Enhancement of Nuclear Safety

Transcription

1 Enhancement of Nuclear Safety Soon Heung Chang Handong Global University May 6, 2015

2 Contents Importance of Energy Fundamentals of Nuclear Safety How to Enhance Nuclear Safety Closing Remarks 2

3 1 Importance of Energy 3

4 Importance of Energy Sharp increase of world-wide energy demand More energy required for economic growth and improvement of life quality Expected energy demand in 2040 to grow over 30% to 2010 Expected electricity demand in 2020 to grow over 40% to 2010 < Expected Demand Increase of Energy and Electricity > Ref. ExxonMobil., The Outlook for Energy: A view to 2040,

5 Contribution of Nuclear Power in Korea Starting with Kori-1 in 1978, now 23 units are installed. Nuclear power in total electricity supply marked 27% in 2013 The cheapest generation cost among power sources in 2013 Coal = 60/kWh, LNG= 160/kWh, Hydro/Solar = 170/kWh, Bio. = 150/kWh, Nuclear = 40/kWh Korea`s the cheapest electricity cost in the world Contribution of High nuclear technology on low electricity charge 1 Short construction period 2 Cheap construction costs 3 Highly-efficient operation Sale Cost [ /kwh] Korea Japan USA Germany UK (EDF Energy) Relative Values Exchange Rate - 1 Yen = 9.87 $ 1 = Euro = penny = 17.3 Ref. Korea EPSIS,

6 2 Fundamentals of Nuclear Safety 6

7 History of Nuclear Safety Atoms for Peace in 1954 Establishment of the IAEA in 1957 The first PSA report for a NPP, WASH-1400 in 1975 Lessons learned from the accidents pushed up the level of nuclear safety TMI-2 accident in No injuries, no measurable health effects - Probability of severe accident was higher than ever believed - Consequences significantly smaller Defense in depth (DID): containment - Importance of human factor and DID - Industry, government act to improve safety: IAEA, INPO, etc. Chernobyl Accident in Health and environmental effects - Psychological and social impacts - Influence of the accident on the nuclear industry worldwide - Importance of nuclear design and operational safety standards - Importance of international cooperation No national borders in nuclear and radiological risks Peer reviews, safety upgrades, bilateral and multilateral assistance efforts, safety conventions, etc. 7

8 Fundamental Principles of Nuclear Safety Management responsibilities Management responsibilities Safety culture Responsibilities of operation organization Independent regulation & verification Strategy of Defense in depth Strategy of Defense in depth Defense in depth Accident prevention & Accident mitigation Fundamental principles General technical principles General technical principles Proven engineering practices Quality assurance Human factor Safety assessment and verification Radiation protection Operating experience & safety research 8

9 Two Methods for Safety Analysis Initiating Events Equipment Reliability Operator Behavior Analysis Use of Results Deterministic Approach DBAs (+Some BDBAs) Single failure criterion For t < T, no action is postulated. (T = 10~30 min) For t > T, no operator errors are postulated. Conservative assumptions; or Best estimate + uncertainty Comparison with absolute acceptance criteria Probabilistic Approach All potentially important events are included Multiple failures and common cause failures Errors in diagnosis and execution are considered throughout the accident sequence As realistic as possible Assessing the safety in relative manner - Important accident sequence - Weak points in design & procedures 9

10 Probabilistic Safety Analysis (PSA) Quantitative risk analysis of nuclear power plants Defining the type of consequences from accidents by PSA Calculating frequency for each consequence by PSA Core damage Radioactive-nuclides release (Containment failure) Dose to public - Early Fatality Risk - Cancer Fatality Risk Methodology Accident scenario : event tree Branch of accident scenario : fault tree 10

11 Probabilistic Safety Analysis (PSA) The Key safety criteria: Core damage frequency (CDF) and Large early release frequency (LERF) CDF LERF US-NRC Criteria < 10-4 /RY < 10-5 /RY INSAG recommendation < 10-5 /RY < 10-6 /RY All the reactors currently operating meet the US-NRC criteria. The values of Gen-III reactors are lower than those of INSAG. (OPR1000, APR1400, EPR, APWR, ABWR etc.) The design goals of Gen-IV reactors are 1/10 values of Gen-III reactors. The decrease of CDF means the enhancement of safety. Also for the current reactors, CDF has to be decreased continuously. 11

12 Safety Goal of US-NRC Individual Risk: Each person should be protected from a severe additive risk to life and health due to the operation of NPPs. Public Risk: The Social Risk due to operation of NPPs should be similar to or less than that of other power generation resources, and it should not become a considerable additive social risk. Quantitative Sub Safety Goal: An annual frequency of damage of nuclear reactor should be less than 10-4 per year, an annual frequency of radiation release from nuclear plant should be less than 10-5 per year. 12

