Paper presented at the 13th Topical Meeting on the Technology of Fusion Power, June 7-11, 1998,Nashville, Tennessee. ------DRAFT------
X-RAYS SURFACE AND VOLUMETRIC HEAT DEPOSITION AND TRITIUM BREEDING ISSUES IN LIQUID- PROTECTED FW IN HIGH POWER DENSITY DEVICES
Mahmoud Z. Youssef, Neil Morley, and Anter El-Azab
School of Engineering and Applied Science, University of California at Ls Angeles Los Angeles, CA, 90095, USA (310) 825-2879 liquid/blanket studied are Li/Li-(V-4Cr-4Ti) and Flibe/Flibe-(ferritic steel). Tritium production rate in these proposed layers and effect of Li-6 enrichment is also ABSTRACT discussed. Exit and bulk temperature rise in the protective layer is discussed in a companion paper In the Advanced Power Extraction (APEX) study, focus is placed on exploring innovative concepts for I. INTRODUCTION fusion power technology that can enhance the potential of fusion as an attractive and competitive energy source. The The initial driver of the APEX study is to develop a study will explore new and "revolutionary" concepts that concept that has the capability for a high neutron wall can provide the capability to efficiently extract heat from load and associated surface heat flux. This stems from the systems with high neutron and surface heat loads while fact that, as currently stands, the average core power satisfying all other functional requirements (e.g. tritium density in present fusion reactors design is much lower self-sufficiency) and maximizing reliability, than that in fission rectors (~0.4 MW/m3 in ITER for maintainability, safety, and environmental attractiveness. example vs. ~ 240 MW/m3 in LMFBR). The proposed The minimum surface and neutrons wall load set for High Power Density (HPD) concepts must satisfy the APEX study is ~1.5 MW/m2 and 7 MW/m2, respectively, functional requirements of the Fusion Power Technology with account taken for peaking factors. One of the (FPT), namely, (1) provision of vacuum environment, (2) concepts under investigation is flowing liquid layer in a exhaust of plasma burn products, (3) power extraction once-though, top to bottom fashion, to protect the FW. from plasma particles and radiation, (4) power extraction This layer, while protecting the FW from exceeding the from energy deposition of neutrons and secondary gamma temperature and stress material limits under high power rays, (5) tritium breeding at he rate required to satisfy density conditions, will exhibit a rise in surface and bulk tritium self-sufficiency, (6) tritium extraction and temperature whose magnitude depends on the mechanism processing, and (7) radiation protection. The other most of depositing both the surface and volumetric heat load. challenging issues in these HPD concepts are reducing In the present study, several candidate materials for the components’ failure rate (increasing mean time before liquid layer are considered, namely, lithium, Flibe, and failure, MTBF), increasing plant availability (reducing Li17Pb83. The surface wall load is caused by the x-rays mean time to repair, MTTR), and satisfying tritium self- radiated from the hot plasma whose magnitude and sufficiency requirement. The minimum neutron wall load spectrum strongly depends on the plasma operating for these concepts are: neutron wall load of 7 MW/m2 conditions (e.g. electron temperature, impurities, etc.). On (average wall load of 5 MW/m2, peaking factor of 1.4) the other hand volumetric heating from incident neutrons and surface heat flux at the first wall. of at least 1.5 is more or less deposited evenly through the layer with MW/m2. much lower steepness. In the present study, profiles of heat deposition rates from surface wall load of 1 MW/m2 Thin and thick convective liquid layers that flow are calculated for three liquid candidates up to a thickness poloidally from the top to protect the first wall are among of 5 cm. The spectrum of the classical Bremsstrahlung the several concepts under investigation. These concepts radiation is considered as the main constituent of this (1,4) were recently investigated . Liquid lithium, Flibe , and surface wall load and comparison is also made to the case Li17Pb83 are candidates protective layers. In the present where these x-rays are considered as mono-energetic study, the Flibe Li2BeF4 was considered (rather than energy source. Volumetric heating from neutrons are LiBF3) since it has 10 times lower viscosity but a high calculated for 7 MW/m2 wall load on a 5 cm-thick liquid melting point of 460 °C. The surface wall load is caused layer followed by 50 cm-thick structure/coolant blanket region (20:80) that has a 15 cm-thick reflector zone by the x-rays radiated from the hot plasma. The spectrum (ferritic steel/water, 90:10) behind it. The combinations of of these rays depends on the plasma operating conditions (e.g. electron temperature, impurities, etc.) Most of the
