Dr. Christian LATGE

Nuclear Technology Department

Nuclear Energy Division

CEA Cadarache

13108 Saint Paul lez Durance, France

Phone : +33 4 42 25 44 71

Fax : +33 4 42 25 78 78

e-mail : christian.latge@cea.fr

IAEA Education &Training Seminar

on

Fast Reactor Science and Technology

CNEA Bariloche, Argentina October 1 – 5, 2012

Sodium Fast Reactors

Interaction Na & materials

Introduction to sodium :

n 1807

Na in the alkali metal family : Name coming

from arabic : al kaja meaning : ashes coming

from sea

Guaranteed impurity levels for nuclear-quality Na

Activation

Clogging

Nuclear reactions

Clogging

Mechanical properties

Corrosion

Tritium

Corrosion

Nuclear reactions

………….

Gas blanket activity

Silver

Lead

Boron

Calcium

Carbon (total)

Chlorine + bromine

Lithium

Sulphur

Uranium

Chromium

Copper

Tin

Magnesium

Manganese

Molybdenum

Nickel

Barium

Potassium

Titanium

Vanadium

Zinc

Aluminium

Basic principle of Sodium Fast Reactor (Pool concept)

Steam

Generator

Intermediate

pump

Intermediate

Heat

Exchanger

Primary

pump

Slab Control

plug

Hot

plenum

Cold

plenum Energy

Conversion

System

Material for SFR subassemblies

DBTT

Needs of kinetics and knowledge on mechanical behaviour

As exemple: ODS

• Kinetics lower / 316 (weight gain by Ni)

• More sensitive to Carbon transfer ?

• Phase transformation due to Nickel transfer

(heater)

• No change in mechanical properties

• Needs :

– Oxidation data (ODS with very small grains :

lower oxidation rate expected ?)

– Phase transformation

– Long term prediction for normal and transient

operating conditions

(from JL Courouau GEDEPEON 2009 July 6th &7th)

Corrosion in primary Na of SFR

Sound austenite

Depleted Austenite

ferrite Na

Four successive stages are the following:

Stage 1: surface cleaning. This corresponds to the dissolution

of oxides and surface inclusions during the first hours. Mass

transfer during this stage is negligible.

Stage 2: austenite dissolution. At a temperature of 570°C or

more, the following stage is the dissolution of the austenite

layer in contact with the sodium and the diffusion of the steel

elements towards the sodium. If the temperature is lower than

590°C, the following stages are generally too slow and

practically do not occur.

Stage 3: formation of a ferrite layer. During a longer period of

time, at a temperature of more than 590°C, the diffusion of

elements from the external austenite layer leads to a

ferritization of the steel. This layer then dissolves and the steel

elements diffuse to the surface.

Stage 4: steady state behaviour. The ferrite layer reaches a

limit value ; its dissolution and the diffusion of elements to the

sodium is equivalent to stoichiometric corrosion of the basic

austenite. The contents reached et the sodium-steel interface

are of the order of 1 to 2% for nickel, 5 to 7 % for chromium

and less than 0.5% for manganese.

[O]< 5ppm, Pierre Baqué model

R = 0 (T< 817.13 K)

R = a . V 0.435 . [O] . exp(-150.5/(T-817.13))

R = mass loss in kg.m-2 per year

a = alloy-dependent coefficient

V = sodium rate (m/s) (< 10 m.s-1)

[O]= oxygen content in ppm (Eichelberger

law)

[O] > 5ppm, Alan Thorley model (for [O] between 0

ppm and high concentrations, but used in France

above 5 ppm and T>817.13 K)

If V 4 m/s, R = (V/4)0.435.104.724 +

1.106xlog10[O] - 3913/(T)

If V > 4 m/s, R = 104.724 + 1.106xlog10[O]-

3913/(T)

Fe Na-Fe-O

Na[O]

NaCrO2

Cr

Ni

Na[C] Cr23C6

Na[Ni]

Fe Na-Fe-O

sodium

Corrosion in sodium

Corrosion in the SFR: a key point even

if it has been shown that corrosion

rates in liquid sodium are very limited.

• In primary Na: generalized corrosion

(depends on material, temperature, O

content, Na velocity,..) mainly in fuel

cladding

• In intermediate Na: Na-water

interaction: generalized corrosion due

to Na-H2O interaction products.

• In all circuits, stress corrosion

cracking, mainly due to aqueous

NaOH at relatively low temperature….

