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