ABSTRACT PHE (Process Heat Exchanger) is a key component in transferring the high temperature heat generated from a VHTR (Very High Temperature Reactor) to the chemical reaction for massive production of hydrogen. A performance test on a small-scale PHE prototype made of Hastelloy-X is currently undergoing in a small-scale gas loop at the Korea Atomic Energy Research Institute. Previous researches on the high-temperature structural analysis of the small-scale PHE prototype had been performed using parent material properties over the whole region. In this study, high-temperature elastic structural analysis considering mechanical properties in the weld zone was performed and the analysis result was compared with previous researches

Hong-Yoon Park

Kee-Nam Song

Sung-Deok Hong

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Copyright © 2012 by ASME 
 
 
 
 
 
HIGH-TEMPERATURE STRUCTURAL ANALYSIS ON A SMALL-SCALE PHE 
PROTOTYPE CONSIDERING MECHANICAL PROPERTIES IN THE 
HEAT-AFFECTED ZONE AND IN THE WELD ZONE 
Kee-Nam Song                            Sung-Deok Hong 
Korea Atomic Energy Research Institute(KAERI)                     KAERI 
P.O.BOX 105 Yusong, Daejon, Rep. of KOREA 
Phone:82-42-868-2254, Fax: 82-42-868-2066 
knsong@kaeri.re.kr  
 
Hong-Yoon Park 
AD Solution 
#1101 Hanjin Officetel, 535-5 Bongmyoung-dong, Yuseong-gu, Daejon, Rep. of KOREA 
 
 
 
ABSTRACT  
PHE (Process Heat Exchanger) is a key component in 
transferring the high temperature heat generated from a 
VHTR (Very High Temperature Reactor) to the chemical 
reaction for massive production of hydrogen. A performance 
test on a small-scale PHE prototype made of Hastelloy-X is 
currently undergoing in a small-scale gas loop at the Korea 
Atomic Energy Research Institute. Previous researches on 
the high-temperature structural analysis of the small-scale 
PHE prototype had been performed using parent material 
properties over the whole region. In this study, 
high-temperature elastic structural analysis considering 
mechanical properties in the weld zone was performed and 
the analysis result was compared with previous researches. 
 
 
 
1.   INTRODUCTION  
Hydrogen is considered a promising future energy 
solution because it is clean, abundant, and storable, and has 
high-energy density. One of the major challenges in 
establishing a hydrogen economy is how to produce massive 
quantities of hydrogen in a clean, safe, and economical way. 
Among the various hydrogen production methods, nuclear 
hydrogen production is garnering worldwide attention since 
it can produce hydrogen, a promising energy carrier, without 
an environmental burden. Researches demonstrating the 
massive production of hydrogen using a VHTR (Very High 
Temperature Reactor) designed for operation at up to 950℃ 
have been actively carried out worldwide, including in the 
USA, Japan, France, and the Republic of Korea (ROK) 
[1,2,3]. 
The nuclear hydrogen program in the Republic of Korea 
(ROK) is strongly considering producing hydrogen by 
employing a Sulfur-Iodine (SI) water-splitting hydrogen 
production process. An intermediate loop that transports the 
nuclear heat to the hydrogen production process is 
necessitated for the nuclear hydrogen program as shown in 
Fig. 1. In the intermediate loop, whereas the HGD (Hot Gas 
Duct) provides a route of a high-temperature gas from the 
nuclear reactor to the IHX (Intermediate Heat Exchanger), 
the PHE (Process Heat Exchanger) is a component that 
utilizes the nuclear heat from the nuclear reactor to provide 
hydrogen. PHE is used in several processes such as nuclear 
steam reforming, nuclear methanol, nuclear steel, nuclear oil 
refinery, and nuclear steam [1]. PHE of the SO3 decomposer, 
which generates the process gas such as H2O, O2, SO2, and 
SO3 at a very high-temperature, is a key component in the 
nuclear hydrogen program in the ROK [2, 3]. 
Recently, KAERI (Korea Atomic Energy Research 
1
Proceedings of the 2012 20th International Conference on Nuclear Engineering 
collocated with the 
ASME 2012 Power Conference 
ICONE20-POWER2012 
July 30 - August 3, 2012, Anaheim, California, USA 
ICONE20-POWER2012-54184
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Institute) established a small-scale gas loop for the 
performance test of VHTR components and also 
manufactured a small-scale PHE prototype made of 
Hastelloy-X. A performance test on the PHE prototype is 
under way in the small-scale gas loop at KAERI as shown in 
Fig. 2. In order to evaluate the high-temperature structural 
integrity of the PHE prototype under the test condition of the 
gas loop, a series of structural analyses on the PHE 
prototype was carried out using parent material properties 
over the whole region [4,5,6,7]. In this study, 
high-temperature elastic structural analysis considering 
mechanical properties in the weld zone was performed and 
compared the results with previous researches. 
 
