Oxygen control systems and impurity purification in lead:

DEN/CAD/DTN/STPA/LIPC LEADER Technical meeting, CADARACHE 5-6 July2012

Oxygen control systems and impurity purification in lead:

Partners : CEA: L. Brissonneau,


Summary

Context Oxygen control systems

Experiments Scale up

Handling of impurities Experiments Scale up

Conclusion


Need for oxygen control

Avoid PbO formation LBE thermohydraulics Risks of plugging

Formation of protective oxide layers To prevent metallic element release To control oxide layers growth

kinetics


Formation of PbO (upper limit) Quite a good agreement between Gromov (1998)

and Ganesan (2006) 350 and 550°C

TwtCO

50002.3%)log( *

TatCO

510032.4%)log( *


Upper limit

Too high oxygen content can lead to PbO precipitation at cold stop ( 350°C)

For 4000 t Pb with 5.10-1 ppm oxygen a cold stop at 350°C (solub limit 1.10-1 ppm) yields 22 kg of PbO

The higher acceptable limit for oxygen content in operation is 8.10-2 ppm.


Formation of magnetite Fe3O4

3Fe + 4PbO = Fe3O4 + 4Pb 3Fes + 2O2 = Fe3O4 = 3/2 Gf(Fe3O4) 4PbOs = 2Pbs + 2O2 = 2 Gf(PbO) 3FeL = 3 Fes = - 3RT ln aFe(L) 4Pbs = 4 PbL = 4 RT ln aPb(L)=0 4OL = 4 PbOL = 4 PbOS = -4 RT ln aO(L) Raoult law : aFe= CFe/C*Fe ; aO= CO/C*O

Or aO(Fe3O4)=a0 Pb-Bi Ganesan :

Fe3O4 RT lnP(O2) = -551.99.103+156.9T

TCC FeO10600355.2log4

3)log( *min

Ox

OPT

TatO 22 .

121349*906.16exp%1,

TT

TOFeG

Pb

OFeaOFePbeqx

O

OO

.121349*906.16exp)

_43

4343


Operating domain• Large domain in stable operating conditions

– 3 orders of magnitude• Narrower domain in transient; cold stop, to limit oxidation kinetic

– One order of magnitude, 10-3 <[O]<10-1 ppm


Extension of operating domain One major limit is PbO precipitation at cold stop

8.10-2 ppm maximum of oxygen.

The dissolution of protective oxides is the lower limit : Fe3O4 at more or less high temperature depending on surface protection

10-4 ppm if claddings are protected 10-5 ppm if hot leg is protected( by Ta?)

Protection of the hot surfaces by Ta could also lead to very low oxygen strategy if no dissolution of Ta occurs

Then Ta oxidation should be avoided ! ? Ta oxidation at oxygen content higher than 10-15 ppm

■ Initial oxygen will be trapped by hot Ta, then colder surfaces will oxidize

■ Any “extra” oxygen must be trapped : ■ hot traps Mg, Al ?■ Reduction by H2 in a dedicated loop ??


oxide/metal limit

1,E-19

1,E-18

1,E-17

1,E-16

1,E-15

1,E-14

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

1,E-07

350 370 390 410 430 450 470 490 510 530 550

Temperature (°C)

O c

on

ten

t (p

pm

)

Ta_Ta2O5

Fe_Fe3O4

No Ta2O5 formation

Fe3O4 dissolution


Accidental conditions Air ingress

Leak in the argon cover gas circuit 52 kg of oxygen in sodium in Superphénix (1990) In lead, very low solubility of O in lead (>103 times at

500°C compared to Na) should lead ■ to surface oxidation : slow o dissolution by vortices■ Rather easy detection in gas phase (N2 or O2 by MS,

GPC…) or by oxygen probe in Pb Water ingress

Leak in SG tubes■ Few dissolution of H2O in Pb■ Detection in cover gas (GPC,

IRS, oxygen probe).

