E-Journal of Advanced Maintenance Vol.12 No.1 (2020) 7-13
Japan Society of Maintenology

Application of Charpy Specimens Reconstituted by Electron Beam
Welding for the Evaluation of Irradiation Embrittlement of Reactor
Pressure Vessels
Seiji SAKURAYA1,*, Yasuo MORISHIMA2, Tetsuya TOYOTA3,and Takayuki
KAMINAGA4
1

Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Higashi-ibaraki-gun,Ibaraki-ken 311-1313, Japan
2
Toshiba Energy Systems & Solutions Corporation, 8, Shinsugita-Cho, Isogo-Ku, Yokohama-shi,
Kanagawa-ken 235-8523, Japan3
Hitachi-GE Nuclear Energy, Ltd,1-1, Saiwai-cho 3-chome, Hitachi-shi, Ibaraki-ken 317-0073,
Japan
4Tokyo Electric Power Company Holdings, Inc., 2-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo, 100-0011,
Japan
ABSTRACT
According to the recent Japanese regulations regarding plant life extension of light water reactors for operation
exceeding 40 years, additional surveillance tests are required for the evaluation of irradiation embrittlement ofreactor pressure vessel materials. The number of loaded specimens in boiling water reactors is limited;
accordingly, securing surveillance specimens is an important issue. Reconstitution of tested Charpy specimens isone way to secure the required number of specimens. Electron beam welding has the advantages of low heat
input and realization of a highly reliable weldment property; therefore, it is a candidate for the specimen
reconstitution method. In this study, applicability of reconstituted Charpy specimens was studied. Electron beam
welding of irradiated surveillance specimens was carried out in the hot laboratory by remote manipulation. Afterthe welding, specimens were processed into the shape of Charpy impact specimens, and Charpy impact tests
were performed. The soundness of the welded joints was evaluated and the obtained results satisfied therequirements of the Japan Electric Association Code.
KEYWORDS

ARTICLE INFORMATION

Reconstitution, Reactor pressure vessel, Electron beam welding, Irradiation
embrittlement, Low alloy steel

Article history:
Received 23 October 2018
Accepted 23 April 2020

1.

Introduction

After the Fukushima Daiichi accident in Japan, regulations were modified to assure the safe plant
operation of light water reactors (LWRs). With regard to the plant life extension of LWRs beyond 40years’ operation, the regulations made changes in the conventional surveillance program anddemanded additional surveillance tests for reactor pressure vessel materials to check their degree ofirradiation embrittlement. However, the number of loaded specimens for surveillance tests is limited.
Accordingly, securing surveillance specimens is important, and the development of a reconstitution
technique for tested Charpy specimens became necessary. There are several candidate reconstitution
techniques such as stud arc welding, surface activated joining (SAJ) and laser welding. However,electron beam welding (EBW) has the advantages of a low heat input and realization of highly
reliable weldment property. EBW is also more suitable for remote manipulation in a hot cell comparedwith other methods.
In order to apply EBW to the reconstitution of the surveillance test specimens, it is necessary tosatisfy requirements (1) and (2) and then implement requirements (3) and (4) according to the Japan
Electric Association Code, JEAC 4201:2007, Method of Surveillance Tests for Structural Materials of*Corresponding author, E-mail: seiji.sakuraya@nfd.co.jp

ISSN-1883-9894/10 © 2010 – JSM and the authors. All rights reserved.

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S. SAKURAYA, et al./Application of Charpy Specimens Reconstituted by Electron Beam Welding for
the Evaluation of Irradiation Embrittlement of Reactor Pressure Vessels

Nuclear Reactors [1].
(1) Visual inspection and cross-sectional observation should find no harmful defects at welds.
(2) The Charpy impact test at the upper shelf energy temperature should show no cracks at welds.
(3) Measurement of the heat affected zone width (WHAZ) should confirm it does not overlap thedeformed area during the Charpy impact test.
(4) Evaluation of the annealing width (WANL) should confirm it does not overlap the deformed
area during the Charpy impact test.
Confirmation test methods using unirradiated materials for these requirements have already beenreported [2].
In this study, applicability of the reconstitution technique by EBW of irradiated materials wasconfirmed.

2.

