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Radiation induced corrosion of steel
Department of Chemistry, Nuclear chemistry
Royal institute of technology
Author: Oskar Nilsson K‐06
Supervisor: Mats Jonsson
2
Abstract
The aim of this thesis was to investigate the influence of aqueous radiation induced oxidants on stainless
steel. This was done by exposing the steel to both radiation and chemically added oxidants under
ambient conditions, i.e. in and near room temperature. When water is exposed to radiation several
oxidizing species are formed, including hydrogen peroxide, which have been known to increase the risk
for corrosion of other materials. Stainless steel is used in many parts in a nuclear power plant, and the
results from this thesis could be useful when elucidating whether the steel is an appropriate material to
use for these applications.
3
Table of Contents
Radiation induced corrosion of steel ............................................................................................................ 1 Abstract ..................................................................................................................................................... 2
Introdution ................................................................................................................................................ 4
The discovery of nuclear fission ............................................................................................................ 4
Structure and components of nuclear reactors .................................................................................... 4
Ionizing radiation .................................................................................................................................. 5
What has been done before ................................................................................................................. 5
Purpose of this study ............................................................................................................................ 7
Experimental ............................................................................................................................................. 8
Chemically added oxidant ..................................................................................................................... 8
Radiation experiments .......................................................................................................................... 9
Results ..................................................................................................................................................... 10
Chemically added oxidant ................................................................................................................... 10
Radiation induced oxidants................................................................................................................. 12
Conclusions ............................................................................................................................................. 15
4
Introdution
The discovery of nuclear fission
In the late 1930:s, scientists discovered that when certain atomic nuclei were bombarded with neutrons
they split into fragments and at the same time released large amounts of energy. This opened the door
to several new applications, and one of the more useful ideas hatched from this breakthrough was to
transform the released energy into electricity. It did not take long before nuclear power plants were
built to utilize this discovery.
In short, the energy released from nuclear fission is basically used to boil water, the steam generated
drives a turbine and the rotational energy in the turbine powers a generator that produces electricity.
Nuclear power stands for roughly 20% of the worlds electricity needs and this number will most
certainly increase in the future as the demands gets larger and the supply of other energy sources
decreases1,2.
Structure and components of nuclear reactors
A nuclear reactor requires a number of components to work. The first and most obvious one is the fuel,
which usually consists of uranium slightly enriched in uranuim‐235, but reactors that operate on
plutonium also exist. Because the core generates significant amounts of heat, a cooling system is an
essential part of a nuclear reactor system. Heat produced from nuclear fission in the core is transferred
away via the cooling system in order to maintain the right temperature and to avoid unnecessary
material degradation. The coolant that is most widely used is regular light water but other cooling
agents such as heavy water and liquid sodium can also be utilized. Another important part is the
moderator that reduces the velocity and thereby the energy of the neutrons so that they become
capable of sustaining a nuclear chain reaction. The moderator consists of light components such as
hydrogen, deuterium or carbon, which leaves the neutrons with the right amount of energy to start the
fission process. Every reactor also has the need for control rods to manage the power level of the
reactor. If anything goes wrong, the control rods are used to shut down the reactor..
5
Control rods contain neutron absorbing materials such as boron or silver that capture the incoming
neutrons and prevent them from continuing the nuclear reaction. The fifth component is usually
thought to be the structure itself where the material used to build the reactor must have weak
absorption of neutrons and having sufficient strength and resistance towards corrosion. Stainless steel
and zircaloy are often used to build metal tubes where the fuel are held and supported. These metal
tubes are called the cladding. Some additional hardware is also necessary to keep the fuel assembly
within the cladding supported, and this material is most commonly constructed out of stainless steel.
The last component is the shield, which protects materials and workers from radiation. The shield is
composed of concrete augmented with iron, lead and water to screen all types of radiation3.
Ionizing radiation
The understanding of the effects that ionizing radiation has on the corrosion of the various parts in a
nuclear reactor system described above is of key importance to operational and maintenance
procedures, as well as the strict safety requirements that has to be met today.
When water is exposed to ionizing radiation, it decomposes into several reactive species (water
radiolysis): •OH, H2O2, O2, H2, •O2–eaq‐, H, which can interact with its surroundings. The steady state
concentrations of these species have been shown to drive the corrosion behavior of a number of
materials, including stainless steel. It is generally thought that H2O2 is the oxidant most responsible for
generating an oxidizing environment that could lead to corrosion of materials in water, when exposed to
radiation4,5.