To-TA

eO nvkr

Empirical models :

Phenomenological model :

)(.).(Re, )()( lsH aadDScShr

To-TA

eO nvkr Use restricted in duration, T, material, Re :

interpolation difficult and experiments required

For generalized corrosion:

Extrapolation possible

Core Fuel clad: A 15/15-25

Ti,

F/M 9-13-18Cr ODS

S. Assembly : F/M 9-

12 Cr

Fixed primary

structures

A 316 LN

Hot primary

structures and

components

(pump, heat ex)

A 316LN

F/M 9-12 Cr

Secondary

structure and SG

A 316 LN

F/M 9-12 Cr

Alternative

coolant or energy

conversion

systems

316L : Na-Ni

T91 : Pb- Bi

ScCO2

• Required data :

– Solubilities in liquid sodium (metallic and non-metallic elements)

– Free energies of formation

– Diffusivities in liquid sodium and materials

• Missing data : (see CRP IAEA next year)

– Solubilities V, Nb, B, W, Al,…

– Apparent solubilities of Fe

• 105 discrepancy assessed Fed+ FeOx + FeOyNat +

FeCz …

• Na4FeO3 =? (FeO)(Na2O)2)

• thermodynamic data (Fe – Na - C – O) system

– Diffusivities (all except Mn [Sudha, 2006])

0.01

0.1

1

10

100

200 300 400 500 600 700 800 900 1000T (°C)

S (

pp

m)

.

FeNiCrMoMn

0.001

0.01

0.1

1

10

100

1000

100 200 300 400 500 600 700T (°C)

S (

pp

m)

.

OHC

Needs of basic data for models

[Gnanasekaran, 1986]

(from JL Courouau GEDEPEON 2009 July 6th &7th)

CORRONa (CORROsion Na) Principle: thermal well with rotating cylinders

and sodium mini-loop for chemistry control - thermal well in gloves box for T control - inert crucible in contact with Na at high T to

avoid any contamination - Na recirculation (mini loop) for chemistry control - rotating cylinders to control hydrodynamics

Constraints : - make sodium fire a negligible risk (double

confinement, leaks detection, very low volume) - thermal control (cooling of the flange)

Corrosion testing device

CEA Saclay - Bat 458 pièce 3

a

b

Purification Purification Cylindre

éprouvette

Recirculation

Moteur

Cylindre

éprouvette

Recirculation

Moteur

LIBS A

Purificat

ion

A

Purificat

ion

1st wall 2nd wall

2 complementarily testing devices Na = 3.1 kg each Operating conditions: T = 500 - 625°C (designed for 750 °C) v = 500 - 10 000 tr/min (Re) [O] = 0,7 à 38 ppm Mini-loop : 1 L/h, 110-250°C with cold trap Crucible : Molybdenum (MLR – 0.7% La2O3) Well : Nickel base alloy 625

A A

(from JL Courouau GEDEPEON 2009 July 6th &7th)

Mass transfer:

•Transport of dissolved species (convective transport) and TH

•transport of particles if necessary(long term)

•Source term

• Use of a model of dissolution-corrosion for release

• Modelling of equilibrium Na liquid/ solid (long term)=> more thermodynamics

• Corrosion (ANACCONDA)

•Baque’s model ([O] below 5 ppm)

•Thorley’s model ([O] above 5 ppm)

Now OSCAR-Na code

•Activation: main sources of radioactivity:

• 58Co (71 days)

• 60Co (1913 days)

• 54Mn (313 days)

•Deposition

• 54Mn, 51Cr are dissolved in Na and mainly

deposited in the pumps and the coldest parts of the reactor (i.e. IHX)

• 60Co: low fraction diffused in hot surfaces

• Use of a model derived from Polley and Skyrme model for deposition

Needs of validation:

-“Contamination witness”

- Feedback from cleaning &

decontamination from SFR

-Basic knowledge (Acropolis,..

Mass brothers,…)

Mass Brothers

Objective : study of mass transfer from steel 316 (Z5 -CND

17 - 13) in PHENIX conditions

Test conditions

«core» : T = 400°C -> 690°C

«I.H.X.» : T = 600°C -> 400°C

[O2] = 0.7 ppm

duration : 23800 h

54Fe (n,p)

54Mn 312 d 834 keV

58Fe (n,)

59Fe 44 d 1099 keV

1291 keV 50

Cr (n,) 51

Cr 27 d 320 keV

58Ni (n,p)

58Co 71 d 811 keV

59Co (n,)

