SYSTEM FOR MITIGATION OF SEISMIC VULNERABILITY OF NUCLEAR INSTALLATIONS AND TECHNOLOGICAL PROCESSES INTRODUCTION

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1 International Symposium on Strong Vrancea Earthquakes and Risk Mitigation Oct. 4-6, 2007, Bucharest, Romania SYSTEM FOR MITIGATION OF SEISMIC VULNERABILITY OF NUCLEAR INSTALLATIONS AND TECHNOLOGICAL PROCESSES C. Ionescu 1, A. Marmureanu 1, A. Grigore 1, M. Popa 1, I.A. Moldovan 1 ABSTRACT The Romanian seismicity is dominated by the Vrancea deep (60-200km) earthquakes which take place in a small volume located at the bend of Carpathian mountains, the place where three tectonical units are interacting: East-European, Intra-Alpine plates and Moesic subplate. Two or three events per century are devastating; having high energy, are felt on large and high populated areas. The achievement of a seismic vulnerability reduction system for industrial and technological processes in the nuclear field intends to reduce possible after-earthquake damages which can take place in nuclear facilities situated in an extended area compared to the usual one affected by Vrancea earthquakes. In this situation are nuclear specific facilities like: IFIN-HH Magurele (Van de Graaff Accelerator), Pitesti reactor situated in Mioveni, Jud.Arges, ICSI Ramnicu Valcea (Experimental Pilot Plant for TRITIUM and DEUTERIUM SEPARATION) and Heavy water plant from Drobeta Turnu Severin-Mehedinti. We intend to implement EEWS in the above sites in order to have a warning decision for earthquakes produced in Vrancea, Campulung Muscel and Herculane areas and its errorfree transmission for activating the safety regulations for these facilities. INTRODUCTION The achievement of a seismic vulnerability reduction system for industrial and technological processes in the nuclear field intends to reduce possible after-earthquake damages which can take place in nuclear facilities situated in an extended area compared to the usual one affected by Vrancea earthquakes. In this situation are nuclear specific facilities like: IFIN-HH Magurele (Van de Graaff Accelerator), Pitesti reactor situated in Mioveni, Jud.Arges, ICSI Ramnicu Valcea (Experimental Pilot Plant for TRITIUM and DEUTERIUM SEPARATION) and Heavy water plant from Drobeta Turnu Severin-Mehedinti. Seismic events are included in risk assessment studies in the site election phase, design and construction of a nuclear facility. IAEA published SS documents (Safety Series) 35-G1 Safety Assessment of Research Reactors and Preparation of the Safety Analysis Report (par. A206, A208 site election, A308 design) and SS (Safety Series) 35-G2 Safety in the Utilization and Modification of Research Reactors ; these events are considered external events which have to be analyzed in the Security report. Romania, as a member state, implemented IAEA requirements and demands. We intend to implement EEWS in the above sites in order to have a warning decision for earthquakes produced in Vrancea, Campulung Muscel and Herculane areas and its errorfree transmission for activating the safety regulations for these facilities. 1 National Institute for Earth Physics, Bucharest, Romania

2 120 C. Ionescu et al. SEISMICITY OF ROMANIA Romania is a moderate seismicity country; on its territory are produced crustal and subcrustal events, which can produce significant damages. Seismicity of Romania results from earthquakes produced in several seismic areas like: Vrancea, Făgăraş Mountains area, Banat-Herculane, Oradea area, Maramureş and South Dobrogea. More, there exist local importance seismic areas like: Jibou and Târnave area, North and West of Oltenia, North of Moldavia, Câmpia Română. The Romanian seismicity is dominated by the Vrancea deep (60-200km) earthquakes which take place in a small volume located at the bend of Carpathian mountains, the place where three tectonically units are interacting: East-European, Intra-Alpine plates and Moesic subplate. Two or three events per century are devastating; having high energy, are felt on large and high populated areas. Figure 1 presents earthquake epicentres produced between in Romania (from ROMPLUS catalogue); Objective 1 represents Tandem IFIN-HH Magurele (Van de Graaff Accelerator), Objective 2 represents Pitesti reactor situated in Mioveni, Objective 3, ICSI Ramnicu Valcea (Experimental Pilot Plant for TRITIUM and DEUTERIUM SEPARATION) and Objective 4, Heavy water plant from Drobeta Turnu Severin-Mehedinti. Figure 1: Romanian seismicity between , after ROMPLUS catalogue. Vrancea seismic area is the most important one, due to the high energy of the produced earthquakes, their macroseismicity areas, persistence and localized epicenters. In the other regions of the country, two virtual lines of moderate seismicity are found: along Meridional Carpathians and Pannonian Depression and along Oriental Carpathians, on SE direction through Peceneaga Camena line.

