Structural Integrity and NDE Reliability II

The “European Pressurized Reactor”’s NDE P. Blin, F. Champigny, EDF Ceidre, France; L. Berhault, EDF CNEN, France

INTRODUCTION

In May 2006, Electricité de France decided to launch the building of the first European Pressurized

Reactor on the Flamanville site in Normandy. The “Flamanville 3” EPR unit is the first one to be

subjected to the French Ministerial Orders of the 10th November 1999 [2] and of the 13th December

2005 [3] from the design phase. According to these orders, the non destructive examinations (NDE)

planned for the in service inspection (ISI) and for the pre service inspection (PSI) must be operational

with a compulsory formal qualification. The PSI is a complete inspection of the main primary and

secondary systems. The PSI’s goal is to perform before the first core loading all the NDE planned for

the future ISI in the same conditions, in order to have a reliable reference for the detection or for the

evaluation of the possible damages during the ISI. The “Flamanville 3” PSI is planned to start end

2010. The program consists of the development and the qualification of the NDE compatible with the

new generation reactor’s stakes. In January 2009, the French government decided to launch a second

EPR planned to be built in Penly (Northwest France) and operated by EDF.

This paper is about:

� the main EPR’s goals and the technological evolutions,

� the main component modifications (which have an impact on the NDE),

� the place of ISI in the general safety demonstration,

� the main inspection goals,

� the NDE qualification process,

� the approach to set up the ISI program, the ISI program with some examples.

Figure 1 - The future EPR unit 3 at Flamanville

THE MAIN GOALS OF EPR

EPR [1] is the result of an evolutionary process based on the feed back of the French N4 unit and the

German Konvoi unit. EPR is in accordance with a progress approach to increase:

� the safety level with several design innovations : the quadruple redundancy for each major safety

system, the corium spreading area, the in-containment refuelling water, a reinforced protection

against airplane crash …,

� the radioprotection level with a decrease of the collective dose per year and reactor : goal of 0,35

Sievert.man/ year,

� the environment goals with a decrease of the wastes,

� the performances with :

� a service life = 60 years,

� an electric power = 1600 MW

� an availability factor = 91 % (outage duration = 14 days, 40 days for a complete outage).

Figure 2 – The main safety systems of EPR

THE MAIN COMPONENT MODIFICATIONS

The vessel

The vessel, with a larger size, benefits from design improvements. The nozzle shell and the RPV

flange are made in a monobloc ring. The nozzle joint on the monobloc ring is performed with the “set

on” principle instead of “set in” for the N4 units. Furthermore, the instrumentation tubes (former-

penetrations on the bottom head ) are now set up on the vessel head.

Corium spreading

area

Heat exchanger

Quadruple

redundancy

of the major

safety

Protection against

airplane crash

In-containment

refuelling water

Figure 3 - The monobloc nozzle shell and the « set-on » nozzles

The control rod driving mechanisms (CRDM)

The major evolution is the CRDM housing design. This Konvoi design is based on a connection with

bolted flanges and the main housing part built with a martensitic steel. Each CRDM housing is made

with four strength welds, including two dissimilar welds. These welds will be examined with

automated ultrasonic and eddy current techniques.

Figure 4 – CRDM housings with 4 welds

The main coolant line (MCL)

The main coolant lines are elaborated in forged austenitic steel with a reduction of welds (monobloc

design for the cold line). Each loop has :

� 4 dissimilar welds with TIG narrow gap and alloy 52,

� 9 homogeneous welds with TIG orbital narrow gap.

The MCL are designed and manufactured according to the « break preclusion » principle. The

consequence of this principle is the absence of whip restraint and a better accessibility. Nevertheless,

the ISI program must be reinforced with a large examination of all these welds. These welds will be

examined with automated ultrasonic techniques. The NDE’s main stake is to obtain the performances

for this inspected component (austenitic structure, large thickness).