60Co 5 y 1173 keV

1332 keV

Contamination

witness

Process for code development and validation

Requirement analysis

Validation

Simulation of real reactors

Experiments on loop

code

Architecture

Models integration

Code validation

Use

Modelling

Bibliography

- reactors

- description of elementary

chemical and physics

phenomena

- basic data

Phenomenological analysis

(hierarchical ranking)

Experimental caraterization - elementary model validation

- parameters determination

Choice of models to integrate in

OSCAR

release OSCAR V2.X

- code

- Validation dossier

Decontamination process before repairing (SPX process)

• SPm : Sulfo Phosphoric modified

• H2SO4 + H3PO4

• Duration : 6 hours

• Temperature : 60°C

Criteria for decontamination process

selection :

– Good efficiency

- low residual dosimetry

– Process easy to implement and

flexibility for various components

– low cost for effluent treatment,

chemical products

- Easy component requalification

prior to re-use

PHENIX - Intermediate Heat Exchanger I - Dose rate

0

500

1000

1500

2000

2500

elevation

µG

y/h

Before cleaning

After cleaning

After decontaminationPrimary sodium outlet

PHENIX IHX activity (exemple)

IHX contamination mainly

due to 137Cs, 54Mn, 60Co

O control strategy in the primary vessel

5 ppm (maximum acceptable value for the

operation of reactors during a limited period

[0-3 ppm] is generally the operational range

recommanded for SFR.

In case of pollution, in SPX, it was

allowed to operate in [3-5 ppm], during 1

month.

Complex behavior of Fe in Na:

Apparent solubilities of Fe

Fed+ FeOx + FeOyNat +

FeCz …

Na4FeO3 =? (FeO)(Na2O)2)

thermodynamic data (Fe – Na - C – O)

Necessity to :

- validate Na Quality requirements

- investigate metallic elements

(pure or complex) behaviour in

sodium (and obtain basic data ie

diffusivities, solubilities,…)

- develop Instrumentation (O

control)

- assess quality control

methodology

O-measurements

Electrolyte material compatible with sodium

Ternary oxides (NaZrO2…)

Grain boundary corrosion (impurities…)

High quality for electrolyte material

Good mechanical thoughness and tightness

To avoid Na leak and thorium debris

To avoid radioactive gas release

- Electrolyte with high density

- Efficient closing system design

Operating temperature: might be a criteria

for the choice of the reference system

High ionic conduction

yttria 8<x<17 % mol. (7-15%mas.)

(ThO2)1-x(Y2O3)x : Opt. 7,5%

molaire

High purity

High mechanical thoughness to

thermal shock

High density 98% (best 99%)

Small homogeneous grains

High purity

Fine design

High quality brazed connection

chemistry, thermal expansion,

Na compatibility

O-meter designs

Long tubes

Pt/air reference

Westinghouse

Pt/air reference

Oxyfra

Small cup Pellet

In/In2O3

Harwell

Interatom, GE, IGCAR

In/In2O3

Ga/Ga2O3

Wetting phenomena

Wetting phenomena, which depend of gas adsorption,

structural material oxidation,… are key interface

phenomena between the coolant and the structural material.

Therefore it is considered as a key factor with regards the

following items:

• accuracy of measurements for some instrumentation

devices such as ultra-sonic based traducers, electro-

magnetic flow-meters, electro-chemical cells,…

• interactions between structural material and liquid metal:

corrosion, embrittlement, stress corrosion cracking….

• mass transfer such as activated corrosion products,

tritium,…

• thermal exchanges in Heat Exchangers, liquid metal

targets,…

• Technology developments, cleaning of residual layer,…

Scientific Council G11 meeting on Wednesday, September 16th, 2009 at CEA/Cadarache

• R&D tracks related to ISI&R (1/2) :

– Surveillance of the core, of core supporting line and of internal structures

• Development of ultrasonic under sodium transducers at 550°C

• Numerical modelling and simulation with CIVA code

– Surveillance of internal structure vibrations

• Study of feasibility for detection of acoustic signature variations

• Analysis of various techniques for this detection (US, strain gauges)

– Sodium leak detection

• Use and develop of qualified techniques (H2 detection in SGU) + in gas laser spectroscopy

• New thermal insulation concept for pipes

– Monitoring of operating parameters

• Looking after improvement of available techniques (ultrasonic, optical fibers…) :

– Measurement of temperature, pressure, level, flowrate, speed, sodium quality …

– Signal treatment

• Innovating processes (ultrasonic, electromagnetic)

