JAERI-Conf 96-010

6.6 Design and Fabrication of He-He

Intermediate Heat Exchanger for HTTR

Hajime KOIKEGAHI

Ishikawajima-Harima Heavy Industries Company, Ltd.

JAPAN

Shigeki MARUYAUA

Toshiba Corporation

JAPAN

Kazuhiko KUNITOMI, Hinoru OHKUBO

Japan Atomic Energy Research Institute

JAPAN

The High Temperature Engineering Test Reactor (HTTR) being constructed

by JAERI has a helium-helium intermediate heat exchanger (IHX) with

approximately lOMff thermal rating in a primary cooling system.

The IHX is a vertical helically coil counter flow type heat exchanger

operated at a very high temperature above 900°C. It transports the nuclear

heat energy of primary helium gas to secondary helium gas, which is to be

used in heat utilization system in future. The IHX has to meet the

requirement on structural integrity as class 1 component for nuclear use

during the service life, so it is one of the most important component in

HTTR. As a member of the HTTR project, TOSHIBA/IHI has been responsible for

the IHX. Our scope covers the design, fabrication, inspection and testing,

installation, quality assurance, research and development.

The helical coil tube bundle is composed of 96 heat transfer tubes with

six layers of helical coils. The outer diameter and thickness of the heat

transfer tube are 31.8mm and 3.5mm respectively. Heat transfer tube material

is Ni-base superalloy Hastelloy XR with high resistance for high temperature

and corrosion in helium atmosphere. In case of internal structures, such as

the heat transfer tubes, it is difficult to meet the elevated temperature

structural design criteria based on the simplified elastic analysis,

especially the creep damage criteria and the limitation of the accumulated

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inelastic strain. So their structural integrity have been evaluated by

inelastic creep analysis approach.

To increase the heat transfer by radiation, the radiation plates are

installed between the helical coil tube layers. The formulas of heat

transfer coefficient include the effects of the tube arrangement and

geometry, such as eccentricity, inclination, flatness, and effect of

radiation plates.

The outer diameter and total height of the outer shell is approximately

2.0m and 10.0m respectively. Inner surface of the inner shell is covered

with thermal insulation to maintain the metal temperature of the inner shell

at the lower level. Material of the inner shell and the outer shell is

commercial low alloy steel, that is 2• l/4Cr-lHo steel. Total weight of the

IHX is 65,OOOkgf.

In order to fabricate the reliable IHX, research and development has

been performed. Main items are as follows:

(l)Making a reliable thick welded joint of Hastelloy XR and developing a

reliable tube-to-tube automatic welder.

(2)Haking a precise helical coil to keep the tolerance of the tube bundle

and assembling the six layers of the helical coil tube bundle precisely.

To assure the integrity of the IHX for nuclear use, very severe inspec-

tions and testings, such as radiographic test, ultrasonic test, creep

rupture test, pneumatic test, helium leak test, are required.

Fabrication of the IHX was successfully completed in September 1994,

and the IHX was installed in the containment vessel in the reactor building

in February 1995.

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JAERI-Conf 96-010

Design and Fabrication of He-He

Intermediate Heat Exchanger for HTTR

H a j i m e KOIKEGAHI

Ishikawajima-Harima Heavy Industries Company, Ltd.

JAPAN

Shigeki UARUYAMA

Toshiba Corporation

JAPAN

Kazuhiko KUNITOHI, Uinoru OHKUBO

Japan Atonic Energy Research Institute

JAPAN

ABSTRACT

The High Temperature Engineering Test Reactor (HTTR) being constructed

by JAERI has a helium-helium intermediate heat exchanger (IHX) with

approximately 1OUW heat capacity in a primary cooling system.

The IHX is a vertical helical coil counter flow type heat exchanger

operated at a very high temperature above 900 °C. It transports the nuclear

heat energy of primary helium gas to secondary helium gas, which is to be

used in heat utilization system in future. The 1HX has to meet the

requirement on structural integrity as class 1 component for nuclear use

during the service life, so it is one of the most important component in

HTTR. As a member of the HTTR project, TOSHIBA and IHI has been responsible

for the IHX. Our scope covers the design, fabrication, inspection and

testing, installation, quality assurance, research and development.

