OVERVIEW ON FINAL STRESS TEST REPORT CERNAVODA NPP Dumitru DINA CEO Nuclearelectrica. 16 th of May 2012 Nuclear 2012 Pitesti, Romania

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1 OVERVIEW ON FINAL STRESS TEST REPORT CERNAVODA NPP Dumitru DINA CEO Nuclearelectrica 16 th of May 2012 Nuclear 2012 Pitesti, Romania 1

2 PREAMBLE On 25 March, 2011, European Council decided that nuclear safety of all EU nuclear power plants has to be revised according to transparent and extended risk assessments, the so-called stress tests ; ENSREG (European Nuclear Safety Regulators) issued in late May 2011 a set of technical specifications based on which regulatory authorities of each member state to require the license holders to reassess the design basis margins of the nuclear safety (stress test); in this context, Cernavoda NPP submitted to CNCAN (Romanian Regulatory Authority) a preliminary stress test report on 12 August 2011 and a final one on 28 October 2011; both preliminary and final stress test reports have been prepared by a reunite team of Cernavoda NPP experts and plant designers, AECL Canada and Ansaldo Italy.

3 FIRST PAGES OF PRELIMINARY AND FINAL STRESS TEST REPORTS

4 STRUCTURE OF THE REPORT CHAPTER 1 GENERAL DESCRIPTION CHAPTER 2 EARTHQUAKE CHAPTER 3 FLOODING CHAPTER 4 LOSS OF ELECTRICAL POWER AND LOSS OF ULTIMATE HEAT SINK CHAPTER 5 SEVERE ACCIDENT MANAGEMENT

5 CHAPTER 1 GENERAL DESCRIPTION Advantages of CANDU 6 technology: natural uranium used as fuel cannot become critical in light water and the energy stored in the reactor core is much less as compared to any other reactor type; light & heavy water inventory in reactor core and systems such as: primary heat transport, moderator, and calandria vault is excessively large ensuring cooling capabilities of the fuel; there are 2 independent, redundant shutdown systems which can independently insert many times more negative reactivity than required to shutdown the reactor; the existence of a secondary control area and two diesel generator sets, one being seismically qualified. Probabilistic Safety Analysis (PSA) : demonstrated that the Core Damage Frequency (CDF) is of 3.3 e-5, three times less than the limit set by IAEA; confirmed that annual safety goals, probabilistically assessed, are met and maintained.

6 CONTAINMENT SYSTEM

7 SHUTDOWN SYSTEMS 1 AND 2

8 CHAPTER 2 - EARTHQUAKE The reviews performed and validated by the National Research & Development Institute for Earth Physics as well as by other international specialized institutions confirmed that : Vrancea seismic source dominates the seismic hazard at Cernavoda NPP; for the maximum historical recorded event, with a magnitude of 7.5 (Richter scale), the corresponding Peak Ground Acceleration (PGA) at the NPP surface is 0.11g; for the maximum estimated event with a magnitude of 7.8, the PGA at the NPP surface is 0.18g; the Design Basis Earthquake (DBE) of the Cernavoda Units 1 & 2 was established as 0.2g on peak horizontal ground acceleration, for a return period of years; recent analyses showed a corresponding PGA of 0,29g at the NPP surface for an earthquake with a probability of occurrence of 1 in years; studies also showed that plant systems and components that ensure safe shutdown, cooldown, containment and monitoring of the reactor core have sufficient margins against seismic events, their seismic capacity being between g.

9 The possibility of an earthquakeinduced severe flooding was taken into account, but the conclusion was that this scenario is not credible (impact of a tsunami featured in black sea, and a possible breaking of the «Portile de Fier» dam or any other romanian dams will mitigate up to Cernavoda). ~140 ~ 65

10 CHAPTER 3 - FLOODING Both Cernavoda Units were so designed and built to avoid or mitigate the impact of internal and external flooding conditions; By design, internal flooding, due to rupture of piping and components containing large sources of water, has been addressed so as to not affect the plant safety functions (control, cooling, containment and monitoring to be available at all times); Regarding external flooding, 2 credible sources have been considered, respectively: floods from Danube river and heavy rainfalls on site and surroundings; Danube river level: the design basis flood level from Danube river has been determined to be 14,13m Baltic sea level, for a return period of years; the site is located at 16,00m Baltic sea level and the buildings are at 16,30m Baltic sea level; therefore, there is no possibility of flooding due to Danube river high level. heavy rainfalls: the absolute maximum rainfall ever recorded on site is 47,3 l/ m2/ hr; the site main drainage header has been sized at 97,2 l/ m2/ hr; according to calculations, a rainfall rate exceeding 10 times the capacity of the drainage system may lead to a temporary storage of water on site with a maximum depth of 20 cm, which is below the ground floor of buildings of 30 cm above the ground elevation.

