VINIT SHUKLA et al.

EXTENT OF TRITIUM CONTAMINATION OF

CRYOGENIC HELIUM CIRCUIT IN A FUSION REACTOR:

MECHANISM AND PROBABLE SCENARIOS

Vinit Shukla

ITER-India, Institute for Plasma Research

Ahmedabad/Gujarat, India

Email: vinit.shukla@iter-india.org

V J Lakehra

Mechanical Engineering Department, Nirma University

Ahmedabad/Gujarat, India

B. Sarkar

ITER-Organization, Route de Vinon sur Verdon - CS 90046, 13067 St. Paul-Lez-Durance

Cedex, France

Abstract

FUSION- has been the ambition among scientists, policy makers and public to a large extent in advanced countries.

The first step towards realization has been conceived by recognition of the ITER project. The ITER project – the first of a kind

plasma based with tokamak configuration fusion reactor, expected to operate with Q = 10 (50 MW input, 500 MW output) has

moved to its construction phase towards realization for operation. This is also the first fusion reactor, which is going through

the licensing process as a nuclear establishment, due to the use of tritium as a fuel, and so a tritium plant in totality. Tritium

along with deuterium is going to be used as a nuclear fuel in this fusion reactor device. Part of tritium will be breeded through

lithium blanket covering first wall of plasma. Fusion reactors having very small burn up efficiencies, ~ .3 to 2 % only [1], of

the nuclear fuel leads to almost all the available unburnt fuel to be pumped out and recycled in order to consume it again.

These fusion devices needs a very high magnetic field in order to control highly energized plasma. This magnetic field is

produced with the help of superconducting coils which in turn cooled to superconducting temperature by super critical helium

@ 4.5 K, supplied by cryogenic plant. The threat to cryogenic plant safety can be dependent on the extent of tritium

contamination in cryogenic fluid. There are some scenarios where tritium can handshake with cryogenic helium, may be in the

rarest of the rare case, but for safety, ‘whatever can happen will happen’, therefore, a research study is necessary at this stage

of development of fusion reactors. This paper is throwing lights on such possible scenarios and mechanism of tritium diffusion

along with extent of contamination. Temperature and upstream partial pressure dependency on permeation is predicted in this

paper and it has been found that permeation is dominant over 300K temperature. Results also shows that, for 100K regeneration

there is no possibility of tritium contamination of cryogenic helium circuit, but at higher temperature regeneration cycles i.e.

300K and 470K this can be a serious threat. Results predict that 600Pa of upstream partial pressure of tritium at 300K, is

sufficient to breach the safety cap i.e. .2GBq/annum or 5.6*10-7 gm/annum. For 470K, even 5.8mPa upstream partial pressure

of tritium is sufficient to breach the safety limit of tritium in cryogenic helium. This study will also be helpful for design

considerations, related to tritium, of the cryoplants for future fusion commercial reactors.

1. INTRODUCTION

It is envisioned in the near future that demand for the more energy will come especially from the developing

countries where rapid urbanization, industrial growth is taking place. Fossil fuel based energy supply jeopardize

the environment sustainability due to large CO2 emissions. At present, more than 80% of the energy requirement

of developed countries is coming from the fossil fuels. By end of year 2050, an expected rise of the world

population will increase from seven billion to ten billion that could lead to two to three times increase in energy

consumption. A new large scale, sustainable and carbon free form of energy is needed urgently needed in order

to meet this requirement. No single technology is meeting this requirement as each has some pros and cons. Future

energy supply may be a combination of fossil fuels, nuclear energy, and renewable energy i.e. solar and wind.

