E-Journal of Advanced Maintenance Vol.6-4 (2015) 131-145
Japan Society of Maintenology

Effect of Ethanolamine Injection on Wall Thinning Rate of PWR Carbon
Steel Components
Takuya FUKUMURA1,*
1

Institute of Nuclear Safety System, Inc., Sata 64, Mikata-gun, Mihama-cho, Fukui 919-1205, Japan

ABSTRACT
For pH control of PWR secondary system water chemistry, some plants have changed to ethanolamine injection.
The purpose of this work was to understand the effect of changing water chemistry on wall thinning rate of the
PWR secondary system due to flow accelerated corrosion. For that purpose, evaluations of water chemistry werecarried out by a mass balance calculation, wall thinning rate measurement by a rotary disk test and wall thinning
rate evaluation based on calculated magnetite solubility. As a result, it was found to be effective to inhibit thewall thinning rate of the PWR secondary system due to flow accelerated corrosion by ethanolamine injection,
but it was not sufficiently effect to neglect wall thinning rate due to flow accelerated corrosion. The effect of thewall thinning rate inhibition also varied greatly for each component of the PWR secondary system. It was foundthat maintenance of the carbon steel used for the PWR secondary system was still required under ethanolamine
injection condition.
KEYWORDS

ARTICLE INFORMATIONPWR, Ethanolamine, Wall thinning rate, Flow accelerated corrosion,
Carbon steel, Water chemistry

Article history:
Received 19 May 2014
Accepted 20 October 2014

1. Introduction
In the pressurized water reactor (PWR) secondary system, carbon steel is used for somecomponents such as piping. Pipe wall thinning management for plant maintenance is carried out
because of flow accelerated corrosion (FAC). For wall thinning due to FAC, many studies have been
carried out and much knowledge has been obtained regarding material factors, flow factors andenvironmental factors of FAC. For environmental factors in particular, temperature dependence,
dissolved oxygen concentration dependence and pH dependence have been reported [1-5].
However, most environmental factor data have been gotten under neutral or all-volatile treatment(AVT) conditions. The AVT has been widely used in PWR secondary systems, such as adding
hydrazine and ammonia to feed water for the purposes of deoxygenation and pH control, respectively.
But recently some plants have changed the PWR secondary system water treatment from AVT toethanolamine (ETA) injection. The purpose of ETA injection is to lower iron amounts carried in thefeed water to the steam generator (SG) by increasing the pH of the feed water. The decrease in theiron concentration level differs for each plant. But iron concentration of feed water down to 10 ppb
has been reported [6].
On the other hand, not enough about the PWR secondary system water chemistry for eachcomponent is known. This is because substances in the PWR secondary system water have complex
variations caused by the liquid-vapor distribution and thermal decomposition in the SG, but analysis
points and frequency of water chemistry measurements are limited. Therefore the effect of ETA
injection on wall thinning rate due to FAC of the PWR secondary system is not sufficiently known.
From this background, this study aimed at evaluating the PWR secondary system water chemistry
under AVT and ETA injection conditions and determining the effect of water chemistry on wall
thinning rate due to FAC.
The reason for the complex variations of the PWR secondary system water chemistry is
considered due to the concentration change caused by the liquid-vapor distribution of volatile*

Corresponding author, E-mail: fukumura@inss.co.jp

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

131

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

substances and ammonia generation caused by thermal decomposition of hydrazine at the SG andmoisture separator-and-reheater (MSR) etc. Therefore, first the PWR secondary system waterchemistry under representative AVT and ETA injection conditions was evaluated by model
calculations considering liquid-vapor distribution and thermal decomposition. Next, the wall thinning
rate change between AVT and ETA injection conditions was evaluated experimentally by the rotary
disk test under AVT and ETA injection water chemistry which was calculated by the model
calculations. Also the wall thinning rate change was evaluated under the model of wall thinning rate
due to FAC is proportional to the magnetite solubility and compared to the result of rotary disk test.

2. Model calculations of PWR secondary system water chemistry
2.1. Method
For model calculations of the PWR secondary system water chemistry, an 800MW class 3 loop
plant was selected and water chemistry of the PWR secondary system was calculated from feed waterchemistry using a mass balance calculation.
Twenty-two major components, described later, of the PWR secondary system were selected forthe water chemistry calculation. Fig.1 is a schematic drawing of the modeled PWR secondary system.
Some of the temperatures and the amounts of water and vapor used in the model calculation are
shown in the drawing.

