silver plating technology, would turn vacuum test on welded parts. out. But the most difficult part was figuring out how to How did we resolve these problems and difficulties? efficiently lay out the cooling piping system, which is Above everything else, we conducted a cost re-estimate. closely connected with the localization of the leak zone. We firmly believe that the cost estimate should be based We reviewed a wide variety of manufacturing on the accurate estimate of the quantity of raw material. methods to avoid a vacuum leak and then conducted As long as you comprehend this method and process, you several preliminary tests in extreme conditions utilizing a will not lose in the battle of price negotiation with prototype. The impact on the silver plated shield panel suppliers. In the actual process, we examined the when it was exposed to the extreme environment was not possibility to manufacture through a prototype and as serious as we feared. As you all recognize, the vacuum established the practical manufacturing method and leak issue is not a simple one. We did experience a process prior to the manufacture. And to minimize the vacuum leak at cryostat thermal shields (CTS), and it risks, we made our best choice by adopting the most took us three months to pinpoint the exact spot as the reliable methods. In other words, we ameliorated and manifold was not sufficiently subdivided. If the cryogenic applied proven technologies instead of introducing new, valve was already installed, we believe it would have uncertain technologies. In some cases, we did mitigate been much easier. This accounts for the importance of the tolerance level. However, mitigating tolerance levels localization. And, we used bellows for joining some should not affect the performance of the device. What we neighboring thermal shield sectors, considering heat are trying to point out is that taking the practical approach shrinkage upon cooling. Based on our observations, it has may enhance the reliability of the device. For example, high leakage potential. So, it is best not to use bellows. we did try to improve the weld by attaching back plates to But if a leak is detected, this is the first spot to look into. parts where the shielding gas could not be delivered. You might assume that using back plates may cause a corrosion problem. But it could be much more dangerous, 4. Superconducting Magnet particularly if you fail to successfully weld the parts with We invested the first two years in establishing the no back plates attached. infrastructure for the concept design, its manufacture and the test. And for the next two years, the engineering design was completed along with the manufacture and test 3. Thermal Shield for the first cable-in-conduit conductor (CICC), as well as We carried out basic R&D and the concept design the facilities for coil manufacture. And then, we managed until 2002. In practice, more detailed design work was to manufacture 4 coils for the next three years by 2003. launched in 2002. The engineering design was provided We will explain later why the progress got delayed. But by Air Liquide and the design for manufacturing was the 7-year work period produced 4 magnets, yet we still supplied by a local company called Wonshin. Then, we had to make some decisions. What was left for us to do started to manufacture full-scale thermal shields in 2004 was to finish manufacturing 30 coils by 2006[6]. and completed in August 2006. We did this by 659 J.S. Bak et al., Lessons Learned from KSTAR Construction and Commissioning As mentioned earlier, the first problem we faced was that there were still too many issues to be resolved and decisions to be made. Even though we were confident with the R&D results of the superconducting magnet, it was still challenging to put the results into practice in the project execution. Additionally, the manufacturing process was not sufficiently evaluated or concretized at the specific engineering phase. Unfortunately, the fundamental problem was that we executed a construction project just like a R&D project.