1. MICE Hydrogen System MICE Collaboration Meeting, CERN, 29 March-2 April 2004 Elwyn Baynham, Tom Bradshaw, Yury Ivanyushenkov Applied Science Division, RAL

2. Scope of the presentation Design changes arising from Safety Review Panel Buffer volumes Separation of vent systems Vent system manifolding Ongoing design issues Hydrogen vent pipe sizes Liquid level control Provisional hydrogen system control sequence R&D programme on metal hydride Hydrogen system layout Response to Review Panel – summary comments

3. Buffer Volumes Original Design One evacuated buffer volume for both absorber and vacuum space venting Separated from volumes by relief valves Assessment from the review Buffer volume is more effective if directly connected Vacuum space RAL safety does not require 52 x volume for vacuum space around absorber Current design gives ~ 8 –10 x volume Absorber volume Design includes buffer volume in the absorber line Window protection – response time Simplification of control

4. Baseline layout PP VP Vacuum pump Bursting disk Pressure relief valve Valve Pressure regulator Pressure gauge 18 K He 14 K He from Cold box Liquid level gauge LH 2 Absorber Vacuum Vacuum vessel LHe Heat exchanger Internal Window Safety window Fill valve Metal Hydride storage unit (20m 3 capacity) Vent outside flame arrester He Purge system Non-return valve Vent outside flame arrester Purge valve 1.6 bar 2.0 bar H 2 Detector P P P Evacuated vent buffer tank VP P X 2 VP Version: 21/11/2003 H 2 Detector Ventilation system Vent outside flame arrester Purge valve H 2 Gas bottle P P Chiller/Heater Unit 1 bar P P 2.0 bar 1.6 bar1.4 bar

5. Zone 2: An area within which any flammable or explosive substance whether gas, vapour or volatile liquid, although processed or stored, is so well under conditions of control that the production (or release) of an explosive or ignitable concentration in sufficient quantity to constitute a hazard is only likely under abnormal conditions. PP VP Vacuum pump Bursting disk Pressure relief valve Valve Pressure regulator Pressure gauge 18 K He out 14 K He in Safety window Metal Hydride storage unit (20m 3 capacity) Non-return valve Purge valve 0.5 bar 0.9 bar H 2 Detector P P P VP1 VP2 Purge valve Chiller/H eater Unit 1 bar P P 0.5 bar 0.9 bar Helium supply Windows: Design pressure 1.6 bar abs Test pressure 2.0 bar abs Burst pressure 6.4 bar diff Hydrogen supply High level vent Buffer vessel Vent outside flame arrester Extract hood H 2 Detector P P Nitrogen supply P P P P 1 m 3 Hydrogen zone 2 Vent manifold P1 PV1 PV7 PV8 PV2 PV3 PV4 HV1 Fill valve Tbed Tchill HV2 HV3 P3 P2 PV6 High level vent Non return valve 0.1 bar Absorber window Hydrogen system - revised baseline layout Tabs

6. Changes in MICE hydrogen system AFC Safety Review Panel recommendations are implemented: Original buffer vessel is removed Vent manifold is added. The manifold is filled with nitrogen. Venting lines are separated. Other changes: Buffer vessel is added in between absorber vessel and hydride bed. Ventilation system is removed. Most of the equipment is now sits under hydrogen extraction hood.

7. Hydrogen absorber - failure mode - vent system Hydrogen must be vented out of the absorber module in two cases: 1) hydrogen window rupture (hydrogen spills out into the room temperature absorber vacuum chamber and floods the lowest points in the absorber vacuum chamber to a depth of 250 mm). Mass flow rate is 116 g/s. -> 150 g/s with margin (calculations by Mike Green) 2) catastrophic vacuum failure (leads to air being plated out on the inner window, this will put a heat load on the hydrogen in the absorber leading to boil-off of the hydrogen). Mass flow rate is ~12 g/s -> 24 g/s with factor 2 in safety. (calculations by Tom Bradshaw)

8. Pipe sizes –hydrogen vent (calculations by Tom Bradshaw) 40K80K300K Length m0.30.510 Diameter mm152540 Velocity m/s109154227 Press drop Bar0.01650.01040.0989 Total0.1258 Mass flow kg/s0.0228 Magnet Mice vacuum space 40K 80K 300K Specific load (W/cm2)3.6 Load (W)5089 Safety factor x2 (W)10178

9. Pipe sizes for hydrogen vent system Summary for direct venting to manifold 10m pipe run LH2 ID=15 mm L=0.3 m ID=25 mm L=0.5 m ID=40 mm L=10 m ID=60 mm L=10 m Overall pressure drop is 0.126 bar for mass flow of 24 g/s Pressure drop is 0.367 bar for mass flow of 150 g/s