M.Z. Youssef, et al - 1- emitted x-rays are in eV- keV energy range and deposited within 0.4 cm and 3.7 cm for 2 and 4 keV x- photoelectric absorption is the main process for bearing rays, respectively. For 6, 8 and 10 keV x-rays, ~84%, with this surface wall load(5). The steepness of power ~50%, and ~28% of the power is deposited in the 5 cm- deposition depends on the x-rays attenuation properties thick layer (~16%, ~50%, and 72% fraction of power inside the convective layer. Volumetric heating from transmitted). This shows that Li is more transparent to x- incident neutrons, however, is deposited evenly through rays than Flibe and volumetric heat deposition can be the layer with much lower steepness. Profiles of power realized at measurable depth inside the Li layer. This deposition rate from 1 MW/m2 surface wall loads on transparency property is shown in Figs. 5 and 6 which layers up to 5 cm thick are given here with comparison to depict the fraction of x-rays transmitted through a given nuclear heating from 7 MW/m2 neutron wall load. layer thickness for photons of various energies. About 87% of the intensity (or power) of 10 keV mono-energetic II. HEAT DEPOSITION PROFILES FROM X-RAYS x-rays can be realized behind a 2 cm-thick Li layer. This fraction is almost null in the case of Flibe. This fraction A. Mono-energetic X-Rays (87%) can be realized in Flibe after a thickness of 2 microns (2 x 10-4 cm) and for 25 keV x-rays, as can be Whether or not the surface load is absorbed at the seen from Fig. 5. surface or volumetrically distributed throughout the liquid layer, is mainly dependent on the x-rays attenuation B. X-Rays from Classical Bremsstrahlung Radiation characteristics of the type of layer under consideration. Figure 1 shows the attenuation length (in microns) versus Surface heating from plasma includes synchrotron photon energy (30 eV-30 keV) of x-rays incident and Bremsstrahlung radiation as well as line radiation perpendicularly on several materials. This length is from impurities(12) . For most part, the incident spectrum is defined as the penetration depth at which the photon mainly due to Bremsstrahlung with superimposed line intensity is 1/e of its initial incident value (i.e. equivalent spectra from impurities. For the sake of comparison with to the mean free path 1/Σ). Attenuation length for an mono-energetic x-rays, the surface load is assumed to be incident angle θ is shorter by a factor of cosθ. Photon constituted of Brem. radiation whose spectrum is function attenuation properties in materials can be found in Refs. of the electron temperature Te. The spectrum of the 6-11. classical Bremsstrahlung radiation is used as a representative spectrum and is given by: Ex The attenuation length for mono-energetic x-rays of 1 - keV inside Li, Flibe, and Li17Pb83 are ~100, ~1, and dN a.ne.ni.gff.e Te ~0.12 microns, respectively. The corresponding length at Ex. dE = , Te in eV, where (1) 5 x T 10 keV are ~1.3 x 10 , ~1000, and ~10 microns. The e attenuation coefficient of Li is ~ 2 orders of magnitude Te = electron temperature lower than in Flibe whereas the attenuation coefficient of a = 9.6 x 10-20 eV1/2 m3 s-1 Flibe is 1-2 orders of magnitude lower than in Li17Pb83. g = Gaunt Factor ~ unity It is clear that Li exhibits larger attenuation depth (AD) Ex = x-rays energy, eV followed by Flibe and Li17Pb83, in that order. Because of dN/dEx = the number of quanta emitted per eV per the very short attenuation length of x-rays in Li17Pb83, second into 4π stredians by plasma of volume 1 m3. the present analysis focuses on profiles of heat deposition rate (HDR) in Li and Flibe and x-rays wall load in The Brem. radiation power, P , is given by: Li17Pb83 is considered to be deposited at the surface br only. The larger attenuation length in Li resulted in an -37 2 1/2 -3 P = 5.35 x 10 Z ne n (Te) , W m , Te in keV (2) appreciably larger HDR than in the Flibe at larger depth. br z ρ Figures 2 and 3 show the HDR profiles inside Li ( =0.534 Z = atomic number of ions g/cc) and Flibe (ρ =1.963 g/cc), respectively, for mono- ne = electron density per m3 energetic x-rays of various energies and for 1 MW/m2 nz = ni = ion density per m3. surface wall load. For x-rays of 10 keV, HDR in Li and Flibe are 6.1 and 0.009 w/cc respectively at depth of 1 cm Integrating Eq. (1) between Ex = 0 and Ex = ∞ gives Eq. (6.5 and 1170 w/cc at surface). For the same x-rays (2) for Z=1. It can be shown that the fraction of x-rays in energy, the HDR profile in Flibe is much steeper than in the energy range E and E is exp(-E /Te)-exp(-E /Te). Li with much larger HDR at the surface. Figure 4 shows 1 2 1 2 the depth in the layer at which a given fraction of the Figure 7 shows the classical Brem. spectrum for incident power is deposited. In a 5 cm-thick Flibe layer, various Te. The energy-integrated spectrum is shown in 100% of the incident power is deposited within a depth of Fig. 8 as a function of the photon energy Ex. For Te= 10 10 micron, 0.01 cm, 0.06 cm, 0.2 cm, and 0.4 cm for 2, 4, keV, the fraction of spectrum below 100 and 300 eV is 6, 8, and 10 keV x-rays. In Li, 100% of the power is ~0.7% and ~2.5% respectively. The corresponding M.Z. Youssef, et al., MS# E156 - 2- fraction for Te=2 keV is ~3% and 