Fig. 1 Schematic drawing of the modeled PWR secondary system

Hydrazine, ammonia and ETA were considered as the substances in the PWR secondary waterchemistry. Hydrazine and ammonia exist under the AVT condition and hydrazine, ammonia and ETA
exist under the ETA injection condition. The water chemistry is changed by the plant itself and theplant operating cycle. In this study, 0.1 ppm hydrazine concentration and 0.4 ppm ammonia
concentration were assumed as the typical AVT feed water chemistry (pH about 9.2) and 0.1 ppm
hydrazine and 9 ppm ETA were assumed as the typical ETA injection feed water chemistry (pH about
9.8) based on reported [6-8] water chemistry; this allowed comparison between the low pH AVT
condition and the high pH ETA injection condition.
Water chemistry for each component of the PWR secondary system was calculated as follows.
When system A branches to system B and system C, mass balance can be expressed as equation (1).
In equation (1), the flow rates of systems A, B, C are FA , FB , FC and the substance concentrations ofsystems A, B, C are C A , C B , C C , respectively.
The flow rates were obtained from a heat balance sheet. The downstream water chemistry was132

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

calculated from the mass balance using the typical feed water chemistry assumed before as the initialvalue, taking into consideration the thermal decomposition and liquid-vapor distribution ofsubstances.
Ammonia in feed water is stable at the plant operating temperature, but hydrazine undergoes
thermal decomposition. Additionally, thermal decomposition of ETA is considered to be negligible
based on actual plant measurement results of organic substances. Therefore in this study only
hydrazine was assumed to experience thermal decomposition, as expressed by equation (2), in the SG
which is the highest temperature component in the PWR secondary system.
Hydrazine concentration time-dependence is expressed in equation (3), assuming a general
first-order kinetics reaction. In equation (3) C 0 is the concentration at time 0, C (t ) is theconcentration at time t and λis the thermal decomposition constant.
Hydrazine, ammonia and ETA are volatile substances and there is a liquid-vapor distribution at
the SG and MSR. The liquid-vapor distribution coefficient K D is expressed in equation (4), where
CV , X and C L , X are substance concentrations in vapor and liquid, respectively. X represents thesubstance being considered, either hydrazine, ammonia or ETA.
In order to execute the water chemistry model calculations, λ of hydrazine in an actual plant
SG and K D of hydrazine, ammonia and ETA in an actual plant SG and MSR need to be determined.
To determine λ and K D , the expected range of λ was assumed as 0.3 to 0.4 min-1 and expected

ranges of K D hydrazine, ammonia and ETA were assumed as 0.1 to 0.4, 1.6 to 4.6 and 0.1 to 0.5,
respectively, from literature data and measurements in an actual plant. Water chemistry model
calculations of the PWR secondary system were carried out usingλ and K D as parameters. For thismodel calculation, feed water chemistry was used as input conditions. The calculated water chemistry
results were compared with the actual plant data, specially obtained at different feed water conditions,then parameter fittings ofλ and K D were carried out.

FA × C A = FB × C B + FC × C C(1)

8N2H4 →

(2)

10NH3 + 3N2 + H2

C (t ) = C 0 × e − λt

KD =

(3)

CV , X(4)

C L, X

2.2. Results of water chemistry model calculations
Optimized values ofλ and K D , shown in Table 1, were obtained as results of the parameter

fittings of λ in equation (3) and K D in equation (4), by comparing water chemistry calculated byequation (1) and the water chemistry in measured the actual plant.
Table 1 Optimized values ofλand K D-1

λ, minK D (Hydrazine)
K D (Ammonia)
K D (ETA)

SG
0.3
0.3
1.9
0.36

133

MSR
0.12
3.4
0.23

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

Fig. 2 shows the relationship between measured values in the actual plant and calculated values(explained in 2.1) of hydrazine, ammonia and ETA concentrations in the PWR secondary system. The
calculated and measured values showed a good correlation, and it was confirmed that the PWR
secondary system water chemistry can be calculated successfully using these model calculations.
1

