Development of water-cooled cylindrical blanket in JA DEMO

The concept of the tritium breeding blanket for Japan’s DEMOnstration fusion reactor (JA DEMO) has been developed with pressure tightness against in-box loss-of-coolant accidents based on a water-cooled solid breeder concept. The cooling conditions are designed on the pressurized-water reactor water conditions which are the coolant temperature of 290 °C–325 °C and the operating pressure of 15.5 MPa, respectively. The point of the blanket design is to reduce the amount of structural material in casing as well as to ensure its pressure tightness. This is because a decrease in the amount of structural material improves tritium breeding ratio (TBR). A cylindrical structure, a thin wall casing structure which ensures pressure tightness and could increase TBR, is feasible. However, a relatively larger useless space is expected between modules when the cylindrical blanket modules are arranged in a vacuum vessel, which could decrease TBR. Therefore, the cylindrical blanket modules are to be in a close-packed arrangement to reduce useless space. The Be12Ti block (which shows a minor swelling compared to Be) is selected to achieve the target TBR as the net Be density is equivalent to the case of the Be pebble. The use of Be12Ti blocks can reduce or remove the cooling piping inside the module as the Be12Ti block has a higher thermal conductivity than pebbles. As a result of the neutronics, finite element method, and computational fluid dynamics analyses, it was found that the target TBR value can be achieved in cylindrical structure blanket that ensure pressure tightness.


Introduction
The missions of Japan's DEMOnstration fusion reactor (JA DEMO) are to realize a steady and stable electric output of over several hundred thousand kilowatts, to ensure the availability sufficient for commercialization, and to ensure Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
overall tritium (T) breeding that fulfills self-sufficiency in fuel [1].The main function of the T breeding blanket are T production and heat recovery for power generation.
The previous concept of the blanket for JA DEMO was not designed taking into account on the pressure tightness requirements on the module enclosure [2,3].However, if the cooling water leaks into the vacuum vessel (VV) after in-box lossof-coolant accident (In-box LOCA), it takes a lot of time to restart the operation.Therefore, a function of pressure tightness (17.2 MPa) against the in-box LOCA must be secured for JA DEMO.By enhancing the pressure tightness of the blanket structure, the number of the ribs which have a structural function including the number of cooling water channels have  to be increased.In these situations, a neutron can be absorbed into the structural materials, thereby the neutrons for T production decreases.The point of blanket design is to reduce the number of rib structures in the box-shaped module as well as to ensure pressure tightness.This is because a decrease in the amount of structural material improves T productivity.
The arrangement of the rib structure in the box-shaped module in consideration of pressure tightness and T productivity is shown in figure 1.The rib structure of the honeycomb-shape has an advantage of reducing the thickness of the rib structure and placing it without any gaps as well as ensuring pressure tightness.The square shape can be arranged without any gaps, but the thickness of the rib structure increases.On the other hand, the thickness of the rib structure for circle-shape can be decreased, but there is useless space between the blanket modules.Table 1 shows the comparison in terms of material percentage between the square shape, honeycomb shape, and circle shape.
In the previous design, the breeding area of the module was divided into 0.1 m-squared cells with rib structure as shown in figure 2(left) [4].However, the problem of the previous concept of the square prism rib structure was a reduction in the volume fraction of T breeding materials.From the three-dimensional neutronics analysis results, the overall tritium breeding ratio (TBR) was calculated to be about 1.0.It was difficult to reach the target of the overall TBR which is at least 1.05 or more for JA DEMO.
As the honeycomb rib structure is higher in pressure tightness than square prism rib structural concept, the area for filling the mixed pebbles T breeder of Li 2 TiO 3 pebbles and Be 12 Ti ones can be enlarged as shown in Fig . 2 (right).Then the overall TBR is improved to increase the packing area of the mixed pebbles.From the three-dimension neutronics analysis results, the target of the overall TBR (>1.05) is achievable with the packing factor to 80% by binary packing [5,6].However, there are concerns about manufacturability because honeycomb blankets are complex structure and have many narrow parts.The number of internal cooling pipe of the U-type in the T breeding area is 249 in the blanket module, and the total number of blanket modules placed in VV reaches 255 972.Therefore, a simplified structure is required to improve fabrication and inspection, and it is essential to reduce the number of cooling pipes in the breeding area as much as possible.On the other hand, the cylindrical shape is advantageous in terms of pressure tightness, and it is possible to allocate a large area with a thin casing structure.Therefore, it can be filled with a large amount of T breeding materials.Furthermore, the cylindrical shape is simple and easy to be fabricated and inspected.However, because there is some space between the cylindrical sub-blanket modules which is not used, the lower productivity of T resulting from the less occupancy of breeding materials and the insufficiency of the shielding ability resulting from the increased streaming of neutrons and gamma rays are concerned.Therefore, the conceptual design of the cylindrical breeding blanket was studied to be adopted in JA DEMO.In this study, the T breeding blanket of the cylindrical shape is proposed for JA DEMO, which has two conflicting elements of T self-sufficiency and pressure tightness.