12%, respectively. On the other hand, the fraction of spectrum above 10 keV is From a practical design point, one would be ~37% for Te= 10 keV and ~2% for Te= 2 keV. This has interested in assessing the depth in the layer at which the implication on the HPD profiles in the Li and Flibe layer. HDR from surface wall load is comparable to the volumetric heating resulting from neutrons interaction C. Surface Heat Deposition Profiles in Li and Flibe with this layer. Figure 16 gives this depth in Li and Flibe for a 1 MW/m2 Brem. radiation of Te=2 and 10 keV. As Figures 9 and 10 show the HDR from mono-energetic shown, a 10w/cc is attainable at depth of ~0.9 cm (Li) and x-rays and Brem. spectrum at Ex/Te of 2 and 10 keV ~0.7 cm (Flibe) for Te=10 keV. Shorter depth is incident on Li and Flibe layer, respectively. At 10 keV, attainable for Te=2 keV (~0.8 cm and 0.1 cm, the mono-energetic x-rays has a more or less HDR of ~ 6 respectively). For a HDR of ~ 50-60 w/cc (which is w/cc throughout the Li layer whereas the HDR for the comparable to neutrons/gamma heating at 7 MW/m2 Brem. spectrum peaks at the surface (HDR= ~9 x 104 neutron wall load, see next section), the depth for Te=10 w/cc) due to the low-energy component <100 eV. and is ~ keV is ~0.08-0.1 cm (Li) and 0.14-0.16 cm (Flibe). The 8 w/cc in the bulk of the layer. At 2 keV, the mono- corresponding depth for Te=2 keV is ~0.15-0.20 cm (Li) energetic x-rays HDR profile is steep (~1.3 x 103 w/cc at and ~0.04 (Flibe). Note that the HDR at and very near to surface and ~ 0.002 w/cc at 1 cm) whereas the Brem. the surface are higher in the Flibe layer than in the Li spectrum has much larger HDR at the bulk of the layer layer for Te=10 keV. (~6 w/cc at 1 cm) but still the low-energy component of the spectrum below 100 eV contributes appreciably to the D. Surface Heat Deposition Profiles in Other HDR at the surface (~4 x 105 w/cc). These features are Materials similar in the Flibe layer case but with much shorter depth as can be seen from Figure 10. The fact that the low- Li17Pb83 is a candidate materials used in protecting energy component of the Brem. spectrum contributes the the FW on one hand and in breeding tritium on the other. most to the HDR near the surface is shown in Figure 11 Because of the high effective Z number, the attenuation where the HDR profiles from 30 energy bins, covering the length is an order of magnitude less than in Flibe for 10 range 30 eV- 30 keV,.are shown for Li. and for a depth of keV x-rays. SiC was proposed as the FW in ICF and the 1 cm. The corresponding profiles for the Flibe layer are volumetric deposition of x-rays in that material has been shown in Figure 12. explored(13). Figure 17 shows a comparison of the attenuation length of x-rays in Vanadium, Iron, and SiC at The large HDR at the surface of the convective layer several photon energies. at 10 keV, the attenuation length can be seen from Figure 13 which shows a comparison of in SiC is ~120 microns as compared to ~12 microns in V the attainable HDR for mono-energetic x-rays and Brem. and 0.8 microns in Fe. The HDR profiles from 1 MW/m2 spectrum. The surface HDR drops faster with increasing classical Brem. radiation at Te=10 keV are shown in Fig. the photon energy in the case of mono-energetic x-rays 18 where it is clear that this wall is deposited almost at than in the case of Brem. spectrum (drops by ~2 orders of the surface in the case of Li17Pb83 while sensible rates magnitudes in the former and by a factor of 4-5 in the can be detected at deeper depths in the case of SiC. latter as Ex/Te varies from 2 keV to 10 keV). For 10 keV, Further examination is underway to assess SiC as a FW the surface HDR is ~ 9 x 104 w/cc in Li and 5 x 105 w/cc material that can cope with high surface and neutron wall in Flibe. These large values are due to the absorption of load without exceeding temperature and stress limits(14-15) low-energy tail of the Brem. spectrum below 80 eV in Li and ~ 200 eV in Flibe whose attenuation length is a III. NUCLEAR HEAT DEPOSITION PROFILES fraction of a micron as can be seen from Fig. 1. This fraction of the spectrum is ~0.4% and ~2%, respectively. The 1-D calculational model used in the neutron/ The HDR profiles near the surface and at the bulk of the gamma ray transport in the Li and Flibe system is shown protective layer are shown in Figs. 14 (depth of 5 cm) and in Fig. 19. On the outboard side, the 5 cm-thick 15 (depth of 0.03 cm). Clearly the surface temperature convective layer is followed by a representative 50-cm- becomes larger as the fraction of the Brem. spectrum thick blanket and 15 cm-thick reflector zone. in the Li below 80 eV (Li) and 200 eV (Flibe) gets larger as in the system, the blanket is made of Li:V4Cr4Ti (80:20) and case of Te=2 keV where this fraction is ~2% and ~10%, made of Flibe:Ferritic Steel (80:20) in the Flibe system. respectively (see Fig 8). This suggests that part of the The reflector considered in both systems is made of surface wall load can be treated as truly surface load Ferritic Steel:water (90:10). It is included to