Problems and Risks of PLEX - nuclear-waste-watch.orgnuclear-waste-watch.org/files/PLEX_Presentation.pdf · towards nuclear power, plant ... • Ageing of components and systems ...

06.10.05 Dr. Helmut Hirsch 1

Problems and Risks of PLEX

Presentation at Joint Project Workshop 2005


Idyllic View of NPP (Paks)


Not-so-idyllic View of NPP (Brunsbüttel)


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.”


Reactor Population of the World:


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.


How to Confuse an Issue with Acronyms…

• PLEX = Plant Lifetime Extension

• PLIM = Plant Life Management

• LTO = Long-term Operation


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)


Ageing of Components and Systems – Influences:

• Irradiation

• Thermal loads

• Mechanical loads

• Corrosive, abrasive and erosive processes

• Combination and interactions of those processes


Typical bathtub-curve of failure rates at an NPP


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…


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)


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…


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


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.


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


“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.


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).

Problems and Risks of PLEX - nuclear-waste-watch.orgnuclear-waste-watch.org/files/PLEX_Presentation.pdf · towards nuclear power, plant ... • Ageing of components and systems ...

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