Figure 5 – The MCL : hot, cold and U loops

The pressurizer

The pressurizer dome is modified with the manhole in a central position and three new aspersion

lances. The discharge nozzles are equipped with a scoop system. These new obstacles are a restriction

for the panoramic radiography, and ultrasonic techniques are recommended. In the bottom head, the

new disposition of the thermal sleeve should reduce the dosimetry of this area.

The steam generator

The steam generator design is similar to the N4 unit with the same tubes (diameter, alloy 690..) An

optimisation of the water box geometry allows a better accessibility for the robotic equipment to reach

the peripheral tubes (maintenance and ISI operations). The feed water inlet nozzles (normal and

auxiliary) are designed to prevent the thermal stratification degradation with thermal sleeves in front

of the inlets dissimilar welds.

THE PLACE OF ISI IN THE GENERAL SAFETY DEMONSTRATION

Design and Manufacturing

At the 1

st Defence in Depth level, qualification (M140 according to RCC-M) and NDT ensure that

components are free of important defects (crack-like defects are not permitted). Despite provisions that

have been taken at the 1st stage of DiD (quality of design and manufacturing), it is postulated a failing

of the first level (wrong design assumption; new damage not expected.)

In Service Inspection ISI is not to be considered as a sole 2

nd DiD level provision: transient book and chemistry follow-up,

maintenance program, monitoring, ensure also that components are operating within the allowable

limits. In most cases, as significant damages or risks that could affect the integrity of the components

have been deleted at the 1st stage, the goals of ISI is to detect non expected phenomena.

THE MAIN INSPECTION GOALS

The EPR nuclear steam supply system design is based on the best choices : the studies integrate a large

feed-back from the French and the German plants, so that hardly any area is concerned by damage

mechanisms. In addition, the manufacturing conditions performed on these components are based on a

high technical experience. A large and formal program of NDT dedicated to manufacturing defects

detection is performed in order to ensure the structure integrity : this leads to a significant reduction of

manufacturing risks. The reliable EPR design and manufacturing enhance the level of confidence. So

that, no ISI degradation is expected. Most NDE applications are being qualified according to the

“conventional” approach (unspecified defect). The purpose of “conventional” qualification is to

demonstrate the performances of the NDE application. The recording threshold is based on a reference

(eg notch / hole ø 2mm..) and one of the qualification goals is the detection sensitivity in the inspected

volume. The technical justifications study the influential parameters contributions on the

performances. Although no postulated defect is expected, the detection capability is assessed on planar

defects in mock-ups or by simulation. Nevertheless, some NDE applications are being qualified with

the “general” approach (postulated defects, eg thermal fatigue defects). The purpose of a “general”

qualification is to demonstrate that the NDE application will enable to detect, to locate and to size the

postulated defects.

Fig.6 – The pressurizer dome with the

discharge nozzles and the aspersion lances

Figure 7 – The SG water boxes

Figure 8 – The feed water thermal sleeves

THE NDE QUALIFICATION PROCESS

The goal of the qualification process is to prove that an NDE application is in accord with the given

functional specifications. It is a structured and formalised step by step process [4][6][7]. The different

actors are reminded below:

� The EDF NPP operator requires functional and performance specifications based on input

datas coming from the EPR project [1] and the manufacturer.

� The EDF nuclear engineering division is in charge of the qualification management.

� The qualification body, whose experts are competent and independent, examines and

approves the capability of inspection applications in accordance with the performances

specifications.

The NDE vendor performs the technical justifications, the practical tests on representative mock-ups,

the inspection procedure and the qualification report (qualification synthesis).

Figure 9 – Qualification Process – main steps

THE APPROACH TO SET UP THE ISI PROGRAM

The set up of the ISI program is the result of safety requirements in adequacy with the EPR’s

efficiency goals. A “plant life management” has been worked out with the following input datas:

safety requirements, component design, calculation, operational plants feed-back, sensitive areas..

This “plant life management” defines the main inspection goals but not the details of the NDE

techniques. On this base, the operational plant ISI feed-back has been studied with:

� 85 qualified NDE applications,

� a large knowledge panel,

� the reliable performances,

� the technical feasibility of the inspection specifications.