Normalized calculated value
11

Hydrazine
Ammonia

0.8

ETA

0.6

0.4

0.2

0
0

0.2

0.4

0.6

0.8

1

Normalized measured value

Fig. 2 Relationship between measured and calculated values of hydrazine, ammonia and ETA
concentrations in the PWR secondary system(Values of hydrazine, ammonia and ETA are normalized by 0.4ppm, 0.2ppm and 10ppm, respectively)

Table 2 shows the calculated water chemistry and pH at the 22 major components of the PWR
secondary system; the input feed water conditions were: 0.1 ppm hydrazine + 0.4 ppm ammonia for
the AVT condition; and 0.1 ppm hydrazine + 9 ppm ETA for the ETA injection condition. In Table 2,
liquid phase water chemistry is shown for the two phase flow part and at the operating temperature pH.
It was found that water chemistry varies at each component of the PWR secondary system and ETA
injection causes high pH throughout the PWR secondary system.
Table 2 Calculated result s of water chemistry
Component
1.Condensate pump
2.LP-Preheater1
3.LP-Preheater2
4.LP-Preheater3
5.LP-Preheater4
6.Deaerator in
7.Deaerator out
8.HP-Preheater
9.SG
10.HP turbine1
11.HP turbine2
12.LP turbine1
13.LP turbine2
14.LP turbine3
15.LP turbine4
16.LP turbine5
17.MSR drain
18.HP-Preheater drain
19.LP-Preheater drain1
20.LP-Preheater drain2
21.LP-Preheater drain3
22.LP-Preheater drain4

AVT condition
Concentration /ppm
Hydrazine Ammonia
0.10
0.40
0.10
0.40
0.09
0.42
0.09
0.42
0.09
0.42
0.09
0.42
0.10
0.40
0.10
0.40
0.17
0.25
0.24
0.23
0.27
0.22
0.48
0.21
0.38
0.22
0.31
0.21
0.25
0.20
0.21
0.18
0.27
0.22
0.06
0.43
0.03
0.45
0.03
0.46
0.03
0.47
0.04
0.47

pH
8.9
8.0
7.4
7.0
6.8
6.8
6.3
6.0
5.7
5.9
6.2
6.9
7.2
7.7
8.1
8.7
6.2
6.3
7.0
7.3
7.9
8.0

134

ETA condition
Concentration /ppm
Hydrazine Ammonia
ETA
0.10
0.03
5.7
0.11
0.03
6.5
0.10
0.03
6.7
0.10
0.03
6.7
0.10
0.03
6.7
0.10
0.03
6.7
0.10
0.00
9.0
0.10
0.00
9.0
0.16
0.01
25.6
0.21
0.01
28.0
0.25
0.01
29.9
0.44
0.01
41.2
0.37
0.01
38.5
0.32
0.01
36.1
0.27
0.00
32.2
0.23
0.00
28.8
0.25
0.01
29.9
0.06
0.03
8.3
0.04
0.03
6.0
0.04
0.03
6.0
0.03
0.03
5.6
0.05
0.03
7.3

pH
9.4
8.5
7.9
7.5
7.3
7.3
6.9
6.5
6.5
6.8
7.1
7.9
8.3
8.8
9.2
9.8
7.2
6.8
7.4
7.8
8.3
8.5

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

3. Wall thinning rate evaluation due to FAC
3.1. Procedure for the rotary disk test
The rotary disk test is one type of corrosion rate measurement; a disk type specimen is rotated athigh speed in order to simulate the high flow condition. In order to evaluate the wall thinning rate due
to FAC, the rotary disk test was executed using carbon steel specimens under PWR secondary systemwater chemistry.
Table 3 shows the chemical composition of the carbon steel tested. Low chromium (0.02 wt%)
carbon steel was used because its wall thinning rate susceptibility was thought to be high. The
specimen diameter and thickness were 275 mm and 3 mm, respectively. The rotation speed was 35
m/s at the outermost edge of the specimens. A high rotation speed was selected to simulate a high wall
thinning rate due to FAC under a turbulent flow condition, although flow rate of the single phase of
the actual plant is as low as 6 m/s. Fig. 3 shows a schematic drawing of the rotary disk test system.
The PWR secondary system simulated water was discharged outside the system to avoid theinfluence of dissolved iron after passing through the system once. The PWR secondary systemsimulated water was made up to the required water chemistry in the chemical control tank, and it washeated to the desired temperature using a heater. Then it was supplied to the test part at a flow rate of
5 dm3/h. This flow rate was selected as sufficient based on the volume of the test section being about
2 dm3.
The wall thinning rate due to FAC ( J ) was calculated using the weight loss, that is the difference
between the pre-test specimen weight ( W0 ) and the after test specimen weight ( W ) divided by the
specimen surface area ( S ) and test time ( t test ) as shown in equation (5). The test time was fixed at
100 hours.