What has been done before
Several studies have been conducted to try and understand the corrosion of steel under different
conditions. There have been studies of both chemically added oxidant and oxidants created under
irradiation. The parameter that has been monitored during nearly all of the experiments is the
Electrochemical Corrosion Potential, or the ECP as it is commonly called. The aim of these studies has
been to find a correlation between corrosion of the material and the change in ECP, and thereby gain
knowledge about the behavior of the material.
6
When explaining what the ECP is you have to take into account all the relevant reactions near a metal
surface that are associated with corrosion under the existing circumstances, this is called the corrosion
reaction system. When hydrogen peroxide is added to pure aerated water the following reactions are
relevant to be able to define the ECP. At the cathode, hydrogen peroxide and oxygen is reduced to
water and hydrogen peroxide respectively. At the anode surface, free hydrogen molecules in solution
are oxidized, discharged and adsorbed on to the metal surface. Another anodic surface reaction that
takes place are that already discharged and adsorbed hydrogen is oxidized back in to solution. Reactions
(1)‐(4) show the compiled corrosion reaction system.
O2 + 2H+ + 2e‐ ⇔ H2O2 (1)
H2O2 + 2H+ + 2e‐ ⇒ 2H2O (2)
H2 ⇔ H2+(ads) + e‐ (3)
H2+(ads) ⇔ 2H+ + e‐ (4)
The Electrochemical Corrosion Potential is then defined as the potential at which the summation of all
the current densities of these reactions becomes zero.
Previous studies have shown that the increased oxidizing environment due to the formation of the
species mentioned formed under irradiation and chemically added hydrogen peroxide does affect the
ECP to a degree that could lead to corrosion. Parts of this shift in the ECP are reversible when fresh non‐
irradiated solution is added but not all (hysteresis), which seems to result from long term changes in the
outer oxide layer6,7.
7
Purpose of this study
The aim of this work is to look at the same problem, but from another angle. The Electrochemical
Corrosion Potential will not be measured during any of the experiments although the material will both
be exposed to radiation as well as chemically added hydrogen peroxide. Instead of looking at the ECP,
the consumption and disappearance of hydrogen peroxide will be measured with a spectrophotometer.
This information can then be used to calculate rate constants for the consumption. The surface of the
material will also be investigated with SEM and IR Absorbance Spectrometer (IRAS) to gain information
of possible changes in the surface structure and composition.
The steel used in this work, both in powder form and in the form of pieces was stainless steel of type
316‐L where the composition of the different elements is listed below in weight percentage8.
Fe, <0.03% C, 16‐18.5% Cr, 10‐14% Ni, 2‐3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S
The goal is to retrieve information, which could be useful to have when stainless steel is considered for
an application that might expose the material to ionizing radiation.
Experi
Chemic
Various
peroxide
Merck st
powder
out in an
through
then add
on the o
350 nm.
perform
respecti
Fig 1. Expe
imental
cally added
amounts of
e on the stee
tandard solu
was then ad
n inert atmo
a Gamma M
ded to a mix
oxidation of I
. Reaction te
med using sol
vely. Figure
erimental setup
oxidant
316‐L stainle
el surface ov
ution. This w
dded to 50 m
sphere by pu
Medical 0,45
xture of Hac/
I‐ by hydroge
emperature w
utions of 0,5
1 shows the
p for the chemi
ess steel pow
ver time. A 0,
as then furth
mL of the hyd
urging with n
μm to 25 mm
/NaAc which
en peroxide w
was varied b
5 mM of pota
setup for th
ically added exp
wder were us
,1 M hydroge
her diluted to
drogen perox
nitrogen gas
m cellulose a
work as a ca
was measure
etween 25, 4
assium perm
he chemically
periment.
sed to measu
en peroxide
o 0,5 mM be
xide solution
. After extra
acetate syrin
atalyst and K
ed spectroph
40 and 55 °C
manganate an
y added expe
ure the deco
solution was
efore reactio
and the who
action, the sa
nge filter. The
KI. The absor
hotometrical
C. Similar exp
nd a 0,1 mM
eriments.
