SYSTEMATIC AND DESIGN SAFETY IMPROVEMENTS OF NPPS IN CZECH REPUBLIC 3.10.2016 ČEZ, a. s. Meeting at IAEA Vienna
Overview of topics ČEZ nuclear fleet (basic features) Systematic measures targeted to improve the balance between NPP power production and safety imperative Concept of stress-test measures in light of design requirements, safety targets and feasibility conditions Examples of design and technical solutions Closing considerations (extension of DB for NPPs in operation) 1
ČEZ nuclear fleet Temelín PWR, 2xVVER-1000 V320 U1 startup: 2000 Thermal Power: 3120 MWt (104% of original) Dukovany PWR, 4xVVER-440 V213 U1 startup: 1985 Thermal Power: 1444 MWt (105% of original) 2
ČEZ nuclear fleet - Original design features VVER-440 V213 (Dukovany) + lower core power larger volume of water (RCS, SGs, bubble condenser) allow reactor cavity flooding, cooling RPV by water/steam circulation (IVR) - older layout (lower separation) lower resistance of structures to hazards (improved) certain weak links related to redundancy of SSC (improved) missing independent UHS for ESW (solved) low pressure contm., SFP outside it VVER-1000 V320 (Temelin) + - younger NPP, more modern and robust design sufficient resistance of structures distinct and full scale redundancy full pressure contm., SFP inside it higher core power lower volume of water configuration of reactor island makes SA mitigation method selection difficult 3
Systematic approach - control of balance between NPP power production and safety imperative ČEZ a. s., Production Division Engineering Dpt. Safety Dpt. NPP Dukovany NPP Temelin NPP Engineering Nuclear Safety Special Processes Project Implementation SAR, PSA, PSR, Safety analysis, Limits & conditions NPP Design Authority NEW we prepare and implement design modifications and provide technical solutions for: Effective power production LTO strategy Safety in all NPP states 4
Systematic approach to NPP Design and safety enhancement in ČEZ The new department in ČEZ Centralized Enginnering: NPP Design Authority??!! Design config. Independent Design Authority role, e.g. Restoration of design basis and requirements Margin management Safety evaluation Evaluation of design changes Real config. Config. document s NPP Configuration management Aging management & LTO program NPP START of operation Operation Maintenance Repairs Modifications NPP Original design lifetime Operation Maintenance Repairs Modifications Plant life extension 5
Restoration of Design Basis Structure of DESIGN and structure of DB/DR Design Why??? Therefore!! DBD = Design Basis Document 1. DBD level NPP/Unit DR 2. DBD level Systems/Civil structures 3. DBD level Equipment 6
Systematic approach - Restoration of Design Basis Definition of DB in IAEA-TECDOC-1791:2016 Design basis of a structure, system or component (SSC) The set of information that identifies conditions, needs and requirements necessary for the design of the SSC including the: Functions to be performed by a SSC of a facility; Conditions generated by operational and accident states that the SSC has to withstand; Conditions generated by internal and external hazards that the SSC has to withstand; Acceptance criteria for the necessary capability, reliability, availability and functionality; Specific assumptions and design rules. Restoration of DBD, level 1 Phase 1 Russian design 7 Phase 2 Modernization Capability of NPP Sum of loads Phase 3 Stress Tests Phase 4 Current NPP Inputs from DBD1 to DBD2 (systems/civil.s.) EDU The Design (incl. DB) shall ensure that NPP capabilities are predominant to NPP loads Assessment is made by analyses
ČEZ NPPs key principles of safety improvements 1. Increased robustness of ALL DID levels 2. Priority (considering specific conditions of operated NPPs): a. Robust SA prevention, b. Feasible SA mitigation 3. Accenting of interfaces (loads, functions, capabilities, agreements, etc.) Redundant divisions of SS Independent & separated Functional Groups (redundant) Single Functional Group (with partial redundancy) Div 1 Div 2 Div 3 FSK A FSK B FSK NO AOO DBAs DEC A (without fuel degradation) DEC B (with fuel melt) 8
Concept of stress-test measures SA Mitigation Severe Accidents DEC B, DiD4 Alternative Systems Provisions for SA mitigation Alternative (mobile) systems Implementation of additional defence levels SA Prevention Design Extension Conditions (SBO, LUHS) DEC A, DiD3b Diverse (Backup) Systems Design Basis Conditions DBA, DiD3a Safety Systems Diverse systems Communication means Additional reinforcements of existing design Verification of adequacy of existing safety systems => implementation of reinforcements Reinf. against floodings Dukovany: - Reinf. of buildings / constructions - UHS, PAMS upgrade 9