The detailed design and construction method of the IHX were approved

by the government in April 1992. Fabrication of the IHX was started in July

1992, and was successfully completed in September 1994. The IHX was

transported from works to HTTR site and was installed in the containment

vessel in the reactor building in February 1995.

This paper describes the design and fabrication of the IHX.

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JAERl-Conf 96-010

1.Introduction

The HTTR is a helium-cooled and graphite-moderated reactor with outlet

coolant temperature of 950*0 and thermal output of 3011?. It is being

constructed at Oarai Research Establishment in Japan Atomic Energy Research

Institute (JAERI). As a member of the HTTR project, TOSHIBA and IHI has

been responsible for the IHX. Our scope covers the design, fabrication,

inspection and testing, installation, quality assurance, research and

development of it.

The detailed design and construction method of the IHX were approved

by the government in April 1992. Fabrication of the IHX was started in July

1992, and was successfully completed in September 1994. The IHX was

transported from works to HTTR site and was installed in the containment

vessel in the reactor building in February 1995. The design and construc-

tion schedule of IHX is shown in Table 1.

From 1973 to 1980, the research and development of direct steelmaking

using high temperature reducing gas, which was taken up as a large-scale

national project by the Agency of Industrial Science and Technology of the

Ministry of International Trade and Industry (MITI), was performed by the

Engineering Research Association of Nuclear Steel-making (ERANS).

As one member of ERANS, IHI was engaged in the research and develop-

ment of 1.5HW He-He IHX. In this project, IHI designed and fabricated the

IHX. Moreover, the IHX was operated in the high temperature helium test

loop over 5000h.

The experiences obtained from this previous project are effectively

utilized for the HTTR project, and contribute to the design and fabrication

of the IHX for HTTR.

2.Outline of IHX

The IHX is employed under extremely severe conditions with the primary

helium temperature of 950*C and pressure of 4.lMPa(gauge), secondary helium

temperature of maximum 905°C and pressure of 4.2MPa(gauge). It transports

the nuclear heat energy of primary helium gas to secondary helium gas.

which is to be used in heat utilization system in future. The IHX has to

meet the requirement on structural integrity as class 1 component for

nuclear use during the service life, so it is one of the most important

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components in HTTR. The basic design condition of the IHX is shown in Table 2.

The configuration and the principal specification of the IHX are shown in

Fig. 1 and Table 3 respectively.

The IHX is a vertical helical coil counter flow type heat exchanger

with approximately 1 OilW heat capacity. The design pressure of the outer

shell is 4.7MPa[gauge] and that of the heat transfer tubes is 0.29MPa. The

design temperature of the outer shell is 430 °C and that of the heat

transfer tubes is 955^.

There are two ways of operation. One is the rating operation mode and

the other is the high temperature operation mode. In case of the high

temperature operation mode, the primary inlet helium temperature is 950 *C

and maximum of the secondary outlet helium temperature is 905^.

The primary helium gas at 950X1 enters at the inlet nozzle located at

the bottom center of the vessel and flows upwards through the outer of

helical coil tube bundles. After transferring heat to secondary helium, the

primary helium is led into the primary circulator and flows down the outer

annular flow path provided between the inner shell and the outer shell in

order to cool the outer shell of pressure boundary.

On the other hand, the secondary helium gas at 300 °C separates at

tubesheet located at the upper part of the vessel and flows into the heat

transfer tubes. It is heated up to maximum 905^ by the primary helium and

collected into the hot manifold header. Then the heated secondary helium

flows upwards inside the central hot gas duct in the center pipe.

3.Design of IHX

Concerning the thermal and hydraulic performance of the IHX, we

adopted the formulas obtained from our previous work of the large-scale

national project performed in 1973-1980. The formulas of heat transfer

coefficient include the effects of the tube arrangement and geometry, such

as eccentricity, inclination, flatness, and effect of radiation plates.

The overall structure of the IHX was designed to form the axial sym-

metrical arrangement in order to decrease the thermal stress and keep the

thermal expansion uniformly. In designing the IHX, careful studies for the

thermal stress and thermal expansion had been made for each part of

structure exposed high temperature and many of experiences obtained from

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the previous project had been employed.

