Problems and Risks of PLEX -...
Transcript of Problems and Risks of PLEX -...
06.10.05 Dr. Helmut Hirsch 4
IAEA on Lifetime, 2001:
“If there are no changes in policy towards nuclear power, plant lifetime is the single most important determinant of nuclear electricity production in the coming decade.”
06.10.05 Dr. Helmut Hirsch 6
Typical Plant Lifetimes
• Some countries have opeating licenses with a fixed plant lifetime (e.g., US: 40 years, Hungary: 30 years).
• Some countries have open licenses with regular safety reviews (e.g., Czech Republic, France, Spain).
• However, a commercial lifetime of 30 to 40 years is generally assumed.
06.10.05 Dr. Helmut Hirsch 7
How to Confuse an Issue with Acronyms…
• PLEX = Plant Lifetime Extension
• PLIM = Plant Life Management
• LTO = Long-term Operation
06.10.05 Dr. Helmut Hirsch 8
Problems Associated with PLEX
• Ageing of components and systems
• Reduction of safety margins due to power uprates and increasing burn-up
• Increasing trend towards “risk-oriented regulation” – further reduction of margins
• Difficult “human resource management” (ageing of personnel, turnover…)
• Continued waste production (not treated here)
06.10.05 Dr. Helmut Hirsch 9
Ageing of Components and Systems – Influences:
• Irradiation
• Thermal loads
• Mechanical loads
• Corrosive, abrasive and erosive processes
• Combination and interactions of those processes
06.10.05 Dr. Helmut Hirsch 11
Ageing of Components and Systems – Effects:
• Reactor pressure vessel embrittlement
• Corrosion of reactor vessel penetrations
• Stress corrosion cracking of pipelines
• Damage of steam generator tubes
• Damage to steel reinforcements in concrete
• Degradation of cables, electronic devices, turbines…
06.10.05 Dr. Helmut Hirsch 12
Ageing of Components and Systems – Consequences:
• Increasing number of incidents and “small” failures (which can potentially develop into accidents)
• Catastrophic failure events – for example, bursting of reactor pressure vessel (PWR, BWR) or pressure tubes (CANDU, RBMK)
06.10.05 Dr. Helmut Hirsch 13
Ageing of Components and Systems – Countermeasures:
• Exchange of components
• Reduction of loads
• Intensification of inspections and plant monitoring
• Reduction of safety margins
Last measure is the cheapest and hence, option preferred by operators…
06.10.05 Dr. Helmut Hirsch 14
Reduction of Safety Margins due to Power Uprates
• Higher loads to fuel elements; in particular: Higher temperature leads to increased corrosion rate
• Higher loads to reactor pressure vessel and components of cooling circuits
• Higher radioactive inventory in reactor core
• Accident sequences are accelerated
06.10.05 Dr. Helmut Hirsch 15
Reduction of Safety Margins due to Increased Burn-up
• Increased corrosion of fuel element hulls increased failure rate, increased failure probability in case of accidents.
• Increased release of fission gases inside fuel rods increased potential for releases in case of accidents.
• Higher radioactive inventory in reactor core.• Handling, transport and storage of fuel becomes
more complicated.
06.10.05 Dr. Helmut Hirsch 16
Consequences of “Risk-oriented Regulation”
• Increased use of probabilistic methods and safety indicators
• Probabilistic analyses do not give a complete picture of the plant state
• Probabilistic analyses cannot take account of ageing processes
• Use of indicators can lead to reduced information for regulatory authority
06.10.05 Dr. Helmut Hirsch 17
“Human Resource Management”
• “Know-how” is usually well documented; “know-why” is contained in the minds of experienced personnel.
• Increasing ageing of workforces in many countries leads to rapid turnover and loss of know-why.
• At the same time, economic pressure incites personnel reductions.
06.10.05 Dr. Helmut Hirsch 18
CONCLUSION
• PLEX leads to risk increase due to ageing.
• Power uprates and higher burn-up further increase hazards.
• Regulatory practice is getting more lenient.
• Competence of personnel is potentially getting worse.
• There are other factors increasing long-term risks, not mentioned here (e.g., terror attacks or climate change).