11 CHAPTER 4 LOSS OF ELECTRICAL POWER AND LOSS OF ULTIMATE HEAT SINK Events and scenarios examined: Loss of off-site power: the plant can operate at reduced power level in the islanding mode, the electrical power being supplied by the turbine generator (T/G) of the running unit; if the above scenario fails to apply, the units can be shutdown in a controlled manner, all safety functions (3c + m) being power supplied by the first set of diesel generators (Cls. III); should first set of diesel generators fails to function due to an earthquake occurrence, all safety functions (3c + m) would be power supplied by the second set of diesel generators (seismically qualified), known as Emergency Power Supply (EPS). Loss of off-site power and of on-site backup sources (SBO): the plant shutdown is ensured automatically either by SDS 1 or SDS 2, which will perform their design function without the need of being supplied with electrical power; cooling of the reactor is ensured by termosyphoning, and the heat transferred to steam generators is discharged to atmosphere via steam discharge valves; the necessary water to the steam generators will be gravitationally fed from the dousing tank inventory using electrical power from batteries to open the valves; the above systems ensures cooling of the reactor for at least 27 hrs, amount of time sufficient to connect electrical power from the mobile diesel generators (3 hrs according to field tests) to the Emergency Water Pumps (EWS); containment function considering SBO is not affected; containment isolation valves will fail close either on loss of their electrical power supply or loss of instrument air; the monitoring of the critical safety parameters will be ensured using electrical power from the batteries, which can continuously supply power for approximately 8 hrs;

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13 REACTOR COOLING BY THERMOSYPHONING

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15 CHAPTER 4 LOSS OF ELECTRICAL POWER AND LOSS OF ULTIMATE HEAT SINK (cont.) Loss of ultimate heat sink: it means loss of Raw Service Water system (RSW); the shutdown systems can be either manually activated from the control room or automatically ensured by process parameters as designed; the heat sink is ensured in the same way as mentioned in the case of SBO except that the second set of diesel generators (EPS) are available and can continue supplying power to Emergency Water Pumps (EWS); containment and monitoring of critical safety parameters will not be affected. Loss of primary Ultimate Heat Sink (UHS) with SBO: it means loss of Raw Service Water system (RSW) and Emergency Water Supply (EWS) systems; critical safety parameters (3c + m) are ensured similarly to the case of loss of primary ultimate heat sink, except that the necessary water to the steam generators is ensured, after 27 hrs, by the fire water tanks or mobile pumps that can be manually connected to EWS system piping, and can be supplied with water from sources other than Danube (town distribution network or two existing deep ground wells).

16 CHAPTER 5 SEVERE ACCIDENT MANAGEMENT Measures to prevent core damage and arrest corium: CANDU 6 has inherent design robustness against core damage; the probability that this severe event to occur is reduced, and the progression of the event (deterioration process) once produced, is slower than in other types of reactors; other aspects noteworthy: use of natural uranium as nuclear fuel, large volumes of heavy and light water (approximately 350t D 2 O in HTS and calandria, and 500t light water in calandria vault) and 2000t in dousing tank, plus different possibilities of water addition from outside; early this year new specific procedures have been issued to address the response to such severe accidents, and the training of target personnel has been completed late august 2011.

17 CHAPTER 5 SEVERE ACCIDENT MANAGEMENT (cont.) Measures to prevent loss of containment integrity: the containment building provides the fundamental barrier protecting the public and the environment in a severe accident by limiting the radioactive releases; the rapid and efficient isolation of the containment building upon the initiation of the event prevent the radioactive releases to the environment; the control of containment slow over-pressurization ensures containment integrity on long and medium term and is achieved with systems performing their design function: dousing systems: Local Air Coolers (LAC); controlled pressure relief required in extreme situations. control and reduction of the hydrogen concentration upon the occurrence of a core meltdown are essential to prevent deflagrations/ detonations that can potentially damage the containment. Hydrogen control is currently achieved by atmosphere homogenization (natural circulation), cooling (LAC), and inerting the atmosphere and controlled ignition (currently available for Unit 2); for both units installation of passive autocatalytic recombiners is considered due to the fact that these recombiners do not need any external supply.