neutronically whereas the rest of the incident load is considered to be account for neutron/gamma ray reflection, regardless of deposited volumetrically throughout the protecting layer. the compatibility concern. No breeding zone is considered The fraction that can be treated as a purely surface heat on the Inboard side which includes a Be tile. The details load (below 80 eV for Li and 200 eV for Flibe can be of the TFC are considered in the model and the obtained from Fig. 8. dimensions shown in Fig. 19 are those found at the mid plane in ITER configuration(16). The analysis was M.Z. Youssef, et al., MS# E156 - 3- performed for 7 MW/m2 neutron wall load using ANISN blanket with natural Li-6 where contribution from Li-6 transport code along with 175n-42g library based on and Li-7 are comparable). In the convective Li layer (and FENDL/1.0 data(17) in P5S8 approximation. the system), there is an optimal Li-6 enrichment (~ 25% Li-6) beyond which the integrated TPR begins to The mean free path of neutrons (MFP=1/Σ) in Li, decrease. This is not the case for Flibe blanket where Flibe, and Li17Pb83 is shown in Figure 20 as a function integrated TPR shows steady increase with Li-6 of neutron energy. At 14 MeV, the MFP is ~ 16 cm in Li enrichment. There is a steepness in TPR profiles near the and 7 cm in Flibe. At all energies above ~ 3 eV, the MFP front surface of the convective layer due to Li-6(n,α) in lithium is larger than those in Flibe by as much as an absorption of low-energy neutrons reflected to the layer order of magnitude . At thermal energies (below 1 eV) the by the Inboard blanket. MFP in lithium is a factor of ~6-8 lower than in Flibe. Thus, the lithium layer is much more "transparent" to The total integrated TPR in the Li/(Li-V4Cr4Ti) high-energy neutrons and much less "transparent" to low- system (Tritium breeding ration, TBR) is ~ 1.05 at 25% energy neutrons as compared to the Flibe. These features Li-6 enrichment (no T is bred in the I/B). The total have direct impact on the nuclear heating rate throughout integrated TPR in the Li layer is shown in Fig. 26 where the system. neutron flux, the dpa, he-4, and h production contribution from Li-6 and Li-7 are also shown. rates in the walls of the V.V. Integrated TPR from Li-7 shows steady decrease with Li- 6 enrichment whereas integrated TPR from Li-6 shows an The maximum volumetric nuclear heat deposition optimal value at 25% Li-6 enrichment. The % rate (VNHDR) in the convective layer is larger in the contribution to the total TBR in the system from the Li Flibe than in the Li as can be seen from Fig. 21 which layer is shown in Fig. 27. The 5 cm-thick Li layer gives the VNHDR across the layer as a function of Li-6 contributes ~23% to the total TBR in the front 55 cm of enrichment. The Flibe-nat.Li6 and Flibe-25%Li6 profiles the at all Li-6 enrichments. Note that the % contribution are similar to Li-50%Li6 and Li-90%li6 profiles. The to total TBR from Li-7 increases with Li-6 enrichment maximum attainable VNHDR at the surface are: and is ~ 35-37%. Most of the tritium from Li-7(n,n’α)t reactions is bred at the front locations where high-energy Flibe Lithium neutrons are found. The corresponding contribution in Natural Li-6 50 w/cc 38 w/cc the Flibe/(Flibe-FS) system increase by enrichment (26%- 25% Li-6 55 w/cc 44 w/cc 32%). 50%Li-6 60 w/cc 49 w/cc 90%Li-6 64 w/cc 54 w/cc The total TBR in the Flibe/(Flibe-FS) system is ~ 0.85 which is lower by ~ 25% than in the Li/(Li- It is larger in Flibe than in Lithium by as much as 30% V4Cr4Ti) system. Figure 28 shows the integrated TPR in (natural Li-6) to 18% (90% Li-6). The VNHDR increases the Flibe layer and the contribution from Li-6 and Li-7 in the layer as Li-6 enrichment increases due to the tritium breeding reactions. As mentioned, there is a steady enhancement in Li-6(n,α) reaction which is exothermic increase in the integrated TPR in the convective layer (Q ~ 4 MeV). In the convective layer of Lithium, (and the system) with Li-6 enrichment. Figure 29 gives VNHDR is due mainly to neutrons heating. Non- the % contribution to the total TBR from the Flibe layer negligible contribution from gamma heating exists in the which increases with Li-6 enrichment, being ~27% at case of Flibe. The profiles across the system are shown in natural Li-6 and ~ 31% at 90%Li-6 enrichment. Thus, for Figs. 22 and 23 for the Lithium/(Li-V4Cr4Ti) and the the same convective layer thickness, the contribution to Flibe/(Flibe-FS) case, respectively. The steepness of the the total TBR in the Flibe system is larger than in the Li profiles in Lithium/(Li-V4Cr4Ti) blanket is much less system by ~ 5-7%. Note also that TBR from Li-7 in the than in the Flibe/(Flibe-FS) blanket . This is due to the Flibe layer is ~50% of the total TBR bred from Li-7 in the fact that more high-energy neutrons reach the blanket entire system. The values cited in the Flibe system does zone in the case of Li layer since the moderation power of not account for tritium bred in the beryllium (one of the Li is much less than Flibe for high energy neutrons (MFP Flibe constituents). is larger, see Fig. 20). Also, as the Li-6 increases, this high-energy component decreases at the back zones V. SUMMARY resulting in a less VNHDR at these back locations. Innovative concepts are being explored and evaluated IV. TRITIUM PRODUCTION RATE (TPR) in APEX study to enhance the capability of removing high power density and surface wall load while satisfying The profiles for TPR in the convective layer are all other blanket functional requirements (e.g. tritium self- shown in Figs. 24 and 25 in the Li and Flibe system, sufficiency) and maximizing reliability, maintainability, respectively. The TPR from Li-6 is the main contributor safety, and environmental attractiveness. The minimum to the integrated TPR (except in case of Li/(Li-V4Cr4Ti) surface and neutrons wall load considered is ~1.5 MW/m2
M.Z. Youssef, et al., MS# E156 - 4- and 7 MW/m2, respectively, with account taken for heat deposited in the layer is larger in the Flibe case than peaking factors. Liquid first wall is among the concepts Li by as much as It is larger in Flibe than in Lithium by as considered in which a flowing layer is introduced from much as 30% (natural Li-6) to 18% (90% Li-6). The HDR the top of the Tokamak to cope with the high surface and increases in the layer as Li-6 enrichment increases due to neutron wall load and to protect the blanket from the enhancement in Li-6(n,α) reaction. The steepness of excessive radiation damage. This convective layer will the HDR profiles in Lithium/(Li-V4Cr4Ti) blanket is exhibit an increase in surface and bulk temperature as it much less than in the Flibe/(Flibe-FS) blanket since more flows poloidally to the bottom of the machine. Liquid high-energy neutrons reach the blanket zone in the case of lithium, Flibe, and Li17Pb83 are among the candidate Li layer (Li is more "transparent" to high-energy neutrons materials considered. In the present work several issues and much less "transparent" to low-energy neutrons as were examined. They are: (a) attenuation characteristics compared to Flibe). and penetration range of the soft x-rays that carry most of the surface wall load, (b) profiles of heat deposition rate For a 5 cm-thick liquid FW, the total integrated (HDR) from x-rays and from neutrons contributing to the tritium production rate (TPR) in the Li/(Li-V4Cr4Ti, rise in the convective layer temperature, and (c) tritium 80:20) system (Tritium breeding ratio, TBR) is ~ 1.05 at produced in the lithium-bearing layer relative to the total 25% Li-6 enrichment (no T is bred in the I/B). Integrated (18) tritium bred in the system. In a companion paper , the TPR from Li-7 shows steady decrease with Li-6 concept description and thermalhydraulics of liquid enrichment whereas integrated TPR from Li-6 shows an FW/Blanket are discussed based on the heat deposition optimal value at 25% Li-6 enrichment. The % characteristics assessed in the present work. contribution from the layer to the total TBR is ~23%. The TBR in the Flibe/(Flibe-FS: 80:20) system is ~ 0.85 The attenuation length of 10 keV mono-energetic x- which is lower by ~ 25% than in the Li/(Li-V4Cr4Ti) 5 rays in Li, Flibe, and Li17Pb83 is ~1.3 x 10 , ~1000, and system. There is a steady increase in the integrated TPR ~10 microns, respectively, i.e., the attenuation coefficient in the convective layer (and the system) with Li-6 of Li is ~ 2 orders of magnitude lower than Flibe whereas enrichment. The % contribution from the layer to the total the attenuation coefficient of Flibe is 1-2 orders of TBR is ~27% at natural Li-6 and ~ 31% at 90%Li-6 magnitude lower than Li17Pb83. Thus, surface wall load enrichment. Thus, for the same convective layer could in principle be deposited volumetrically over a thickness, the contribution to the total TBR in the Flibe measurable depth in the convective layer of Li and to a system is larger than in the Li system by ~ 5-7%. Note lesser extent in Flibe while it is deposited at the surface in that the representative blanket placed behind the 5 cm- the case of Li17Pb83 due to its high attenuation thick liquid layer is not optimized for TBR nor tritium is coefficient. The incident x-rays consist mainly of bred in inboard blanket. Bremsstrahlung spectrum and line radiation from impurities and cover a wide range of energies in the eV- In the present work, the surface wall load is keV range. In the present study, classical Brem. radiation considered to be due to classical Bremsstrahlung was considered at various electron temperature Te. For 10 spectrum. Actual spectrum should consider radiation from keV Brem. radiation of 1 MW/m2, heat deposition rate plasma impurities. Such radiation was recently assessed(19) 4 5 (HDR) at the surface is ~ 9 x 10 w/cc in Li and 5 x 10 in ITER using a circular plasma cylindrical with a radius w/cc in Flibe. These large values are due to the of 4 m and is shown in Fig. 301. An effort is underway to absorption of low-energy tail of the Brem. spectrum compare results based on this spectrum to the results cited below 80 eV in Li and ~ 200 eV in