Integrated Plant Assessment to enable LTO in Gösgen

Transcription

1 Integrated Plant Assessment to enable LTO in Gösgen Dr. Jens-Uwe Klügel, NPP Goesgen-Daeniken (CH) Folie 1

2 Overview Summary Overview on actual Swiss Regulations related to LTO Post-Fukushima Safety Assessment and Actions Long Term Operation Strategy (emphasis on safety aspects) Summary and Discussion Folie 2

3 Summary Overview on Swiss Regulations related to LTO Operating plants legally have an unlimited operating licence As long as the plants can be operated safely Obligation for permanent safety upgrades as long as these upgrades are in compliance with the state of back fit technology Since 2003 gradual implementation of a new atomic legal system originally intended to regulate the oversight process for new reactors (at that time planned) New Nuclear Energy Law (2003) New Nuclear Energy Decree (2004) Several new Regulations on the level of the Federal Ministry (UVEK) New generation of safety instructions issued by ENSI Law Decrees Regulations Instructions Ordinances Folie 3

4 Summary Overview on Swiss Regulations related to LTO After Fukushima political decision on long term phase-out, with still open discussions on Legal Prohibition of New Builds (?) Limitation of Operating Time (Referendum) (?) Possible compromise: LTO and Investment Program ENSI Safety Instruction A03 (2014) on Periodic Safety Review requires a detailed Safety Assessment of LTO for plant operation longer than 40 years Physical State of the Plant and Key Components An Operational Lifetime Management A Backfitting Concept with binding Time Schedule Practical no limitations (60-80 years operation feasible) Folie 4

5 Discussion/ Questions Long Term Safe Operation How safe is safe enough for long term operation? How to measure the safety level? Practical experience from Switzerland: Original design basis not sufficient for long term operation example large increase in seismic hazard assumptions Permanent plant upgrades frequently quick fixes without a thorough review of the safety concept of the plant Safety improvements may appear to be of limited benefit or economically not efficient the weakest member in a functional chain defines the benefit of plant modifications INSAG 25 and a draft IAEA TECDOC suggest a powerful decision making process ( IRIDM Integrated Risk Informed Decision Making) Folie 5

6 Development of Long Term Safety Upgrade Program Objectives 1) Restoration and increase of «lost design margins» 2) Design Basis Extension to withstand rare events by the help of qualified safety systems 3) Minimisation of risk of unfiltered radioactivity releases into the environment in case of a Beyond Design Basis Severe Accident Increased hazard, increased uncertainty Includes demonstration that MCCI (molten core concrete interaction) can be stopped without base mate penetration (ground water protection) Folie 6

7 IRIDM + Cost-Benefit Considerations Seismic Upgrade Safety benefit measured in risk reduction and compliance with new safety requirements (in terms safety functions) Assessment of Costs based on similar projects and on the results of feasibility studies with additional consideration of production loss risk Additional criteria: Licensibility Full Requalification Aseismic base isolation Nuclear Island Benefit + ++(+) ++ Costs --(-) -- -(-) Weak protection against common mode failures To be performed during power operation high risk of production loss Extension of SBO System Customer expectation: Realistic contract prices To meet objective 3 (Minimization of releases) : Implementation of 58 PARs and an additional dry Iodine Filter in the FCVS

8 Long term Actions Design Basis Extension Safety Objective: «Plant shall be capable to withstand a long term loss of offsite power scenario with loss of all 4 classified diesel generators (SBO) combined with a LOCA condition and secondary side leaks» -- currently scenario on safety level 4 (DiD) Design Basis Extension Realm of AM and SAMG Without additional single failure Single Failure Criterion SBO +large LOCA SBO+ LOCAupto 80 cm 2 SBO + LOCA 25cm 2 Existing SBO system shall be functionally expanded Probability Folie 8

9 New Functions of the expanded bunkered SBO system New technological and seismic scram function (digital) Secured ventilation system with air filtering 2 x 100% additional HP-Safety pumps (automatic start)6x100% Automatic secondary side cooldown with predefined cooldown rate Extension of accident management instrumentation/monitoring Remote operation of dedicated to SBO system RHR 5x100% with reserve train; sump operation Passive isolation of small bore pipes outside containment elimination of bypass scenarios Manual isolation of the first pressurizer safety valve Increase of battery capacity to at least 72 hours Increase of storage tank capacity by a factor of 2 Folie 9

10 Summary and Topics for Discussion Safety level for LTO of operating plants shall meet the following requirements: Risk (CDF, LERF) shall be comparable with generation 3 plants, but risk reduction can be achieved by other technical means General compliance with key defence in depth principles shall be achieved Minimum 2 independent water intakes, N+2 design for safety systems; design basis extension to cope with rare events that are currently BDBA (safety level 4a) Technical solutions plant specific but shall meet similar objectives (for AREVA plants) For NPP Goesgen the Risk- (and Cost)-informed Internal Decision Making (IAEA IRIDM process) was successfully applied to develop the Long Term Operation Safety Upgrade Program Folie 10