The ISI choices must be in accordance with the major EPR requirements such as the security

policy (radiography ), the collective dose and the outage duration.

The ISI program is set up with the following principles:

� Launching new developments for the new components (new designs).

� Adapting or upgrading some NDE applications already performed and qualified for the 58

operational plants.

� Retaining ultrasonic techniques instead of radiography (when it’s possible).

� Retaining automated applications for dosimetry / accessibility situations.

Other actions are lead to consolidate the ISI program:

� A large panel of mock-ups with notches.

� A better involvment of the NDE vendors in the qualification process.

� A benchmarking and technical exchanges organised with Olkiluoto 3 in Finland.

EDF NPP

OPERATOR

NDE VENDOR

EDF

Nuclear

Engineering

Division QUALIFICATION

BODY

Performance

specifications

Qualification report

TJ, practical tests,

inspection procedure..

Qualification

certificate NDE specifications / call for bids

THE ISI PROGRAM

The EPR’s ISI program is composed of 40 NDE applications with a qualification on the main primary

and the main secondary systems. Moreover, it’s necessary to add televisual inspections of the

internal part of the main components (RPV, vessel head, SG, pressurizer..). In comparison, 85 NDE

are required for the 58 NPP (on four different sets). On this program:

� Half are automated NDE with robotic equipments, under the responsibility of specialized

vendors. All the robotic equipments must not contaminated and for that, a new in vessel

machine is required.

� Half are “manual” applications with qualified inspectors.

� Some of them are new applications and specific to EPR (MCL, CRDM..).

� Half are based on ultrasonic techniques (35 % for the operational NPP).

This program includes the following examinations (not exhaustive):

� CRDM housing welds (homogeneous and dissimilar).

� MCL welds (homogeneous and dissimilar).

� RPV welds and head closures stud/nuts.

� SG and Pressurizer housing welds.

� SG tubes,

� MSL and MFWL welds.

Automated NDE examples – AREVA NP

Fig. 10 –In Vessel Inspection Machine Fig. 11- CRDM housing weld inspection

Fig. 12: MCL inspection equipment and MCL mock-up

CONCLUSIONS

EDF is involved in the building of the first EPR reactor in France to anticipate the future needs

concerning the electricity production means. To be in accordance with the regulations (French

Ministerial Order of the 10th November 1999) and with the Flamanville 3 PSI goals starting from end

2010, EDF is performing a large development and qualification program with about 40 NDE

applications. The design and the manufacturing approach which includes manufacturing NDT is

reliable and generally no postulated defect is expected. Therefore, the ISI program requires a lot of

examinations with a high level of qualification assessment. EDF is using the large feed-back coming

from the operational NPP NDE, for example the In Vessel Inspection. However, the new designs of

some EPR components require new automated NDE equipments to examine these areas, eg the MCL

and the CRDM housing welds. The stake is to ensure the performances for these new components.

To conclude, since 2007, EDF and its industrial partners are involved in this program in order

to be in accordance with the safety goals an with the industrial performances of this new unit.

REFERENCES

1) EDF DIN CNEN : Projet EPR France.

2) Arrêté du 10/11/1999 relatif à la surveillance en exploitation du CPP et du CSP des réacteurs

nucléaires à eau sous pression.

3) Arrêté du 13/12/2005 relatif aux équipements sous pression nucléaire.

4) P. Blin, The END qualification process at EDF, 5 th international Conference on NDE in

Relation to Structural Integrity for Nuclear and Pressurized Components, San Diego, May

2006

5) P. Blin - F. Champigny - L. Berhault , Les END de l’EPR, Journées Cofrend, Toulouse, Mai

2008

6) RSE-M : Règles de Surveillance en Exploitation des matériels Mécaniques des îlots nucléaires

REP - 1997-2005.

7) European methodology for qualification, ENIQ, réf EUR 17299 EN 1997.