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atw 2018-03v6


atw Vol. 63 (2018) | Issue 3 ı March ENVIRONMENT AND SAFETY 158 32. A. Carnino, M. Gaparini, Defense in depth and development of safety requirements for advanced reactors. Workshop on Advanced Nuclear Reactor Safety Issues and Research Needs, Paris; February 18–20, 2002. 33. IAEA, Defence in Depth in Nuclear Safety, IAEA; INSAG-10, IAEA, Vienna, 1996. 34. J.N. Sorensen, G.E. Apostolakis, T.S. Kress, D.A. Powers, on the role of defense-in-depth in risk informed regulation. Presented at PSA’99, Washington DC, USA, August 22–25, La Grange Park, IL, USA: American Nuclear Society; 1999. 35. M. Modarres, Advanced nuclear power plant regulation using risk-informed and performance-based methods, Reliability Engineering and System Safety, College Park, MD 20874, USA, 2009. 36. H.G. Kang, T. Sung, An analysis of safety-critical digital systems for risk-informed design, Reliability Engineering and System Safety, Taejon 305-600, South Korea, 2002. 37. I.S. Kim, T.K. Kim, M.C. Kim, B.S. Kim, S.W. Hwang, K.C. Ryu, Suitability review of FMEA and reliability analysis for digital plant protection system and digital engineered safety features actuation system. KINS/HR-327; 2000. 38. I. S. Kim, S.K. Ahn, K.M. Oh, Deterministic and risk-informed approaches for safety analysis of advanced reactors: Part II, Risk- informed approaches, Reliability Engineering and System Safety, Daejeon 305-338, Republic of Korea, 2010. 39. M.C. Jacob, J.P. Rezendes, Development of risk informed safety analysis approach and pilot application. Westinghouse, WCAP-16084-NP, rev 0, September, 2003. 40. DOE, USNRC, Next generation nuclear plant licensing strategy – a report to congress, August, 2008. 41. M.J. Delaney, G.E. Apostolakis, M. J. Driscoll, Risk-informed design guidance for future reactor systems, Nuclear Engineering and Design, Cambridge, MA 02139-4307, USA, 2005. 42. G.E. Apostolakis, How useful is quantitative risk assessment?, Risk Anal. 24, 515–520, 2004. 43. G.E. Apostolakis, M.W. Golay, A.L. Camp, A.L. Duran, D.J. Finnicum, S.E. Ritterbusch, June 4–5, A new riskinformed design and regulatory process. In: Proceedings of the Advisory Committee on Reactor Safeguards Workshop on Future Reactors, Report NUREG/CP-0175, pp. p237–p248, US Nuclear Regulatory Commission, Washington, DC, 2001. 44. A. Lyubarskiy, I. Kuzmina, M. E. Shanawany, Advances in Risk Informed Decision Making – IAEA’s Approach, Vienna, Austria, 2011. Authors Mohsen Esfandiari Gholamreza Jahanfarnia Department of Nuclear Engineering Science and Research Branch Islamic Azad University, Tehran, Iran Kamran Sepanloo Ehsan Zarifi Reactor and Nuclear Safety Research School Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran. Applied Reliability Assessment for the Passive Safety Systems of Nuclear Power Plants (NPPs) Using System Dynamics (SD) Yun Il Kim and Tae Ho Woo 1 Introduction A new kind of passive system is investigated in case of an accident in nuclear power plants (NPPs). Conventional passive systems have the limitations in the conditional integrity like the piping system of the coolants. In this paper, the free-falling of emergency coolants are proposed where the flying machine, drone, is imported to carry out the coolants on the upper position of the containment building. In the cases of the Fukushima and Chernobyl, the piping systems were blown away. So, the emergency coolants couldn’t flow into the reactor core position where the reactor fuels were making continuous very high energy without stabilizing of the power level. Although the integrity of the piping injection systems have been investigated as the good conditions, the previous history couldn’t give the satisfactions to the public. During the Fukushima disaster, the operator had been seeking for the prime minister to take a permission to open the gas leak valve in the containment building when the reactor pump was out of order and the hydrogen gases were produced continuously. Eventually, the hydrogen explosion happened and the four plants were collapsed within several days after East-Japan earthquake impact on the Fukushima coast and its related areas. Furthermore, even if there was an opportunity to make use of the sea water in order to cool down the reactor core, the operator didn’t use it for keeping the expensive reactor structure from the saluted sea water in which the material corrosions could been happened and the material could be in the significantly damaged situation. Then, all kinds of the cooling systems were gone permanently. The dangerous radioactive contaminations to the environment have been done continuously. Considering the