Abduct available energy, sustainability, no CO2, absence of long-lived radioactive waste and limited risk of

proliferation makes nuclear fusion worth pursing over other sources of energy. Fusion is the process in which two

small nuclei like hydrogen, fuse together at very high temperature and pressure to make a big nuclei and yield

energy release. Nuclear fusion is the process which empowers the sun and stars. At high temperature and pressure

any gas becomes plasma, a fourth state of matter. Plasma is nothing but an electrically charged gas in ionized

form. To get energy from nuclear fusion this process has to be replicated on earth. In order to replicate this process,

gases are heated to extremely high temperatures (150 million 0C). The fusion reaction that is easiest to accomplish

VINIT SHUKLA et al.

is the fusion of hydrogen isotopes, deuterium extracted from water and tritium produced from lithium breading in

fusion itself. A magnetic chamber, called as Tokamak, is designed where nuclear fusion reaction is going to take

place, is part of nuclear fusion reactor. Tritium is a radioactive material with a half-life of ~12.3 years[2] and

should be handled carefully. Comparing an expected yearly consumption of 1.5*105 grams in the fusion reactor

and .8 microgram annual limit of incorporation indicates that future fusion reactors do present potentially an

environment tritium risk. Present work is carried out in order to assess the contamination of cryogenic helium

with tritium. 0.2GBq of tritium radioactivity in cryogenic helium is defined as the safe limit of operation for

cryogenic plant. However, there are many possible scenarios where this limit is under threat and should be

assessed very carefully.

2. POSSIBLE SCENARIOS

Fusion reactors like JET uses tritium as fuel [3] during specific campaign and tritium along with deuterium will

be used in ITER [4] and upcoming fusion devises. Part of tritium will be breeded through lithium blanket covering

first wall of plasma. Fusion reactors having very small burn up efficiencies, ~ .3 to 4 % only [1] [5], of the nuclear

fuel leads to almost all the available unburnt fuels (D+T) to be pumped out and recycled in order to consume it

again. Pumps to serve this purpose needs to run in the surrounding magnetic field and neurotic environment and

cryo-pumps emerges as a top choice. Cryo-pumps provide a cooled surface of charcoal as an adsorber bed to trap

the gaseous molecules generated after plasma burn. Adsorber beds are cooled down to 5K with the help of

cryogenic liquid helium being supplied from the Cryo-plant with an intermediate cold box in order to provide

better controllability. The contamination of cryogenic helium with tritium arises here, will be extended to cryo-

plant and may lead to various factors to be taken care of while designing cryogenic system. Schematic shown

below represents the tritium flow inside the fusion reactors.

FIG. 1. Schematic of tritium flow in typical fusion plant

2.1 Permeation through cryopumps

Firstly, during nominal operation of the plant, tritium can permeate through the metallic walls in to cryogenic

helium. Torus Cryopumps are supplied 4.5K SHe @ 5bar. Torus vacuum space for ITER is of the order of

~1350m3[3] and needs to be pumped out of the order of 10-4Pa in between two plasma shots. This means that all

the flue gases generated due to plasma burn needs to be pumped out with torus Cryopumps. 4.5K pumping circuit,

cooled with SHe, will be made up of panels coated with charcoal. Cryopumps will undergo regeneration phase

sequentially. There, three regeneration phases, which are foreseen as regeneration at 100K, 300K and 470K

temperature level. 100K regeneration will be used to evaporate all the hydrogen isotopes including He, Ne

impurities, and 300K regeneration will be used to release Ar, O2, N2, CO, CO2 etc., and 470K regeneration will

be used as to release H2O, D2O and T2O. Nominal operation time for a cryo-pump is 1200 sec and other Cryo-

pumps will be either in standby or in regeneration mode. Permeation of tritium at cryogenic temperatures is not

possible hence during nominal operation this phenomenon is insignificant. At high temperatures, permeation

dominates and thus has to be checked during regeneration phase. Hence, tritium permeation during regeneration

need to be assessed. The torus cryopumps will experience 50,000 regeneration cycles @ 100K over the period of

Unburnt tritium

Unburnt tritium

VINIT SHUKLA et al.