The helical coil tube bundle is composed of 96 heat transfer tubes

with six layers of helical coils. Maximum coil diameter is 1310mm and

effective height of coils is 4870mm. The outer diameter and thickness of

the heat transfer tube are 31.8mm and 3.5mm respectively. To determine the

tube thickness, the differential pressure between the primary helium and

the secondary helium was adopted. The pressure of the secondary helium is

controlled a little higher than that of the primary helium in order to

prevent the fission products from releasing to the secondary helium

boundary.

The heat transfer tubes are supported by the tube support assemblies

and the center pipe is hung with the tube support assemblies for the

purpose of decreasing the thermal expansion difference between the center

pipe and the tubes. The helical coil tubes are connected with the hot

manifold header and the cold tubesheets by the lower and upper connecting

tubes. Material of the heat transfer tubes, the hot manifold header and the

cold tubesheets is Ni-base superalloy Hastelloy XR with high resistance for

high temperature and corrosion in helium atmosphere, which is developed by

JAERI. The geometry of lower connecting tubes and hot manifold header is

shown in Fig. 2

To increase the heat transfer by radiation, the radiation plates,

which are thin curved plates, are installed between the helical coil tube

layers. Moreover these radiation plates inserted between the layers of

helical coil tube bundle are also effective on restraining the flow induced

vibrations of the heat transfer tubes.

To evaluate the structural integrity of the HTTR components, including

the IHX. "Elevated Temperature Structural Design Guide for the HTTR

components (HTTR ETSDG)' was prepared by JAERI. HTTR ETSDG is composed of

the simplified elastic analysis approach and the inelastic analysis

approach.

In case of internal structures, such as the heat transfer tubes and

the hot manifold header, the metal temperature is over 900 *€ during the

steady state operation. Though the primary stresses are limited within the

lower level, it is difficult to meet the elevated temperature structural

design criteria based on the simplified elastic analysis approach,

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JAERI-Conf 96-010

especially the creep damage criteria and the limitation of the accumulated

inelastic strain. To estimate the creep damage and the creep strain

reasonably, more detailed creep analysis approach, which includes the

stress relaxation and effects of load histories, have been performed.

The example of creep analysis results of the hot manifold header is

shown in Fig. 3 and Fig. 4. The analytical model of the hot manifold header

is shown in Fig. 3 and Fig. 4 shows the equivalent creep strain versus time.

Creep strains at evaluation point increase in the first thermal load cycle

and the increment of creep strain are limited small in the second or third

thermal load cycle.

The outer diameter and total height of the outer shell is approxi-

mately 2.0m and 10.0m respectively. Inner surface of the inner shell is

covered with thermal insulation to maintain the metal temperature of the

inner shell at the lower level. Material of the inner shell and the outer

shell is commercial low alloy steel, that is 2*l/4Cr-lHo steel.

4.Fabrication of IHX

The fabrication sequence of IHX is shown in Fig.5. Four parts of IHX,

tube bundle, center pipe with thermal insulation, outer shell and inr<er

shell, were fabricated in parallel and were assembled in order.

To fabricate the reliable IHX, many of technical investigations and

preparations were conducted. Development of the IHX manufacturing process

is shown in Table 4. The major investigations are as follows:

(1) Establishing a reliable thick welded joint of Hastelloy XR with high

resistance for cracking and high temperature creep strength same as the

base metal.

(2) Developing a reliable tube-to-tube automatic welder at narrow space.

(3) Developing a precise helical coil bending method to keep the tolerance

of the tube bundle.

(4) Establishing a reliable assembling process of six layers of the helical

coil tube bundle precisely.

(5) Establishing a reliable assembling process and examination method of

thermal insulation structure.

To make the reliable thick welded joint of Hastelloy XR with not only

low cracking susceptibility but also high creep strength similar to the

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JAERI-Conf 96-010

base metal, IHI cooperated with JAERI in the development of the filler

metal. On the other hand, we investigated the best welding method and

condition for thick welded joint and the narrow-gap TIG welding procedure

was established.