Specification of JA DEMO
The JA DEMO reactor assumed that the major parameters of the reactor are a plasma major radius of ∼8.5 m and a fusion output of 1.5 GW [7].A conceptual design of JA DEMO is shown in figure 3. The main components are the blanket segment which is a component with several blanket modules fixed in the back plate, divertor cassettes and VV and superconducting coils.The blanket structure is manufactured using the reduced-activation martensitic steel (F82H) [8], which T breeder and neutron multiplier are Li 2 TiO 3 [9] and Be 12 Ti [10], respectively.The divertor plate consists of the W monoblock and F82H cooling tubes and substrates.The cooling system of JA DEMO is designed based on a pressurized water reactor (PWR) water conditions which are the coolant temperature of 290 • C-325 • C and the operation pressure of 15.5 MPa, respectively.At an energy of 14.06 MeV, the total neutron emission from the plasma is 5.3 × 10 20 n s −1 .The maximum neutron wall load (NWL) is 1.66 MW m −2 , the average NWL is 1.0 MW m −2 , and the heat wall load (HWL) due to radiation from the plasma is 0.5 MW m −2 as summarized in a table of figure 3.

Design requirements of the T breeding blanket for JA DEMO
The most important requirement is that the overall TBR required in the design to satisfy the T self-sufficiency is 1.05 or more.The target of the TBR on the calculation is defined to match the target of the overall TBR.This is described in section 3.1.The breeding T in the blanket shall be continuously recovered with helium purge gas introduced inside.In order to generate electricity, on the other hand, it is necessary to recover the heat load generated by radiation from plasma and nuclear heat generation by neutrons.The NWL and HWL are loaded to the T breeding blanket and the conditions of the coolant water are shown in section 2. The next required structural strength is to be robust so that the blanket casing does not damage even in the in box LOCA.The thickness of the spherical shell plate for the first wall (FW) was estimated to be 3.3 mm based on the Japanese Industrial Standard of 'construction of pressure vessel [11]' for the design pressure of 17.2 MPa (under the situation of the in-box LOCA) with the corrosion allowance of 0.25 mm.The design standard applied for ensuring the structural soundness during the operation is described in section 3.2.The selection of neutron multiplier is important in terms of safety.This is because hydrogen is generated when beryllium (Be) reacts with hot steam during the in-box LOCA.This is described in section 3.3.Finally, in consideration of vertical position stability and high beta accessibility in JA DEMO, the ratio of the plasma minor radius (a p ) to the distance from the plasma center to the conductor wall (r wall ) is 1.35 (=r wall /a p ).Therefore, the radial thickness of the blanket module is less than 0.65 m.The requirements for the JA DEMO blanket design are summarized in table 2.

The target of the TBR on the calculation
To determine the target of the Overall TBR for the JA DEMO, it is necessary to consider the loss of T in the fuel cycle, provision of a start-up inventory of T for another fusion power plant, the 6 Li burning for T breeding materials, T decay (5.5% per year), etc.The fuel cycle of the JA DEMO assumes direct internal recycling as adopted in the EU DEMO [12], but the amount of T loss in this cycle has not yet been identified [13].Therefore, the target overall TBR of the JA DEMO is set at 1.05 with reference to the EU DEMO [14,15].In addition, if the start-up inventory of T is not supplied to the next fusion reactor, it is said that the target value can be reduced to 1.02-1.03[14,15].Moreover, concerning errors in nuclear data, when following the European approach, such errors are no considered margins.On the other hand, an operation scenario in which the amount of T required for start-up is gradually increased using T generated by DD operation is under study.In order to achieve steady operation by this method, DD operation is required for a long period of operation time and a large amount of power [16].Therefore, the target value of overall TBR for the JA DEMO was assumed to be 1.05, which takes into account the provision of a start-up inventory of T for another fusion power plant.The blanket coverage for the calculation of the TBR was estimated to consider the divertor, port (NBI, ECH, instrumentation equipment), safety limiter, T fuel supply system, and killer pellets of the disruption mitigation system, gap between blanket modules.The breakdown is shown in figure 4. The evaluation of the TBR in the cylindrical-type blanket covers sub-modules and does not take into account the gap between modules.Therefore, the coverage of the cylindrical-type blanket is 85.3% considering the gap area of 3.6% (44.3 m 2 ).The aperture area of the NBI and ECH systems was estimated from the energy of the heating and current drive required for the steady and pulsed operation of JA DEMO.However, the component design is not fully thought out, so provisional values will be set.Therefore, the target local TBR values of T breeding blanket required for calculation is 1.244 (=1.05/0.844),respectively.