omposition o
s made from
on took place
ole reaction
ample was fi
e filtered sam
bance of I3‐ d
lly at a wave
periments w
irridiumhex
8
of hydrogen
m a 30%
e. The
was carried
ltered
mple was
depending
length of
ere
xachloride,
8
Radiati
Six ident
using 3 μ
these pi
radiatio
polishing
tempere
being ex
with ICP
peroxide
the radia
Fig 2. Expe
ion experim
tical pieces o
μm, 1 μm an
eces were th
n during this
g. They were
ed Millipore
xposed to rad
P to quantify
e and measu
ation induce
erimental setup
ments
of stainless st
nd 0,25 μm d
hen exposed
s time. The p
e then put in
water before
diation and w
the amount
ured for its co
ed corrosion
p for the radiat
teel 316‐L w
diamondpast
to Millipore
pieces were r
n small bottle
e irradiation
was used as
of dissolved
onsumption
experiments
ion experiment
were polished
e respective
e water for 9
rinsed and cl
es that fit in t
. The other t
reference. T
d metal ions.
exactly like t
s.
ts.
d, first with 1
ly to get the
4,5 h, three
eaned with e
the gamma s
two samples
The water an
The sixth pi
the powder
1200 μm carb
surface grad
of which we
ethanol duri
source toget
s were left in
d steel samp
ece was exp
was. Figure 2
bonpaper an
dually smoot
ere also expo
ng and after
ther with 10
the water w
ples were the
osed to hydr
2 shows the
9
nd then
ther. Five of
osed to
r the
ml room
without
en analyzed
rogen
setup for
9
Result
Chemic
Two sets
powder
1,0 g in 4
shows, t
expecte
Fig 3. Hyd
When p
consum
Fig 4. Hyd
0
0
0
0
0
0
conc. (mM)
0000000
conc. (mM)
ts
cally added
s of experim
(100 mesh)
40 mL with b
the speed of
d.
rogen peroxide
erforming th
ption of the
rogen peroxide
0
0,1
0,2
0,3
0,4
0,5
0,6
0
00,10,20,30,40,50,60,7
0
oxidant
ents were d
in aqueous e
both contain
f hydrogen pe
e consumption
he same set o
peroxide. Th
e consumption
2000
1000 20
one in 25°C
environment
ing an initial
eroxide cons
over time (s), c
of experimen
his is displaye
over time (s), c
4000
tid (s
000 300
tid (
measuring t
t, one with 1
l hydrogen p
sumption inc
containing 1,0 a
nts on 316‐L
ed in figure 4
containing 1,5 a
0 60
)
00 4000
(s)
he consump
1,5 g of Fe in
peroxide conc
creases when
and 1,5 g of Fe p
L stainless ste
4.
and 3,0 g of 316
000
5000
tion of hydro
40 mL Millip
centration o
n more powd
powder.
eel powder t
6‐L stainless ste
8000
6000
ogen peroxid
pore water a
f 0,5 mM. A
der is added
there is no de
eel powder.
1,0 g
1,5 g
1,5 g
3 g
de over Fe
nd one with
As figure 3
, which is
etectable
When th
permang
with pur
Fig 5. Pota
Fig 6. Iridi
All the s
can mea
samples
(Fe, Ni a
0
0
0
0
0
0
conc. (mM)
0
0
0
0
0
conc. (mM)
he powder w
ganate and i
re iron. This
asium permang
um hexachlorid
ample soluti
asure concen
s examined w
and Cr) had b
0
0,1
0,2
0,3
0,4
0,5
0,6
0 2
0
0,02
0,04
0,06
0,08
0,1
0,12
0
was exposed
ridium hexa
is displayed
ganate consump
deconsumption
ions were an
ntrations dow
with ICP show
been dissolve
2000 4000
2000 40
to a stronge
chloride the
in figure 5 a
ption over time
n over time (s),
nalyzed with
wn to nano s
wed any sign
ed.
0 6000
tid (s)
00 6000
tid (s)
r oxidant tha
re was consu
nd 6.
e (s), containing
containing 3,0
an Inductive
scale (10e‐9)
n that none o
8000 10
8000
an hydrogen
umption of t
g 3,0 and 6,0 g o
and 6,0 g of 31
ely Coupled P
of a wide ra
of the three m
0000 1200
10000 120
n peroxide, li
the oxidants
of 316‐L stainle
16‐L stainless st
Plasma (ICP)
ange of elem
most commo
0
3 g
6 g
000
3
6
ke potassium
just like the
ess steel powde
teel powder.
