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Topical Conference

Improving Nuclear Safety through Operating Experience Feedback

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Evolutionary Design

Fundamental objectives for the development of future NPPs

High safety level

Competitiveness against other power generating plants,

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Economic

The EPR competes successfully against a coal fired power plant.

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Safety

Probabilistic objectives and targets

the integral core melt frequency, considering all plant states and all types of events shall be less than 10-5/r.y.

the risk of large releases shall be “practically eliminated”, large releases being defined as releases beyond the acceptable limits in terms of consequences: no permanent relocation, no need for emergency evacuation outside the immediate vicinity of the plant, limited sheltering, and no long term restrictions in consumption of food.

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Safety

Two fold strategy:

Improvement of the preventive level of the defense-in depth concept:

prevention of deviation from normal operation

detection of deviation from normal operation and provision of means to prevent the propagation to accident conditions,

mitigation of accidents,

Implementation of additional technical features to mitigate the consequences of severe accidents avoiding the necessity of stringent off-site countermeasures.

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EPR Safety System Configuration

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EPR Safety System Configuration

On the basis of the approaches implemented in existing French and German plants, a safety system configuration has been established, which combines the advantages of a system configuration, which allows mutual back-up of existing systems with the concept of providing a high degree of redundancy and the separation of functions.

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Passive Features in the EPR

Larger steam generator and pressurizer volumes to slow plant response and increase grace periods,

Safety injection system suction line directly from IRWST, which is located inside the containment, in order to avoid switchover from injection mode to recirculation mode,

Lower core elevation relative to the cold leg cross over piping which limits core uncovery during SB LOCA,

A large dedicated spreading area outside the reactor cavity to prevent the molten core-concrete interaction by spreading and subsequent flooding of the corium,

A large water source in the IRWST, draining by gravity into the corium spreading area.

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Safety Approach for Severe Accidents

Request from licensing authorities:

Situations that would lead to large early releases such as containment bypass, strong reactivity accidents, core melt with reactor coolant system at high pressure or global hydrogen detonation, have to be “practically eliminated”. If they cannot be considered as physically impossible, design provisions have to be taken to design them out.

All other solutions, including the low-pressure core melt accidents have to be mitigated by design measures, so that the corresponding radiological consequences would necessitate only very limited protective measures in area and time.

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Safety Approach for Severe Accidents

The EPR follows the deterministic approach with the objective to strengthen the design measures in such a way that a “practical elimination” of large releases is achieved. This implies technical measures to avoid early containment failure by transient events as well as measures to ensure long-term integrity of the containment.

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Feedback from AREVA NP GmbH (Germany)

Operating experience is drawn from the following sources:

all reportable events in AREVA NP GmbH-built nuclear power plants (reporting according to regulatory authority guidelines)

all reportable event reports issued by the German Association for Plant and Reactor Safety (GRS)

all reports issued by the GRS from the network of the Incident Reporting System of the IAEA/OECD which are of relevance to nuclear power plant operators

reports selected by Framatome ANP GmbH from the network of the American Institute of Nuclear Power Operations (INPO) which are considered important to nuclear power plant operators

reports selected by the German Association of Large Power Plant Operators (VGB) from the network of the World Association of Nuclear Operators (WANO).

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Feedback from AREVA NP SAS (France)

The information comes from the INPO (American Institute of Nuclear Power Operations) data base, from event files of EDF and from FROG (Framatome Owners Group).

Usage of generic investigations results given by AREVA NP & EDF for special cases.

Utilization of IAEA & OECD publications.

Internal information in AREVA NP coming, in particular, from the construction sites, and Nuclear Services Operations.

Relations with EDF; on specific problems, "Working Groups" are organized with the objective of information exchange and definition of necessary actions.

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Feedback from German Utilities

According to German regulations, operating German nuclear power plants must report all accidents, incidents and other events and classify their reports according to significance. Thus, these so-called "Notifiable Events" constitute a collection of all incidents observed in German plants, which might be relevant to safety.

The German Association for Plant and Reactor Safety (GRS) considers all events which must be reported, either in Germany or world-wide. All events which are significant in the opinion of GRS, are distributed to the operators of all German nuclear power plants, in the form of so-called "GRS Information Notices".

Notifiable Events as well as the GRS Information Notices are examined by the Utilities' experts regarding their relevance for the EPR.

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Typical Examples and Countermeasures introduced in the EPR Design - System design

Avoidance of Sump Clogging

Trash racks above the heavy floor openings

Heavy floor openings

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Typical Examples and Countermeasures introduced in the EPR Design - System design

Retaining basket

CHRS strainer

SIS stainerRetaining basketSIS

stainer

Avoidance of Sump Clogging

Large retention baskets, sump strainers

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Typical Examples and Countermeasures introduced in the EPR Design - System design

IRWST

IRWST

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Typical Examples and Countermeasures introduced in the EPR Design - System design

Mitigation of SGTR - design features of the EPR :

The delivery head of the Medium Head Safety Injection System (MHSI) is below the secondary safety valves set point

Detection of the affected steam generator on a straightforward symptom (water level measurement in the affected SG)

Increase of t he steam generator secondary volume

The safety demonstration based on this design allows for demonstrating that the radiological criteria are met with high margins.

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Typical Examples and Countermeasures introduced in the EPR Design - Component design and material

N4 EPR

Steam Generators

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Typical Examples and Countermeasures introduced in the EPR Design - Component design and material

N4

EPR

Pressurizer

»s

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Typical Examples and Countermeasures introduced in the EPR Design - Component design and material

Reactor Coolant Pumps

The primary coolant pumps are a development of the model N24 that are used in N4. They are equipped with standstill seals in order to ensure complete tightness of the pump sealing after stop of the pump.

Reactor Pressure Vessel Internals

The design of the internals of the RPV is very close to those of N4 with some geometrical adaptations (241 assemblies 17x17 instead of 205 assemblies 17x17 for N4). Adaptations were taken from Konvoi plants, e.g. the control rod guides.

Thermal sleeves

In several operating plants there is a thermal sleeves. On the EPR there are no thermal sleeves on the nozzles connecting the MCL and the RHRS.

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Typical Examples and Countermeasures introduced in the EPR Design - Radiation Protection

The annual collective dose will be restricted to 0.5 man Sv per 1 GW net electric power.

In parallel to optimization of works, design evolutions which have an impact on radiation protection, have been identified.

Optimization of the source term

Reduction of dose rate

Reduction of exposure time under radiation field

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Typical Examples and Countermeasures introduced in the EPR Design - I&C

Improvement of the elaboration of the functional diagrams with appropriate tools and organizational measures

The definition of requirements for design and qualification of equipment has been undertaken through the work on I&C.

Testing and validation on site of level 1 and 2 I&C will be improved and easier with the implementation of a tester for the verification of the software equations and of a simulator for the verification of the images, alarm sheets, operating procedures.

Also with regard to the grounding concept, the experience gained from past experience will be taken by improvements in the EPR design.