Stress analysis for the blanket structure
Thermal stress during normal operation was evaluated for a cylindrical-type blanket concept.With the material data for F82H, the minimum ultimate tensile strength as Su and the primary membrane stress intensity as Sm are assumed to be 444 MPa and 165 MPa at 400 • C, respectively [17].In the evaluation during the normal operation, the primary + secondary stress is evaluated considering the thermal stress due to the steady temperature distribution at 100% rated operation.Specifically, it is confirmed that the maximum stress of primary + secondary stress is 3 Sm (=495 MPa) or less.

Neutron multiplier for JA DEMO blanket
In order to efficiently breed the T fuel, Be with a relatively small threshold energy (⩾1.8 MeV) of the neutron multiplication reaction as (n,2n) is used in the JA DEMO blanket.A suppression of hydrogen generated by the reaction between Be and high-temperature vaper during in-box LOCA is important from the viewpoint of ensuring the safety of JA DEMO.As a result of the preliminary analysis, thermal runaway occurs when the temperature exceeds 680 • C of the Be, and hydrogen generation continues until the oxidation is completed [18].Therefore, in JA DEMO, a beryllide such as Be 12 Ti or Be 12 V is adopted to suppress the amount of hydrogen generated during the in-box LOCA.Beryllide is an intermetallic compound of Be and is known to reduce the amount of hydrogen generated to about 1/100-1/1000 compared to pure Be [19,20].The temperature leading to thermal runaway is also 1200 • C, which is higher than that of pure Be [18].In addition, since the swelling of the beryllide is small, it can be used as a block.Beryllide is scientifically stable and does not pose a major problem when in contact with T breeding materials [21].

Allowable design parameters for the JA DEMO
The requirements of proposed blanket concepts are confirmed by meeting target parameters regarding pressure tightness, T breeding, and heat removal through the neutronics using the MCNP-5 [22] with nuclear library of the FENDL-3.0 [23], finite element method analysis using ANSYS code, and computational fluid dynamics analysis using ANSYS Fluent.In the evaluation, thermal design (confirmation of cooling water conditions and allowable temperature of materials), structural design (confirmation of stress conditions), and nuclear design (confirmation of T productivity) are evaluated and confirmed.
Table 3 shows the parameters to be confirmed in each analysis.From table 3, the flow rate is determined from the viewpoint of control of the wall thinning in the pipe, and the cooling water condition is determined with reference to the PWR.The pressure drop in the primary cooling system was estimated to be 1.2 MPa including an allowable value for the pressure drop in the blanket modules of the 0.5 MPa [24].In addition, the design pressure of the pressurizer is assumed to be 17.2 including a margin of 0.5 MPa in the operating pressure of the 15.5 MPa for the blanket modules.Therefore, the pressure drop in the blanket modules must be kept below about 0.5 MPa.
The allowable temperature of F82H, Li 2 TiO 3 , and Be 12 Ti is determined from the 0.2% yield strength decrease with aging hardening, from the viewpoint of the vapor pressure, in terms of thermal runaway during in-box LOCA, respectively.Finally, the requirement of the pressure tightness during the in-box LOCA in the blanket casing was set to 17.2 MPa of the operating pressure.The conceptual design of a breeding blanket for JA DEMO with a cylindrical structure is explored to achieve structural simplicity, pressure tightness (17.2 MPa), and engineering feasibility.A cylindrical structure is proposed that can ensure the maximum TBR productivity and maintain a simplified breeding blanket concept.The point of the conceptual design is that by using beryllide blocks with a higher thermal conductivity than pebbles, it is possible to simplify the inside of the blanket based on the exclusion of the inside cooling pipe and increase TBR with increasing Be density.In this concept, the FW of the blanket is covered with 0.5 mm-thick tungsten (W) to suppress erosion by physical sputtering.3 mm thick cooling layer is arranged in the middle of FW with a thickness of 9.6 mm.Thus, the thickness of the FW with W coating is 10.1 mm in total.
Figure 5 shows the two cylindrical concepts of (a) a gear type concept and (b) a central cooling piping concept.In figure 5(a), the beryllide block has a gear-shaped shape, and the gap is filled with Li 2 TiO 3 pebbles with a packing factor of 80% by binary packing.Thickness of the Li 2 TiO 3 pebbles layer is 2 mm in the hemispherical part and 9 mm in the body part.In addition, this concept is that the nuclear heating in the T breeding area is removed by contact heat transfer in the area where the beryllide block and the inside wall in the casing are in contact.In figure 5(b), a T breeder of Li 2 TiO 3 pebbles was filled with a packing factor of 80% on the entire surface between the cylindrical structure's internal surface and the beryllide block's external surface to ensure maximum T productivity.However, among the using blanket materials, the Li 2 TiO 3 pebbles have low thermal conductivity, and it is necessary to install a new cooling piping inside the beryllide block.In this double cooling pipe, a pipe with an inner diameter of 4.5 mm is loaded into a pipe with an inner diameter of 8.0 mm, and the cooling water flowing from the rear through the center folds back near the FW and flows  backwards through the outside of the double cooling pipe.In both concepts, the distance between the beryllide block and the inner casing is adopted as a thickness that maximizes the TBR value.