20 years. For the regeneration @ 300K, 3500 cycles are considered i.e. each pump will be regenerated @300K

once a week. Regeneration cycle for 470K is computed to be as 1000 cycles.

2.2 Accidental scenario

Tritium inside the vacuum vessel is kept within 1kg of limit in order

to keep the amount below deflagration limit of hydrogen isotopes.

Vacuum vessel has many ports for the controls during plasma

operation as well as for fueling and pumping operations. The unburnt

tritium will be pumped out to tritium separation plant through

installed cryopumps. Cryopumps are cooled down to 4K temperature

level with liquid helium and will undergo regeneration time to time

in order to avoid tritium concentration more than 120g [3][6].

However, during 100K regeneration almost all the tritium will be

desorbed and pumped out, but in any accidental such as breaking or

leakage cryopumps cooling pipes will lead to handshaking of tritium

with cryogenic helium. Partial or incomplete 100K regeneration will

lead to high partial pressure of tritium in cryopumps and permeation rate of tritium to cryogenic helium @300K

can be significantly high. Tritiated helium can enter in to cryoplant area if there is any leakage of braking occurs

at cryogenic loop separator. The below simplified block diagram represents the process and possibility of

handshaking of tritium and helium.

3. MECHANISM OF TRITIUM CONTAMINATION OF HELIUM

Mass diffusion of tritium through SS wall is the mechanism via which

tritium is having possibility to get mixed with cryogenic helium. There

are various process involved in this mechanism as shown in figure

below. There are two kind of processes involved during

hydrogen/tritium and metal interaction; 1: Surface Processes i.e.

adsorption, dissociation, recombination and desorption and 2: Bulk

Processes i.e. interstitial diffusion due to concentration gradients,

thermos migration and trapping

The thermal hydrogen molecules that are adsorbed by the metal surface

dissociate into constituent atoms. These atoms can diffuse through the

bulk of the solid or back towards the front surface. When hydrogen atoms reach the front surface (recycling) or

the back surface (permeation), before leaving the solid, they must recombine into molecules (recombination).

3.1 Adsorption of tritium

When the tritium molecules dissociates upon adsorption, it is referred to as the dissociative adsorption of

hydrogen. In order to dissociate the tritium molecules, the amount of kinetic energy of tritium must be greater

than the energy of the dissociative adsorption. Dissociative adsorption will take place if (i) the kinetic energy of

T2 molecule that collides with the surface was above the activation energy for dissociative adsorption 𝐸𝑎𝑑 (.08eV

for BCC Fe)[7] and (ii) the surface site where T2 will struck is unoccupied.

3

2𝑘𝑇 = 𝐸𝑎𝑑

Where k is Boltzmann constant and T is the temperature of the gas. Temperature of the gas is calculated as 619K

in order to have dissociative adsorption at surface. The regeneration temperature is close to 500K which is below

than 619K. However we can neglect this phenomenon and can expect the possibility of dissociative adsorption of

T2 to happen[8].

FIG. 3. Schematic of permeation process of

gases in metals

FIG. 2. Simplified block diagram represents

the process and possibility of handshaking of

tritium and helium

VINIT SHUKLA et al.

3.2 Migration of T2 from surface to bulk

Migration of T2 will take place in three stages namely (i) Surface adsorption, (ii) migration between surface to

bulk and (iii) diffusion. It is noted that high barrier will be there is second and third stage as compared to first

stage, which will work against the driving force for the diffusion process. However, it will much more depend

upon the many other factors like voids present etc. Therefore influence of this phenomenon is neglected in this

report.

Diffusion

Diffusion is the process which is governed by the concentration gradient. Atoms or the substance move from high

concentration to lower concentration till the equilibrium is reached. Tritium molecules moves from upstream of

the plate to downside of the plate. Diffusion process is very much influenced by the temperature of the molecules.

At higher temperatures, energy of the molecules becomes higher and due to this diffusion rate increases rapidly.

