2.5.2.3.2 Lithium purification system sub-loop

The lithium purification sub-loop, shown in Figure 2.5.2-10, consists of a system of hot and cold traps to remove various impurities and auxiliary supporting equipment (small EMP, flow meters, valves, trace heating, and connections to argon/vacuum headers). Since planned and unplanned maintenance capability are required during operation, full redundancy is provided. If a trap requires regeneration, or in the unlikely event of a fault (as indicated by the impurity monitoring systems), the alternate trap will be valved in. The trap will then be removed to a hot cell during the next scheduled maintenance for regeneration or repair. Because of the high activation of the trapped impurity products, fully remote handling is required. Localized shielding around the traps is also needed to permit limited personnel access to the loop cell.

The major impurity product expected, in terms of quantity, is the deuterium deposited in the lithium jet by the beam. Tritium is produced by direct reactions of the beam with the lithium, as well as by capture of low energy return neutrons by Li-6. Total tritium production is estimated at 10 g/y. It is essential to minimize the tritium inventory in the system, since this could be the dominant source term in the event of a radiological release. Tritium is removed by the cold trap, with protium sparging, or, as an option, by hot trap with yttrium getter.

The most highly radioactive impurity is expected to be Be-7, a 53-d half-life material produced from (d,n) and (d,2n) reactions with lithium [8,9,10]. If not removed, this product will build up to a saturated activity of 4.5 x 1015 Bq. The cold trap will remove Be-7, but some is expected to plate out around the loop, and will very likely dominate the remote handling requirements. Oxygen will also be removed by the cold trap and corrosion products will be removed by the hot trap. The hot traps will be used to remove primarily nitrogen and carbon. Both are common impurities in lithium. Nitrogen forms highly corrosive compounds with lithium and may build up from air contamination during repair exchange of components and adhesion to component surfaces. Carbon can build up from HX tube leakage.

Figure 2.5.2-10. Lithium purification sub-loop.

Figure 2.5.2-11. Lithium loop impurity monitoring sub-loop.

2.5.2.3.3 Impurity monitoring loop

The impurity monitoring system is shown in Figure 2.5.2-11. A system of valves permits sampling of the lithium side stream either on entry or exit of the purification system. Both on-line and off-line monitoring of the impurities in the lithium are performed. The off-line system provides for simple removal of a sample of the lithium into a shielded container for chemical analysis in the remote handling facility. The disadvantage of this system, in addition to requiring remote chemical analysis, is the delay in the availability of the results. The on-line system [11,12,13], in contrast, provides results in real time, and can be used to perform a safety function (e.g., air in-leakage or HX tube failure). This system will, at a minimum, contain a hydrogen membrane diffusion meter, and a resistivity monitor. The latter provides primarily an indirect measurement of the nitrogen concentration. Nitrogen and oxygen meters may also be added if development of these is successful. Preliminary design provides complete interchangeability of all of the impurity meters. Complete redundancy of the impurity monitoring loop will permit continued operation in the event of a component failure. Replacement of the failed component will be performed during the next scheduled or unscheduled maintenance.

2.5.2.4 Target system arrangement

An isometric view of the IFMIF target system that corresponds to the flow diagram of the lithium loop system is shown in Figure 2.5.2-12. The cross sectional views and plan views of the target system are also shown in Figure 2.5.2-13 and Figure 2.5.2-14, respectively. A vacant room just under the lithium cooler room is used to house the inert gas ventilation system. The exchange and maintenance of the components (cold trap, hot trap and impurity monitoring equipment) in the impurity control room will be accessed from the upper room. The organic cooler room has a large upper space which is used to transfer the components to each floor room at the initial stage of target system installation. A layout around the target assembly and differential pumping system, which interfaces with the HEBT, is shown in Figure 2.5.2-15. The evacuation ports of the beam target side are to be set up in the test cell and their pumps will be installed in the side room of the test cell.

2.5.2.5 Lithium loop components design description

In the lithium purification system sub-loop, as described in the Section 2.5.2.3.2, a cold trap and two kinds of hot traps are set up, with redundancy. These components are shown in Figure 2.5.2-16. Oxygen, beryllium and corrosion products in the flowing lithium are to be trapped by cold trap. Hydrogen isotopes (H, D, and T) are to be trapped by the cold trap or, as an option, the hot trap containing yttrium getter.

Figure 2.5.2-12. Isometric view of IFMIF target facility.

Figure 2.5.2-13. Cross sectional view of IFMIF target facility (all dimensions in m).

Figure 2.5.2-14. Plan view of IFMIF target facility (all dimensions in m).

Figure 2.5.2-15. Layout of target assembly and differential pumping system.

Figure 2.5.2-16. Cold and hot traps (gettering materials are shown in cross hatched areas; all dimensions in mm).

Table 2.5.2-3. Design parameters of cold trap and hot traps

Another hot trap with titanium getter material is to remove nitrogen that comes from the atmosphere during repair or exchange of the components and from the adhesion on the inner surface of the lithium components. The design parameters of these components are shown in Table 2.5.2-2. The saturation levels of these impurities (O, H isotopes, N and Be) in the lithium loop will be controlled under 20 wppm.

The Electro Magnetic Pump (EMP) of the ALIP center return-duct type in the main lithium loop is shown in Figure 2.5.2-17. The design maximum flow rate is about 145 L/s and the developed pressure is 0.47 MPa at the input power of 467 kVA, 27 Hz. The stator coil will be divided into more than two blocks with parallel connection to avoid the full flow down at the failure of one short circuit.

The lithium heat exchanger of U tube type is shown in Figure 2.5.2-18. The lithium flows the shell side and its inventory is about 4500 L. The number of inside fine tubes of each size of 25.4-mm outer diameter x 2.6-mm thickness are 434 and their total heat transfer area is about 495 m² . The required heat transfer area is about 388 m², so it has a margin of about 30%.

Target Facilities 5/17