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PbLi/T database: status of the knowledge. I. Ricapito , ENEA CR Brasimone, FPN-FISING. OUTLINE. Solubility and Sieverts’ constant in PbLi Bulk diffusivity in PbLi Mass transfer PbLi-gas He in PbLi Possible developments. Solubility and Sieverts’constant.

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PbLi/T database:

status of the knowledge

I. Ricapito, ENEA CR Brasimone, FPN-FISING


OUTLINE

  • Solubility and Sieverts’ constant in PbLi

  • Bulk diffusivity in PbLi

  • Mass transfer PbLi-gas

  • He in PbLi

  • Possible developments


Solubility and Sieverts’constant

  • The knowledge of the function linking the tritium concentration solubilized in LLE with the corresponding tritium partial pressure at equilibrium, CT=f(PT), is of basic importance for the LLE breeder blanket concept because of the strong impact on:

  • tritium permeation rate from the blanket into HCS;

  • requested capacity of the Coolant Purification System for a given value of allowed T partial pressure in HCS


Solubility and Sieverts’constant

Impact of Sieverts’ constant on the tritium permeation rate for PPCS-HCLL


Solubility and Sieverts’constant

Sieverts’ law validity range /1

No deviation from Sieverst’s law (Reiter)

Deviation from Sieverts’ law (Wu)


Solubility and Sieverts’constant

Sieverts’ law validity range /2

From Polcaro (1983)

Absorbed hydrogen weight (sample weight = 172 mg) as a function of time of absorption (in min.) is shown at various hydrogen pressures: 1. PH2=20.87 kPa. 2. PH2=30.80 kPa. 3. PH2=47.01 kPa. 4. PH2=53.30 kPa. 5. PH2=77.41 kPa. 6. PH2=86.63 kPa. 7. PH2=100.11 kPa.

One can see that the 5 fold increase in pressure (from plot 1 to 7) gives rise to about 7 fold increase of solubility (reviewed by A. Pisarev).


Solubility and Sieverts’constant

Different values of Sieverts’ constant from different authors (and different techniques)

Absorption technique

Aiello

Desorption technique


Solubility and Sieverts’constant

Sieverts’ constant: last results from SOLE campaign (2005), absorption technique

mol m-3 Pa-0.5 SOLE (A. Aiello)

mol m-3 Pa-0.5(Reiter)


Bulk Diffusivity

Typical H2 pressure rise P(t) after saturation of the sample from gas phase and fast evacuation of the hydrogen atmosphere (desorption technique)

From Reiter, 1991

Curve (a) is desorption from the sample, container and vacuum walls. Curve (b) is a control run without the sample. Curve (c) is the difference giving desorption from the sample.

Parameters of the experiment: T=591K, P=1.01 ×105Pa, tL=72h, m=250 g


Bulk Diffusivity

Diffusion coefficient of hydrogen isotopes in LLE vs temperature

Reiter, 1991


Bulk Diffusivity

Comparison of the bulk diffusion coefficients obtained by Terai (1), Reiter (2),Shibuya (3), Fauvet (4)

(1) D=2.5 10‑7exp(‑27000/RT) m2s‑1

(2) D=4.03 10‑8 exp(‑19500/RT) m2s‑1

(3) D=2.62 10‑9 exp(‑6630/RT) m2s‑1

(4) D(450°C)= 1.5×10‑9 m2s‑1

Terai’s values are the highest, probably because determined in high hydrogen partial pressure, with reduced residual surface effects


Mass transfer PbLi-gas

Hydrogen transfer from LLE to gas phase: mechanisms related coefficients /1


Mass transfer PbLi-gas

Hydrogen transfer from LLE to gas phase: mechanisms related coefficients /2

mass transfer in the metal boundary layer hl

adsorption coefficient Ka

recombination coefficient Kr, with

Results from A. Viola* (1991)

*Results have been achieved assuming valid the D diffusivity and Sievert’s constant values as measured by Reiter


Mass transfer PbLi-gas

Effectivemass transfer coefficient: simplified description of the tritium desorption from LLE into a gas phase: J=KD(Cbulk ‑ Cinterface)

TERAI’s experiments (1991) on Tritium release from Pb16Li and influence of H2 partial pressure on it

PH= 1E3 Pa

KD[ms‑1]=2.510‑3 exp(‑30.7kJmol‑1/RT); T=600-1100K, PH2=1000 Pa


He in PbLi

Formation of He bubbles and tritium trapping could have an important impact on the blanket operation

Henry’constant (from L. Sedano)

Diffusivity(from L.Sedano)


Possible developments

  • Uncertainty remains about the range of validity of the Sieverts’ law. On the other hand, there isn’t consensus on the Sieverts’ constant values. Taking into account the big impact of such issues on the LLE based blanket, there is the urgent need to find reliable and agreed data. A new task is presently open in EU for a further experimental activity. Anyway,an international collaborations should be of outstanding importance in this field.

  • Reference Tritium diffusivity values in bulk LLE (Terai and Reiter) are spread in less than one order of magnitude. A sensitivity analysis should be done in order to evaluate the impact of the different diffusivity values on the tritium permeation rate into HCS: need of modelling implementation.

  • Only few data on T/LLE-gas mass transfer coefficients are available. A new set of data should be extracted from TRIEX experimental campaigns, planned in the next two years. To do it, the implementation and validation of mathematical models in this ambit appears as a priority.


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