The weldments of tube-to-tube joints at narrow space were performed by

the automatic orbital-bore-welder and the weldments of tube-to-manifold

joints and the curved connecting tube weldments were performed by manual

TIG welding method. Tube-to-tubesheet welded joints were welded by the

automatic internal-bore-welder. The automatic welders were newly developed

for the fabrication of the IHX. Appearance of automatic TIG welding of

tube-to-tube is shown in Fig.6.

The heat transfer tubes were helically coiled by the coil bender and

the bending conditions were examined by trial fabrication of a mock-up. To

assemble the six layers of the helical coil tube bundle, helical coils are

required the high precision. They are constrained by the forking implements.

Fig.7 shows the helical coil tube bundle of third and fourth layer.

The tube bundle was assembled in vertical position. The completed ap-

pearance of tube bundles is shown in Fig.8 and Fig.9.

Though the hot manifold header and the cold tubesheets had a compli-

cated geometry, they were machined from Hastelloy XR forging by the

numerical controlled machining center. Fig.10 shows the appearance of the

machined hot manifold header.

The thermal insulation structure of inner shell is composed of thermal

insulation and inner liner. Thermal insulation was installed inside of

inner shell. To absorb the thermal expansion, inner liner is separated five

parts of vertical direction and six parts of circumferential direction. The

space between tube bundles and thermal insulation structure of inner shell

was controlled precisely. Fig.11 shows the appearance of thermal insulation

structure inside of the inner shell.

The outer shell, inner shell, top head and bottom head were cold

rolled or hot pressed, then assembled as the welding structures. Concerning

the low alloy steel weldments, pre-heating and post weld heat treatment

were done for stress relief of the welded joints.

To assure the integrity of the IHX for nuclear use, very severe in-

spections and testings are required. For example, radiographic test,

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ultrasonic test, liquid penetrant test, magnetic particle test for base

metal and welded joint, creep rupture test for Hastelloy XR material,

fracture toughness test for reactor pressure boundary material, hydrostatic

test, pneumatic test, helium lesk test for pressure boundary.

The completed appearance of the IHX waiting for shipping is shown in

Fig. 12 and Fig. 13 shows the installation of the IHX in the reactor building.

5. Conclusions

(1) The IHX, which is one of the most important component in HTTR. was

successfully constructed in January 1995.

(2) To increase the heat transfer, the radiation plates, which are also

effective on restraining the flow induced vibration, were installed between

the helical coil tube layers.

(3) To evaluate the structural integrity of the IHX, detailed creep

analysis was performed and creep strain and creep damage were estimated

reasonably.

(4) To fabricate the reliable IHX, many of technical investigations were

conducted and manufacturing process of the IHX was developed.

6.Acknowledgments

The design and fabrication of IHX for HTTR was conducted by TOSHIBA

and IHI under contract with JAERI as a member of HTTR project. Permission

to publish this work is gratefully acknowledged. The authors would like to

take this opportunity to thank the members of the technical staff of JAERI.

7.References

(1) S. saito, Present Status of HTTR Project and Associated International

Cooperation, The 2nd JAERI Symposium on HTGR Technologies, Oct. 21-23(1992)

(2) JAERI, Proceedings of Third JAERI Seminar on HTGR Technologies, Nov. 7-

8(1994). JAERI-Conf 95-009, (1995.3)

(3) K. Kunitomi, H.Koikegami et al., Structural Design for an Intermediate

Heat Exchanger of the HTTR, J. At. Energy Soc. Japan, Vol.37, No. 4, pp. 316-

326, (1995.4)

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Table 1 IHX construction schedule

YEAR

HTTRMILESTONE

Approval of design andconstruction method

Design

Production ofmaterial

Fabrication

Installation

1991

ConstructStart

V

C

C

1992

n

3

i

1993 1994

RPVONV

|

C

1995

3

1996

PressureTestV

T a b l e 2 I H X b a s i c d e s i g n c o n d i t i o n

Number of unit

Heat capacity

Design pressureOuter she 11Heat transfer tube

Design temperatureOuter shelIHeat transfer tube

Operating condition

F lu idPrimarySecondary

Flow ratePrimarySecondary

PressurePrimarySecondary

TemperaturePrimary

I n l e tOutlet

SecondaryIn letOutlet

1

10MW

4.7HPa[gauge](

Ratingoperation

Helium gasHe I i urn gas

Max. 15ton/hMax. Hton/h

<i.1MPa[gauge]4.2MPa[gauge]

