Life Time of an SPM Electrolyser in a Water Detritiation System
Ion Cristescu
Forschungszentrum Karlsruhe, Postfach 3640 D-76021 Karlsruhe, Germany,+ 49 7247 82 3757 e-mail: ion.cristescu@hvt.fzk.de
The Combined Electrolysis Catalytic Exchange (CECE) method in combination with
Cryogenic Distillation (CD) was chosen for tritium recovery from tritiated water which will
be produced during ITER operation. One of the key components with impact to both thetritium inventory and safety is the electrolyser. The solid polymer electrolyser type is
proposed but the main concern is the life time in tritium environment. On overview of main
activities devoted to the life time of a SPM and carried out at Mound facility-US, TPL JAERIand TL Karlsruhe are presented in this paper.
I.

the cells have, for the most part, relied on the

Introduction
For ITER, the Water Detritiation System(WDS) is one of the key systems to recover as
much tritium as possible and consequently tominimize any potential impact to the environment.
The most suitable process for water detritiationand tritium recovery is the well known CECE
process in combination with CD process for final
tritium enrichment [1].
In a WDS facility based on the CECE process,the electrolysis unit contains almost the entire
amount of tritium involved in the separation
process. Usually the water hold-up of theelectrolysis

unit

based

on

solid

polymer

membrane (SPM) electrolyte is three to five times
larger than the water hold-up of the Liquid Phase
Catalytic Exchange (LPCE) column.
One of the key issues related to the SPM
electrolyser is the lifetime under tritiated water
processing. Studies that have been conducted tomathematically predict long-term performance oftime-independent

virginproperties

of

the

polymeric materials. However, SPM properties
can significantly change as functions of time andexposuretoelevated

temperatures

due

to

degradation and/or aging. This provides numerous
motivations for different kind of investigations [2].
Another important aspect under consideration,
which can be effectively demonstrated on
different types of SPM, is the effect of sulfonationon their properties. Since changes in the level ofsulfonation lead to dramatic changes in thephysicalproperties

of

the

material,

theinvestigation in this area is increasing in the lastyears.
The following issues have to be considered
for operation of a SPM:
- Water also travels across the membrane in the
direction of proton movement. This makes it
necessary to periodically pump the transported
water back to the anode side.

- Other metal cations will also occupy the proton

filters and ion exchange column, flow meter, andsites in the SPM. The metal cations bond morecell, and back into the side of the H2O-O2strongly to the SPM and therefore are difficult toreservoir. The gases are gravity separated frombe removed. This cause the cell to develop a highthe water inside the reservoirs on both the H2 andresistance across the SPM, therefore requiring aO2 sides of the system.

higher voltage difference to maintain a given

Three types of electrolysis cells have been

current through the cell. This, in turn, results intested: one test with a regenerative cell, five tests

parasitic heat losses due to ohmic heating and canwith a screen hardware cell, and three tests with aresult in overheating and burn up of the SPM.

pneumatic seal cell.

- Water is necessary to the structure of the

Tritium concentrations of 1 to 300 Ciml-1 in apolymer. If the material is dried out, the resistancesingle addition of tritiated water were used in thefirst goes up, then the material become brittle andfirst four tests. Total cell operating time until SPE

cracks easily.

failure was recorded for these tests. The final five

In addition to these issues which are
specifically for electrolysers in service withtests were designed to measure SPE life time attritium concentration of 1, 10, and 100 Ciml-1.

normal water, the damage which may be produced

The experimental results are presented inby the tritium environment has to be quantified

Table 1, and the outcomes can be summarized as

and the life time estimated as function of provided

follow:dose.

- No precise determination of the useful SPM
lifetime can be made from the data gathered in

II.

Electrolysis of Tritiated Water in Solid-

tests; several additional parameters affecting thepolymer Electrolyte Cells at Mound Facility

lifetime were not sufficiently controlled.

US- The presence of iron and other impurities
An investigation of the electrolysis of tritiatedwater using General Electric Company solid
polymer electrolyte (SPE) cells was carried out at
MRC-Mound [3]. Several operating systems werebuilt and tests done on three types of cell designs.
The experimental rig to measure the lifetime of a
SPE is shown in Figure 1. The main components
are the electrolysis cell, pump for water
circulation, two reservoirs for hydrogen andoxygen respectively, and an ion exchange column.
Water circulating in this system goes out of thebottom of the H2O-O2 reservoir, through the pump,affected the electrical resistance of the SPM. At
high tritium level, such impurities will always bepresent due to radiolysis of the metallic materialsof system construction. Even with a ion exchange
resin provided in the last experiments, lowering
the concentration of Fe+3 , the Nafion itself is an
ion exchange material and will increase theresistance and heating inside the SPM.
-

Another issue is the electrical and water

circulation parameters as they combine to cause
heating of the SPM. For non tritiated water 2.6 V
were required to maintain 50 A compared with 3.6
V when tritiated water was processed. To lower

the effects of resistance heating, the water flowrate can be increased and/or add refrigeration to
the circulation loop.