18 CHAPTER 5 SEVERE ACCIDENT MANAGEMENT (cont.) Measures for limiting the radioactivity release impact emergency planning : plant response to severe incidents/ accidents is according to on-site emergency plan; emergency response personnel has been adequately selected and trained; emergency exercises take place periodically and involve plant and contractor personnel along with local and national authorities with responsibilities in such tasks; more protocols and contracts are in force with various economic operators and institutions for ensuring an adequate response to incidents/ accidents.

19 ON-SITE EMERGENCY ORGANIZATION ON-SITE EMERGENCY CONTROL CENTER A1. COMAND UNIT EMERGENCY MANAGER CERNAVODA NPP MANAGEMENT REPRESENTATIVE AT CONSTANTA/ CERNAVODA CITY HALL CNCAN CNCAN INSPECTO R EMERGENCY TECHNICAL OFFICER EMERGENCY HEALTH PHYSICIST (EHF) EMERGENCY ADMINISTRATIVE OFFICER PUBLIC RELATION OFFICER AT CONSTANTA/ CERNAVODA CITY HALL TECHNICAL SUPPORT GROUP OPERATION SPECIALIST REACTOR PHYSICS SPECIALIST SAFETY ANALYSES SPECIALIST FUEL HANDLING SPECIALIST PROCESS SYSTEMS SPECIALIST COMPONENTS SPECIALIST ENGINNERING SPECIALIST MAINTENANCE SPECIALIST EHF ASSISTENT RADIO OPERATOR SUPPORT ADMINISTRATIVE PERSONNEL IN OECC - FAX/ TELEPHONE OPERATOR - LOGGER A2. COMAND UNIT SUPPORT PERSONNEL E. PERSONNEL RESPONSIBLE WITH PUBLIC INFORMATION TRANSPORTATION SERVICES PERSONNEL MEDICAL PERSONNEL SHIFT SUPERVISOR ASSEMBLY AREAS RESPONSIBLES ON-SITE/ OFF-SITE SURVEY TEAM Legenda: IN-STATION SURVEY TEAM INTERVENTION GROUP LEADER INTERVENTION GROUP C. EMERGENCY RESPONSE TEAM ON-SITE EMERGENCY ORGANIZATION UNTIL THE ON-SITE EMERGENCY CONTROL CENTER IS ACTIVATED COMMUNICATION LINE AVAILABLE ONLY UNTIL THE ON-SITE EMERGENCY CONTROL CENTER IS ACTIVATED MAIN CONTROL ROOM OPERATOR B. MAIN CONTROL ROOM PERSONNEL INTERVENTION COORDINATOR SECURITY ACCESS PERSONNEL RADIOACTIVE SAMPLES ANALYSES GROUP D. INTERVENTION SUPPORT PERSONNEL

20 EXERCISE AT ON-SITE EMERGENCY CONTROL CENTER

21 CHAPTER 5 SEVERE ACCIDENT MANAGEMENT (cont.) Loss of Spent Fuel Bay (SFB) cooling: in case of a prolonged loss of Spent Fuel Bay (SFB) cooling, make-up water is required to prevent uncovery of the spent fuel bundles; in this way cooling (boiling and evaporation) and proper disposal of the residual heat is ensured; based on calculations it was shown that water inventory existing in spent fuel bay is sufficient for 9 days until radiological fields start to increase and 15 days until first fuel bundle become uncovered; the way on how to use external make-up water was procedured and practiced, using firetrucks and mobile pumps; the process required to build a make-up water line, seismically qualified, has started. the severe accident phenomenology in CANDU 6 technology is analysed, explained and suported by research and development data collected by international specialized institutions over 40 years.

22 SPENT FUEL BAY

23 FINAL CONCLUSIONS The detailed evaluation performed at Cernavoda proves that both Cernavoda NPP Units meet the nuclear safety requirements under the project while having sufficient design margins against severe earthquake and flooding, SBO, and loss of ultimate heat sink; New ways to respond to severe accidents have been identified and procedured; Design modifications to prevent and limit severe accidents aftermath that can lead to core meltdown have been identified, among which we mention: additional fire water system in the reactor vessel; additional water supply system and overpressure protection system in the reactor vault; environmental qualification of certain measurement and control loops; capacity increase and seismic qualification of class I/IIbatteries, etc. The following additional safety features have been decided to be implemented into the next two years: R/B filtering ventilization system; passive hydrogen auto catalytic recombiners; R/B gaseous concentration monitoring system. These changes are implemented in accordance with the priorities set by Cernavoda NPP specialists with plant designers.