Thermal analysis for the cylindrical-type blanket.
Thermal analysis is performed to confirm the temperature distribution of the blanket concepts based on the maximum NWL (1.66 MW m −2 ) and heat load (0.5 MW m −2 ) in the JA DEMO condition.The heat load of the hemispherical part is defined with the zenith angle of θ as follows: Heat load = 0.5 MW m 2 × cosθ.
In thermal analysis, the contact heat transfer rate between the Li 2 TiO 3 pebble bed and contact surface was assumed to be 2000 W (m•K) −1 , and the contact heat transfer rate between the F82H structural and the Be 12 Ti block was determined from Tachibana's equation [25].Figure 6 shows the cooling flow of the cylindrical blanket with a gear type concept (a).In this blanket concept, since there is no cooling pipe in the inside of the blanket, so it is only cooled by the casing of the F82H. Figure 7 shows the distribution of the temperature for the coolant water, the inner wall for the body area, and the inner wall for the hemisphere.As a result of flow analysis for one submodule, the coolant temperature was increased at the inlet and outlet of the submodule was 4.38 • C and the pressure drop was 48.5 kPa.In this concept, since a stagnant water area occurs immediately after turning back in the hemispherical area, a bypass flow line is designed to cool the stagnant  Figure 8 shows the cooling flow of the cylindrical blanket with a central cooling piping concept (b).In this blanket concept, the T breeding area is cooled by the double cooling pipe in the center after the cooling the casing of the blanket.Figure 9 shows the distribution of the coolant velocity and temperature for the hemisphere and double cooling pipe.Since a cooling channel is provided in the body part, unlike type (a), there is no stagnant water area in the body part.In the hemispherical area, on the other hand, a stagnant water area exists immediately after the coolant water leaves the cooling channel.However, since the inner wall temperature is within about  300 • C, it is not a big problem.As a result of flow analysis, the coolant temperature of the submodule was increased at the inlet and outlet for the casing area and double cooling area were 22 • C and 9 • C, and the total pressure drop was 123 kPa.
Figures 10 and 11 shows the temperature distribution for each concept.The allowable temperature of Li 2 TiO 3 , Be 12 Ti, and F82H was limited to 900 • C, 1000 • C, and 550 • C, respectively.As a result of thermal analysis on both cases, it was found that the casing structure considering contact heat transfer as shown in figure 10 and the double cooling pipe in the center of the beryllide block as shown in figure 11 were designed to satisfy the operational temperature window of the T breeding material and structural materials.