Experimental ProceduresFig. 1 shows the general concept of reloading and reconstitution procedure for surveillance test
specimens by using tested Charpy specimens under consideration in BWR. In the surveillance
program for LWRs, test specimens are irradiated and removed from reactors for Charpy impact tests,
and non-deformed areas of tested specimens are cut and reloaded into reactors; these are called insert
materials. After an appropriate period, the reloaded insert materials are removed from the reactor. The
insert materials are V-notched and reconstituted as Charpy impact test specimens by EBW.
Fig. 2(a) is a top view showing the specimen configuration before welding. Support materials
made of the same steel were used to fix the insert and tab materials, and will be removed after EBW.
These insert and tab materials were welded together in the configuration shown in Fig. 2(b) by
two-path EBW in order to suppress deformations by EBW. First, the V-notch side was welded under ahigh beam current condition (28.5 mA) and then the specimen was reversed and the back side waswelded under a low beam current condition (26.5 mA). The detailed welding conditions are listed inTable 1.
Fig. 3(a) shows a photo of a reconstituted specimen after the Charpy impact test obtained in theauthors’ previous work [2]. The simulated insert and tab materials made of base metal of unirradiatedlow alloy steel were welded by the EBW procedure described above, and subjected to the Charpy
impact test. No cracks and no deformations were observed at the weld part after the Charpy impact
test. Fig. 3(b) shows a photo of a reconstituted specimen with the simulated insert material made ofweld metal of unirradiated low alloy steel after the Charpy impact test. As in the case of the simulatedinsert material made of base metal, no cracks and no deformations were observed at the weld partafter the Charpy impact test. These results showed the soundness of the EBW part of reconstituted
specimens with insert materials made of both base metal and weld metal.
Materials used in this study were forged SFVQ1A [3] which were surveillance specimens
irradiated to 2.2×1018 n/cm2 (E>1MeV) in a Japanese BWR. After removing from the reactor, thespecimens had been subjected to the Charpy impact test and then machined to be insert materials. Thetab materials and support materials are unirradiated SFVQ1A forged materials. Since the objective of
this study was confirmation of applicability of the reconstitution before and after EBW, the process of
reloading into reactor was skipped. The insert materials were reconstituted and four specimens wereprepared. After external observations, one specimen was cut and subjected to cross-sectional
observation and a Vickers hardness test, and the other three specimens were subjected to Charpy
impact tests.
With regard to the evaluations for WHAZ and WANL, following procedures were adopted. WHAZand WANL affect the length of the test specimens used for reconstitution. The length of the specimensmust be long so as not to overlap with WHAZ or WANL and the deformed area during the Charpy impact
test. WANL, 1.1mm, was calculated by using temperature distributions during EBW in unirradiatedmaterial [2] with the method specified by the of JEAC 4201:2007 [1]. In general, since the thermal
properties such as thermal conductivity hardly changes due to neutron irradiation [4,5], the same
WANL was applied for the irradiated material as for the unirradiated material. The material propertiesof the reconstituted part were examined to check whether or not they met the requirements of JEAC
4201:2007 [1].

8S. SAKURAYA, et al./Application of Charpy Specimens Reconstituted by Electron Beam Welding for
the Evaluation of Irradiation Embrittlement of Reactor Pressure Vessels

Fig. 1 Reloading and reconstitution procedure of surveillance test specimens
Table 1 EBW conditions
V-notch side

Conditions

Accelerating voltage (kV)

Back side
58±2%

Beam current (mA)

28.5±5%

Welding speed (mm/s)
Degree of vacuum before welding (Pa)26.5±5%12.5±2%≤9.9×10-3(a) Top view(b) Side viewFig. 2 Specimen configuration

9S. SAKURAYA, et al./Application of Charpy Specimens Reconstituted by Electron Beam Welding for
the Evaluation of Irradiation Embrittlement of Reactor Pressure Vessels(a) Base metal [2](b) Weld metal
Fig. 3 Photos showing specimen appearances after the Charpy impact test

3. Results and Discussion
3.1.

Visual Inspection

Fig. 4 shows the images of external observations of four sides of the reconstituted specimen
including welds. No welding defects were found in these external observations. The deformation
caused by EBW was small, and the step between the insert and tab materials was within the 0.2 mm
tolerance specified in JEAC 4201:2007 [1].

