Hydrogen Isotope Research Center - Toyama Univ.


Data Base for Tritium Solid Breeding Materials (Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4) of Fusion Reactor Blankets --- Yoshiaki FUTAMURA

3. Review of data for Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4

3.1 The outline of database for Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4

  The data for solid breeding material, Li2O are described in chapter 4, the data for Li2TiO3 in chapter 5, the data for Li2ZrO3 in chapter 6, and the data for Li4SiO4 in chapter 7. In order to understand the rough degree and extent of reliability on those collected data, the present status of existing data for Li2O, Li2TiO3, Li2ZrO3, and Li4SiO4 are shown in Table 3-1

Table 3-1 Present Status of Existing Data for Ceramic Breeder Materials
① Physical and thermal properties

Materials
Li2O Li2TiO3 Li2ZrO3 Li4SiO4
1. Crystalline structure ○: 4.1.1 ○: 5.1.1 ○: 6.1.1 ○: 7.1.1
2. Molecular weight ○: 4.1.2 ○: 5.1.2 ○: 6.1.2 ○: 7.1.2
3. Density and Li density ○: 4.1.3 ○: 5.1.3 ○: 6.1.3 ○: 7.1.3
4. Melting point ○: 4.1.4 ○: 5.1.4 ○: 6.1.4 ○: 7.1.4
5. Thermal conductivity ○: 4.1.5 ○: 5.1.5 ○: 6.1.5 ○: 7.1.5
6. Thermal expansion ○: 4.1.6 ○: 5.1.6 ○: 6.1.6 ○: 7.1.6
ic heat ○: 4.1.7 ○: 5.1.7 ○: 6.1.7 ○: 7.1.7
8. Heat capacity ○: 4.1.8 ○: 5.1.8 6.1.8 No data
9. Vapor pressure ○: 4.1.9 ▲: 5.1.9 ▲: 6.1.9 ▲: 7.1.9
10. Thermal diffusivity ○: 4.1.10 ○: 5.1.10 ○: 6.1.10 △: 7.1.10


<② Mechanical properties>

Materials
Li2O Li2TiO3 Li2ZrO3 Li4SiO4
1. Young's modulus ○: 4.2.1 ○: 5.2.1 ○: 6.2.1 ○: 7.2.1
2. Poisson's ratio ○: 4.2.2 ○: 5.2.2 ○: 6.2.2 ○: 7.2.2
3. Tensile strength △: 4.2.3 No data No data △: 7.2.3
4. Compressive strength △: 4.2.4 No data △: 6.2.4 △: 7.2.4
5. Bending strength △: 4.2.5 ▲: 5.2.5 ○: 6.2.5 △: 7.2.5
6. Rupture strength No data △: 5.2.6 △: 6.2.6 No data
7. Crush strength No data ▲: 5.2.7 No data No data
8. Thermal creep rate ○: 4.2.8 △: 5.2.8 ▲: 6.2.8 ○: 7.2.8
9. Vickers hardness No data △: 5.2.9 △: 6.2.9 No data
10. Thermal shock resistance △: 4.2.10 △: 5.2.10 △: 6.2.10 △: 7.2.10
11. Thermal cyclic loading properties ▲: 4.2.11 ▲: 5.2.11 ▲: 6.2.11 ▲: 7.2.11


<③ Chemical stability and compatibility>

Materials
Li2O Li2TiO3 Li2ZrO3 Li4SiO4
1. Compatibility with water ○: 4.3.1 ○: 5.3.1 ○: 6.3.1 No data
2. Compatibility with structural material △: 4.3.2 ○: 5.3.2 ○: 6.3.2 ○: 7.3.2
3. Compatibility with Beryllium No data No data ○: 6.3.3 ○: 7.3.3
4. Compatibility with acid No data △: 5.3.4 No data No data
5. Compatibility with reprocessing liquid No data ▲: 5.3.5 No data No data


<④ Hydrogen, Water and Tritium solubility>

Materials
Li2O Li2TiO3 Li2ZrO3 Li4SiO4
1. Hydrogen solubility ○: 4.4.1 ▲: 5.4.1 No data No data
2. Water vapor solubility ○: 4.4.2 No data No data No data
3. Water vapor adsorption ○: 4.4.3 No data No data No data
4. Hydrogen adsorption △: 4.4.4 No data No data No data
5. Tritium solubility ○: 4.4.5 No data No data No data