– Measurement of gas into liquid sodium

L1 Continuous Monitoring

L2 Periodical Inspection – NDE of welding joints for core supporting structures

• Development of ultrasonic under sodium transducers at 200°C

• Development of ultrasonic techniques from outside sodium medium

• Numerical modelling and simulation with CIVA code

• Development of alternative techniques such as EMAT

– In sodium telemetry & surface metrology

– Need of under sodium robots • R&D studies associated to L3 et L4 : see L4 program hereafter

Internal structure

l

l= c*t/2

Telemetry

SE

NS

OR

Properties of sodium

Sound velocity in sodium varies little with temperature and is given by the following relationship:

C (m/sec) = 2577.2 - 0.5234 100 < < 370°C

Consequences: Property used for telemetry and visualisation in sodium facilities, and for acoustic detection of events in Na

2000

2100

2200

2300

2400

2500

2600

0 200 400 600 800 1000

Temperature (°C)

So

un

d v

elo

cit

y (

m/s

ec)

Série1Series 1

Trapping gas pockets at the solid-liquid interface if :

Non wetting solid-liquid system

The roughness is such that [Johnson69] :

slope discontinuities exceeding Y

la << lc la : crevices size

lc : capillary length = gLV

Trapping gas pockets at the solid-liquid interface

Non-wetting system :

y > 90°

Rough solid surface

Liquid

Solid Gas

pocket

Acoustic coupling of ultrasonic transducers for SFR In-Service Inspection

Sodium temperature and Magnitude of the transmitted signal as a function of time

250

275

300

325

350

375

400

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Time (h)

Te

mp

era

ture

(°C

)

0

10

20

30

40

50

60

70

80

90

Ma

gn

itu

de

pe

ak

-to

-pe

ak

(m

V)

T Na (°C)

Mpp (mV)

Acoustic coupling between two media = Acoustic waves transmission at the interface

Issue : acoustic coupling

During periodic examinations of the reactor at shutdown, TNa

180°C.

However, without special precautions, when a TUSHT is immersed

in sodium for the first time at this temperature, its acoustic

coupling is not achieved. Current solution : gold plating* surcharge, tricky implementation

*Gold plating the active face of the sensor under vacuum makes it possible

to achieve the acoustic coupling of the TUSHT at ~110°C

liquid

sodium

TUSHT

Structure to

be inspected

Acoustic

coupling

Ultrasound

Good acoustic coupling between sodium

and the active face must be achieved.

(TUSHT = Traducteur UltraSonore Haute Température)

TUSHT = Traducteur UltraSonore Haute Température

The CEA has developed and qualified an ultrasonic transducer to be

used at nominal power in an SFR.

This sensor is known as a High-Temperature Ultrasonic Transducer

and has been qualified for an operating temperature up to 600°C.

Context : TUSHT

Diaphragm (active face) of the transducer is made of 304 L austenitic stainless steel

L3 Special Inspection

L4 Repair

Scientific Council G11 meeting on Wednesday, September 16th, 2009 at CEA/Cadarache

Study of a global intervention, with :

- Defueling : see « Fuel Handling » studies

• Need of in sodium handling with external storage

- Sodium draining of reactor block :

• Analysis of needs ans associated durations

• Need to prevent caustic corrosion

- Televisual and volumetric inspection in radiating environment

- Sodium filling

- Refuelling

- Repair operations are done in gas atmosphere (can induce defueling and sodium draining)

- Study of in sodium tightness (design of under sodium bell)

- Analysis of tools for repair :

• Sodium traces to be swept (gas blowing/brushing/laser...)

• Machining (milling/grinding/laser…)

• Welding (TIG/laser…)

- Need of under sodium robots assuming efforts of repair tools :

• Analysis of available materials

• Definition of specific robots

• R&D tracks related to ISI&R (2/2) :

Other risk: stress corrosion cracking

Overview on materials

Basic principle of Sodium Fast Reactor (Pool concept)

Steam

Generator

Intermediate

pump

Intermediate

Heat

Exchanger

Primary

pump

Slab Control

plug

Hot

plenum

Cold

plenum Energy

Conversion

System

Main issue: Na-H2O mitigation

Na + H2O NaOH + ½ H2 – 141 kJ/molNa

Na

Water

Steam Generator

750 MW

Sodium-water reaction

Na

H2O

SGU Na-H2O : a violent and exothermal chemical reaction

Main reaction

Na + H2O NaOH + ½ H2 + 162 kJ/water mole (at

500°C)

Complete, quasi-instantaneous and non-reversible

reaction

Many secondary reactions

2Na + NaOH 2 1 [O2-]Na + [H-]Na Na2O + NaH

Equilibrium reaction depending on sodium

temperature and hydrogen dissolved and hydrogen

partial pressure equilibrium

Above about 300°C, and with sodium in excess,

hydroxide is decomposed in sodium oxide and

hydride (reaction 1)

Above 410°C, reaction (2) occurs only if PH2

reach Pequilibrium in cover gas; The experimental

conditions doesn’t satisfy this condition; Thus the

decomposition of NaOH is total.