Figure 1. The experimental rig at Mound facility
Table 1. Experimental results of SPM lifetime at Mound facility
Test
No.
1
2
3
4
5
6
7
8
9

Tritium
Cell operating time
concentration(min)-1(Ciml )
300
765
1
366
10
498
150
373
1
10
10
10
100

Exposure time(days)

SPM Lifetime(days)

70
203

273

49
111
22

49
111
22

Total Dose
(Mrad)

24.5
84.4
59.1
134
265

Additional tests have been carried out toIII. Life Time Investigation of SPM at
Tritium Process Laboratory (TPL) -JAERI

measure the effect of dose on the water uptake

and Toshiba Corporationand fluorine released. Since the branch of sulfonic

Detailed Investigations have been carried out
at TPL-JAERI in order to estimate the life time ofa SPM [4]. The outcome of these experiments wasnecessary to develop a maintenance procedure forthe electrolysers to be used in ITER. Components
of an electrolyser have been gamma ray irradiatedacid in SPM is hydrophilic, the water uptake may
be correlated with the ion exchange capacity. The
influence of dose on the water uptake is shown in
Figure 2, and as can be seen no serious
deterioration is observed in the case where theirradiation dose is less than 600 kGy.

and the effects evaluated.

30

Three main organic compounds of theelectrolysis cell have been tested:

SPM

25

piece of these compounds was irradiated by the
gamma ray up to 850 kGy. The reference for thisdose is based on the fact that tritiated water of 250
Cikg-1 provides in two years a dose of 530 kGy.

Water uptake [%]membrane, gaskets and electric insulators. A
20

15

10

The dose of 850 kGy is a conservative figure forthe foreseen working time of one year for each5

electrolyser from ITER WDS. The durability wasevaluated as a series of tensile strength, and as anion exchange capacity of the membrane.
No serious damages for the strength and theion exchange capacity of the membrane (Nafion)
have been observed up to 850 kGy. For gasket
materials (AFLAS) also, no damage was observed
up to 500 kGy. The insulator materials (PFA and
FEP) lost their strength at 200 kGy and 300 kGy,
respectively. As far as tensile strength and ion
exchange capacity of the membrane is concerned
the electrolysis cell could be used for two years
under the ITER conditions, in the case where PFA
and FEP are replaced by the other materials suchas polyimide resin.

0
0

100

200

300

400

500

600

700

800

900 1000

Dose [kGy]

Figure 2. SPM water uptake versus dose
One of the irradiation effects is the releasingof fluorine and therefore the dose provided to a
SPM can be quantified as well by the amount offluorine released. As is shown in Figure 3, theamount of the fluorine ions dissolved is almost
linear with the dose. This correlation may be usedduring functioning of the SPM electrolyser to findout the dose provided to the membrane.
During development of different SPM forvarious applications, the possibility of improving
the structure of SPM by radiation exposure wasconsidered as well. A correlation between the inpurpose dose provided to SPM and the dose

average energy for beta decay is more than 5

provided by tritiated water environment can beyears.

done. Close to ITER-WDS situation is one surface
treatment carried out by Toshiba Corporation with

IV. Activities on SPM Lifetime at TLK

the aim modifying the surface structure of the

Karlsruhecommercial Nafion117, by low dose electron

Quantity of dissolved fluorine [mg/g-dry Nafio

beam (EB) exposure [5].

An experimental rig with the aim toinvestigate the behavior of a small electrolysis cellbased on SPM has been developed at TLK [6].

20

The process was conceived in order to allow
operation of tritiated water in a closed loop.
Therefore, in addition to the electrolysis cell,15

which produces tritiated hydrogen and oxygen, acatalyst bed was inserted along the process withthe aim to convert the products of the electrolysis

10cell to water. The catalyst bed was tested for one
month continuous operation with demineralized
water. A scheme of this experimental rig is shown

5

in Figure 4. Several buffer vessels are in theexperimental rig in order to allow to feed and
0
0

100

200

300

400

500

600

700

800

900 1000

Dose [kGy]empty the process. The water circulation between
different components of the experimental rig is
realized only gravitationally, therefore the relative

Figure 3. Dissolved fluorine versus dose
Low dose EB treatment was shown to beeffective in the reduction of methanol crossover,
600 µC/cm2 exposure reducing crossover to 7%of that of the parent material and an improvementof up to 51% in the maximum power when used
in a fuel cell was found compared with anuntreated material
The calculated time to get an equivalent
exposure of 600 µCcm-2 but coming from tritiatedwater of 250 Cikg-1and considering 5.9 keV theelevation between components was carefully
adjusted.
The experiments performed at TLK have been
focused on the following issues:- To investigate the behaviour of a small
electrolyser cell based on a SPM over a long
period functioning with tritiated water, withtritium activity of 1.2 Cikg-1- To compare the mechanical properties such as
tensile strength and elongation for a solid polymer
membrane before and after exposure to tritiatedand demineralized water.

