The MICE Hydrogen System Safety Review
Introduction
Tom Bradshaw, Yury Ivanyushenkov, Elwyn Baynham, Tony Jones, Mike Courthold and Matthew Hills
Rutherford Appleton Laboratory
Overview of talks
1. Introduction (TB)
• Design philosophy
• Basic operation including hydride bed
• Basic design calculations
• Motivation and approach – R&D cycle
• Safety review process
2. Process and Instrumentation Diagrams (MH)
3. Control System (MJDC)
• Overview of control system
• Prototype flow diagrams & control sequences
• Pumps and Instrumentation
• Implementation and hardware
4. Hall Infrastructure and R&D Cryostat (AJ)
5. HAZOP and failure analysis (YI)
Introduction
The muon ionisation cooling experiment is an pre-cursor to a neutrino factory.
Its objective is to demonstrate muon cooling – i.e. produce a collimated beam of muons.
This is achieved by cooling and slowing down the muons in an absorber (Hydrogen, Helium or plastic) before accelerating them in an rf field.
The absorber for use with liquid hydrogen or helium consists of a chamber with thin aluminium windows. This requires a hydrogen delivery system which is the subject of this review.
The design of the absorber and its implementation is the subject of a separate safety review.
Safety Review Process
We are here
There are two phases to the implementation of the hydrogen delivery system:
•R&D Phase where a single system is developed and tested on a test cryostat which represents an absorber.
•Implementation phase where the delivery system is matched to a real MICE absorber
The objective of the R&D phase is to demonstrate a safe hydrogen delivery system for the absorber.
This will consist of a first model MICE hydrogen delivery system together with a test cryostat that does not have thin windows but does contain the same instrumentation.
Objectives of R&D
Cross section of Absorber
a) Windows are mounted off RT interface – see thermal model later
b) Space for change in pipe dimension close to magnet
c) Large “bucket” at base to contain any rupture
This is not the subject of this reviewWindows are rated up to:
Design pressure 1.6barTest pressure 2Burst pressure 6.4
Safety Review Process
KEK Absorber design
Past ExperiencesPage Operation/Cause Result Venting/
purging operation
Leak into enclosed space
Air leak into system
Other
81 Thawing plugs with oxy acetylene torch
Explosion
82 Sanding causing sparks Explosion 83 Purging using blower Explosion 85 Oxygen accumulation from
air leak Explosion
86 Smoking near hydrogen Explosion 87 Plugged vent line Explosion 89 Plugged line Explosion 91 Hydrogen trapped because of
plug (non cryogenic) in vent line
Explosion
93 Use of hair dryer to warm cryostat
Explosion
95 Formation of hydrogen in a uranium plant
Explosion
97 Rupture of liquifier high pressure lines venting into room
Explosion
Past Experiences
Page Operation/Cause Result Venting/purging operation
Leak into enclosed space
Air leak into system
Other
100 Warming up cryostat with hair dryer
Fire
101 Reactor test cell caused shed to fill with hydrogen
Explosion
103 Rupture of Bourdon tube Fire 105 Combustion in reactor from
leakage through valve stem Fire
107 Dewar leak Explosion 109 Battery case explosion Explosion 110 Overpressure of turbine Plant failure 112 Incorrect purging operation Explosion Percentages * 42% 37% 21% 16%
Hydrogen incidents listed in “Control of Liquid Hydrogen Hazards at Experimental Facilities” by A A Weintraub.
Hydrogen Accidents - Industrial
Number of Percentage of TotalCategory Incidents Accidents
Undetected leaks 32 22Hydrogen-oxygen off-gassing explosions 25 17Piping and pressure vessel ruptures 21 14Inadequate inert gas purging 12 8Vent and exhaust system incidents 10 7Hydrogen-chlorine incidents 10 7Others 35 25
Total 145 100
Source: Safety Standard for Hydrogen and Hydrogen Systems, NASA NSS 1740.16, p.A-109
Design Philosophy
We have three absorbers and have three independent hydrogen systems, this is to:
•Avoid consequential failures – a failure or fault in one is easier to deal with than a fault on a large system
•This will ease the staging for MICE as only one absorber is required early on
•Smaller systems are easier to work on
Design Philosophy
Other considerations:
Minimise venting – many accidents are caused during this process
MICE has to be flexible – there will be many filling cycles of the absorbers and we want to minimise the amount of hydrogen that we have – hence the use of a hydride bed
Control system automates the filling, emptying and purging system (many accidents from ineffective purging)
Must be safe in the event of a power loss or system shut-down (looking at default valve positions)
No surfaces below the BPt of Oxygen – this is to prevent cryopumping of oxygen on any surface that may come into contact with hydrogen in the event of a failure
Safety volumes to contain gas, relief valves to prevent back flow in case of catastrophic release
RAL Codes
Hydrogen zones definition according to RAL Safety Code No.1:
Zone 0: An area or enclosed space within which any flammable or explosive substance, whether gas, vapour, or volatile liquid, is continuously present in concentrations within the lower and upper limits of flammability.