Reaction rates depend on temperature

ORIGINS : Normal operation of steam generator induces

damage of heat exchange tubes

tube corrosion : mainly in welding zones, inducing leaks

due to cracking

thermal chocks : when under-saturated water is injected at

super heater inlet (Phenix), inducing thermal fatigue,when

fluctuation of heat exchange conditions

impossible tube expansion: buckling, inducing

differential expansion with envelope

tube bundle vibrations : hydraulic effect of sodium flow,

inducing tube wear

1200°C Pressure

Temperature

Time (s) Time (s)

Effects: chemical,

mechanical,

thermal

No leak Micro leak small leak evolution

Wastage effect

Sodium-water reaction

Excellent operational feedback from Phenix &

SPX (and also from international feedback)

; nevertheless tracks for improvement:

Reduction of Na transit time

Signal processing

Other (complementary?) solutions to be deeply

analysed

(Acoustic detection, electrochemical H-meter,…)

Electro-chemical H-meter

(Courtesy of IGCAR)

Lead-bismuth properties (55.5% Bi):

- Low melting point (125°C)

- No chemical reaction with water (but it may

violently vaporise depending on conditions )

- Lead oxidised with possible precipitation of PbO

- Significant corrosion, protective coating

necessary: Aluminium coatings, or oxygen

content controlled to maintain a protective

oxide film at the surface (introduction of

steam+H2 or oxygen by an equilibrium

method using PbO pellets)

- Possible interaction with Na: Exothermal formation of BiNa3 (137 kJ/mol LBE)

- Very large operating feedback available on this coolant in ADS, especially with spallation targets (TECLA, MEGAPIE, EUROTRANS, VELLA programmes)

0,010

1E-11

1E-09

1E-07

1E-05

0,001

0,1

10

100 200 300 400 500 600 700

T (°C)

Co

, p

pm

EPB

Contamination

Oxydation Dissolution

• Reactivity between Bi and Na :

– Production of BiNa3, stability up to 845°C

– Low solubility of Bi in Na up to 650°C.

– JAEA, study (Icone 2003) : Pb-Bi in liquid Na.

• Exothermal reaction 137 kJ/mol Pb-Bi.

Interaction between Na and LBE (bismuth)

Corrosion phenomenology after sodium leak

Impact of the thermal insulation system

Sodium temperature effect :

- at low temperature (350°C) : outside

radial migration (by capillary)

predominates rather than migration to the

wire detector located in the lower 180°

cone distance (BPR and RUR tests)

- at high temperature, the sharper reaction

between sodium and the heat insulation

material creates a shell of reaction

products limiting the rise of sodium by

capillary (RUR tests)

Corrosion studies

Zone 1 : Na almost pur and material without any significant corrosion

Zone 2 : solid magma dark greyish : oxides (Na2SiO2)

Zone 3 : brittle and rather green (presence of metallic ions Fe++, Fe+++, Cr++)

Zone 4 : layer very green with mainly Na2O

The main result is the identification of a typical

corrosion mechanism called « anodic

dissolution », confirmed by other tests (Mod); it is

mainly due to sodium pulverizationduring its

propagation in the insulating material and

subsequent oxidation.

The oxygen content increases near the surface of

the insulating material (at the Na interface) (very

similar to the so-called corrosion phenomena in

wet conditions « Pile of Evans »)

A tool for the designer and manufacturer

Design and Construction Codes for SFR

RCC-MR/RCC-MRx

(from a contribution from Odile Gelineau AREVA

in CP-ESFR Seminar))

CODE = tool providing sets of requirements on materials procurement, design, analysis,

construction qualifications, examinations, surveillance and tests

Rules based on feedback from relevant industrial experience

It provides several advantages :

- Guide for the designer : checklist of all necessary verifications

- Provide an overall consistency to guarantee the structural integrity of a component

- Make easier relationships (and clarify contractual dialog) between Sub-contractors, Manufacturers and Suppliers (and Safety Authorities)

- Reduce costs and improve efficiency through standardisation : simplify the documents, the practices