Fig. 4 Photos showing appearances of a Charpy impact test specimen after being reconstituted byEBW

3.2.

Cross-sectional Observation

Before the cross-sectional observation, the specimen was mechanically polished and chemicallyetched with nital in order to evaluate WHAZ. The cross-sectional observation was made with an optical
microscope. Fig. 5 shows a cross-sectional image of a reconstituted (welded) specimen. The welding
paths from the V-notch side and the other side (back side) overlapped at the center of the specimen,
and no welding defects were observed for the cross-sectional observation, the same as for the externalobservations. JEAC 4201:2007 [1] defines WHAZ, containing the weld and generally called the heataffected zone, as half of the width of the colored region by etching, which can be calculated as theaverage of the widths measured at 2.5 mm, 5.0 mm and 7.5 mm from the back side of the specimen.

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S. SAKURAYA, et al./Application of Charpy Specimens Reconstituted by Electron Beam Welding for
the Evaluation of Irradiation Embrittlement of Reactor Pressure Vessels

Table 2 shows the evaluated WHAZ of the reconstituted specimen made of irradiated insert material by
EBW along with WHAZ of reconstituted specimens made of unirradiated insert materials by EBW [2],SAJ [1] and laser welding [1]. WHAZ values of the specimens welded by EBW were smaller than thatof the specimens welded by SAJ and laser welding, and there were no differences between WHAZ
values of the specimens made of irradiated insert material and unirradiated insert material.
As noted above, WANL was calculated by using temperature distributions during EBW inunirradiated materials, and WANL for EBW with the current conditions was evaluated as 1.1 mm,
which is much smaller than that for other reconstitution techniques [2]. Since the required length of an
insert material is determined by considering WHAZ, WANL and the width of plastic deformation formedby the Charpy impact test [1], the reconstitution by EBW can produce specimens with shorter lengths
of insert materials than other reconstitution techniques, which leads to great benefits when the lengthof non-deformed area in the original surveillance specimen is short.

Fig.5 Cross-sectional image of reconstituted (welded) specimen for the Charpy impact test
Table 2 WHAZ values [1,3]Reconstitution method
WHAZ (mm)3.3.

EBW (Irradiated)

0.8

EBW (Unirradiated)

0.8[2]

SAJ

1.2[1]

Laser welding

1.6[1]

Vickers Hardness TestAfter the cross-sectional observation, the Vickers hardness test was carried out on the crosssection of the specimen in accordance with JIS Z 2244:2009, Vickers Hardness Test [6]. The test load
was 0.98 N and the measurement interval was 0.2 mm. Fig. 6 shows the results of the Vickers
hardness test along the measurement lines at 2.5, 5 and 7.5 mm from the surface of the tab material on
the back side of the specimen, passing through the tab material, welds and the insert material.
Hardness of base metal and welds were about 200 HV and 500 HV, respectively. Hardness of the heataffected zone around the welds was larger than that of base metal because of the rapid heating andcooling during the EBW. The hardening area was defined as the area where hardness was larger than
300 HV because the hardness of the base material was less than 300 HV. The insert and the tabmaterials had almost the same hardness because the insert material was hardly embrittled byirradiation. Table 3 summarizes the widths of the hardening areas. The widths of the hardening areas
on the measurement lines at 2.5 mm and 7.5 mm from the back side of the specimen were wider thanthat on the measurement line at 5.0 mm from the back side of the specimen, that is, the center of the11S. SAKURAYA, et al./Application of Charpy Specimens Reconstituted by Electron Beam Welding for
the Evaluation of Irradiation Embrittlement of Reactor Pressure Vessels

specimen. Half the average value of the widths of the hardening area was calculated as 0.65 mm,
which was smaller than 0.8 mm, the WHAZ evaluated by the cross-sectional observation. Considering
the measurement interval of the Vickers hardness test, the hardening area can be considered to beequivalent to WHAZ.