<⑤ Irradiation Effects>

Materials
Li2O Li2TiO3 Li2ZrO3 Li4SiO4
1. Physical integrity △: 4.5.1 No data △: 6.5.1 △: 7.5.1
2. Swelling ○: 4.5.2 No data ○: 6.5.2 ○: 7.5.2
3. Grain growth △: 4.5.3 No data △: 6.5.3 △: 7.5.3
4. Li transport △: 4.5.4 No data △: 6.5.4 ▲: 7.5.4
5. Thermal conductivity ○: 4.5.5 ○: 5.5.5 ○: 6.5.5 ○: No data
6. Young's modulus No data No data ▲: 6.5.6 No data
7. Tensile strength No data No data No data No data
8. Compressive strength No data No data ▲: 6.5.8 No data
9. Bending strength No data No data ▲: 6.5.9 No data
10. Tritium diffusivity ○: 4.5.10 ○: 5.5.10 ○: 6.5.10 ○: 7.5.10
11. Tritium residence time ○: 4.5.11 △: 5.5.11 ○: 6.5.11 ○: 7.5.11
12. Tritium release △: 4.5.12 △: 5.5.12 △: 6.5.12 ▲: 7.5.12
13. Tritium retention ○: 4.5.13 △: 5.5.13 △: 6.5.13 △: 7.5.13
14. Helium retention ○: 4.5.14 △: 5.5.14 △: 6.5.14 △: 7.5.14
15. After heat ▲: 4.5.15 ▲: 5.5.15 ▲: 6.5.15 ▲: 7.5.15
16. Class C Waste disposal rate ▲: 4.5.16 ▲: 5.5.16 ▲: 6.5.16 ▲: 7.5.16


Appendix Data
<⑥ Thermal properties of Ti2O doped Li2TiO3>

Materials
Li2O Li2TiO3 Li2ZrO3 Li4SiO4
1. Effect of Ti2O doping on thermal properties of Li2TiO3 - ○: 5.6.1 - -
Notes :
1 : ○: Good data.
2 : △: Limited data.
3 : ▲: Very limited data. (More investigations are required)
4 : Blank : Non existing. (More investigations are required)


3.2 Physical and thermal properties

  It is considered that the data for physical and thermal properties of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 is almost reasonably complete.
  With regard to the data for vapor pressure of Li2TiO3, Li2ZrO3 and Li4SiO4, only a single set of limited data is available. So more investigations are required in order to develop a reliable database for Li2TiO3, Li2ZrO3 and Li4SiO4.
  In tritium breeding ratio (TBR), Li2O is considered to be the only ceramic candidate among Li2TiO3, Li2ZrO3 and Li4SiO4 for achieving the TBR larger than unity in absence of a neutron multiplier.

3.3 Mechanical properties

  The database for the mechanical properties is, in general, more limited than for the physical and thermal properties. The important variables in establishing correlation are porosity and grain size, temperature and fast-fluence/burn-up. There is a reasonably complete database of Young' modulus and Poisson's ratio for Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4.
  More data are needed for the rupture and crush strength of Li2O, the tensile, compressive bending and crush strength of Li2TiO3, the tensile, rupture and crush strength of Li2ZrO3, and the rupture and crush strength of Li4SiO4. Moreover, more data are needed for the creep properties of Li2ZrO3.

3.4 Chemical stability and compatibility

  The chemical stability and compatibility properties are important in establishing upper temperature limits, purge gas composition and impurity control.
  Lithium contained in Li2ZrO3 sintered compacts immersed in water, is slowly but completely dissolved within one month, whereas no dissolution of lithium contained in Li2TiO3 sintered compacts is detectable after a 40 days immersion. Also, no uptake of moisture from room air after 6 months exposure is reported on Li2TiO3. Both Li2TiO3 and Li2ZrO3 ceramics are easily soluble in hydrochloric acid.
  The database of breeder/stainless-steel is reasonably complete. It is considered that the database of the compatibility with water and with structural materials (steel) for Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 is reasonably complete. With regard to breeder compatibility with Be, data are needed for Li2O and Li2TiO3. In laboratory tests, the interaction of beryllium with Li2ZrO3 and Li4SiO4 was found to be negligible up to 650°C.78) Interaction of Li2TiO3 with steel is less than that of Li2ZrO3.
  More data are needed for Li2O, Li2ZrO3 and Li4SiO4 with regard to the compatibility with acid. Moreover, data of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 are needed for the compatibility with reprocessing liquid.

3.5 Hydrogen, Water and Tritium solubility.

  The database of hydrogen, water, and tritium solubility for Li2O is reasonably complete.
  Tritium solubility and transport have been investigated in significant detail for Li2O, which is the only breeder material for which multiple single-crystal tritium diffusion measurements have been made.
  The tritium solubility data for Li2O/H2O are quite good, but the solubility data for Li2O/H2 system are quite scattered and sensitive to the measurement technique, moisture impurity control, and fabricated form. The desorption/decomposition data for moisture release from LiOH and Li2O have a factor of 10 scatter. Adsorotion, as with solubility, needs to be determined more reliably for both the Li2O/H2O and Li2O/H2 systems. Adsorption for Li2O/H2 and Li2O/H2O system needs to be more reasonably characterized.
  Solubility/adsorption/desorption mechanisms are only poorly characterized for Li2ZrO3, Li4SiO4 and Li2TiO3 ceramics.
  More investigations are requested to acquire the database of hydrogen, water and tritium solubility for Li2TiO3, Li2ZrO3 and Li4SiO4.