10. Pipe sizes for hydrogen vent system 30m pipe run LH2 ID=15 mm L=0.3 m ID=25 mm L=0.5 m ID=40 mm L=30 m ID=60 mm L=30 m Overall pressure drop is 0.307 bar for mass flow of 22.8 g/s Pressure drop is 1.1 bar for mass flow of 150 g/s ID=100 mm L=30 m Pressure drop is 0.1 bar for mass flow of 150 g/s or Overall pressure drop is 0.07 bar for mass flow of 22.8 g/s ID=15 mm L=0.3 m ID=25 mm L=0.5 m ID=60 mm L=30 m Proposal

11. Level Control – what variations do we need to respond to: Level will vary due to temperature changes in the absorber Variation in density of LH2 could give ~ 1 – 2 litres volume change Such changes cannot be accommodated in small pipes 25mm dia = 2.2m/litre Such level changes will be relatively slow under normal operating conditions Energy to go from 14 – 18K ~ 50kJ for 20 litres Nominal heat load /absorber is few W Time 14 – 18K is ~ 5 – 10 hrs Most significant effect will be intermittent gas boil off due to changes in level – especially so for the horizontal pipe Hydrogen level control – design considerations

12. Level Control – Where is best place to monitor/control level Absorber neck tube Insufficient volume Horizontal pipe Not practical Vertical pipe Need to thermalise the horizontal pipe Small volume available Main absorber volume Ullage - 2 litres is 10% Temperature of absorber body will be uniform Increase in volume will cause very little boil off Less active role for control system – hydride bed External buffer volume 1m^3 could absorb ~ 0.5 –1 litre before activating the relief system – assuming no return to the hydride bed - need further work Hydrogen level control – design considerations

13. Chiller on Set Tchill = Tchill_initial Start PV1,2,3,4 closed VP1 on, PV6 Open Cooling system On Start Pressure Control Loop Start Vac Monitor Open Pv1,Pv2 Tbed<Tbed1 And P3<1.e-5 P1  Pset1 Close PV1,PV2 Stop Pressure Control Loop Set Tchill = Tchill_low Open PV3 Hlevel>Hlevel1 H2 System Ready Increment/Decrement Tchill Empty Sequence P3<1.e-5 Vac monitor Pressure Control Yes No Yes No Yes No Provisional Hydrogen System Control Sequence Control logic – Fill Sequence

14. Open PV4 Close PV1,PV2 Set Tchill = Tchill_low Close PV1,PV2,PV3 P2<0.1bar AND Tabs>100K H2 System Empty Empty Sequence Yes No Provisional Hydrogen System Control Sequence Empty Sequence

15. R&D programme on metal hydride storage system Conceptual question: a small-scale rig vs. a full-scale prototype ? Decision: go for a full-scale system which later will be used in MICE. R&D goals: Establish the working parameters of a hydride bed in the regimes of storage, absorption and desorption of hydrogen. Absorption and desorption rates and their dependence on various parameters such as pressure, temperature etc. Purity of hydrogen and effects of impurities. Hydride bed heating/cooling power requirements. What set of instrumentation is required for the operation of the system? Safety aspects including what is the necessary set of safety relief valves, sensors and interlocks. Status Programme on hold pending funding approval for 2004/05

16. RF Zone Hydrogen system layout H2 3 hydrogen systems

17. Hydrogen Gas Handling & Venting system Remove buffer tank and vent the hydrogen out directly - implemented Remove relief valves in the hydrogen vent lines and have burst disks only – retained Completely separate vent system for the absorber and vacuum spaces - implemented Detail specification of the Relief valve – work in progress Is hydrogen detector appropriate in the vacuum line – still under consideration Hydrogen detectors are needed in the ventilation system and in the personnel space around the experiment – will be implemented Examine the level to which piping should be Argon jacketed – will be addressed Replacing the flame arrestor with a vent pipe with an inert atmosphere - implemented Adopt Fermilab requirement vacuum system volume 52x H2 liquid volume – not implemented Safety Review Panel – Main Points – status review

18. R & D on the Metal Hydride system The use of hydride system requires active control. The panel suggested an scaled model test. It also asked the group to examine the safety issues associated with this system R&D proposal defined and submitted Safety Review Panel – Main Points

19. Practicality of using intrinsically safe electrical equipment – response already drafted Pipe joints – will be as requested Detection of Hydrogen in Personnel areas – agreed Attention to Interlocks, alarms and control system - ongoing. Continuation of HAZOP assessment – agreed Response to Absorber system leak scenario - ongoing Potential of liquid hydrogen sloshing in warmer part of the feed pipe – to be addressed in level control. Leak between the helium and hydrogen compartment in Absorber unit - ongoing Safety Review panel – Additional Points

20. Agree level monitoring and control principles Range of parameters to control Control accuracy required Where to implement Design calculations required Engineering design required Define relief valves Pressure range confirmation Response speed required Identify supply availability Argon Jacketing H2 and He leaks Hydrogen system next design steps