EUROPEAN UNION “STRESS TESTS” National Progress Report of Bulgaria applicable to Kozloduy Nuclear Power Plant Nuclear Regulatory Agency September 2011 TABLE OF CONTENTS TABLE OF CONTENTS ....................................................................................................................2 LIST OF TABLES..............................................................................................................................4 LIST OF ABBREVIATIONS ..............................................................................................................5 INTRODUCTION ...............................................................................................................................9 1 EXECUTIVE SUMMARY..........................................................................................................10 1.1 STRESS TEST AIM AND OBJECTIVES......................................................................................10 1.2 SCOPE OF STRESS TESTS.....................................................................................................10 1.2.1 Nuclear Facilities Covered by Stress Tests ............................................................................... 10 1.2.2 Scenarios Covered by Stress Tests........................................................................................... 11 1.2.2.1 Initiating Events ................................................................................................................ 11 1.2.2.2 Loss of Safety Functions .................................................................................................. 11 1.2.2.3 Severe Accident Management ......................................................................................... 11 2 PROJECT ORGANIZATION AND MANAGEMENT................................................................12 2.1 PROJECT INITIATION .............................................................................................................12 2.2 MAIN ROLES OF THE PROJECT PARTICIPANTS .......................................................................12 2.3 METHODOLOGY FOR ANALYSIS..............................................................................................12 2.3.1 Determination of the Inputs Set.................................................................................................. 12 2.3.2 Methodology for Performance of Stress Tests........................................................................... 13 3 GENERAL DATA FOR KOZLODUY NPP...............................................................................14 3.1 KOZLODUY NPP GENERAL DESCRIPTION ..............................................................................14 3.1.1 Site Characteristics .................................................................................................................... 14 3.1.2 Major Facilities and Structures on the Site................................................................................. 15 3.1.3 Spent Fuel Storage Facilities – SFSF and DSFSF .................................................................... 16 3.1.4 Licensing Status ......................................................................................................................... 16 3.2 MAIN DATA FOR UNITS 3 AND 4 .............................................................................................17 3.2.1 Key Features of Units 3 and 4.................................................................................................... 17 3.2.1.1 Type of Reactor ................................................................................................................ 17 3.2.1.2 Thermal Power ................................................................................................................. 18 3.2.1.3 First Criticality Date........................................................................................................... 18 3.2.1.4 Spent Fuel Pond (SFP)..................................................................................................... 18 3.2.2 Systems Ensuring or Supporting the Fundamental Safety Functions........................................ 18 3.2.2.1 Reactivity Control..............................................................................................................20 3.2.2.2 Reactor Cooling to the Ultimate Heat Sink....................................................................... 21 3.2.2.3 SFP Cooling to the Ultimate Heat Sink............................................................................. 23 3.2.2.4 Containment Cooling to the Ultimate Heat Sink ............................................................... 24 3.2.2.5 Location, Time Constraints and Power Supply Sources for Heat Removal Channels..... 24 3.2.2.6 AC Power Supply.............................................................................................................. 25 3.2.2.7 DC Power Supply Batteries .............................................................................................. 27 3.3 MAIN DATA ON UNITS 5 AND 6...............................................................................................27 3.3.1 Main Characteristics of Units 5 and 6 ........................................................................................ 27 3.3.1.1 Reactor Type ....................................................................................................................27 3.3.1.2 Heat Power ....................................................................................................................... 29 3.3.1.3 First Criticality Date........................................................................................................... 29 3.3.1.4 Spent Fuel Pond (SFP)..................................................................................................... 29 3.3.2 Systems Ensuring and Maintaining Fundamental Safety Functions.......................................... 29 3.3.2.1 Reactivity Control..............................................................................................................32 3.3.2.2 Reactor Heat Removal – Ultimate Heat Sink ................................................................... 35 3.3.2.3 SFP Heat Removal by the Ultimate Heat Sink ................................................................. 39 3.3.2.4 Containment Heat Removal to the Ultimate Heat Sink .................................................... 39 3.3.2.5 Location, Time Constraints and Power Supply Sources for Heat Removal Channels..... 41 3.3.2.6 AC-DC Power Supply. ...................................................................................................... 42 3.3.2.7 DC Power Batteries .......................................................................................................... 44 3.4 MAIN DATA FOR SFSF AND DSFSF ......................................................................................45 3.4.1 Main Characteristics of the Spent Fuel Storage Facility ............................................................ 45 3.4.1.1 Location and Properties of the Site .................................................................................. 45 3.4.1.2 Main Design Solutions...................................................................................................... 45 3.4.2 Main Characteristics of the Spent Fuel Dry Storage Facility...................................................... 49 3.4.2.1 Location and Properties of the Site .................................................................................. 49 3.4.2.2 Main Design Solutions...................................................................................................... 49 3.4.2.3 Systems and Equipment Description................................................................................ 49 3.4.2.4 Heat removal from SFP to the Ultimate Heat Sink ........................................................... 51 3.5 SCOPE AND MAIN RESULTS OF THE PSA...............................................................................51 3.5.1 Scope and Main Results of the PSA of Unit 3 and 4.................................................................. 51 3.5.2 Scope and Main Results of the PSA of Units 5 and 6................................................................ 52 3.5.3 Scope and Main Results of the PSA of the SFSF...................................................................... 53 4 KOZLODUY NPP STRESS TESTS CURRENT STATUS .......................................................54 4.1 CHRONOLOGY OF STRESS TESTS PERFORMANCE .................................................................54 4.2 INDIVIDUAL STRESS TESTS STATUS.......................................................................................54 4.2.1 Earthquakes ............................................................................................................................... 55 4.2.1.1 Design Basis..................................................................................................................... 55 4.2.1.2 Safety Margins Evaluation................................................................................................ 55 4.2.2 Flooding...................................................................................................................................... 55 4.2.2.1 Design Basis..................................................................................................................... 55 4.2.2.2