Stress analysis for the cylindrical-type blanket.
In order to evaluate the thermal stress of the cylindrical blanket design, stress analysis based on the temperature distribution in the casing obtained by heat transfer and flow analysis was performed.The results indicated that for the gear type concept,  the primary and secondary stress values for the casing structure were below the allowable stresses (=495 MPa) in all evaluation lines as shown in figure 12.
Figure 13 shows the stress distribution of the F82H casing and double cooling pipe for the central cooling piping concept.As shown in figure 13(bottom-right), it can be seen that the maximum stress value (556 MPa) exceeds the allowable stress.However, this maximum stress occurs locally at the connection between the hemispherical structure and the cylindrical body, which is manifested in the mesh division problem and should not be considered in stress evaluation.Therefore, the results indicated that for the central cooling piping concept, the primary and secondary stress values for the casing structure and double cooling pipe were below the allowable stresses (=495 MPa) in all evaluation lines as shown in figure 13.

TBR evaluation for the cylindrical-type blanket.
Specifications such as the shape and dimensions of the cylindrical-type blanket are designed on thermal (see section 4.2.2) and stress (see section 4.2.3)analyses.In the calculation model, a cylindrical blanket casing, Be 12 Ti block, Li 2 TiO 3 pebbles (homogeneous), and W coating are modeled.In addition, the ratio of Be 12 Ti and Li 2 TiO 3 in the T breeding area is filled at a ratio of 1-4, which has the best T breeding ratio.The purge gas flowing in the T breeding area is added to the Li 2 TiO 3 pebbles as a homogeneous material.A regular hexagonal reflecting (mirroring) boundary is defined around the cylindrical submodule and a volumetric neutron source for the plasma is set at a distance of 20 cm from the tip of the hemispherical part.14.06 MeV of DT neutron was isotropically emitted from the volumetric source.In addition, the backplate (shield) and VV are modeled at the rear of the module to perform the backscatter to the blanket submodule as shown in figure 14.
As a result of the neutronic analysis, the local TBR of (a) the gear type concept and (b) the central cooling piping concept were estimated to be 1.21 and 1.24, respectively, using the blanket with a thickness of 0.6 m.It was found that the target local TBR (⩾1.24) can be achievable with the (b) central cooling piping concept, and the start-up of T for the next fusion reactor can be secured.On the other hand, if there is no need to secure the inventory for the start-up of T (target local TBR ⩾ 1.21), (a) the gear type concept can be adopted for the JA DEMO.In addition, figure 15 shows an image of the blanket module viewed from the surface.It was found that the local TBR could be improved by about 0.01 when a beryllide rod was loaded into the through hole (diameter of 18 mm) between the modules.On the other hand, this analysis was calculated for the sub-modules for the load at the outer equatorial plane location.However, when blanket modules are placed in the VV to cover the plasma, the outer blanket modules create useless space in the rear.The inner blanket module also creates useless space in the front.Assessing the impact of the TBR on the 3D considering this useless space is a future work.

Radiation shielding effect of cylindrical blanket
The radiation shielding of the box and cylindrical blanket placed on the inboard side of JA DEMO was compared.Figure 16 shows the MCNP calculation model for the JA DEMO design.This model provides the dimensions and arrangement of the blanket modules, divertor cassettes, back plate, vacuum vessel, toroidal and poloidal field coils, and maintenance port for the blanket and divertor, and the difference in neutron and gamma-ray shielding effect for blanket concepts between box-shape (such as honeycombs-type) and cylindrical shape is confirmed on the inboard side.With the assumption of toroidal axisymmetry, a 22.5 • sector of the reactor can be modeled with reflecting boundaries.14.06 MeV neutrons are emitted from the plasma volume.The distribution of the neutron generation rate is defined based on the plasma equilibrium equations.The distributions of neutron generation at the center and edges of plasma are about 11% and 0.1%, respectively.5.3 × 10 20 n s −1 neutrons at 14.06 MeV are estimated to be emitted from plasma.In figure 16, the VV and backplate are modeled as homogeneous.The VV is modeled in SS316L of 50% and water of 50 %.On the other hand, the casing of the back plate is modeled in SS316 with a thickness of 50 mm, inside area which is modeled in F82H of 80% and water of 20%. Figure 17 shows the neutron distribution when viewed from the plasma side when the cylindrical blanket is arranged on the inboard side.In the figure 17, it was found that the neutron flux in the gap of the cylindrical blanket was increased by neutron streaming.In addition, table 4 shows the displacements per atom (DPA) and neutron flux at the back plate, vacuum vessel, and TF insulation material.As can be seen from table 4, when a cylindrical blanket is introduced, it was found that if the thickness of the rear wall was increased by about 50 mm, the shielding capacity could be obtained as well as that of a box-type blanket.