13 Probabilistic Safety in Korea Korea NPPs: meeting all probabilistic safety criteria. Core Damage Frequency (CDF): < 1.0 x 10-5 /yr - Shin Kori - 1,2 (OPR1000): 6.94 x 10-6 /yr - Shin Kori - 3,4 (APR1400): 1.09 x 10-6 /yr Early and Cancer Fatality Risk: meeting US-NRC Criteria Goal Estimated Values US-NRC Criteria Early Fatality Risk 2.15 x 10-8 /yr 5.0 x 10-7 /yr Cancer Fatality Risk 4.04 x 10-9 /yr 2.0 x 10-6 /yr 13

14 Progress and Issues in Nuclear Safety Safety enhancement of APR1400 from OPR1000 in Korea CDF level decreased to 1 / 7 - Contributed Design Modification 1 Refueling Water Storage Tank (RWST) In-containment RWST (IRWST) 2 Increased battery capacity (4 hours 8 hours) 3 Safety Depressurization System (SDS) Pilot Operated Safety Relief Valve (POSRV) < APR1400 > 14

15 3 How to Enhance Nuclear Safety 15

16 Nuclear Safety after the Fukushima Accident The basic cause of the Fukushima accident - Decay Heat Removal Failure from Station Black-Out All the NPPs automatically shut down by detecting earthquake. Decay heat - continuously generated after the shutdown due to the fission products decay Loss of offsite power due to Earthquake & Loss of emergency power due to Tsunami Occurrence of Station Black-Out (SBO) Failure of Decay Heat Removal Emergency Diesel Generator 1hr operation Tsunami Fukushima NPP safety system Earthquake Offsite Power Supply 16

17 How to Enhance Nuclear Safety Coping strategy and enhancement ways for SBO Reinforcing emergency alternate AC (AAC) power source - Movable generator vehicle - Cross-Tie design between units Minimizing failure probability of AC power restoration (within 9.5 hours) - Enhancing procedure and education training - Improving equipment and accessibility Applying systems to protect containment integrity - Emergency Containment Spray Backup System (ECSBS) - Containment Filtered Venting System (CFVS) Installing ultimate heat sink Improving safety culture 17

18 How to Enhance Nuclear Safety: IPSS Integrated Passive Safety System (IPSS) Installing additional water tank on the top of auxiliary building outside containment Functions of IPSS using natural phenomena as passive driving force : 1 Decay heat removal 2 Safety injection 3 Containment cooling 4 In-vessel retention 5 Filtered venting High licensibility from application of non-safety grade Minimized design modification and high accessibility from simple design < IPSS > 18

19 How to Enhance Nuclear Safety: IPSS Enhancement of passive safety for current operating NPPs New developing NPPs with new passive safety design (PAFS, Hybrid-SIT). Necessity of safety enhancement for current operating NPPs. - Need of change from active-centered response using fire engine, movable generator vehicle to passive-centered response using fixed passive systems Safety enhancement based on the cost-benefit Cheaper than emergency power sources Recovery of public acceptance for nuclear power safety Improving public acceptance by enhancing safety for aging and operating NPPs 19

20 How to Enhance Nuclear Safety: Containment Cooling Protecting the containment integrity to prevent large release of radio-nuclides Containment spray system Installed in conventional PWRs Most effective for cooling Emergency containment spray backup system (ECSBS) Injecting water by fire trucks Containment heat exchangers for future plants Passive cooling for containment Condensing steam in containment < Containment cooling system in APR1400 > 20

21 How to Enhance Nuclear Safety: Containment Venting Containment protection by controlled venting of steam and non-condensable gases Filtered venting system (FVS) Passive depressurization by pressure difference Radionuclide filtering Decontamination performance - Aerosol: % - Iodine: 99.9 % 21

22 How to Enhance Nuclear Safety: Safety Culture Safety Culture Concentration of attitude and sense of organization and individual that treat safety problem as an overriding concern Need of perception about importance of safety for all members in organization (from CEO to worker) Need of absolute sense that success in safety is the best Sense of duty to completely follow the procedure (Manual) 22

23 How to Enhance Nuclear Safety: Safety Culture Composition of safety culture Safety policy establishment Safety responsibility allocation Safety custom settlement Training & Qualification Management Reward & Punishment Inspection and review Policy Level Manager Worker Safety Culture Management structure Securing material & human resources Self-regulatory activities Attitude with critical mind Thorough & prudent approach Active information exchange & communication 23

24 How to Enhance Nuclear Safety: Risk-informed Regulation Risk-informed regulation (RIR) An approach incorporating an assessment of safety significance or relative risk Risk information = Safety barometer of a nuclear facility Risk analysis must be carried out as the overall safety estimation Application of RIR Supplement of deterministic safety regulation Meeting safety criteria and enhancing safety Examining the design validity and balance of design Improving availability in operation 24

25 4 Closing Remarks 25

26 Closing Remarks Most of the worldwide NPPs are safe in terms of fatality risk. Continuously needed to enhance the safety of NPPs - To decrease the core damage frequency - To prevent and mitigate a severe accident Importance of preparedness and provision for SBO - Passive decay heat removal by the IPSS To protect the integrity of containment by cooling and filtered venting To establish the firm safety culture in nuclear safety To improve and apply the risk-informed regulation more 26

27 Thank You 27