Examples of solution - Dukovany: Reinforcement of buildings / constructions Project / building Goal Completion Reinforcement of buildings / constructions (Reactor building, Machine hall, Central pumping station, ) Buildings / constructions are resistant against extreme hazards (seismic, snow, wind) with return period 10 000 years 2015 10
Examples of solution Dukovany: Elimination of original design deficiencies Project Goal Completion New independent safety UHS (vent. towers for ESW) UHS operability in extreme conditions (wind), independence 2015 11
Examples of solution Dukovany: Elimination of original design deficiencies Project Goal Completion Improvement of redundancy: 3. Super - EFW pump Separated 3. Super-EFW pump. All EFWPs can be used for coping with SBO (connectivity to AAC grid). 2015 12
Diverse systems Functions covered prevention of SA: Secondary heat sink RCS / SFP / contm. makeup Diverse emergency AAC power source (coping with SBO) Habitability of control rooms Communication means Basic principles: Increase of diversity and redundancy in execution of key safety functions Designed/qualified for extreme conditions Rating removal of residual heat Operation without site external support (72 hrs.) 13
Diverse systems (cont d) Project Goal Completion Secondary heat sink RCS / SFP / contm. makeup Connection of alternate means for second. heat sink Diverse qualified RCS / SFP / contm. makeup (TB50, TM) 2013 2014 AAC DGSs AAC power sources 2014 14
Diverse systems (cont d) Principles of AAC grid for TEMELIN and DUKOVANY (6 kv) AAC DG 1 AAC DG 2 6kV, 3,2 MW, 4 MVA 6kV, 3,2 MW, 4 MVA Blok č. 2 Blok č. 1 DGS DGS DGS 6kV, 7,9 MVA 2GX R 1GX 2GV R 1GV 2GW 1GW 7GK Výměn. stanice Strojovna BJ BK CJ CK Rozv. normál. napájení 7GJ Výměn. stanice Strojovna BJ BK CJ CK Rozv. normál. napájení Temelin 2xVVER 1000 NPP Temelin: Layout scheme of EEPS and AAC grid SZN 1 SZN 2 SZN 3 SZN 4, 5 Dukovany 4xVVER 440 15
Alternative systems Functions covered: Alternative RCS / SFP / contm. makeup Alternative power sources Communication means, radiation monitoring tools, backup (remote) emergency control center Basic principles Mobile & Portable Flexible (multipurpose) Emergency drills & skills Not fully qualified to extreme requirements (protection against external hazards by distance and light covering or sheltering) No classification 16
Alternative systems (cont d) Alternative RCS / SFP / contm. makeup Water sources (tanks, open water area) Fire pump Flexible connection (hoses) Special tool for coupling to various pipelines outside contm. 17
Alternative systems (cont d) Project Goal Completion Alternative mobile power sources Mobile DGs (approx. 350 kw) + cable sets, 2014 Multipurpose portable power sources For valves, measuring instruments 2014 18
SA mitigation provisions - DUKOVANY Project of IVR Goal Completion Reactor cooling in SA conditions IVR method 2014 Passive hydrogen recombiners Systems rated for SA scenarios 2015 Depressurization RCS during SA Containment vacuum breaker Long-term heat removal from containment Prevention of high pressure melt ejection Manual connection of bubbler tower air traps (H 2 management) New system (active or passive) with heat exchangers Design preparation, implementation since 2018 REACTOR AXIS REACTOR HALL Reactor cooling Vacuum breaker SG box inlet valve siphon corium A,B004 ESF compartment VZDUCHOTECHNIKA vent. centrum 19
SA mitigation TEMELIN: finding the way (effectivity, feasibility) Plan of analytical and design activities 15 16 17 18 19 Depressurization RCS Injection of the coolant into RPV IVR ExVC Conditions in the contm., long-term stabilization SA in SFP Depressurization RCS - analytically confirmed sufficiency capability of pressurizer safety valves Melt cooling is not resolved yet: IVR big uncertainties (high thermal power, reactor configuration doesn t allow natural circulation), the need of implementation new active (also passive) systems, ExVC feasibility and effectivity also not confirmed, more passive method but core catcher missing, 20
IVR x ExVC for VVER1000 AP1000 natural water circulation VVER 1000/320 active system, implementation of active equipment (pump, heat sink) and passive equipment (flow deflector, RPV surface coating) Ex-vessel coolability In-vessel retention EPR core catcher IVR mitigates only consequences of SA in core VVER 1000/320 more passive system, implementation of passive equipment only (barriers for melt pool, sacrificed materials) + 13,680 m (R0, Z0) R 375 1320 360 CV810 (0.0,1.8) (R0, Z0) + 14,324 m (0.0,1.8) 2905 2795 400 3195 1140 CV811 (R0, Z0) (0.0,1.8) CV821 + 20,700 m HIT=2.0m HIT=2.0m HIT=2.0m HIT=2.659m (R0, Z0) (0.0,2.509) + 19,200 m + 13,665 m ExVC mitigates consequences of both SA in core and SFP 21
The End => Questions? 22