  
 
2.   FE MODELLING 
 
Structure of a PHE prototype 
A schematic view of the inside of the PHE prototype is 
illustrated in Fig. 3, and detailed shapes of the flow plates 
for the primary and secondary flows are shown in Fig. 4. 
The PHE prototype to be 3kW of heat transfer rate is 
designed as a hybrid concept [8] to meet the design pressure 
requirements between a nuclear system and hydrogen 
production system. That is to say, the hot nitrogen gas 
channel has a compact semicircular shape, similar to a 
printed circuit heat exchanger, and is designed to withstand 
the high pressure difference between loops, while the 
sulfuric acid gas channel has a plate fin shape with sufficient 
space to install and replace the catalysts for sulfur trioxide 
decomposition. 
All parts of the PHE prototype are made from Hastelloy-X 
of high-temperature alloy. Grooves of 1.0 mm in diameter 
are machined into the flow plate for the primary coolant 
(nitrogen gas). Waved channels are bent into the flow plate 
for the secondary coolant (SO3 gas). Twenty flow plates for 
the primary and secondary coolants are stacked in turn, and 
are bonded along the edge of the flow plate using a 
solid-state diffusion bonding method. After stacking and 
bonding the flow plates, the outside of the PHE is covered 
with the Hastelloy-X plate of 3.0 mm in thickness. A 
schematic view of the PHE prototype with attached pipelines 
is shown in Fig. 5. 
 
Fig. 1 Nuclear Hydrogen System 
 
Fig. 2 Small-Scale gas loop  
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Fig. 3 Inside of Process Heat Exchanger 
 
 
 
a)  primary flow plate     b) secondary flow plate 
Fig. 4 Flow plates. 
 
 
 
Fig. 5 Process Heat Exchanger Prototype 
 
 
FE modeling 
Figure 6 shows overall dimensions and each part of the 
PHE prototype from the 3-D CAD modeling. Based on Fig. 
6, FE modeling using I-DEAS/TMG Ver. 6.1 [9] was carried 
out and analyses such as a thermal analysis and structural 
analysis are carried out using ABAQUS Ver. 6.8 [10]. For 
the sake of simplicity and understanding the overall behavior 
of the PHE prototype, the FE model is composed of 546,764 
2-D linear quadrilateral shell elements and 911,012 3-D 
linear solid elements made of 830,304 brick elements, 
80,348 wedge elements, and 360 tetrahedron elements. 
 
 
 
Fig. 6 Parts of a PHE Prototype 
 
 
In the FE model the inflow/outflow of the primary and 
secondary coolants and the boundary conditions of the 
primary/secondary flow plates for a thermal analysis under a 
test condition of 850℃.were shown in Ref. [11]. 
Weld zones of the PHE prototype are modeled as shown 
in Fig. 7 where weld bead along the edges and heat affected 
zone (HAZ) are represented. The mechanical properties in 
the weld zone including a heat affected zone were obtained 
by the instrumented indentation method [12, 13].  
 
 
Fig. 7 FE model in the weld zone 
 
 
Pressure boundary condition for structural analysis 
According to the test condition of the small-scale gas 
loop, in/out-flow pressure for the primary and secondary 
coolant is 3.0MPa and 0.1MPa, respectively. 
 
 
 
3.  ANALYSIS 
 
Thermal analysis 
Figure 8 shows the thermal analysis results of the PHE 
prototype inside/outside under the fixed test condition of the 
small-scale gas loop. According to Fig. 8, the temperature 
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distribution is nearly symmetrical along the vertical axis and 
maximum temperature of the outside represents about 
837.15℃. 
 
 
Fig. 8 Temperature distribution of PHE outside 
 
 
 
Fig. 9 Displacement constraints for structural analysis 
 
 
High temperature elastic structural analysis using parent 
material properties 
Based on the thermal analysis result, a high temperature 
elastic structural analysis was performed imposing 
displacement constraint condition at each end of the 
primary/secondary flow pipelines as shown in Fig. 9, 
considering the pipeline stiffness of the small-scale gas loop 
[7]. Tables 1 and 2 represent the material properties of 
Hastelloy-X [14]. Figure 10 represents the stress distribution 
under temperature/pressure condition at the pressure 
boundary of the PHE prototype using parent material 
properties. The maximum local stress of 272.33 MPa around 
the edge between the top plate and side plate exceeds the 
yield stress of the parent material (239.7 MPa at 746℃) by 
13.6%. 
 