3.6 Irradiation effects

(1) Radiation effects on the properties for Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4

  The data for the physical and thermal properties of irradiated Li2O are reasonably complete. However the data for the mechanical properties, such as tensile, compressive and bending strength, have been scarcely obtained.
  The data for physical, thermal and mechanical properties of irradiated Li2TiO3 are almost not obtained.
  With regard to the irradiated Li2ZrO3 and Li4SiO4, the data for the physical properties are reasonably complete, but the data for thermal and mechanical properties are almost not obtained except the swelling properties.
  The data for tritium diffusivity and tritium residence time of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 are reasonably good.
  The data for tritium release of Li2O, Li2TiO3 and Li2ZrO3 are almost reasonably good, but these of Li4SiO4 are very limited. So more investigations for these data will be needed.
  The data for tritium retention of Li2O is reasonably complete, but these of Li2TiO3, Li2ZrO3 and Li4SiO4 are limited, or are the value at the specified temperature. So more investigations for these data will be needed.
  The data for Helium retention of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 are almost reasonably good.
  The data for after-heat and Class C Waste disposal rate of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 are very limited, so more investigations will be required.

(2) Irradiation behavior

  Under conditions of temperature levels of 500, 700, 900°C and up to 3% lithium burn-up, Li2ZrO3 showed that swelling was low, physical integrity was excellent, no change of grain size was observed, and tritium and helium retention was very low. On the contrary, Li2O did high swelling at 3 % burn-up.
  After irradiation to 3% burn-up, there was a significant reduction in the thermal conductivity of Li2O at low temperatures, i.e. under 400°C. At higher temperatures, thermal conductivity values were unchanged or were even higher than the unirradiated values.78)
  No testing of irradiation behavior of Li2TiO3 ceramic was almost made to date, except for a few tests of tritium and helium retention, and tritium release. However, the authors suppose that the behavior will be similar to that of Li2ZrO3 from our view of reference materials.

(3) Tritium release

  For safety and economical reasons, the tritium release rate must be enough large that the tritium inventory in the blanket does not become excessive. Tritium residence time (τ) defined as the average time a triton spends in the breeder between generation and release, can be used to relate the tritium inventory to the tritium generation rate.
  Tritium residence times were investigated for Li2O, Li2ZrO350) and Li4SiO478) at various temperatures.
  The effects of lithium burn-up on tritium release for Li2ZrO3 was studied at 4.5%, 7.6% and 9.5% lithium burn-up. Results of tritium residence times reveal no degradation in the tritium release.
  For the comparison of the tritium release behavior of Li2ZrO3 and Li2TiO3 with comparable microstructure, heating test runs were made at 300°C, 250°C, 200°C, in He+0.1% H2 purge gas, at 2.4 l-hr-1 flowrate. Examples of test results are shown in Fig.5.6 and 6.8. These results indicate that Li2ZrO3 and Li2TiO3 behave similarly. For Li2ZrO3 a good tritium release is observed down to 200°C, i.e., 40% tritium released within about 120hr. For Li2TiO3 a larger decrease in the tritium release between 250°C and 200°C is observed. This difference in behavior with Li2ZrO3 reflects the difference in the shape of the tritium release peaks in the linear heating run i.e., sharper peak for Li2TiO3 than for Li2ZrO3.
  The irradiation behavior of Li2ZrO3 is very good up to 9.5% lithium burn-up. The tritium release performance of Li2ZrO3 and Li2TiO3 is excellent. Since the equivalent temperature, which corresponds to a tritium residence time of one day, is desirable to be lower from a design point, the tritium release performance of Li2ZrO3 and Li2TiO3 is superior to Li2O and Li4SiO4. Because, Li2O and Li4SiO4 either are not releasing tritium at low enough temperature and/or are too reactive with water.
  In general, the properties for Li2TiO3 are similar to Li2ZrO3, but with important differences - for example, moisture uptake and neutron activation are significantly lower in the titanate.
  The data for tritium release and tritium retention is the most important, so more these data of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 are needed according to the extent of the existing data t respectively. Also more data for helium retention of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 are needed in detail.

(4) Waste disposal

  With respect to waste disposal, one must consider the production of long-life radionuclides. For those breeder materials, the radioactivity after 1 year is very low in comparison with that of the structural materials. In all cases, activation of the structural materials is higher than that of ternary ceramic breeder materials. The long-life radionuclides, such as 94Nb(L1/2 = 2×104 yr), are decay products from Li4SiO4, Li2ZrO3 and Li2TiO3. However Li2O does not present a problem for waste disposal. With no impurities, the U.S. Class C waste disposal rating for Li2TiO3 is roughly equal to that for Li2O and Li4SiO4 and more than 10 times lower than Li2ZrO3.
  Afterheat levels in Li2TiO3 are 20~50 times more than in Li2O and Li4SiO4, but 2~100 times lower than Li2ZrO3.
  The data for after-heat and U.S. Class C waste disposal rating of Li2O, Li2TiO3, Li2ZrO3 and Li4SiO4 is very limited, so more these data is needed.


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