For the case of tritium in stainless steels, diffusion rate is significant if the temperature is higher than 300K. At

cryogenic temperatures this is insignificant.

Desorption

If sum of the energy of two neighboring T atoms on the surface is above than that of desorption energy, a

recombination desorption will takes place and finally the T atoms will combine to molecules and tritium

contamination of cryogenic helium may take place.

4. EXTENT OF THE TRITIUM CONTAMINATION

4.1 Literature review

Various studies are made regarding the permeation behavior of the hydrogen isotopes in various metals so far

considering different boundary conditions such as type and thickness of material, upstream and downstream

partial pressure and temperature conditions [9]. Results obtained in different studies shows that the data related to

tritium permeation in metals is quite spread, however, this may be attributed due to different boundary condition

chosen during study. Study performed on the permeation of tritium inside SS-304 and SS-316, temperature

ranging from 25oC to 222oC, shows that permeation is mainly attributed by grain boundary diffusion [10]. In this

direct measurement of tritium initial concentration in the range of 0.005ppm to 0.007 ppm by weight, is

considered. It is also reported that surface effect of the specimen is limited to only 5 micron [10]. Tritium

permeation where the specimen was exposed to high pressure, in the range of 0.1MPa to .69MPa, of gaseous

tritium and temperature is the range of 295 to 430K for up to 6yrs also has been reported [11]. Results revealed

that surface finish has much influence on steady state diffusion; e.g. deuterium permeation was always less when

the specimen surfaces were prepared by phosphoric acid electro polishing than when a 320-grit finish is used. In

order to diminish the oxides effect on the measurement, specimen were tested while in contact with LiD powders,

where contact with LiD powder should reduce the protective oxide layer on most austenitic steels. It was also

observed that calculated diffusivities were not affected by surface condition and hydrogen diffusivity in austenitic

steel is independent of hydrogen concentration. Isotopic mass effect also has an influence on the hydrogen

transport in austenite. Data shows that isotopic effect on diffusivity and permeability can be adjusted by classical

inverse square root of hydrogen and tritium mass [11]. In order to have surface effect on the permeation,

permeation reduction factor (PRF) can be taken. PRF value close to 1000 is considered to be a good approximation

[12],[13]. Transient and steady state analysis of hydrogen permeation is also studied using a gas phase permeation

technique at 100 to 350 0C [14]. Results echoes that up to 80% deformation of the stable 310 alloy made only a

relatively small change in transport properties. Tritium permeation in aqueous form is also studied by H Nakamura

et al. 2004[13], as the result, the permeation rate was found to be about three order smaller than that of the gaseous

tritium. Measurements were also performed in the temperature range of 500K to 1200K and upstream hydrogen

pressure of .001 to .1 MPa [15]. In order to reduce the surface effects, all the specimen were polished to .3 micron

alumina finish and annealed it at 1200K for more than three hours. Results reflected for lower temperature and

lower pressure, half power dependence on the upstream pressure in not valid any more. Data related to tritium

permeation at ultra-low partial pressures is also studied [16]. Observation has been made that at sufficiently low

pressure, the pressure dependency of the permeation must go with first order. It was also explained that this

VINIT SHUKLA et al.

phenomenon is a result of the diatomic nature of the hydrogen in the gas phase and the atomic nature of hydrogen

in dissolved phase: dissociative chemi-absorption is an interceding process, and is dependent on the first power

of the pressure, and eventually becomes rate-limiting process at some low value of the driving pressure.

Permeation of tritium from first wall made of stainless steel is calculated as 10-6 gm/day [17]. It was observed that

in order to reduce the permeation, entrance surface of the wall must be clean while passivation of the exit surface

is not so effective.

Tritium/hydrogen isotope permeation in stainless steel at low temperature (~100K) is very much limited and not

studied well. Cyclic loading and unloading on tritium partial pressure and temperature variations of the metallic

plate could also affect the tritium permeation behavior but in terms of overall permeated inventory is not varying

too much[18]. In the current study tritium partial pressure in the range of 2 to 20kPa is considered and temperature

in the range of (100K-570K) is considered. Table 1 and table 2 summarizes the literature available for transport

properties of hydrogen and its isotopes.