3 International Symposium on Strong Vrancea Earthquakes and Risk Mitigation 121 In these areas, crustal earthquakes are taking place (5-30 km depth); they are low energy, followed by numerous aftershocks which are located at the intersection of fractures like: faults between Fagaras and Transylvanian and Loviştei Basins, fractures between Meridional Carpathians and Pannonian Depression, active in Timisoara area, faults system from Oradea area, Saint Gheorghe fault in North Dobrogea. VRANCEA SEISMIC AREA The Vrancea subcrustal zone is a particular and complex seismic region, a place where at least three major tectonical units are converging: the East-European plate and Intra-Alpine and Moesic subplates (Constantinescu et al., 1976). The strongest seismic activity in Romania is concentrated in the depth domain between 60 and 220km. The particularity of Vrancea area comes from the focal volume with an extremely reduced extension in the horizontal plane, where 3-5 major earthquakes (M W >7.0) are generated per century. In the last sixty years 4 Vrancea strong earthquakes were recorded: November 10,1940 (M=7.7, 160km depth), March 4, 1977 (Mw=7.5, 100 km depth), August 30, 1986 (M=7.2, 140 km depth) and May 30, 1990 (M=6.9, 80 km depth). The 1977 event had a catastrophic impact, nearly 35 buildings collapsed and 1500 casualties, majority of them in Bucharest. Earthquake epicentres (Figure 1) are concentrated on a 30x70 km area, with an average epicentral distance to Bucharest of 130 km. More than 90 % of the subcrustal events (including all major events Mw>7) have inverse faulting, nearly vertical tension axis and quasi-horizontal pressure axis. The maximum magnitude determined by using hazard analysis studies is M w =7.7 (M GR =7.7) (November 10, 1940 earthquake). In ROMPLUS catalogue, a magnitude M w = 7.9 (M GR =7.7) is written for the 1802 earthquake. We consider this value as the maximum observed magnitude for Vrancea area. The case study regarding EEWS implementation took place at Bucharest tandem (Van de Graaff Accelerator) situated at IFIN-HH Magurele. FAGARAS-CAMPULUNG-SINAIA AND TRANSYLVANIAN DEPRESSION SEISMIC SOURCES The Fagaras-Campulung-Sinaia seismic area is situated in the Eastern part of the Meridional Carpathians and is characterized by shocks with magnitude less than M w =6.5. Here took place the most important crustal event since This event occurred in January 26, 1916 (M w =6.4), event which was followed by a significant sequence of aftershocks. In this area prevails slip faulting, with nodal planes NV-SE oriented (Enescu et al. 1996) and extensional tension field. The Fagaras-Campulung-Sinaia crustal source geometry and earthquake epicenters distribution (M W 3.0), for events produced between 984 and April 2006, are presented in Fig.1. For the definition of the source geometry were taken into account all produced events, instrumental and historical ones, and was taken into account also the Intra-Moesic fault direction and localization.

4 122 C. Ionescu et al. The maximum instrumental magnitude for Fagaras source is M w = 6.5 (1916 earthquake). Under the influence of these seismic zones are two important facilities: Pitesti reactor and ICSI Ramnicu Valcea (Experimental Pilot Plant for TRITIUM and DEUTERIUM SEPARATION). BANAT, DANUBIANA AND IBAR-SERBIA SEISMIC SOURCES Pannonian Depression and Carpathians orogen are meeting along the Western border of Romania. Even that there are no major geostructural and tectonic differences, two distinct seismic areas can be identified, namely: Banat area at South and Crisana-Maramures area at North. Banat area seismicity is characterized by earthquakes with magnitude M w >5, but less than 5.6. Available fault plane solutions (Radulian et al., 1996) are suggesting the compressive character of the tension field E-W oriented. This conclusion is in agreement with Grunthal and Stromeyer (1992) which concludes that extensional regime in Pannonian Basin implies an E-W compression in Intra-Carpathians region Maximum instrumental magnitude is M w =5.6 (July 12, 1991). The maximum possible magnitude is M w =6.1. Seismic zone called Danubian, after Atanasiu (1961), represents the western extremity, near Danube River, belonging to the orogen unit of the Meridional Carpathians. Seismic rate is relatively high, especially at Serbian border and along Danube. Instrumental earthquakes magnitude is less than Mw=5.6. The maximum possible magnitude is M=6.1. The Serbian seismic source IBAR, situates at the Western border of Romania is of crucial importance for the Drobeta Turnu Severin town seismic hazard. In this place, there have been numerous crustal earthquakes with Ms>5. The maximum instrumental magnitude is Ms=6.6. The maximum possible magnitude is M=7.1 Under the influence of these seismic sources is the nuclear facility Heavy water plant - Turnu Severin. WARNING TIME - VRANCEA SEISMIC SOURCE The geometry of the Vrancea seismic source facilitates the creation of an early warning system for facilities situated in this area. ( Early Warning System for Bucharest, F.Wenzel, M. C. Oncescu, M. Baur, F. Fiedrich, C. Ionescu). For the Tandem IFIN-HH (Van de Graaff Accelerator) facility, the warning time is between 25 and 30 seconds, time obtained from velocity difference between P- and S- waves coming from Vrancea epicenters (Fig. 2, 3).