Oxides formed must be reduced H2 loop Filtering



Circuit purification : filtering

Several types of liquid filters was tested Metallic mesh ; dynalloy, Poral (CEA)

Filtration efficiency depends on : Liquid metal properties (viscosity, density,..) Particles : nature, form, size, concentration Temperature Flow velocity Filters medium characteristics (geometry, porosity, pressure drop...) Its location in system

Temperature max : 400°C Flow velocity : 0.5 m/s, but filtration rate 0.2 cm/s (related to filter

area, <2 cm/s recommended by manufacturers) Far from elbows… Need of a auxiliary « loop » or cartridge to have flow rate compatible

with filters characteristics


Poral

Dynalloy

Pall cartridge

Atomic ratio Cr:1 ; Fe: 2, Pb:8, Bi :10Other impurities : In, Sb, Si, Al,


Filtration characteristic Magnetite part of the duplex layer might be removed by the

LBE flow magnetite formation 10 kg/year Stella few grams ( 8g on 250 cm²) are trapped on classical

filters for P 1 bar■ About 30 m² (three cartridge filter 10m² EFIT Type)

Need of high level of maintenance with radiocontamination problems (54Mn, 60Co…)

Impurity in LBE : In, Sb, Al, Si ■ Might lead to high quantity depending on their initial

content

Use of H2 to reduce lead oxide 1 kg of PbO ( +1% / saturation at 400°C / 6000 t) needs

min. 110l H2 1 kg Fe3O4 needs 410 l H2 : But H2 efficient enough ?

■ H2 , H2O management (T, Po…)? Bubbling is necessary to reduce the larger oxides


Purification strategy

Re-start aftermaintenance or repair

Initial start-up

Off-normal operatingconditions

Normal operation

Operations :

Liquid phase :- Thin black dust

PbO + Bi + (Fe+Cr)ox.

µm size- PbO, mixed ox.

crystalLarge size-mm/cm

Liquid phase :- Fe and Cr oxides0.01-0,1 µm size- Non-reducible

Slag (aggregatesStructure) : PbO +

Bi + (Fe+Cr)ox.

Impurities : Phenomenology :

Liquid metal :- Diffusion

- Nucleation andcrystal growth

- Sedimentation andcoagulation- Adhesion

Gas phase :Thin black dust

PbO + LBEµm or lower, sphere

Aerosols : - Evaporation

- Condensation- Partial oxidation- Accumulation

Liquid metal :- PbO precipitationon nucleation sites(on cold surface oron solid particles)- Crystal growth

- Porous - adhesive- Limited dissolution

- Accumulation

Purification method :

Liquid filtration :- Coagulation/concentration

- adhesion strength- Deep bed filtration

Continuous operationFilter medium regeneration

Deep bed gas filterContinuous operation

Liquid filtration :- Stable oxides trapping

Special purification

H2 gas bubbling :- Breaking of the crystals

- PbO reductionSpecial purification

High T – H2

H2 or H2O/H2 gas bubbling : - PbO reduction

Continuous operation

Alternative purification systemsuch as settling/sedimentation

Re-start aftermaintenance or repair

Initial start-up

Off-normal operatingconditions

Normal operation

Operations :

Liquid phase :- Thin black dust

PbO + Bi + (Fe+Cr)ox.

µm size- PbO, mixed ox.

crystalLarge size-mm/cm

Liquid phase :- Fe and Cr oxides0.01-0,1 µm size- Non-reducible

Slag (aggregatesStructure) : PbO +

Bi + (Fe+Cr)ox.

Impurities : Phenomenology :

Liquid metal :- Diffusion

- Nucleation andcrystal growth

- Sedimentation andcoagulation- Adhesion

Gas phase :Thin black dust

PbO + LBEµm or lower, sphere

Aerosols : - Evaporation

- Condensation- Partial oxidation- Accumulation

Liquid metal :- PbO precipitationon nucleation sites(on cold surface oron solid particles)- Crystal growth

- Porous - adhesive- Limited dissolution

- Accumulation

Purification method :

Liquid filtration :- Coagulation/concentration

- adhesion strength- Deep bed filtration

Continuous operationFilter medium regeneration

Deep bed gas filterContinuous operation

Liquid filtration :- Stable oxides trapping

Special purification

H2 gas bubbling :- Breaking of the crystals

- PbO reductionSpecial purification

High T – H2

H2 or H2O/H2 gas bubbling : - PbO reduction

Continuous operation

Alternative purification systemsuch as settling/sedimentation



Oxygen supply devices implementation




Oxygen supply : gas phase H2/H2O equilibrium

= 1/11 at 550°C for 10-6 wt% (NRI) 1 month, 5 litres Less success in CORRIDA (FZK)

■ 1000 kg LBE ■ Poor solid/gas mass transfer

Ar/O2 or Ar/O2/H2O injection Manual control Main parameters

■ Gas flow rate■ PO2 pressure (0.1-1% in Ar)■ LBE flow rate■ LBE temperature

Seems to work by local injection Better stability achieved with H2O


Oxygen supply by gas phase

Advantages Same device for O2 control and purification by H2. No operation on the device in normal operation Quite easy to control automatically

