Design of ITER thermal shield cooling network considering flow distribution and thermal load Kwanwoo Nam1 , Youn-Kyu Kim2, Wooho Chung1, Craig Hamlyn-Harris3, Namil Her3

1. ITER Korea, National Fusion Research Institute, Daejeon 305-333, Republic of Korea 2. Mecha T&S, Jinju 660-808, Republic of Korea 3. ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France

ICEC25 July 7~11, 2014, Enschede, Netherlands

Abstract Thermal Shield (TS) in the ITER tokamak cuts off the radiation heat load from the vacuum vessel/cryostat transferring to the magnets operating at 4.5 K. The TS will be cooled down by 80 K helium gas supplied from cryoplant. The helium goes through the cooling tubes attached on the TS. The TS consists of a lot of panels, which are to be connected by bolted joints. The panels have their own cooling tube routings and they are connected to the end of cryo-distribution lines by manifold piping. As the composed piping for the TS cooling is complex, the flow distribution is one of the major concerns for the design of TS cooling network. This paper describes the design of TS cooling tube and manifold, taking the flow distribution and the thermal load into account. The TS hydraulic network was modeled in details by a dedicated program. Frictional pressure drop in the pipes and local losses at all piping components in the TS were considered in the model. It was found that coolant flow rates in some panels were insufficient compared with its design values. Orifice installation was proposed in order to improve the flow distribution in the cooling tubes. Thermal analysis was also performed for the manifold feeder and ring, the surfaces of which are exposed to the warm surface. The helium temperature rise through the manifold feeder and ring due to incident radiation was obtained and its effect on the radiation shielding performance of the TS was evaluated.

1. Introduction

Acknowledgement: This work is supported by Ministry of Science, ICT and Future Planning of Republic of Korea under an ITER Project Contract.

The TS specifications

Main material : SS304LN

Panel thickness : 10 mm, 20 mm

Emissivity : < 0.05 (silver coated)

Helium coolant : 80 ~ 100 K, 1.8 MPa

Cooling tube: 13.72 OD, 2.24t, welded on the panel

The ITER Thermal Shield (TS) is to be located between the vacuum vessel/the cryostat and the magnet for minimizing radiation heat load for the successful operation of the magnet.

Cooling network

The TS manifolds (TSM) connect all the cooling tubes in the TS panels to the cold valve box (CVB).

The TSM consists of rings (circular pipe adjacent to the CTS body) and feeders (straight pipe which connects the ring to the CVB).

The ring and the feeder are attached on the CTS and the cryostat by supports.

The sizes of the ring and the feeder: DN65, DN50

3. Flow Analysis Method

The cooling network consists of 8 sub-circuits; each sub-circuit has cooling tubes in parallel connection.

The TS cooling tube network has 100% redundancy; all the active (operating) cooling tube has identical one for redundant purpose in the case of accident in the operating tubes.

Each sub-circuit has its control valve; the flow rate in each circuit can be regulated by the control valve.

Introduction

The flow analysis for the TS cooling network was performed using AFT FathomTM.

Fathom is a graphical platform for modeling incompressible flow in pipe networks.

Temperature of helium is assumed as constant in the cooling network.

The sub-circuits are independent each other, hence analyzed separately. The control valve in the CVB is not included in the model. Total flow rate is assigned to the sub-circuit as a input.

TSM #1

Bernoulli equation neglecting potential energy

Theory

Energy conservation in piping

Pressure drops

- Pipe

- Elbow and tee branch: data from Crane (1988)*, Idelchik (1994)*

- Orifice

lPghvPghvP 22221

211

2

1

2

1

2

2

1v

D

LfPl

2

2

1vKPl

* Ref: AFT Fathom 7.0 Users Guide

vDRe

Modeling in Fathom

Properties

Helium density: 9.3574 kg/m3, viscosity: 9.3789 μPa-s (@ 1.8 MPa, 90 K)

Pipe roughness (ε) = 1.54 µm

4. Flow distribution results

lower VVTS (TSM #6)

Lower VVTS manifold (TSM #6) and lower ECTS manifold (TSM #5) are presented as typical cases. Orifices are installed at the tube routing where the flow rate is larger than the design value.

VVTS cooling tube CTS cooling tube

ITER thermal shield

TS manifolds

TS flow diagram

Simplification of bend modeling

Many bends in the real tube routing

The tube routing is simplified as the tube with single equivalent bend.

K of the single bend is calculated by the summation of those of all bends.

Design flow rate for the TS panel = Incident radiation divided by helium enthalpy change between inlet and outlet

Analyzed flow rate through the TS panel should be as close to its design flow rate as possible. Pressure drop shall be lower than 100 kPa. Maximum temperature of TS panel should be lower than 140 K (equivalent to ~ 1 W/m2 heat

load to magnet).