Table 1 Material properties of Hastelloy-X 
 
 
 
Table 2 Mechanical properties of Hastelloy-X 
 
 
 
 
Fig. 10 Stress contour using parent material properties 
 
 
High temperature elastic structural analysis using 
mechanical properties in the weld zone 
Table 3 represents the normalized mechanical properties 
of Hastelloy-X in the weld region obtained by instrumented 
indentation technique. The stress distribution under 
temperature/pressure condition at the pressure boundary of 
the PHE prototype using material properties in the weld 
zone is same as Fig. 10 because of using a same elastic 
modulus in elastic analysis. The maximum local stress of 
272.33 MPa around the edge between the top plate and side 
plate exceeds the yield stress of the weld material (269.5 
MPa at 746) only by 1.02%. From this analysis results, we 
found an interesting observation as follows. When we 
consider the mechanical properties in the weld zone, the 
degree of exceeding the yield stress becomes smaller due to 
the increase of yield stress of the weld material. Therefore, 
considering the design margin or safety margin, different 
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judgment may be made when considering the mechanical 
properties in the weld zone. 
 
 
Table 3 Normalized mechanical properties of Hastelloy-X in 
the heat-affected zone and in the weld zone 
 Yield stress Tensile strength 
Parent material 1.000 1.000 
Heat affected zone 0.962 0.998 
Weld zone 1.094 1.120 
 
 
4.   CONCLUSIONS 
 
In order to find out the high-temperature structural 
integrity of the PHE prototype, a series of structural analyses 
on the PHE prototype was carried out using parent material 
properties over the whole region. In this study, 
high-temperature elastic structural analysis considering 
mechanical properties in the weld zone was performed and 
compared the results with those using parent material 
properties. As a result of the analysis, we draw the following 
conclusions. 
1. The degree of exceeding the yield stress becomes 
smaller due to the increase of yield stress of the weld 
material. 
2. Considering the design margin or safety margin, 
different judgment may be made when considering the 
mechanical properties in the weld zone. 
 
 
References 
 
(1) Lee, W. J. et al., “Perspectives of Nuclear Heat and Hydrogen,” 
Nuclear Engineering and Technology, Vol. 41, No. 4, pp. 413-426 
(2009). 
(2) US DOE, Financial Assistance Funding Opportunity 
Announcement, NGNP Program (2009). 
(3) AREVA, NGNP with Hydrogen Production Pre-conceptual 
Design Studies Report, Doc. No. 1209052076-000 (2007). 
(4) Song, K. N. et al., “High-Temperature Structural Analysis 
Model on the Process Heat Exchanger for Gas Loop (I),” Trans. A 
of KSME, Vol. 34, No. 9, pp. 1241-1248 (2010). 
(5) Song, K. N. et al., “High-Temperature Structural Analysis 
Model on the Process Heat Exchanger for Gas Loop (II),” Trans. 
A of KSME, Vol. 34, No. 10, pp. 1453-1460 (2010). 
(6) Song, K. N. et al., “High-Temperature Structural Analysis of a 
Small-Scale Prototype of a Process Heat Exchanger (III),” Trans. 
A of KSME, Vol. 35, No. 2, pp. 191-200 (2011). 
(7) Song, K. N. et al., “High-Temperature Structural Analysis of a 
Small-Scale Prototype of a Process Heat Exchanger (IV) - 
Macroscopic High-Temperature Elastic-Plastic Analysis,” Trans. 
A of KSME, Vol. 35, No. 10, pp. 1249-1255 (2011). 
(8) Kim, Y. W. et al., “High Temperature and High Pressure 
Corrosion Resistant Process Heat Exchanger for a Nuclear 
Hydrogen Production System,” R.O.K Patent # 10-0877574 
(2008). 
(9) I-DEAS/TMG Analysis User Manual Version 6.1 (2009). 
(10) ABAQUS Analysis User’s Manual, Version 6.8 (2009). 
(11) Song, K-N et al., “ High-Temperature Structural Modeling on 
the PHE Prototype for the Gas Loop,” ICONE19-43005 (2010) 
(12) Song, K-N et al., “Measurement of Mechanical Properties in 
Weld Zone of Nuclear material by Instrumented Indentation 
Technique,” Proceedings of KWS Autumn Meeting (2010). 
(13) ISO TR29381 : Metallic Materials-Instrumented Indentation 
Test for Measurement of Indentation Properties (2008). 
(14) Hastelloy-X Alloy website, www.haynesintl.com. 
 
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HIGH-TEMPERATURE STRUCTURAL ANALYSIS ON A SMALL-SCALE PHE PROTOTYPE CONSIDERING MECHANICAL PROPERTIES IN THE HEAT-AFFECTED ZONE AND IN THE WELD ZONE

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HIGH-TEMPERATURE STRUCTURAL ANALYSIS ON A SMALL-SCALE PHE PROTOTYPE CONSIDERING MECHANICAL PROPERTIES IN THE HEAT-AFFECTED ZONE AND IN THE WELD ZONE

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