Drawbacks Rely on sensors if non equilibrium gases are used Need for exchange coefficient if equilibrium gases are

used Risks of oxide formation Large flow rates (Dilution) Gas purification (FP, AP, T, Po,) and recycling Risk of contamination exposure for operators


Oxygen supply for large scale facilities, gas phase

An auxiliary loop, type CORRIDA, to supply oxygen in the pool ? XT-ADS 0.45 g/h, T =400°C

Q(O2)=5.8 cm3/min Q(Ar/O2)≈600 cm3/min Min. LBE flow to avoid PbO precipitation : 6 kg/min

EFIT 9 g/h, T =400°C Q(O2)=116 cm3/min Q(Ar/O2)≈12 l/min Min. LBE flow to avoid PbO precipitation : 360 kg/min

No pumping problems

Exchange coefficient in kg/m².h tested in CORRIDA Not too far from what is required for XT-ADS two orders of magnitude lower than what would be required

for EFIT :■ Higher flow rates need experimental validation

LBE mass flow :318 kg/ min in CORRIDA


Test interpretations :

Stella experiments performed to estimate fundamental parameters of PbO dissolution were not successful

Oxygen content evolution observed in other parts of the test line show that the oxygen sensors deliver a local measure of oxygen concentration

reflect the heterogeneous oxygen distribution in the system.

Tests highlight various mechanisms in competition : Oxygen supply by dissolution of PbO pellets Reduction of oxygen by hydrogen from the cover gas (Ar 5% H2) Dissolution of Fe3O4 protective layers in low range of oxygen

concentration (<10-7 wt%) or of the residual particles present in the coolant

consumption of oxygen by oxidation of the walls or of the metallic corrosion products coming from dissolution of metal walls.


Solid phase supply for large scale facilities

Need of fluid saturated deviation to prevent Fe-Cr oxides reaction with the pellets

O supply driven by flow rate and temperature

Large device 15-50 kg PbO(1 - 3.5 kg O)

EFIT 9 g O /h One filling per 4 – 16 days

Several devices are needed per auxiliary loops or cartrides

Several filling operations per year even for oxidation rate one order of magnitude lower

Use of the mass exchanger on an auxiliary loop Maintenance : problem of activated products

in cold areas (54Mn, 60Co)IPPE MX, Martynov, ICONE 17

150cm


Solid mass exchange

Advantages No gas management No risks of plugging (oxide formation) Quite easy control by flow rate and

temperature

Drawbacks More complex design for MXp More maintenance : pellets filling

■ Personal exposure Risks of oxide precipitation on pellets

■ Sluggish kinetic for dissolution


Conclusion

Oxygen supply seems difficult at large rates in classical devices

Gas phase supply would need further experiments to demonstrate the ability of large exchange coefficient

Solid phase supply was not clearly demonstrated■ More complex design to be tested■ Automatic filling of the device ?

Personal exposure problems

Purification techniques have been defined Filter characteristics, cold trap

■ Longer experiments are needed Maintenance problem


Thanks for your attention


Open questions

Sensors location At the entrance of the core At the entrance of each heat exchanger In each secondary loop

Oxygen supply Gas phase or solid phase One auxiliary loop per heat exchanger ?

■ Independant oxygen delivery Solid mass supply in the pool ? High oxygen supply rate / steel passivation Maintenance or filtration operation

Filtration In the auxiliary loop or large filter cartridge ? Maintenance operations


Recommandations for Sensors locations

Because of non homogeneous concentration, it is necessary to use at least three sensors. They shall be placed in the coolant flow in the zones with maximum, minimum and intermediate temperatures (supposedly, in the range from 460 to 540 С).

If there are zones with low rate of coolant temperature variation at their outlet, it is reasonable to install additional sensors.

Before each zone with large exchange area In each secondary loop to check the good working

of the oxygen supply device


1,00E-10

1,00E-09

1,00E-08

1,00E-07

1,00E-06

1,00E-05

1,00E-04

1,00E-03

0 20 40 60 80 100time (h)

C (

% m

as

s)

0

100

200

300

400

500

T (

°C)

S 82

S 81

S 85S 83

temperature

by-pass test line n°2

lost of levelin testing tank

lost of levelin testing tank due to a leak

Co min

Co*

Oxygen control process studiesby solid mass exchange method

• Solid PbO dissolution test N°2 in STELLA3 pellets at T=500 °C for only 90 hours with a flow rate Q=1 m3/h (u=0.12 m/s) and [O]~10-5–10-8 wt%

No more pellets in the dissolution device after test !

Documents

Oxygen control systems and impurity purification in lead: