Alloying of steel and graphite by hydrogen in nuclear reactor

Abstract

In traditional power engineering hydrogen may be one of the first primary source of equipment damage. This problem has high actuality for both nuclear and thermonuclear power engineering. Study of radiation-hydrogen embrittlement of the steel raises the question concerning the unknown source of hydrogen in reactors. Later unexpectedly high hydrogen concentrations were detected in irradiated graphite.
It is necessary to look for this source of hydrogen especially because hydrogen flakes were detected in reactor vessels of Belgian NPPs.
As a possible initial hypothesis about the enigmatical source of hydrogen one can propose protons generation during beta-decay of free neutrons поскольку inasmuch as protons detected by researches at nuclear reactors as witness of beta-decay of free neutrons.

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Alloying of steel and graphite by hydrogen in nuclear reactor
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2017 IOP Conf. Ser.: Mater. Sci. Eng. 175 012050
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Alloying of steel and graphite by hydrogen in nuclear reactor
E Krasikov
Laboratory Head, National Research Centre «Kurchatov Institute», 123182 Moscow,
Russia.
E-mail: ekrasikov@mail.ru
Abstract. In traditional power engineering hydrogen may be one of the first primary source of
equipment damage. This problem has high actuality for both nuclear and thermonuclear power
engineering. Study of radiation-hydrogen embrittlement of the steel raises the question
concerning the unknown source of hydrogen in reactors. Later unexpectedly high hydrogen
concentrations were detected in irradiated graphite.
It is necessary to look for this source of hydrogen especially because hydrogen flakes were
detected in reactor vessels of Belgian NPPs.
As a possible initial hypothesis about the enigmatical source of hydrogen one can propose
protons generation during beta-decay of free neutrons поскольку inasmuch as protons detected
by researches at nuclear reactors as witness of beta-decay of free neutrons.
I. Introduction
It is known that in traditional power engineering hydrogen may be one of the first primary source of
equipment damage [1]. This problem has high actuality for both nuclear and thermonuclear power
engineering [2]. Particularly reactor pressure vessels (RPV) of the WWER-440/230 project were
manufactured without stainless cladding that is were in contact with primary circuit water and
accessible for hydrogen as a product of RPV wall corrosion. Analysis of the combined radiation-
hydrogenation embrittlement of the 48TS type vessel steel was performed in [3] where at the mention
of the American [4] and own data question concerning unknown source of hydrogen in metal that was
irradiated in nuclear reactor in hermetic ampoules (was named as “irradiation-produced hydrogen”
(IPH) was raised.
2. Materials and Methods
Table 1 lists chemical composition of the RPV steel used (48TS type). A-543 type US steel takes for
comparison.
Table 1. Chemical composition of the RPV steels A-543 and 48TS (%%mass)
4% solution of H2SO4 was used for additional electrolytic hydrogenation of the specimens (current
density 0,1A/cm2). Hydrogen concentration was determined by thermal degasation method at
Type
C
Si
Mn
P
S
Cu
Cr
Mo
Ni
48TS
0,16
0,30
0,43
0,014
0,011
0,11
2,75
0,67
0,16
А543
0,14
0,18
0,20
0,011
0,015
0,07
1,60
0,50
3,01
1
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IOP Conf. Series: Materials Science and Engineering 175(2017) 012050 doi:10.1088/1757-899X/175/1/012050
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temperatures up to 1000°C with gas chromatograph (thermal conductivity detector) registration of gas
released.
3. Experimental results and discussion
Determination of the hydrogen content in the irradiated steel fulfilled in the USA went to unexpected
result: hydrogen content noticeably exceeded the quantity rated at (n,p) transmutation reaction: less
than 0,1 ppm.
Results of the IPH concentration in steel analysis carried out in the USA are shown in Table 2 [4].
One can see that the greater the fast neutron fluence (FNF) the greater the hydrogen content.
Table 2. Dependence of the IPH concentration in steel versus FNF (E>1MeV)
FNF, ×1018сm-2; tirr.=225-300°С
0
7
200
400
IPH concentration, ppm; t°degasation=1000°С
0,2
0,9
1,7
2,1
Ageing of the steel at 100-325°C during 48 hours revealed that IPH is not diffusible up to irradiation
temperature that is IRH are in the irradiation produced traps. Inasmuch as IPH at temperatures of
mechanical tests was immovable indicated values were subtracted from total quantity of hydrogen
measured.
In I.V. Kurchatov Institute at several experiments was determined that steel specimens irradiated at
relatively low (100-140°C) temperatures in sealed Ar contained ampoules hydrogen content was many
times higher relatively initial content but was independent on FNF (Table 3) [3].
Table 3. Dependence of the IPH concentration in steel versus FNF (E>0,5MeV)
FNF, ×1018сm-2; tirr.=100-140°С.
0
100
170
190
270
450
500
IPH concentration, ppm; tdegasation=300°С.
0,2
2,9
4,3
13,3
24,9
9,8
3,1
Degasation kinetics are plotted in Figs 1, 2.
060 120 180 240 300 360 420
0
2
4
6
8
10
300
*300
*250
*200
300
280
200
*200
100
200
*200
Quantity of hydrogen released, ppm
Time of ageing at given temperature, min.
100
*300
Figures near curves - floating specimen temperature
010 20 30 40 50 60 70
0
10
20
30
40
50
4,5 1020сm-2,tirr.=140°С
2,7 1020сm-2,tirr.=125°С
2,7 1020сm-2,tirr.=125°С+2hours Н2
Quantity of hydrogen released, ppm
Time of ageing at 300°С, min.
Figure 1. IPH degasation kinetics for irradiated
steel (4,5×1020сm-2 at 140°С)
Figure 2. Hydrogen degasation kinetics for
irradiated and irradiated+ hydrogenated steel
As one can see from Fig.1 that RIH discharge starts when heating temperature exceeds the irradiation
temperature. It means that RIH is accumulated in radiation defects (traps).
2
ICCMPT IOP Publishing
IOP Conf. Series: Materials Science and Engineering 175(2017) 012050 doi:10.1088/1757-899X/175/1/012050

Rather later data appear оn unexpectedly high hydrogen concentrations in stainless steels irradiated
in BWR type reactors (Fig.3 [5]) and high generations of hydrogen and helium in nickel [6].
Figure 3. IPH content in 304 SS versus FNF (E>1 MeV)
Surprisingly high hydrogen concentrations were revealed in irradiated graphite [7]. Table 4 presents
the results of the thermal degasation of the GR-280 type graphite.
As it is seen hydrogen concentrations in irradiated specimens is one-two orders of magnitude higher
than in unirradiated ones.
Table 4. Results of the thermal degasation of the GR-280 type graphite
FNF, сm-2
(Е>0,5MeV)
Irradiation
temperature,
С
Quantity of hydrogen released, ppm
Degasation temperature, С
Total
1000
1800
ppm
0
2,2
1,5
4,2
2,9
6,4
4,4
11022
500
20,8
49,7
41,2
19,5
-
-
1342
864
20,8
49,7
1383
883
21021
1100
-
-
369
327
369
327
It is necessary to look for enigmatic source of hydrogen especially because in frame of inspections
numerous flows were detected in the forged rings of the reactor pressure vessels in the Belgian nuclear
power plants Doel 3 and Tihange 2 [8,9]. The owner Electrabel claimed that flaws were “most likely”
hydrogen flakes.
One of the unobvious but probable initial hypothesis on enigmatic source of the hydrogen in
operating nuclear reactor is generation of protons as a product of beta-decay of free neutrons (lifetime
~15 min.) [10].
3
ICCMPT IOP Publishing
IOP Conf. Series: Materials Science and Engineering 175(2017) 012050 doi:10.1088/1757-899X/175/1/012050

References
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Russian)
[2] Alekseenko N 1997 Radiation Damage of Nuclear Power Plant Pressure Vessel Steels. ANS p 97
[3] Krasikov E 1974 Investigation of hydrogen embrittlement and hydrogen diffusion in irradiated
steel, Ph.D Thesis, Moscow (in Russian).
[4] Brinkmann C 1970 Effects of Hydrogen on the Ductile Properties of Irradiated Pressure Vessel
Steels. Report IN-1359, NRTS, Idaho Falls
[5] A.I. Jacobs 1987 Hydrogen buildup in Irradiated Type-304 Stainless Steel. ASTM STP 956. F.A.
Garner, and N. Igata, Eds. ASTM, Philadelphia, pp 239-244
[6] Greenwood L, Garner F and Oliver D 2004 Surprisingly Large Generation and Retention of
Helium and Hydrogen in Pure Nickel. Journal of ASTM International, April, vol.1, №4. Paper
ID JAI11365, pp 529-539
[7] Biriukov A, Krasikov E 1998 Impact of neutron irradiation on graphite dehydrogenations. VANT,
ser. Thermonuclear fusion №1-2 pр 3-8. NRC “Kurchatov Institute, Moscow (in Russian)
[8] Tweer I 2016 Flawed Reactor Pressure Vessels in the Belgian NPPS Doel 3 and Tihange 2.
Comments on the FANC Final Evaluation Report 2015
[9] ORNL 2015 Evaluating of Electrabel Safety Cases for Doel 3/Tihange 2: Final Report (R1).
ORNL/TM-2015/59349, Nov
[10] Mostoyoi Yu 1996 Neutron yesterday, today, tomorrow. Successes of physics (UFN), vol.166 №9
pp 987-1022 (in Russian)
4
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IOP Conf. Series: Materials Science and Engineering 175(2017) 012050 doi:10.1088/1757-899X/175/1/012050