Zone 1: An area within which any flammable or explosive substance, whether gas, vapour, or volatile liquid is processed, handled or stored and where during normal operations an explosive or ignitable concentration is likely to occur in sufficient quantity to produce a hazard.
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.
Intention is to have no Zone 0 or 1 regions in the design
System Overview
•Gas Delivery System
•Hydride bed for gas storage
•Control Valves, pumps, alarms and indicators
•Buffer volume
•Control System
•Controllers
•Interface to the rest of MICE
•Test Cryostat
•Cryocooler
•Instrumentation
•Hydrogen volume
Window rupture
Must be safe in the event of a window rupture:
•Introduction of a buffer vessel limits pressure excursions
•Pipework sized to accommodate gas release
•Assumes mixing of gas - cold from absorber + buffer volume
•Temp in buffer calc on basis of constant Cv - this is optimistic for Tgas ~50K but pretty good for Tgas >100K
•For large outflow through relief valve the algorithm is not correct because the valve essentially shuts
•Buffer volume gives a huge safety margin over just the pipe system with vol ~ 0.1m^3 for 50m of 50mm dia pipe
•The buffer vessel will keep the gas warmer due to its thermal mass - this is not included - it will increase the pressure rise
•Typically with 1m^3 Tgas ~100K pressure rise rate is 0.1 bar/sec valve opening time of 0.1-0.2 sec would be OK
Expected boil-off rate
Latent heat 446000 J/kg
Power into liquid 10179 W
Hydrogen boiled off (kg/s) 0.022823 kg/s
Start mass of liquid 1.544 kg
Liquid density 70.288
Start pressure (bar) 0.5 or 1
Rgas 4157
dt 0.2
Buffer vol 1 m^3
density 300K 0.08 kg/m^3
relief valve pressure 1.60E+05 Pa
outlet mass flow 1.20E-02 kg/s
Buffer vol pressure rise
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 5 10 15 20
time secs
pre
ssu
re P
a
0
50
100
150
200
250
300
350
tem
per
atu
re
Effectiveness of Buffer Volume
What is temperature of Outer Window ?
Thermal balance between radiation [to inner window at 18K] and conduction to 300K
Particular concern is that the centre of the outer window will fall below condensation point of Oxygen
Pipe sizes
Diameter (cm) 30
Area (cm2)706.858
3471
x2 1413.71
6694
Specific load (W/cm2) 3.6
Load (W)5089.38
0
Safety factor x2 (W)
10178.7602
Latent heat (J/g) 446
Hydrogen boiled off (g/s) 22.822
Vel sound 1321.34 m/s
0
0.5
1
1.5
2
2.5
3
0.01 0.015 0.02 0.025 0.03 0.035
Pipe diameter m
Pre
ss
ure
dro
p B
ar
Gas at 300K
Choked flow RT
Gas at 40K
Estimates of pipe sizes required in the case of a catastrophic vessel rupture
Pipe transitions are inside vacuum space for venting
CERN measured worst case x2
Hydrogen Storage Trade-off
Options for hydrogen storage:
A) in a low pressure tank Pros: truly passive system Cons: - size (about 30 m3), 3 tanks are required; - dispersed system with long pipes => difficult to collect hydrogen in case of leak; - not feasible for neutrino factory (where to put them ?). B) in a metal hydride bed
Pros: - very compact system (<1 m3) => easier to collect hydrogen in case of leak; - hydrogen is stored as a solid compound; - more feasible for neutrino factory. Cons: not a passive system => requires active heater/cooler.
Cryocooler
0
0.5
1
1.5
2
2.5
13 14 15 16 17 18 19 20 21 22 23
Temperature K
Pre
ssu
re A
tm
Maintaining a positive pressure
Cryocooler operation will keep temperature in range 14-20K
Helium gas will be introduced to keep pressure in system positive
The use of helium to maintain a positive pressure needs thought as it will be added after the hydrogen has condensed
Summary
The hydrogen system is being developed through an R&D process
Many aspects of the safety have been considered through calculation, design and review
We have a well defined safety review process
The design is well advanced and will be detailed in the following talks
MICE Hydrogen System
END