TABLE 1. DIFFUSIVITY OF HYDROGEN ISOTOPES REPORTED AT DIFFERENT

TEMPERATURE AND PRESSURE LEVEL

Sr.

No

.

Pre

ssu

re R

an

ge

[Pa

]

Tem

per

atu

re

Ra

ng

e [K

]

Ga

s a

t su

bst

rate

Met

al

thic

kn

ess

[mm

]

Met

al

Diffusivity

D0*exp(-ED/RT) [m2/sec]

Ref

eren

ce

D0 and

ED

[J/mol.]

@300K @500K

1. 1-105 323-773 D2 .198 Pd-25 pct Ag

alloy 1.87*10-7

24685 9.4*10-12 4.9*10-10 [19]

2. -- 300 H2 -- α-Fe -- -- 7*10-9 [18]

3. -- 558 T2 -- Incoloy 800 -- -- 4.4*10-11 [12]

4. 50-700 298-595 T2 -- SS 304/316 2.9*10-6

36750 1.7*10-16 2.1*10-8 [10]

5. 103 to

106 500-1000 H2 .1 - .3 SS 316 6.32*10-7

47800 3*10-15 6.4*10-12 [15]

6. 105 to

3*105 350-700 D2 .025

Austenitic

Steel

4.7*10-7

53122 2.6*10-16 1.3*10-12 [20]

7. 100 to

3*104 373-573 H2 .195 AISI 310

7.16*10-7

53000 4.2*10-16 2.1*10-12 [14]

8. -- 423 T2 .5 SS 316L -- -- 5*10-13 [13]

9. 1200 298-573 -- -- SS 316 -- 1.4*10-16 6*10-12 [21]

10. -- 645-965 H2 -- SS 304 1.22*10-6

54872 3.4*10-16 2.3*10-12 [22]

11. 2*108 223-423 H2 -- Austenitic

Steel 8.9*10-7

53600 3.7*10-16 2.1*10-12 [23]

From the table above, it is very much clear that the diffusivity of hydrogen isotopes in austenitic steels @300K is

in the range of 10-16 m2/sec and @500K is in the range of 10-12 m2/sec. Diffusivity of hydrogen and tritium can be

estimated by square law of molecular weight as, 𝐷𝑇2

𝐷𝐻2= √

𝑀𝐻2

𝑀𝑇2

[11] [23].

VINIT SHUKLA et al.

TABLE 2. PERMEABILITY OF HYDROGEN ISOTOPES REPORTED AT DIFFERENT

TEMPERATURE AND PRESSURE LEVEL S

r. N

o.

Pre

ssu

re R

an

ge

[Pa

]

Tem

per

atu

re

Ra

ng

e [K

]

Ga

s a

t su

bst

rate

Met

al

thic

kn

ess

[mm

]

Met

al

Permeability [mol. m-1sec-1Pa-1/2]

Ref

eren

ce

P0 and

EP

[J/mol.]

@300K @500K

1. 1 to 105 323-773 D2 .198 Pd-25 pct

Ag alloy 3.43*10-8

6156 2.9*10-9 7.8*10-9 [19]

2. -- 558 T2 -- Incoloy

800 -- -- 7.8*10-17 [12]

3. 103 to 106 500-1000 H2 .1- .3 SS 316 2.7*10-7

61700 4.9*10-18 9.7*10-14 [15]

4. 105 to 3*105 350-700 D2 .025 Austenitic

Steel 8.47*10-8

58887 4.7*10-18 5.9*10-14 [20]

5. 2*108 223-423 H2 -- Austenitic

Steel 1.2*10-7

59800 4.6*10-18 6.78*10-14 [23]

From the table above, it is very much clear that the permeability of hydrogen isotopes in austenitic steels @300K

is in the range of 10-18 mol. m-1sec-1Pa-1/2 and @500K is in the range of 10-14 mol. m-1sec-1Pa-1/2.