Design criteria

TC

Qm

p

rad

To improve the design of TS manifold by avoiding flow mal-distribution

To check the effect of flow distribution on the TS thermal characteristics

2. Objectives

Data from Idelchik (1994)* Sharp-edged orifice

2375.02

11707.0

p

orifice

p

orifice

orifice

p

orifice

5. Thermal effects

6. Conclusion

Effect of flow distribution on VVTS panel temperature

Design flow rate - Outboard upper: 4.69 g/s - Outboard lower: 6.54 g/s - Upper port: 5.79 g/s - EQ port: 4.64 g/s - Lower port: 5.09 g/s - He temp: inlet = 80 K, outlet = 100 K

Calculated flow rate (orifice installed) - Outboard upper: 4.69 g/s (not consider excessive flow) - Outboard lower: 5.6 g/s, He outlet temp = 103.4 K - Upper port: 5.0 g/s, He outlet temp = 103.2 K - EQ port: 4.64 g/s (not consider excessive flow) - Lower port: 5.09 g/s (not consider excessive flow)

Tmax= 115.1 K

Hot spot temperature is still below 140 K (design recommendation) in spite of local small flow.

Tmax= 116.7 K

Flow analysis model

CATIA model

A1

B C D

E

A2

- A1: lower ECTS ring + lower ECTS cylinder + side STS ring, A2: lower ECTS ring + lower ECTS cylinder

- B,D: Irr. lower ECTS ring + lower ECTS cylinder, C,E: Irr. lower ECTS ring + lower ECTS cylinder + side STS ring

- ST: VVTS EQ regular port

Branch line

0

1

2

3

4

5

6

7

A2 A1 A2 A1 A2 A1 A2 A1 A2 A1 A2 A1 A2 E D C B A1

Calculatedflow rate(g/s)

Designflow rate(g/s)

0

1

2

3

4

5

ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST

Calculatedflow rate(g/s)

Designflow rate(g/s)

0

1

2

3

4

5

ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST

Calculatedflow rate(g/s)

Design flowrate (g/s)

0

1

2

3

4

5

6

7

A2 A1 A2 A1 A2 A1 A2 A1 A2 A1 A2 A1 A2 E D C B A1

Calculatedflow rate(g/s)

Design flowrate (g/s)

Reference Orifice*

Reference Orifice* △P = 24 kPa △P = 21 kPa

Lower ECTS ring + cyl + side STS

VVTS EQ port

*Location: A2 (9 ea), size: 3.2 mm

Branch line

Coolant temperature rise in the feeder and the ring - Feeder/ring outside the CTS are exposed to radiation from cryostat.

- Maximum length of ring: ~ 80 m (for the ECTS)

- Maximum length of feeder: ~ 36 m (for the lower CTS)

- Flow distribution result from the flow analysis was used for the

temperature calculation.

- Local heat load increase is acceptable because total heat load to

magnet has about 20% margin*.

Ring pipe outside CTS

ECTS manifold ring

80.3 K, End of feeder

80.0 K

End of ring, 82.3 K

Connected to the end of ring

Inlet/outlet temperature

Heat load (W)

Heat load increase (%) Max. temp.

ECTS 20O sector 80 K – 100 K (reference) 24.08 - 127.4 K 82 K – 102 K 25.56 6.2 128.9 K

1

111

cm

e

eeFwhere

)()( 44300ieioP

TAFTTCm

, A = πDL/2

em = 0.15 (manifold emissivity)

ec = 0.5 (cryostat emissivity)

Heat load to feeder/ring

CATIA model

sector-3

TYPE-A

TYPE-B

sector-2

sector-1

sector-4 sector-5

sector-6

sector-7

Feeder Collector

Feeder

ring

TYPE-A TYPE-B sector-3 sector-2 sector-1 sector-4 sector-5 sector-6 sector-7

Branch line

Flow analysis model

Result

lower ECTS (TSM #5)

2 6

5

8 4

1

3 9

7

10 11

0

1

2

3

4

5

6

7

8

Calculatedflow rate (g/s)

Design flowrate (g/s)

0

1

2

3

4

5

6

7

8

Calculatedflow rate(g/s)

Design flowrate (g/s)

Reference Orifice*

△P = 86 kPa △P = 78 kPa

*Location: S1, S7 (18 ea), size: 3.0 mm Flow distribution along 360 degree sector

Variation: ~ 3.94%

Branch line

A B S-3 S-2 S-1 S-4 S-5 S-6 S-7

1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11

Result

Effect of coolant temperature rise on the local heat load to magnet

Flow distribution in the ITER TS cooling network is simulated and its thermal effect is investigated. Orifice installation is proposed to improve the flow distribution. The flow balancing design by the orifice is satisfactory from the view point of the ITER TS thermal performance. The selected emissivity of manifold feeder and ring is acceptable due to moderate coolant temperature rise.

*K. Nam et al, Thermal analysis on detailed 3D models of ITER thermal shield, Fusion Eng Design, 2014, in press.