Flibe whose in this manuscript. attenuation length is a fraction of a micron. This fraction of the spectrum is ~0.4% and ~2%, respectively. At the bulk of the layer, lower HDR are attainable at measurable depth. For example, at 1 cm depth, the HDR is ~10 w/cc (Li) and 8 w/cc (Flibe). For a HDR of ~ 50-60 w/cc (which is comparable to neutrons/gamma heating at 7 1 The volume and surface area for such a cylinder are 20% MW/m2 neutron wall load), the depth for Te=10 keV is (volume) and 10% (surface) greater than for the actual ~0.1 cm (Li) and ~0.2 cm (Flibe). This suggests that part ITER elliptical shape. The density profile was flat with ne of the surface wall load can be treated as truly surface 20 -3 load whereas the rest of the surface load is considered to = 10 m . The temperature was parabolic (Te = 20 keV be deposited volumetrically. (1-(r/a)2)). The impurity mixture was 64 % H, 10 % He, 2 % Be, 1% C, and 0.2 % Ne. The radiation losses were Flibe is more powerful material in attenuating mostly Bremsstrahlung, but there are losses from line high-energy neutrons due to inelastic scattering in radiation from the impurities and from radiative Fluorine and (n,2n) reactions in beryllium. For the same recombination. The line radiation losses are convective layer thickness and neutron wall load, nuclear underestimated by perhaps as much as 50% or more because the calculation did not include transport effects". M.Z. Youssef, et al., MS# E156 - 5- Attenuation Length of X-Rays Versus Photon Energy
6 10 Lithium Beryllium 10 Flibe
4 Lead 10 Mono-Energetic Li17Pb83 Photons 1
2 10 2 keV (Li) 4 keV (Li) 6 keV (Li) 0.1 10 0 8 keV (Li) Attenuation Length (microns) Length Attenuation 10keV (Li) 2 keV (Flibe) 10 -2 4 keV (Flibe)
1 2 3 4 5 0.01 10 10 10 10 10 6 keV (Flibe) X-Ray Enery (eV) 8 keV (Flibe) Depth in Layer, cm 10keV (Flibe)
Figure 1: Attenuation Length of X-Rays In Lithium, 0.001 Beryllium, Flibe, Lead, and Li17Pb83 VS. Photon 20 40 60 80 100 120 140 160 Energy Power deposited, %
Figure 4: Depth in Convective Layer at which a given Fraction of Incident Power is Deposited from Mono- 5 10 energetic X-Rays. Surface Wall Load = 1 MW/m2 104
1000
1 100
10 0.8 1 1 keV (Li) 2 keV (Li) Thickness=2000 microns 0.1 4 keV (Li) 0.6 6 keV (Li) Thickness=3000 microns Thickness=4000 microns 0.01 8 keV (Li) Thickness=5000 microns 10 keV (Li) 0.4 Thickness=10000 microns Power Deposition Rate, w/cc Rate, Deposition Power 0.001 Thickness=20000 microns Transmission Thickness=50000 microns 012345 Thickness=70000 microns Distance from Surface, cm 0.2
Figure 2: Power Deposition Profiles of Mono-Energetic 0 0 3 4 4 4 4 4 X-Rays Incident on Lithium 0 10 5 10 1 10 1.5 10 2 10 2.5 10 3 10 X-Ray Energy (eV)
Figure 5: Fraction of Photons Transmitted Through Various Thickness in Lithium Surface Wall Load = 1 MW/m2 10 5
1 kev (Flibe) 1000 2 keV (Flibe) 4 keV (Flibe) 6 keV (Flibe) 10 8 keV (Flibe) 10 keV (Flibe)
0.1
Power Deposition Rate, w/cc 0.001 012345 Distance from Surface, cm
Figure 3: Power Deposition Profiles of Mono-Energetic X-Rays Incident on Flibe M.Z. Youssef, et al., MS# E156 - 6- 1 1 Thickness=2000 microns Thickness=3000 microns Thickness=4000 microns Thickness=5000 microns 0.8 0.8 Thickness=10000 microns Te= 2keV Thickness=20000 microns Thickness=50000 microns Te= 4keV Thickness=70000 microns 0.6 Te= 6keV 0.6 Te= 8keV Te=10keV 0.4 0.4 Transmission
0.2 Fraction below Ex 0.2
0 0 0 3 4 4 4 4 4 0 10 5 10 1 10 1.5 10 2 10 2.5 10 3 10 10 100 1000 104 105 X-Ray Energy (eV) Photon Energy, eV
Figure 6: Fraction of Photons Transmitted Through Figure 8: Integrated Classical Bremsstrahlung Spectrum at Various Thickness in Flibe (Li2BeF4) various Electron Temperature Te as a Function of Photon Energy Ex.
0.01 30 X-rays Energy Group 0.001 Surface Wall Load = 1 MW/m2 105 0.0001 Li 2 keV-mono
-5 2 keV-Bremss.(30g) 10 1000 Te = 1 keV (30g) 10 keV-mono. -6 10 keV-Bremss.(30g) 10 Te = 2 keV (30g) Te = 4 keV (30g) 10 Photons/eV 10-7 Te = 6 keV (30g) Te = 8 keV (30g) 10-8 Te = 10 keV (30g) 0.1
10-9 Power Deposition Rate, w/cc 100 1000 104 105 0.001 X-ray Energy, eV 012345 Distance from Surface, cm Figure 7: Classical Bremsstrahlung Spectrum at Various Electron Temperature (30 photon energy group) Figure 9: Comparison of Power Deposition Profile of Mono-energetic X-Rays of Te=2 and 10 keV and Classical Bremsstrahlung Spectrum Incident on Lithium (Depth = 5 cm)
M.Z. Youssef, et al., MS# E156 - 7- 107 Surface Wall Load = 1 MW/m2
5 Flibe 10 2 keV-mono. 105 Surface Wall Load = 1 MW/m2 2 keV-Bremss.(30g) Te = 10 keV 30-100 eV 10 keV-mono. 100-300 eV 1000 300-500 eV 800-1000 eV 10 keV-Bremss.(30g) 1000 1000-2000 eV 2000-3000 eV 3000-4000 eV 10 5000-6000 eV 6000-7000 eV 10 7000-8000 eV 8000-9000 eV 0.1 10000-12000 eV 12000-14000 eV 14000-16000 eV Power Deposition Rate, w/cc Rate, Deposition Power 0.1 16000-18000 eV 18000-20000 eV 0.001 20000-22000 eV 22000-24000 eV Power Deposition Rate, w/cc 24000-29000 eV 012345 0.001 sum Distance from Surface, cm