5. METHODOLOGY

The present work is performed considering suitable diffusivity and solubility of tritium in stainless steels as

reported in many literatures. Diffusivity and solubility of tritium in SS are used in the calculation are taken from

the reference[20] . Diffusivity for tritium in SS-304 is given by the relation [20] as

𝐷 = 4.7 ∗ 10−3 𝑒𝑥𝑝−(12900/𝑅𝑇) (𝑐𝑚2

𝑠𝑒𝑐) , and solubility as 𝑆 = 1.28 ∗ exp(

−1400

𝑅𝑇)

𝑐𝑐(𝑁𝑇𝑃)

𝑐𝑚3.𝑎𝑡𝑚1/2

Permeation through metal walls can be described by following relation

𝐽 =𝑃

𝑑(√𝑃𝑢 − √𝑃𝑑)

Where,

J is permeation flux [mol.m-2.s-1], P permeability coefficient (D*S) [mol.m-1.s-1], d is thickness of the metal wall

[m], Pu and Pd are the partial pressure of species in upward and downward side respectively.

Considering 1.5 mol/m3 as deflagration limit in cryopumps, for 100K regeneration the partial pressure of tritium

is calculated as 1.25kPa. For 300K this partial pressure may reach to 3.75kPa theoretically, considering no 100K

regeneration has been taken place previously, as 300K regeneration tritium partial pressure will be depended upon

the inefficiency of previous 100K regeneration. Similar approach has been followed for 470K regeneration also.

Calculation has been performed for all three cases of regenerations. Total time for the calculation has been taken

as 20 years. In order to estimate the permeated tritium, initial concentration at upstream and downstream side of

the plate is considered. Initially it is assumed that there is no tritium is present at the downside of the plate, but

upstream concentration is considered as fixed one. After dt time interval, permeated moles of tritium is calculated

and hence concentration at the downstream end is estimated. In the second iteration downstream concentration

has been updated from iteration one while considering upstream concertation as a constant. dt time interval

considered for the iteration is similar to the regeneration time for 100K, 300K and 470K regenerations. Permeated

tritium is considered to accumulate at downside of the plate and no back flow is considered in the calculation.

Downside tritium partial pressure has been estimated from the accumulated moles and is used in next dt time

interval. These steps are followed for the total time considered. Results are compared with the allowable limit.

VINIT SHUKLA et al.

6. RESULTS AND PLOTS

Considering all the inputs and methodology as described above,

following results are obtained for the amount of permeated tritium to

cryogenic helium. FIG. 4 explains the permeation dependency on

temperature. Graph depicts that permeation rate is very small at low

temperatures (<300K), but the rate increases exponentially after

300K, as shown in FIG. 4, therefore confirming that permeation is a

high temperature phenomenon and at cryogenic temperatures it can

be neglected. FIG. 5 explains the permeation dependency on

pressure. Permeation rate increases almost linearly w.r.t upstream

partial pressure considering fixed downstream partial pressure. It

crosses the safety limit when the upstream partial pressure is ~47kPa.

Fig. 6 compares the permeated tritium in cryogenic helium and

maximum allowed tritium and results reflects that at 300K

regeneration the permeated tritium is insignificant and will always

be within the allowable limit even though complete failure of 100K

regeneration is considered. During 100K regeneration, almost all the

hydrogen isotopes will be pumped out so partial pressure of tritium

will be very small during 300K regeneration. At 470K, when the

permeation rate will be higher due to high temperature, partial

pressure of tritium is calculated considering 99.999% efficiency of

previous regeneration cycles and it was observed that after 11

regeneration cycles at 470K, allowable tritium limit is breached as

shown in FIG.7.