5 International Symposium on Strong Vrancea Earthquakes and Risk Mitigation 123 Figure 2a. Warning time for Tandem IFIN- HH (Van de Graaff Accelerator) nuclear facility for a Vrancea 100km depth earthquake Figure 2b. Warning time for Tandem IFIN-HH (Van de Graaff Accelerator) nuclear facility for a Vrancea 150km depth earthquake. WARNING TIME - FAGARAS SEISMIC SOURCE For the Ramnicu Valcea facility, the warning time is around 10 seconds, for the Pitesti facility is around 12 seconds and for Bucharest- Tandem IFIN-HH (Van de Graaff Accelerator) facility is about 27 seconds (Fig. 4). Figure 4. Warning times for Ramnicu Valcea, Pitesti reactor and Bucharest- Tandem IFIN- HH (Van de Graaff Accelerator) facilities

6 124 C. Ionescu et al. WARNING TIME - IBAR (SERBIA) SEISMIC SOURCE The maximum instrumental magnitude is Ms=6.6 (April 8, 1893); for the Turnu Severin- Halanga facility, the warning time is around 16 seconds (Fig.5). Figure 5. Warning time for Turnu Severin facility IMPLEMENTATION OF THE WARNING DISTRIBUTION SYSTEM AND, RESPECTIVELY OF THE LOCAL CONFIRMATION SYSTEM IN CONSIDERED SITES Warning distribution is the last stage in the seismic warning process. In the case of nuclear facilities, a maximum safety distribution and confirmation of the signal containing the seismic warning is used. Seismic data received from the national network is analyzed in real time by the early warning software (Figure 6); this software sends valid warnings to a server which distributes it simultaneously to all facilities which have to be warned. All facilities, except Tandem accelerator -which does not have a local seismic sensor and is warned directly-, are using a local seismic sensor for local confirmation of the warning sent by the central early warning software. Each module has his unique IP address, so every facility is warned separately, taking into account local-desired specific warning levels. Figure 6. The warning distribution system

7 International Symposium on Strong Vrancea Earthquakes and Risk Mitigation 125 EARLY WARNING SOFTWARE Early warning decision is taken by specialized software which recognizes, in a time-window, the necessary conditions for earthquake detection. The software is able to ensure uninterrupted seismic signal analysis and is also capable to resume transmissions when the communication links permit that (Fig.7). Data is acquired from K2/ETNA accelerometers by using RS232 or TCP/IP communication. The purpose of this software is to issue the warning alarm and send it to users. Figure 7. Main screen of the early warning software This software supports up to 6 K2/ETNA accelerometers. He is able to forward raw data to other acquisition systems, as if they are connected directly to the k2/etna accelerometer. This is ensured by up to 6 TCP/IP servers which can be configured in File Configure communication menu. All the parameters of the acquisition system can be configured here: channel names, channel type, sample rates, warning conditions, acquisition source etc. This software is a client and a server in the same time; is a client when it receives data and a server to other acquisition applications. The software permits user defined trigger levels; this can be adjusted depending on the warning specific conditions. All the warning levels are kept in a database; accessing this database is password protected. The software permits monitoring on certain channels of data; other ones can be skipped in the analysis procedure.

8 126 C. Ionescu et al. In the warning process is used also a spectral analysis, in order to avoid false alarms, generated by strong local noise (sensor accidental shock, heavy vehicles, human activities). Figure 8. Warning levels window The software permits 8 levels of warning; these levels are a function of recorded acceleration (Fig.8). Log Window contains the history of all parameters concerning communication link, digitizer state of health, GPS, free space on PCMCIA cards (Fig.9). Figure 9. Log window of early warning software

9 International Symposium on Strong Vrancea Earthquakes and Risk Mitigation 127 CONCLUSIONS Until now was accomplished a vulnerability reduction system for nuclear facilities. The studies had, as objective, the implementation, at sites mentioned above, of the early warning system. The implementation scheme permits probing and improvements of system reliability, without affecting the user. REFERENCES Baresnev, I., G. Atkinson (1977): Modeling finite-fault radiation from the ωn spectrum, Bull.Seism.Soc.Am., 87, 1, Ionescu, C.,A. Marmureanu (2005), Rapid Early Warning System (REWS) for Bucharest and Industrial Facilities, presentation at Caltech University. Oncescu, M.C., K.P. Bonjer (1997): A note on the depth recurrence and strain release of large Vrancea earthquakes. Tectonophysics, 272, Wenzel, F., M.C. Oncescu, M. Baur, F.Fiedrich (1999): An Early Warning System for Bucharest. Seism. Res. Lett., 70, 2,