# Status, Features, and Future Development of the LIFUS5/Mod4 Experimental Facility Design
## 4 Facility Operational Modes  
### Facility States  
The facility will have seven main states that can be reached through operator control. These states are:  
1. **Cold drained. ** In this state the facility is completely shut down, no PbLi is present in the piping and the loop, and all the alloy present in the facility is stored in the loading and draining tanks. The heating wires are shut down throughout the plant except for the loading tank, in which they are kept in a regulation state to avoid alloy solidification. The only valves which are actuated in this state are the electric control valves that keep the pressure inside the loading tank under control. 2. **Hot drained. ** In this state, the facility is brought to temperature but PbLi is present only in the loading/draining tanks. This state is reached before the loading of the facility for a test or after a test is completed. All the regulation cables, except for those heating the tanks' draining lines, are on and the control system is regulating the pressure in the loading and draining tanks. 3. **Hot loaded. ** In this state, part of the alloy has been transferred to the storage tank and the facility is ready to be filled. Here, the isolation valves are still closed and the PbLi does not fill the piping, TEU, or test section. The control system is regulating the pressure in every zone of the facility. 4. **Hot filled. ** This state immediately precedes the test. Here, the facility is filled with alloy, the loading and draining tanks are isolated from the system, and the pressure control system is regulating the pressure in all the zones of the facility. 5. **Test. ** In this state, the facility performs the test. The exact state of the facility will depend on the details of the test execution; they will be defined in subsequent phases of the design. 6. **Gas analysis. ** This state is reached after the test is completed and the gas analysis phase is taking place. Here, the hydrogen system valves are opened one at a time and  
Figure 4: LIFUS5/Mod4 preliminary CAD drawing. Highlighted in red: the isolation valves and the upgrade points. the facility is slowly depressurized by collecting and transporting the gas mixture present inside it to the analyzer. 7. **Acid wash.** This state is a special state in which after returning to the cold-drained state the facility can be cleaned by circulating an acidic solution to dissolve the reaction products. Before each test, the facility begins in the cold-drained state. The startup procedure consists of bringing the facility to temperature by activating the heating wires and the relative control system and heating all the components. This is performed before PbLi loading to avoid the formation of any plug in the system that would impair facility operation; the relative state is referred as to hot drained. From this state, PbLi is then loaded into the recirculation tank by applying a suitable pressure differential between this tank and the loading tank. The state reached is called hot loaded. After all the alloy needed for the test has been transferred to the recirculation tank, the loading and draining tank are isolated and the facility is then filled to completeness by applying a pressure differential between the piping system and the recirculation tank. The final state reached before the test is referred to as hot filled. Right after the filling is complete, the facility will be switched to the test execution state, where the experiments are performed and the data acquired. At the end of each test, the gas analysis phase is begun, where the facility is slowly depressurized. Any gas present in the piping system or the tanks is collected and analyzed to determine the amounts of reaction products generated during the test and infer the amounts of reactants. During this phase, the facility will be flushed a few times with pure argon from the pressurization system to scrub all the hydrogen present in the PbLi loop and any that might have diffused into the alloy or facility components.