case of the Fukushima nuclear accident, the piping system has the crucial fault that the safety system can’t make any role in the post-accident or on-accident. Piping in the NPPs should be incorporated with the alternative coolant supply method. So, the detached system from plant building could be imagined in this study. The merit of the passive system is operated without in-site electricity. So, the natural circulation or gravity could be acted for the designed system by injection of the coolants. However, even the action of switch of the system operation should be done to start. So, the manual based stating action is needed for the operation of passive system. As the same condition of the Environment and Safety Applied Reliability Assessment for the Passive Safety Systems of Nuclear Power Plants (NPPs) Using System Dynamics (SD) ı Yun Il Kim and Tae Ho Woo

atw Vol. 63 (2018) | Issue 3 ı March initial action, the detached lifted coolant carrying by drone is similar in the starting state. However, the non in-site power is supplied by the battery in the drone’s flying system. ‘Passive’ means that the power is not used from the in-site system of the plant. The battery is supplied from the external energy source. So, the drone could be considered as one for constructing the passive system in NPPs. There are the comparisons of the passive systems in Table 1. Type Natural circulation Gravity Free-fall Power | | Tab. 1. List of passive systems. Non in-site electricity Non in-site electricity Non in-site electricity, Battery or engine installed in drones | | Fig. 1. Simplified configuration of NPPs in the accident. | | Fig. 2. Passive systems of NPPs. ENVIRONMENT AND SAFETY 159 There are some passive safety system related papers. Cho et al. worked for the passive auxiliary feedwater system (PAFS) [Cho et al. 2016]. In addition, Gou et al. studied that the thermal hydraulic investigations were done for a new type of passive residual heat removal system (PRHRS) [Gou et al. 2009]. Park et al. showed that the advanced modular integral type rector is investigated by the natural circulation performance [Park et al. 2007]. 2 Method 2.1 Overview Figure 1 shows the simplified configuration of the NPPs in the accident where the water tank is carried by the drones. The water falls as the free-fall for the water tank in which the water are entering to the reactor building. The passive action by the free-fall is done completely, which could be used in the case of the piping based injection system failure. There are some passive systems in Figure 2 where the natural circulation and gravity are shown. In this paper, the free-fall is described. There are the conceptual comparisons of passive systems of NPPs in Figure 3 that the water falls down from flying drone containing water tank and the water is injected from the conventional water tank attached to the reactor building. This is revolutionary different from the conventional passive system in which the piping integrity should be kept. Otherwise, in the free-fall system, the reservoir could be an active role on or after accident. So, | | Fig. 3. Conceptual comparisons of passive systems in NPPs. this means that the post-accident safety system is installed in this new system. In the current commercial NPPs, there is not any kind of the post-accident safety system. It has been experienced in Chernobyl as well as Fukushima cases that it was impossible to make the coolant enter into the reactor core where the nuclear fuels were continuing the nuclear reactions and producing the heats. Table 2 shows the specifications of the condensate water storage tank as the emergency water tank [The Virtual Nuclear Tourist, 2016]. Newly developed drone could supply 500 kg [Air- Mule, 2016]. Therefore, it takes about 1,137 times supplies to carry the tank water. If one uses 10 units of drone, it reduced to about 113 times. However, | | Fig. 4. Major factors for the free fall of coolants. Tank (Condensate storage tank) Mass flow rate Content | | Tab. 2. Specification of emergency water tank. the coolant carrying quantity is changeable by the situation and carrier design. 2.2 Cooling by the free-fall The modeling of this paper is to show the capability of the free-fall coolant in which this should make the enhanced integrity to the piping based injection systems. So, the major factor of the fee-fall coolants is the coolant quantity with mass flow rate which is 150,000 gallons (567,812 liters, 568,500 kg water) 200 ~ 400 gallons/min. Environment and Safety Applied Reliability Assessment for the Passive Safety Systems of Nuclear Power Plants (NPPs) Using System Dynamics (SD) ı Yun Il Kim and Tae Ho Woo