85OtJ390t;

300°C

775-C

).29HPa

43O°C9 5 5 ^

High temperatureoperation

Helium gasHelium gas

Max. 12ton/hMax. 12ton/h

4. 1MPa[gauge]4.2HPa[gauge]

95O°C39OT3

300°C860°C

(Max. 905°C)

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T a b l e 3 IHX p r i n c i p a l s p e c i f i c a t i o n

Type

Number of unit

Heat capacity

Design temperature(Heat transfer tube)

Heat transfer tubeOuter diameterThicknessMaterialNumberPitchNumber of coil layers

Radiation plateThicknessMaterial

ShellMaterialOuter diameterHeight

Helical coil counter flow

1

10MW

955°C

31.8mm3. 5mm

Haste H o y XR96

47mm6

5 mmHastelloy XR

2-1/4Cr-1MoApprox. 2.0mApprox. 10.0m

Table 4 Development of IHX manufacturing process

ITEMS

Reliable welded joint ofHastelloy XR

Reliable automatic welderat narrow space

Preci se helical coi1 tubebundles

Reliable thermal insulationsystem

CONTENTS

(1) Development of filler metal with highcreep strength

(2) Accumulation of creep test data on weldedjoint

(3) Establishment of reliable high efficientwelding process

(1) Development of automatic orbital-bore-welder for tubs-to-tube welding

(2) Development of automatic internal-bore-welder for tube-to-tubesheet welding

(1) Design of reliable tube support structure(2) Development of helical coil tube bender(3) Establishment of assembling process to

make the precise tube bundles

(1) Design of reliable thermal insulationstructure

(2) Establishment of assembling process toinstall thermal insulation

(3) Establishment of examination method ofthermal insulation structure

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Secondary HeliumOutlet n

\J Secondary Helium Me!

Hattrlali Haitelloyalloy XR

Primary HeliumOuilo!

Center Pipe

'rimary HeliumInlet IromCirculator

Inner Shell

Outer Shell

Helically CoiledTube Bundle

Hot Manifold Header

Primary Helium Outlet

Primary HeliumInlet

Fig. 1 Conf igurat ion of IHX

10.0

0 . 0 "

VTube n n Tha rma1< * 3 1 . a 0 - 0 > x 3 . 5 ) l n i u l o t i o n

Fig.2 Geometry ofhot manifold header

Point 1 (Inner)

\

A

( 3 r d c y c l t ) /

Point 1 (Outer)

200 400

Time (h)

600 800

F i g . 4 Example of creep analysis results

of hot manifold header

Fig.3 Analytical model of

hot manifold header

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Heal ltans(6f lube(Haslelloy XR)

Helical coil Tube bundle

Secondary inlet nozils(2'/4Cf iMo)

Tubesheet / Upper connecting lubes(Haslelloy XR) (Haslelloy XR)

Top head

Outer shell(2V»CiiMo)

Ouler shell (Hydroslsiic lesi)

Inner shell(2 VI C M Mo)

\

Tube bundles (completed)

Fig.5 Fabrication sequence of IHX

IHX (completed)

|] Jf Ouler shell / Inner shell

Fig.6 Automatic TIG welding of tube-to-tube

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F i g . 7 H e l i c a l c o i l t u b e b u n d l e

i i ^ B l L 1 ^ ^ ^ ^ ^ ^

F i g . 8 T u b e b u n d l e s ( G e n e r a l v i e w )

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Fig.9 Tube bundles (Lower connecting tubes)

Fig.10 Machined hot manifold header

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F i g . 1 1 T h e r m a l i n s u l a t i o n i n s i d e o f i n n e r s h e l l

F i g . 1 2 G e n e r a l v i e w o f I H X ( C o m p l e t e d )

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F i g . 1 3 I n s t a l l a t i o n o f I H X

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