0 0.5 1 1.5 Figure 10: Comparison of Power Deposition Profile of Distance from Surface, cm Mono-energetic X-Rays of Te=2 and 10 keV and Classical Bremsstrahlung Spectrum Incident on Flibe Figure 12: Power Deposition Profile and Contribution (Depth = 5 cm) from Each x-ray Energy Range for Classical Bremsstrahlung Radiation Incident on Flibe (Depth = 1 cm)
105 Surface Wall Load = 1 MW/m2 4 10 30-100 eV 7 Te = 10 keV 100-300 eV 10 300-500 eV 1000 800-1000 eV 1000-2000 eV 6 2000-3000 eV 10 100 3000-4000eV 5000-6000 eV 6000-7000 eV Mono. (Li) 10 7000-8000 eV 105 8000-9000 eV Brem. (Li) 10000-12000 eV 1 12000-14000 eV Mono. (Flibe) 14000-16000 eV 4 16000-18000 eV 10 Brem. (Flibe) 0.1 18000-20000 eV 20000-22000 eV 22000-24000 eV 0.01 24000-29000 eV 1000 Power Deposition Rate,Power Deposition w/cc sum 0.001 100 0 0.5 1 1.5 Distance from Surface, cm 10
Figure 11: Power Deposition Profile and Contribution 1
from Each x-ray Energy Range for Classical w/cc Surface, at Density Power 0 5 10 15 Bremsstrahlung Radiation Incident on Li (Depth = 1 cm) Photon Energy or Te, keV
Figure 13: Surface Power Density from Mono-Energetic X-Rays and Bremsstrahlung Spectrum as a Function of Photon Energy/Electron Temperature Te
M.Z. Youssef, et al., MS# E156 - 8- 1 107
2 keV-Bremss.(Li) 5 Li/V (Te=10 keV) 10 2 keV-Bremss.(Flibe) 0.8 10 keV-Bremss.(Li) Flibe/FS (Te=10 keV) 10 keV-Bremss.(Flibe) Li/V (Te=2 keV) 1000 0.6 Flibe/FS (Te=2 keV)
10 0.4
0.1 Power ,w/cc Power 0.2 0.001 Depth Convective in Layer, cm 0 10-5 0 20 40 60 80 100 012345 Power Density, w/cc Distance from Surface, cm Figure 16: Depth in the Convective Layer as a Function of Figure 14: Power Deposition Rate from 1 MW/m2 the Attainable Power Deposition Rate (Classical Surface wall Load in Li and Flibe Convective Layer Bremsstrahlung Spectrum) (Classical Bremsstrahlung Spectrum)-depth 5 cm
107
10 4 106 3 Vanadium 2 keV-Bremss.(Li) 10 2 keV-Bremss.(Flibe) Iron 105 SiC 10 keV-Bremss.(Li) 10 2 10 keV-Bremss.(Flibe) 4 1 10 10
0 10 1000 Power ,w/cc Power
-1 10 100 -2 10
10 Attenuation Length (microns) 10 -3 0 0.005 0.01 0.015 0.02 0.025 0.03 1 2 3 4 5 10 10 10 10 10 Distance from Surface, cm X-Ray Enery (eV)
Figure 15: Power Deposition Rate from 1 MW/m2 Figure 17: Attenuation Length of X-Rays In Vanadium, Surface wall Load in Li and Flibe Convective Layer Iron, and SiC VS. Photon Energy (Classical Bremsstrahlung Spectrum)-depth 0.03 cm
M.Z. Youssef, et al., MS# E156 - 9- 107 Surface Wall Load = 1 MW/m2 100
5 10 Lithium (Brem Te=10keV) Lithium-Nat. Flibe (Brem Te=10keV) Flibe.Nat. 1000 Li17Pb83 (Brem Te=10keV) Li17Pb83.Nat SiC (Brem Te=10keV) 10 10
0.1
0.001 1 Power Deposition Rate, w/cc 10-5
012345 Mean Free Path, cm Distance from Surface, cm 0.1 Figure 18: Comparison of Power Deposition Profiles from 10-6 0.0001 0.01 1 100 104 106 108 Classical Bremsstrahlung Radiation Incident on Several Neutron Energy, eV Materials (depth = 5 cm) Figure 20: Neutron Mean Free path in Lithium, Flibe, and 0 Void 191.4 Li17Pb83 269.5 CS Coil 279.5 280.7 Gap Torque Cylinder 290.8 SS3316lw Lithium (Nat.) 388.88 70 Flibe (nat.) Winding Pack 398 Lithium (25%Li6) SS316lw Flibe (25%Li6) Gap 404.6 411.6 60 Lithium (50%Li6) Thermal Back Plate 456.6 Flibe (50%Li6) Shield Lithium (90%Li6) Vaccum Shielding Blanket (80:20,316SS:water) 470.6 50 Flibe (90%Li6) Vessel Cu-H2O 473.1 Gap 488.1 Manifold 503.4 40 FW Plasma 513.4 Be-Tile ```` 515.1 SOL 515.6 30 SOL 533.7 Liquid Layer 1018.7 Wall Load = 7 MW/m2 Blanket (20:80,Structure:Liquid) 1041.8 20
1046.8 w/cc Rate, Deposition Heat 1096.8 10 Reflector (90:10,316SS:water) 1111.8 012345 1177.12 Distance from Surface, cm Gap 1187.12 Back Plate Gap 1251.5 1311.5 Figure 21: Comparison of the Volumetric Nuclear Heat Vacuum Vessel 1331.5 Deposition Rate in the Convective Layer in Case of Gap 1349.5 Lithium and Flibe for Various Li-6 Enrichment TFC Front SS316lw
Winding Pack
1449 TFC Rear SS316lw 1469 Figure 19: 1-D Calculational Model used in the Analysis
M.Z. Youssef, et al., MS# E156 - 10- 100 -5 Wall Load = 7 MW/m2 1.2 10 Total (natural)
-5 Total(25%Li6) 1 10 Total (50%Li6) 10 Natural Total (90%Li6) 25% Li-6 8 10-6 50% Li-6 90% Li-6 -6 1 6 10 Flowing Lithium layer -6 Reflector 4 10 Heat Deposition Rate,Heat Deposition w/cc Li/V (0.8-0.2) Flibe Layer = 5 cm 0.1 -6 0 10203040506070 2 10 Distance from Surface, cm
Tritium Production Rate, T/n.sec Rate, Production Tritium 012345 Figure 22: Volumetric Nuclear Heat Deposition Rate in Distance from Surface, cm the Li/(Li-V4Cr4Ti)/Reflector System Figure 25: Total Tritium Production Rate in the Flibe Flowing Layer as a Function of Li-6 Enrichment
100 Wall Load = 7 MW/m2
Natural 25% Li-6 10 50% Li-6 90% Li-6 0.3 TBR-6 (layer) TBR-7 (layer) Lithium layer = 5 cm TBR-Tot. (layer) 1 0.25
Flowing Flibe layer 0.2
Heat Deposition Rate, w/cc Rate, Deposition Heat Flibe/FS (0.8-0.2) Reflector 0.1 0.15
0 10203040506070 TBR Distance from Surface, cm 0.1 Figure 23: Volumetric Nuclear Heat Deposition Rate in the Flibe/(Flibe-FS)/Reflector System 0.05
0 Natural 25% Li6 50% Li6 90% Li6
1 10-5 Li-6 Enrichment Lithium Layer = 5 cm Figure 26: Tritium Breeding Ratio in the Convective Li 8 10-6 Layer as a Function of Li-6 Enrichment.
