0

5

10

15

20

0 5 10 15 20

Heli

um

In

ven

tory [

kg

]

Time [min]

Process Pipe (Liquid ) [kg]

Process Pipe (Vapour ) [kg]

Annular Space (Vapour) [kg]

Investigation of Thermal Equilibrium Around an Accidental Event And Impact on

Possibly Enclosed Surrounding Environment

Problem Definition

Sarkar Biswanath, Shah Nitin, Choukekar Ketan, Kapoor Himanshu, Kumar Uday, Das Jotirmoy, Bhattacharya Ritendra, Vaghela Hitensinh, Muralidhara Srinivasa

ITER-India, Institute for Plasma Research, Gandhinagar and 382016, India

Accidental scenario of

cryogenic transfer line

(major seismic activity or

any unprecedented

mechanical events)

Process failure

(loss of insulation vacuum)

Physical failure

(Rupture of Process pipe and OVJ)

Change in temperature

& pressure of surrounding

enclosed volume

Assumptions and Modelling

Process Pipe

Process Pipe

Cold He

(5 bar, 5 K)

Annular space

Mixture

of Dry air

+ Cold

Helium

Qconv1

Qrad1 Cold He

Enclosed Volume

Qconv2

Qrad2

Outer Vacuum

Jacket

Results from ASPEN HYSYS® modelling

Further attention to safety

Preliminary test proposal

Development of detailed model in ASPEN HYSYS®

Process

pipe Crack as a pipe

Annular

Space

Enclosed

Volume Relief valve

Qconv2 Qrad2 Qconv1 Qrad1

1.0

2.0

3.0

4.0

5.0

0 5 10 15 20

Press

ure [

ba

r(a

)]

Time [min]

Process Pipe [bar(a)]

Annular Space [bar(a)]

Enclosed Volume [bar(a)]

• Cold helium / liquid nitrogen cryogenic

transfer line is enclosed inside duct

made of concrete sheet with normal leak

tight sealing.

• Control valves for simulating leak

through process pipe and OVJ.

• Mass flow meters for measuring the

amount of helium entering into OVJ and

further to Enclosed Volume (EV).

• The facility of ventilation for relieving

the pressure inside EV will be provided.

• Quantifying an accidental event requires near reality assumptions. It is to be

understood that the accidental events are the driving factor for ascertaining

the safety of the designed system.

• The minimum design temperature of surrounding components and systems

should be decided based on minimum temperature possible in such

enclosed environment with a more realistic approach.

• The impact on process pipe and OVJ due to stored energy of gaseous

helium in OVJ annular space and mixture (air + helium) in EV respectively

should be considered, as it will act similar to a pneumatic testing of a vessel

with a leak.

References 1. Chorowski M. et. Al, Risk analysis update of the LHC cryogenic system following the 19th September 2008 incident, Proceedings of ICEC-23/

ICMC 2010, pp 879-884

2. Barron R. F. , Cryogenic Heat transfer, 1999, , ISBN-1-56032-551-8

3. Holman J. P., Heat Transfer

Validation of Average Temperatures using ANSYS Fluent ®

t = 0 seconds t = 5 seconds t = 10 seconds t = 15 seconds t = 20 seconds t = 29 seconds t = 1 seconds t = 2 seconds t = 25 seconds

A: 300 K

H: 300 K

A: 291 K

H: 289 K A: 279 K

H: 278 K

A: 259 K

H: 257 K

A: 242 K

H: 233 K

A: 236 K

H: 223 K

A: 233 K

H: 220 K

A: 229 K

H: 216 K

A: 226 K

H: 214 K

A: Global average temperature from ANSYS Fluent ®

H: Global average temperature from ASPEN HYSYS®

Pressure after 18.5

min 3.86 bar [a]

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50 60

Ma

ss f

low

[k

g/s

]

Time [s]

Process Pipe outflow [kg/s]

Annular space outflow [kg/s]

High initial mass flows due

to large differential pressure

~ 202 K

Temperature equalization

at ~ 282 K at 18.5 min

.

..

....

mixp

Theliumpairp

mixcm

QTcmTcmT

heliumair

airair

mm

mx

.. radconvT QQQ

Validation using

analytical modeling

• Smooth crack having equivalent circular cross

section of 10 mm diameter across the thickness of

process pipe

• Discharge area of rupture disc on OVJ is ~ 507

sq.mm

• Enclosed Volume (EV) is occupied with stagnant

dry air at 300 K and 1 bar(a).

• EV is fairly tight for helium, air or mixture of

helium with air (worst case scenario) for exhaust

• Heat transfer through conduction mode has been

neglected

• The concrete wall of EV has been considered at

300K

• Uniform thermal mixing has been assumed

• Stratification of the flows is not considered, as

vertical column of stagnant dry air is considered

in EV [2]

Process parameters at t = 18.5 min (t = 0:

considered to be the rupture of process pipe)

Process

Parameters

Process

Pipe

Annular

space EV

Pressure

bar (a) 3.86 3.86 3.86

Temperature

(K) 282 282.2 283.1

Composition Helium Helium Air (x=0.71) +

Helium (x=0.29)

Pressure Profile for first 60 s

• High helium inventory is normally expected in Cryogenic

Transfer Lines (CTL) during operation of fusion machine.

• In an accidental scenario, the possibility of cold helium

release is evident due to complete breakage of process pipe

and Outer Vacuum Jacket (OVJ)

• The present study aims to estimate the lowest possible

temperature and change in pressure in the surrounding

environment due to the possible accidental scenario,

especially in a closed volume.

The parameters of helium mass flow from OVJ to EV are varied as a function of time.

The same temperature of mass flow is assigned for the entire length of the OVJ, for successive time steps.

Realizable k-epsilon viscous model was employed with enhanced wall treatment.

Temperature , Mass flow from OVJ

to EV at opening of rupture disc

Pressure Profile

Temperature profile

Helium Inventory

Mass flows for first 60s

The lowest temperature has been observed to be function of (i) cold helium inventory, (ii) size of opening in process pipe, (iii) discharge area of safety rupture

disc of OVJ, (iv) size of the surrounding duct or mass of surrounding air.

Unstable flows,

Higher heat loads

LIQUID HELIUM /

NITROGEN SOURCE

T

WARM HELIUM OR

NITROGEN GAS

T

T

T

T

RECOVERY SYSTEM/

VENT

T TT

V

V

V

P F

P F

ENCLOSED VOLUME

PROCESS PIPEOVJ

T

THERMAL IMAGING SYSTEM

P: Pressure Transmitter

T: Temperature Transmitter

F: Flow Transmitter

V: Valve

Conclusion • EV’s pressurization profile demands detailed experimental investigation,

considering the most severe case of accidental scenarios based on, (i) maximum

cold helium inventory, (ii) size of EV and (iii) ventilation requirements, which has to

be considered while designing the subsystems of large fusion reactor related

devices.

• For the purpose of investment protection, the outer vacuum jacket needs to be

designed for internal pressure and with the careful design of rupture disc

considering the maximum inventories in the process pipe.

• Ventilation systems have to be designed considering the possible pressurization of

the enclosed volume.