FIG.6. Tritium permeated during 300K regeneration FIG. 7. Tritium permeated during 470K regeneration

7. CONCLUSION

As results reflect that tritium contamination of cryogenic helium is

impossible through permeation during 100K regeneration mode.

Tritium permeation rate increases exponentially if the upstream

partial pressure of the tritium is more than 45kPa and temperature is

in the range of 300K or more, and even if such favorable conditions

exits, it takes approximately continuous exposure of ~100 days to

breach the safe limit. As the permeation rate increases at high

temperatures, possible threat exists at high temperature regenerations

i.e. 300K and 470K regenerations. Tritium permeation at high

temperatures arises only with the existence of inefficiency in the

previous regeneration cycles which in turn increases the permeation

rate. For 300K regenerations, upstream pressure of 1.2kPa

(considering complete failure of 100K regeneration) will take ~121 regeneration cycles of 90 min each to break

the safety limit of tritium contamination. Condition even get worst for 470K regeneration, where upstream partial

pressure of only 5.86mPa, takes only 11 regeneration cycles of 50 min duration each to breach the safety limit.

FIG. 8 shows the efficiency of previous regeneration cycles vs safe regeneration cycles for 300K and FIG. 9 shows

0.0E+00

2.0E-06

4.0E-06

6.0E-06

8.0E-06

1.0E-05

1.2E-05

0 500 1000 1500 2000 2500 3000 3500

Cu

mm

ula

tive

tri

tiu

m [

gm

]

Regeneration cycles

300K regeneration

Tritium [gm]

Limit [gm]

0.0E+00

5.0E-07

1.0E-06

1.5E-06

2.0E-06

2.5E-06

3.0E-06

0 10 20 30 40 50

Cu

mm

ula

tive

tri

tiu

m [

gm]

Regeneration cycles

470K regeneration

Tritium [gm]

Limit [gm]

FIG. 8. Safe 300K regeneration cycles vs

efficiency of previous regeneration

0.E+00

2.E-08

4.E-08

6.E-08

8.E-08

1.E-07

200 250 300 350 400

Cu

mm

ula

tive

tri

tiu

m [

gm]

Temp [K]

Temperature dependencey on permeation

Tritium[gm]

0.0E+00

5.0E-08

1.0E-07

1.5E-07

2.0E-07

2.5E-07

3.0E-07

0 20 40 60 80

Cu

mm

ula

tive

tri

tiu

m [

gm]

Pressure [kPa]

Pressure dependencey on permeation

Tritium [gm]

Limit [gm]

FIG. 4. Permeation dependency on temperature

FIG. 5. Permeation dependency on pressure

0

200

400

600

800

1000

1200

0 20 40 60 80 100

30

0K

Re

ge

ne

rati

on

cyc

les

Efficiency in previous regeneration [%]

Safe 300K regeneration cycles vs efficiency in previous regeneration

Series1

VINIT SHUKLA et al.

the inefficiency 470K regeneration vs safe regeneration cycles

respectively. Therefore, in order to prevent the contamination of

cryogenic helium at 300K and 470K regeneration, cycle time and

partial pressure to be optimized.

ACKNOWLEDGEMENTS AND DISCLAIMER

Authors would like to express their kind gratitude towards Mr. Hiten Vaghela, Mrs. Deepti, Mr. Akhil Jha, Mr.

Mohit Jha and Mr. Anuj Garg for their technical support and suggestions. The views and opinions expressed

herein do not necessarily reflect those of the ITER organization.

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FIG. 9. Safe 470K regeneration cycles vs

inefficiency of previous regeneration

0

15

30

45

60

75

90

105

120

135

150

1.00E-05 2.10E-04 4.10E-04 6.10E-04 8.10E-04 1.01E-03

47

0K

Re

gen

era

tio

n c

ycle

s

Inefficiency [%]

Safe 470K regenearation cycle vs inefficiency of previous regeneration

Series1