V16

V13

~ 100 cm

3

B2

V01
V11
V02
V17
~ 100 cm

B1
V19

V08

HTO

O 2

Tritium
retentionsystem

V14

H 2O
H 2

V18

V15

3

Catalyst
bed

V04

HT
V12

V07

V05

H 2O
V10

HTO
~ 100 cm

3

V03

B3

Electrolyser
V09
V07

V06

HTO < 150 cm

V20

3

Tritium activity: 1-10 CiKg

N 2

-1

Total activity < 1,5 Ci

Figure 4. The TLK experimental rig for SPM life time measurement
During six months continuous operation of the

behaviour, the instabilities due to the relative

experimental rig, the voltage drop applied on the

movement of the electrodes when pressure

electrolysis cell was maintained constant and thefluctuation occurred.

was

The chemical composition of tritiated watercontinuously recorded. A similar electrolysis cellprocessed in the first experimental rig was

was in function with demineralised water in themeasured after two and six months operation. In

same working conditions. For this second set-up

Table 2, the chemical composition of tritiatedthe current through the electrolysis cell was also

water withdrawn from the experimental rig after

continuously recorded. In Figure 5, the behaviour

two and six months operation is presented. Theof the cell current of the two electrolyser cells

amount of cations in the tritiated water changed

over six months functioning period is shown. Thevery slight after three months operation. The

current

throughtheelectrolysis

cellcurrent in both electrolysis cells had a similar

general trend is to decrease, probably due to theirelongation for the SPM used in the two

fixation within the SPM.

electrolysis cell and for one virgin SPM cells are

The mechanical properties such as tensile

presented. The differences of tensile strength andstrength and elongation of the membranes used atelongation between the two SPM in service withTLK during the investigation of the two small

tritiated and demineralised water are very small

electrolysis cell in operation with tritiated andand there is not reason to consider them as

demineralized water have been measured.

provoked by β radiation of tritium.

In

Ratio cell current to starting cell current (%)

Table 3, the average values for tensile strength andc e ll c u rre n t - tritia te d w a te r
c e ll c u rre n t- d e m in e ra liz e d w a te r

1 .1

1 .0

0 .9

0 .8

0 .7

0 .6

0 .5
0

50

100

150

200

250

W o rk in g tim e

Figure 5. Cell current behaviour of the two electrolysis cells
Table 2. Chemical composition of tritiated water after two and six months operation
Kation/Anion(mgl-1)

Feeding water(mgl-1)

Al
Ca
Fe
P
S
Si
Ti
Chloride
Fluoride
Phosphate
Sulfate
pH

< 0.2
0.11
<0.05
<0.5
<0.5
0.68
<0.5
0.09
0.45
0.15
0.26
5.5

After two month
operation(mgl-1)
6.1
4.9
2.6
6.0
4.3
7.8
4.2
6.99
37.6
7.8
9.1
3.0

After six month
operation(mgl-1)
5.0
3.3
0.87
4.1
4.7
8.9
0.4
3.2
22.7
8.4
10.9
3.8

Table 3. Comparison of tensile strength and elongation of the three SPM

Virgin SPM
Tensile strength when force wasin the fibre direction (MPa)Elongation when force was in thefibre direction (mm)Tensile strength when force wasright angles to the fibre direction(MPa)Elongation when force was rightangles to the fibre direction (mm)V.

SPM in operation withdemineralized water

SPM in operation withtritiated water

26.8

20.1

19.1

61.1

26.6

30.5

21.1

18.9

18.1

42.7

22.7

22.7

Conclusions
Beside some manufacturing aspects, such that

improper selections of cell assembly parameters

VI. References[1] ITER Design Description Document – WBS
3.2.E Water Detritiation System

as compression and gasket design could give riseto premature membrane failure, many parameters[2] J. Tammy Uan-Zo-Li, The effects of Structure,including fuel cell operation temperature, pressure,

Humidity and aging on the mechanicaland relative humidity may have a significant

properties of polymeric ionomers for fuel celleffect on membrane life. However, within a given

application, PhD thesis, Virginia Polytechnic

set of operation conditions, certain intrinsic

Institutemembrane characteristics could affect membrane[3] R.E. Ellis, Electrolysis of Tritiated Water indurability dramatically.

Solid Polymer Electrolyte Cells, DOE Report

The available experimental results may
constitute a good basis to consider that the
replacement of the electrolysis cells in ITER

1982.
[4]

T.Yamanishi,

Study

on

durabilityofelectrolysis cell of WDS, TPWG Meetingshould not be required before one year full2005

operation. Nevertheless, further investigation areneeded for a better understanding of the damage[5] L.J.Hobson, Modified Nafion 117 as anmechanism of different SPM and experimentally

Improved Polymer Electrolyte Membrane forproven of an ITER relevant scale electrolyser in

Direct Methanol Fuel Cells, Journal of theservice with tritium.

Electrochemical Society, 148[6]

I.Cristescu,

et

al.

Studies

about

the

performances and required improvements to
use a solid polymer electrolyser in a CECE
process, EFDA Report November 2003