6 10-6
-6 Total (natural) 4 10 Total(25%Li6) Total (50%Li6) Total (90%Li6) 2 10-6
012345 T. Production Rate, T/neutron.sec Distance from Surface, cm
Figure 24: Total Tritium Production Rate in the Lithium Flowing Layer as a Function of Li-6 Enrichment
M.Z. Youssef, et al., MS# E156 - 11- Figure 29: Ratio of Tritium Breeding in the Convective Layer to the System as a Function of Li-6 Enrichment TBR-6 (ratio) (Flibe Flowing Layer) TBR-7 (ratio) 0.4 Lithium layer = 5 cm TBR-Tot. (ratio) 10-14 0.35 H 64% ITER He 10% -15 0.3 10 Be 2% ) 0.25 C 1% -2 -16 Ne 0.2% 0.2 m 10 -1
Ratio Zeff = 1.72 0.15 10-17 0.1
0.05 10-18 0 Natural 25% Li6 50% Li6 90% Li6 10-19 Li-6 Enrichment
20 -3 -20 ne = 10 m Figure 27: Ratio of Tritium Breeding in the Convective 10 2 Te = 20 keV (1-(r/a) )
Layer to the System as a Function of Li-6 Enrichment Radiated energy flux ( MW Hz calculated by H. Scott (Lithium Flowing Layer) -21 10 with the CRETIN code LLNL
-2 -1 2 3 4 5 TBR-6 (layer) 10 10 1 10 10 10 10 10 TBR-7 (layer) E = hν (eV) 0.3 TBR-Tot. (layer)-w/o Be Flibe layer = 5 cm Figure 30. X ray and UV spectrum of the radiation losses 0.25 from the ITER main plasma.
0.2 REFERENCES
0.15
TBR 1. R.W. Moir, “Liquid First Wall for Magnetic Fusion Energy Configuration”, Nuclear Fusion, Vol. 37, No. 4, 0.1 1997. 2. N.C. Christofilos, J. Fusion Energy, 8 (1989) 97.. 0.05 3. R.W. Moir, Fusion Eng. Des. 5, (1987) 269.
0 4. R.W. Moir, Nucl. Eng. Des. 29 (1995) 34 Natural 25% Li6 50% Li6 90% Li6 5. I. kaplan, “Nuclear Physics”, Addison-Wesley Pub. Li-6 Enrichment Comp., INC., Reading Massachusetts, Palo Alto, London, (1964). Figure 28: Tritium Breeding Ratio in the Convective 6. D.E. Cullen, et al., “Tables and Graphs of Photon Layer as a Function of Li-6 Enrichment (Flibe Flowing Interaction Cross Sections from 10 eV to 100 GeV Derived Layer) from LLNL Evaluated Photon data Library (EPDL) Part A: Z = 1 to 50 and Part B: Z = 51 to 100, Vol. 6, Part A and Part B Rev. 4, Rep. UCRL-5000400, Lawrence Livermore TBR-6 (ratio) National Laboratory, CA., 1989 0.6 TBR-7 (ratio) Flibe layer = 5 cm TBR-Tot. (ratio) w/o Be 7. J. A. Bearden and A. F. Burr Rev. Mod. Phys. 39, 125
0.5 (1967) 8. M. Cardona and L. Ley, Eds. Photoemission in Solids I. 0.4 General Principles (Springer-Verlag, Berlin, 1978). 9. J. C. Fuggle and N. Martensson, J. Electron Spectrosc. 0.3 Relat. Phenom. 21, 275 (1980). Ratio 10. S. Kraft, J. Stumpel, P. Becker, U. Kuetgens, Rev. Sci. 0.2 Instrum. 67, 681 (1996). 0.1 11. J. R. De Laeter, K. G. Heumann, J. Phys. Chem. Ref. Data 20, 1313 (1991). 0 12. J. Wesson, “Tokamaks”, Clarendon Press Oxford, (1987). Natural 25% Li6 50% Li6 90% Li6 Li-6 Enrichment 13. A. El-Azab and M.Z. Youssef,” X-Ray Deposition in Inertial Fusion Graphite and Silicon-Carbide First Walls”,
M.Z. Youssef, et al., MS# E156 - 12- Proceedings of the 16th IEEE/NPSS Symposium on Fusion Engineering, 1995, pp. 33-36. 14. A. El-Azab and M.Z. Youssef, “X-Ray Absorption in Low-Z Materials and Impact on First Wall protection Schemes in Inertial Confinement Reactors, in these Proceedings. 15. A. El-Azab, private communication, University of California, Los Angeles, 1998. 16. “Technical Basis for ITER Detail Design Report, Cost Review, and Safety Analysis”. ITER Document, International Thermonuclear Experimental Reactor, (November, 1996). 17. A.B. Pashchenko, “Completion of FENDL-1 and Start of FENDL-2, INDC (NDS)-352, IAEA Nuclear Data Section, International Atomic Energy Agency, (March, 1996). 18. A. Ying, N. Morley, M. Youssef, K. Gulec, and M. Abdou, "Concept Description and Thermalhydraulics of Liquid Surface FW/Blankets for High Power Density Reactors", in these Proceedings. 19. D. Post, private communication, International Thermonuclear Experimental Reactor, ITER, San Diego Joint Working Site, U.S.A., ITER Memo, 9 January, 1998.
M.Z. Youssef, et al., MS# E156 - 13-