Conclusion
The conceptual design of a breeding blanket for JA DEMO with a cylindrical structure is explored to achieve structural simplicity, pressure tightness (17.2 MPa), and engineering feasibility.A cylindrical structure is proposed that can ensure maximum TBR productivity and maintain a simplified breeding blanket concept.The point of the conceptual design is that by using beryllide blocks with a higher thermal conductivity than pebbles, it is possible to simplify the inside of the blanket based on the exclusion of the inside cooling pipe and increase TBR with increasing Be density.In this concept, the FW of the blanket is covered with 0.5 mm-thick W to suppress erosion by physical sputtering.3 mm thick cooling layer is arranged in the middle of FW with a thickness of 9.6 mm.Thus, the thickness of the FW with W coating is 10.1 mm in total.Two cylindrical blanket concepts were considered.In the gear-shape concept (a), the nuclear heating in the T breeding area is removed by contact heat transfer in the area where the beryllide block and the inside wall in the casing are in contact.In the central cooling piping concept (b), on the other hand, a T breeder of Li 2 TiO 3 pebbles was filled on the entire surface between the cylindrical structure's internal surface and the beryllide block's external surface to ensure maximum T productivity.However, among the using blanket materials, the Li 2 TiO 3 pebbles have low thermal conductivity, and it is necessary to install a new cooling piping inside the beryllide block.As a result of thermal analysis on both cases, it was found that (a) the casing structure considering contact heat transfer and (b) the double cooling pipe in the center of the beryllide block were designed to satisfy the operational temperature window of the T breeding material and structural materials.Therefore, it was found that using blocks with a higher thermal conductivity than pebbles allow for less cooling piping inside the module.In the neutronics analysis for the local TBR, both design cases for the cylindrical structure were estimated to be (a) 1.21 and (b) 1.24, respectively.Accounting for a coverage loss of 1.3% because of NBI, EC, and diagnostic areas, and of 7.5% because of divertor areas, and 2.5% because of safety limiter and disruption mitigation system, the estimated Overall TBR amounts to (a) 1.02 and (b) 1.05, respectively.Therefore, the target of the overall TBR (>1.05) can be achievable with (b) central cooling piping concept.Finally, since the rib structure is changed from the honeycomb type to a cylindrical type, neutron streaming increases.Therefore, it was found that the thickness of the backplate, which plays a role in radiation shielding, should be increased by about 50 mm.

Figure 1 .
Figure 1.Characteristics of the shape for the rib structure related the pressure tightness.

Figure 2 .
Figure 2. Square prism ribs-structure (left) and Honeycomb ribs-structure (right) for the JA DEMO blanket.

Figure 3 .
Figure 3. Configuration and specification for JA DEMO reactor.

Figure 4 .
Figure 4. Coverage of the T breeding blanket around the plasma.

Figure 5 .
Figure 5.The cylindrical blanket concepts with a beryllide block, (a) gear type concept and (b) central cooling piping concept.

Figure 6 .
Figure 6.Coolant flow for the gear type concept.

Figure 7 .
Figure 7. Distribution of the temperature for the coolant water (left), the inner wall for the body area (middle), and the inner wall for the hemisphere (right).

Figure 8 .
Figure 8. Coolant flow for the central cooling piping concept.

Figure 9 .
Figure 9. Distribution of the coolant velocity of the hemisphere (upper-left) and the double cooling pipe (upper-right), and distribution of the temperature of the inner wall for the hemisphere (bottom-left) and the double cooling pipe (bottom-right).

Figure 11 .
Figure 11.Temperature distribution for the blanket sab-module (left) with double cooling pipe (right).

Figure 12 .
Figure 12.Stress distribution of the F82H casing for the gear type concept.

Figure 13 .
Figure 13.Stress distribution of the F82H casing and double cooling pipe for the central cooling piping concept.

Figure 14 .
Figure 14.MCNP calculation model for the cylindrical submodule blanket.

Figure 15 .
Figure 15.Location of sub-modules and through-holes in the blanket module.

Figure 16 .
Figure 16.Calculation model of the radiation shielding.

Figure 17 .
Figure 17.Distribution of the neutron flux.

Table 1 .
Percentage of material in each blanket shape.

Table 2 .
Requirements of the JA DEMO blanket design.

Table 3 .
Design parameter of the T breeding blanket.

Table 4 .
Neutron irradiation of the VV, back-plate and TF insulation material.