J=

W0 − WS × t test(5)

Eight representative components of the PWR secondary system were selected for testing thewater chemistry calculated in section 2.2. The numbers in parentheses correspond to the number of
each component in Table 2. The components were: Condensate pump (1); LP-preheater 2(3);LP-preheater 4(5); Deaerator out (7); HP-preheater (8); SG (9); HP-turbine 1 (10); and MSR drain(17).
Table 3 Chemical composition of carbon steel test material

Cr
0.02

C
0.002

Si
Tr.

Mn
0.05

P
S
N
0.004 0.002 0.0025

135

Ni
0.01

Cu
0.01

Fe
Bal.

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

Fig. 3

Schematic drawing of the rotary disk test system

3.2. Results of rotary disk test
Fig. 4 shows some photos of the outer appearance of the post-test specimens. The specimens
were covered with black magnetite oxide film and partially worn. The wear situation differeddepending on the water chemistry and temperature. The AVT condition showed more severe wear thanthe ETA injection condition for the LP-preheater 4 and Deaerator out. In the AVT condition, no
remarkable wear was observed at 274ºC, but remarkable wear was observed at 180 and 142ºC.
Furthermore observations by scanning electron microscope showed fish-eye type wear which iscommon in FAC.

ETA injection

AVT

LPpreheater4
water
chemstry142ºC

Deaeratorwater
chemistry
180ºC

100 μm

SG waterchemistry
274ºC
100 mmFig. 4

Specimen surface appearances after rotary disk test136

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

Fig. 5 shows measurement results of wall thinning rate due to FAC obtained by the rotary disk
test. The wall thinning rates due to FAC of the condensate pump and SG were almost the same under
AVT and ETA injection conditions, but for other components wall thinning rates due to FAC under the
ETA injection condition were reduced remarkably compared to the AVT condition.

17.MSR drain
ETA

10.HP turbine1

AVT

9.SG
Component 8.HP-Preheater
7.Deaerater out
5.LP-Preheater4
3.LP-Preheater2
1.Condensate pump
0.0

0.2

0.4

0.6

0.8

1.0

FAC rate, g/m2/h

Fig. 5

Measured FAC rates in AVT and ETA injection conditions for the rotary disk test
(Numbers for components refer to Table 2.)

3.3. Wall thing rate evaluation procedure based on magnetite solubility
The difference of wall thinning rate due to FAC between the AVT and ETA injection conditions
was evaluated from the viewpoint of magnetite solubility.
A carbon steel surface which contacts with high temperature deaerated water as in the PWR
secondary system, is covered with magnetite (Fe3O4) oxide film which is formed by the Schikorr
reaction expressed in equation (6).
Fe + 2H2O → Fe(OH)2 + H2
3Fe(OH)2 → Fe3O4 + 2H2O + H2

(6)

FAC is a phenomenon in which dissolution of magnetite produced on the carbon steel surface ispromoted by the fluid flow. On the magnetite surface, magnetite and iron ion are in equilibrium andthe iron ion concentration on the magnetite surface is equal to the magnetite solubility. The FAC
model of FAC rate is proportional to the concentration difference between surface and bulk iron ion
concentrations expressed in equation (7), where CS is magnetite solubility, Cb is iron concentration of
bulk water and k is mass transfer coefficient. In this model, wall thinning rate due to FAC becomes
higher when magnetite solubility is high. Fig. 6 shows a schematic of this model. Furthermore
equation (7) can be approximated as equation (8) when Cb is sufficiently smaller than CS.