Fig.6 Results of Vickers hardness test
Table 3 Widths of the hardening areas
Measurement
Widths of the hardening areas
positions from surface
Hardening area A Hardening area B
(mm)
7.5

1.6

1.8

5.0

0.8

0.8

2.5

1.4

1.4

Average

1.3

3.4

Charpy Impact Test
The specimens reconstituted with EBW were machined into the specimens for the Charpy impact
test with dimensions of 10×10×55 mm. Charpy impact tests were carried out in accordance with JIS Z
2242;2005, Method for Charpy Pendulum Impact Test of Metallic Materials [7], at 100°C. Charpy
impact test results summarized in Table 4 shows that all specimens had 100 % ductile fracture surface.
Therefore, it shows that the Charpy impact tests were performed at the test temperature in the upper
shelf energy region. The upper shelf energy of reconstituted material was 214 J, which was about 5 %different from that of non-reconstituted one. After the Charpy impact test, no cracks and nodeformations were observed at the weld by EBW as shown in Fig. 7, indicating that the requirementsdescribed in JEAC 4201:2007 was satisfied [1].
Table 4 Results of Charpy impact testSpecimen ID

Test temperature (°C)

Percent ductile
Fracture (%)

Lateral expansion (mm)Absorbed energy (J)L1E2100100

2.21

209

L151

100

100

2.24

214

L161

100100

2.25

220

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S. SAKURAYA, et al./Application of Charpy Specimens Reconstituted by Electron Beam Welding for
the Evaluation of Irradiation Embrittlement of Reactor Pressure Vessels

Fig. 7 Photos showing appearance of the Charpy impact tested specimen

4. Conclusion
Applicability was evaluated for the reconstitution technique using EBW to obtain irradiatedspecimens (fluence of 2.2×1018 n/cm2) for the Charpy impact test.
Visual inspection and cross-sectional observation found no welding defects at welds. And, theCharpy impact test at the upper shelf energy temperature showed no cracks at welds. These results
satisfied the requirements of JEAC 4201:2007 [1].
WHAZ of reconstituted specimens was estimated to be sufficiently small as 0.8 mm and wasalmost same as calculated WANL, 1.1mm. Evaluated values of WHAZ and WANL should be considered inthe design of the insert material length so that WHAZ and WANL of reconstituted specimens do notoverlap the deformed area during the Charpy impact test.
In summary, the reconstitution technique of irradiated specimens using EBW satisfied therequirements of JEAC 4201:2007 [1].

Acknowledgement
This work was conducted as a joint study between Japanese BWR-user utilities (Tokyo ElectricPower Company Holdings, Inc., Chubu Electric Power Co., Inc., Tohoku Electric Power Co., Inc.,
Hokuriku Electric Power Company, Chugoku Electric Power Co., Inc., Japan Atomic Power
Company, and Electric Power Development Co., Ltd), and BWR manufacturers (Toshiba Energy
Systems & Solutions Corporation and Hitachi-GE Nuclear Energy, Ltd).

References
[1]
[2]
[3]
[4]
[5]
[6]
[7]

The Japan Electric Association: “Method of Surveillance Tests for Structural Materials of NuclearReactors”, JEAC 4201:2007 (2007).
Y. Morishima, T. Ogawa, T. Toyota, T. Ishizaki, S. Sakuraya and T. Kaminaga: “Applicability Evaluationof Reconstituted impact test specimen by electron beam welding for RPV Surveillance Test”, Abstractsof 15th academic conference on Japan Society of Maintenology, Fukuoka, Japan, July, pp.259-266 (2018).
Japanese Standards Association: “Quenched and Tempered Alloy Steel Forgings for Pressure Vessels”, JISG 3204:2008(2008).
R.K. Williams, R.K. Nanstad, R.S. Graves and R.G. Berggren: ''Irradiation effects on thermal conductivityof a light-water reactor pressure vessel steel'', Journal of Nuclear Materials, Vol.115, Issues2-3, pp.211-215(1983).
W.S. Ryu, D.G. Park, U.S. Song, J.S. Park and S.B. Ahn: ''Effects of irradiation on thermal conductivity ofalloy 690 at low neutron fluence”, Nuclear Engineering and Technology, Vol.45, Issues2, pp.219-222(2013).
Japanese Standards Association: “Vickers Hardness Test”, JIS Z 2244:2009(2009).
Japanese Standards Association: “Method for Charpy Pendulum Impact Test of Metallic Materials”, JIS Z
2242:2005 (2005).

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