, which is a d
ents. None o
on elements
g
g
3 g
6 g
11
m
experiment
er.
device that
of the
of the alloy
1
RadiatiThe first
The solu
using IC
The stai
before e
the stee
with fig
surface
there we
also exa
Fig 7. SEM
ion inducedt experiment
ution was pla
P. The ICP an
nless steel p
exposure to r
el surface bef
8, which is t
structure. Th
ere no clear
mined with
M surface pictur
d oxidationt that expose
aced in the g
nalysis did no
ieces that w
radiation, fig
fore and afte
he correspon
hree pieces w
and visible s
ICP, which a
re of 316‐L piec
ed the mater
amma sourc
ot show any
ere exposed
g 5 and 6 bel
er exposure (
nding image
were expose
surface differ
s before did
ce with 1000 in
rial to radiati
ce and expos
Cr, Ni or Fe
d to radiation
ow shows a
(94,5 h) with
after irradia
d to radiatio
rences betw
not show an
magnification b
ion had 10 g
sed to radiati
in detectable
n was first m
scanning ele
h a magnifica
ation, there i
on and two w
een the piec
ny signs of di
before radiatio
of 316‐L in 1
ion for 64,5
e concentrat
echanically p
ectron micro
ation of 1000
s little or no
were exposed
ces. The irrra
issolution.
n exposure.
10 mL Millipo
h and then e
tions in the s
polished and
scope (SEM)
0. When com
difference i
d only to wat
adiated solut
12
ore water.
examined
solution.
d examined
) picture of
mparing fig 7
n the
ter and
ions were
2
Fig 8. SEM
M surface picturre of 316‐L piecce with 1000 in magnification aafter 94,5 h raddiation exposur
e.
133
14
When looking at the first experiments that were done with the stainless steel powder, it is obvious that
the material does not react with the weakest of the three oxidants, hydrogen peroxide under the
present conditions. The hydrogen peroxide was not consumed catalytically on the steel surface or by
oxidization of the material. Previous studies have indicated that steel surfaces could be sensitive to
hydrogen peroxide under certain conditions that might increase the risk for corrosion. However, this
behaviour could not be verified with ICP or by monitoring the reaction using a spectrometer under the
current reaction conditions. The experiment where the steel was exposed to radiation, causing the
water to undergo water radiolysis, showed no different result and further strengthens the claim that it is
a resistant and sturdy material under the conditions used in this work.
When performing the same experiments as the ones with hydrogen peroxide there is a clear
consumption of the oxidant observed. The species causing these results were potassium permanganate
and iridium hexachloride and they are both stronger oxidants then hydrogen peroxide, but the ICP
measurements showed no sign of dissolution. The experiments show that hydrogen peroxide is not a
strong enough oxidant to react with the stainless steel in powder form.
The material in the form of pieces behaved in exactly the same way as the powder. The ICP
measurement gave the same results and the SEM images did not show that anything had happened on
the surface upon irradiation.
15
Conclusions The obvious conclusion to be drawn from this thesis is that stainless steel is inert and very resistant to
hydrogen peroxide and ionizing radiation in and near room temperature. This indicates that the steel is a
very good material to use in radioactive environments at room temperatures.
16
References
1 http://www.world‐nuclear.org/info/inf16.html, World Nuclear Association, 2010‐09‐01 2 K.J Green, D. Gulatti, J.C. Steele, Nuclear Power Station Design, Wiley Encyclopedia of Electrical and Electronical Engeneering, publ. online 2009, p.660 3 Wiley, John & Sons, Inc, Nuclear Reactors, Kirk‐Othmer Encyclopedia of Chemical Technology, p.7‐8 4 D. Fu, X. Zhang, P.G. Keech, D.W. Shoesmith, J.C Wren, Electrochimica Acta 55 (2010) 3787‐3796 5 G. Choppin, J.O. Liljenzin, J. Rydberg, Radiochemistry and Nuclear Chemistry 2nd Edition (1995) p.175 6 R.S. Glass, G.E. Overturf, R.A. van Konynenburg and R.D. McCright, Gamma radiation effects on corrosion‐I. Electrochemical mechanisms for the aqueous corrosion processes of austenitic stainless steel relevant to nuclear waste disposal in tuff, Corrosion Science, vol 26, No 8, p 577‐590, 1986 7 Shunsuke UCHIDA, Naoto SHIGENAKA, Masahiko TACHIBANA, Yoichi WADA, Masanori SAKAI, Kazuhiko AKAMINE and Katsumi OHSUMI, Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (I), Journal of NUCLEAR SCIENCE and TECHNOLOGY, Vol. 35, No. 4, p. 301‐308 (April 1998) 8 http://www.azom.com/Details.asp?ArticleID=2382, Azom Materials, 2011‐01‐25