2 NTW - Safety Assessment of Ageing

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Safety assessment ofnuclear reactors ageing

Frederic Menage

NTW - Exploratory workshop

"Ageing of nuclear power

plants: a threat to nuclearsafety? "

19thMarch 2014


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Who is IRSN?

IRSN, Publicassessment

Research

into risks

Stakeholders(CLIs)

THE PUBLIC

Operator

Designers and constructors

Publicauthorities

Parliament

ASN, ASND

Supreme Committee for Transparencyand Information on Nuclear Safety - HCTISN


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Who is IRSN?

Safety assessment of nuclear reactors ageing

The French TSO,

Independent from operators

Detailed knowledge of installations

Safety watchtower (operational experiencefeedback monitoring)

Conducts its own independent research on safetyissues, including ageing management


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Introduction


Most NPPs have been designed with a givenlifetime in mind (e. g. 40 years in France)

For economical reasons, most operators want tooperate NPPs beyond this timespan

Meanwhile


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EXPERIENCEFEEDBACK

R&D

Opportunities for

improvement


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MORE STRINGENTSAFETY

OBJECTIVES

Coexistence of old

and new reactors


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Under what safety conditions can aprolonged reactor operation be accepted,

taking into account the fact that safertechnology is available ?

Managing timedependent effects

Reducing the safetygaps between old

and new plants


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Managing time-dependent effects

Ageing management

Ability to prevent, anticipate and cope withdiscrepancies

Plant modifications

Obsolescence management

Human resources and knowledge management

Coping with industrial and environmental changes

Key issues of long term operation


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Reducing the safety gaps between old

and new plants

Operating experience feedback

Periodic safety reviews

Enhancing prevention of accidents

Reducing radiological consequences of accidents

Enlarging the scope of PSA studies

Improving operation conditions



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Summary /Conclusions

1. LEVEL

2. Level

3. Level

4. Level

Title of presentation

Ageing management


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Ageing management : objectives


To maintain availability andeffectiveness of all SSCs importantfor safety

Replaceable SSCs

Non-replaceableSSCs


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Ageing management : key issues

Knowledge of degradation mechanisms

Experience feedback, R&D

Evaluating the effectiveness of scheduledmaintenance to detect these mechanisms

If necessary enhancing maintenance effectiveness

Plant monitoring (especially when degradationmechanisms are not well known)

Repairing/replacing before safety issues occur



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Expanding qualification durability

Qualification : demonstrating the ability of SSCs towork in extreme conditions resulting fromaccidents (pressure, temperature, dampness)

Usually these demonstrations make assumptionsabout the lifetime of the SSC

If the lifetime is extended, so shall be thedemonstration.



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Periodic safety

reviews


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Periodic safety reviews : objectives


To assess the cumulative effects of plant ageingand plant modifications, operating experience,technical developments and siting aspects.

Including an assessment of plant design andoperation against current safety standards andpractices

To ensure high level of safety throughout theplants operating lifetime.


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Periodic safety reviews


By nature, PSRs are the mostefficient way to reduce the gap

between old and new plants


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Enhancing preventionof accidents


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: objectives


To search for high impact solutions, able

to prevent severe accidents (i.e. coremelt) and mitigate consequences moreefficiently

To enlarge the scope of design accidentsand the robustness of their assessment

Design basis accidents

Severe accidents


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: key issues


Adding new plausible accident scenarii to the safetyanalysis report

For example, accidents specific to shutdown states

Lengthening the time limit for operator actions.

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Design basis accidents


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: key issues

S f t t f l t i

Using PSAs to identify ways of improvement andcheck their effectiveness.

Ways of improvement depend on the state of thedesign :

Improving the reliability of electrical sources

Increasing water storage for safety functions

Post Fukushima improvements

Severe accidents

2 NTW - Safety Assessment of Ageing

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