41 ESFR SP5 - Education &Training - Sodium behaviour and safety – CEA Cadarache 16-11-2010

Intermediate Heat eXchanger :

Tnom : 400°C < 550°C Pnom : 4 bars

Na/Na

Steam Generator :

Tnom (Na) : 345 < 525°C –

Tnom (H2O) : 240 <490°C

Pnom : 190 Bars

Na/H2O

Secondary Circuit :

Tnom : 345<525°C

Pnom : 4 bars

Na

Vessels, internals:

Tnom : 400 < 550°C

Na

SFR specificity and RCC-MR

42 ESFR SP5 - Education &Training - Sodium behaviour and safety – CEA Cadarache 16-11-2010

The RCC-MR code has been developed to take into account

those specificities :

• Significant Creep and associated

damage modes (time-dependent damages)

• Sensitivity to Buckling

• Materials able to sustain high temperatures

• Design rules for particular components

SFR specificity and RCC-MR

Time-dependent fracture

Shear

buckling

It has been presented to French Safety Authorities and used for:

- The design and construction of components for SUPERPHENIX and PHENIX (Heat Exchangers, Pumps, Tanks, pipes,…)

- The design of European Fast Reactor

- The studies for the lifetime extension of PHENIX

- The Indian PFBR

- The SFR project

- The Vacuum Vessel of ITER

43 ESFR SP5 - Education &Training - Sodium behaviour and safety – CEA Cadarache 16-11-2010

Code organization : RCC-MR/RCC-MRx

Sections Contents

Section 1

Equipements

General requirements

Design rules for : Class 1, 2, 3 components and their

supports, for handling mechanisms

Technical Appendices with material databases in

appendix A3

Section 2 Materials

Section 3 Examination and testing methods

Section 4 Welding

Section 5 Fabrication

44 ESFR SP5 - Education &Training - Sodium behaviour and safety – CEA Cadarache 16-11-2010

• Materials (Section 2) :

– Material selection

– Material Reference Specifications taking into account

experience of procurements

• Give process for a part qualification

• Examination and testing methods (Section 3)

– Physical and mechanical testing methods

– Current NDE practices

– Qualification and certification of NDE personnel

• Welding (Section 4) :

– Acceptable filler materials and their procurements

– Acceptance tests

– Reference data sheets

– Acceptable welding procedure and their qualification

• Fabrication (Section 5)

– Forming and tolerances

– Surface treatments, Rules for cleanliness

Code organization - The Other Sections

45 ESFR SP5 - Education &Training - Sodium behaviour and safety – CEA Cadarache 16-11-2010

Code organization

Consistency

of technical

provisions in

each section

of the code

46 ESFR SP5 - Education &Training - Sodium behaviour and safety – CEA Cadarache 16-11-2010

An application : damage modes in a SFR

Shear

Buckling

Buckling

under

Pressure

Excessive

Deformation

Vibration

Fatigue Fatigue under

thermal transients

High cycle

Fatigue

Progressive

deformation

Creep-Fatigue

Thank You very much for your kind attention!

A free level of sodium exits in the main vessel, above the core

and under the upper closure of the vessel.

This provision allows for an easier design and operation of all

the penetrations in the vessel that

are necessary for (either during operation or maintenance):

- fuel handling in the core,

- movement of core control devices

(neutrons absorber rods),

- core monitoring (instrumentation),

- handling of components other than fuel,

that are located in the vessel (core feed pipes,

pumps, heat exchangers, according to the

design of the reactor,

- in service inspection of the vessel and its

internal structures.

It is necessary to have a correct knowledge of key

phenomena in the cover gas:

- Heat transfer, that occurs according to different mechanisms,

mainly: .convection in gas,

.radiation from the sodium surface towards

emerged structures,

-Mass transfer: evaporation / condensation of sodium vapours.

- Sodium deposits.

Shématisation des processus de transfert de l'oxygène :Figure 1 :

Transfert par diffusion au travers de la couche limite

Transfert par diffusion au travers de la pellicule d'oxyde

Transfert par diffusion au travers de la couche limite

Ciel d'Argon

Sodium Liquide

Transfert par convection naturelle

Transfert par convection

Purification par cristallisationd'oxyde de sodium sur piège froid

Injection oxygène

dans le ciel d'argon

dissolution de la pellicule d'oxyde

Réaction chimique

à l'interface pellicule / Na ( l )

Na

Argon

Contamination (ie 137Cs)

Heat and mass transfer in the Upper gas plenum