137

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

J = k (C S − C b )(7)

J = kC S(8)In order to determine the magnetite solubility, equations (9) to (15) were taken into consideration
as the main dissolution reactions of magnetite.
Fe3O4 + 6H+ + H2 ↔ 3Fe2+ + 4H2O

(9)

Fe3O4 + 3H+ + H2 ↔ 3Fe(OH)+ + H2O(10)

Fe3O4 + 5H2O + H2 ↔ 3Fe(OH)3-+3H+↔ 3HFeO2-+3H++H2O(11)

Fe3O4 + 5H2O + H2 ↔ 3FeO22- + 6H+ + H2O(12)

Fe3O4 + 9H+ ↔ 3Fe3+ + 4H2O + 1/2H2(13)

Fe3O4 + 6H+ ↔ 3Fe(OH)2+ + H2O + 1/2H2(14)

Fe3O4 + 3H+ +2 H2O ↔ 3Fe(OH)2+ + 1/2H2(15)

A reaction constant K is defined for each reaction. For example, the reaction constant K1 is shownas equation (16). [Fe2+] and [H+] are concentrations of Fe2+ and H+, respectively. PH2 is partial pressureof hydrogen. The relationship between the Gibbs free energy ΔG0 and the reaction constant K isestablished in equation (17) from thermodynamics. In equation (17), R is the gas constant and T is
absolute temperature. Regarding equation (16), Fe2+ concentration is shown in equation (18), using pH= -log[H+] and equation (17). Only the partial pressure of dissolved hydrogen, the pH at thetemperature of interest and ΔG0 need to be known. The reaction constant can be determined using
the concentration of Fe2+ calculated in equation (18).

[ Fe 2+ ]3
K1 =[ H + ]6･PH 2(16)∆G 0 = − RT ln K

(17)

1
∆G 0
1
log[ Fe ] = − ⋅- 2 pH + log PH 2
3 2.3026 RT
3

(18)

2+

Regarding equations (10) to (15), this reaction constant can also be determined. The partialpressure of dissolved hydrogen can be shown as equation (19) from Henry’s law. In equation (19) χis dissolved hydrogen mole fraction and KH is a proportionality constant. Regarding equation (9), Δ
G0 is expressed by equation (20), where G10 , G 20 , G30 , G 40 , G50 are Gibbs free energies of Fe2+, H2O,
Fe3O4, H+, H2, respectively. The Gibbs free energy at specific temperature T, ΔG0(T) is shown in0equation (21), where C p (T ) is specific heat at constant pressure. Regarding the ion species forwhich specific heat is not known, it was calculated by equations (22), (23) and (24) based on a
Criss-Cobble corresponding theory[10].

138T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

PH 2 = K H ⋅ χ(19)∆G 0 = 3G10 + 4G20 − G30 − 6G40 − G50(20)

Cp 0 (T )dT − (T − 298) S 0 (298)
298
T

T

G 0 (T ) = G 0 (298) + ∫ Cp 0 (T )dT −T ∫
298

T

0
0
S abs
(T ) − S abs
(298)
T
ln
298
0
0
S abs (T ) = A(T ) + B(T ) ⋅ S abs
(298)

(22)

C p0 ]T298 =

(23)

0
0
(T ) = S conv
(T ) − 20.92 ⋅ Z
S abs
0

(21)

(24)

0

In equations (22) to (24), S abs (T )，S conv (T )，Z are absolute entropy, entropy and valence ofion, respectively. A(T) and B(T) are constants determined by the ion species. Because of the lack ofA(T) and B(T) values at high temperature, the linear relationship in equation (23) was assumed fortemperatures over 473K.
Solubility of magnetite

CS : solubility of magnetite at surface
Deaerated high temperature water
FAC rate : J = k (CS-Cb)

Carbonsteel= k CS ( ←Cs>>Cb)

Magnetitelayer

k : coefficient of material transfer

Cb : solubility of magnetite at bulk

Fig. 6

Distance from surface

Schematic drawing of the FAC model

3.4. Results of wall thinning rate evaluation based on magnetite solubility
Fig. 7 shows magnetite solubility obtained using the calculation procedure described in section
3.3 and water chemistry under the AVT and ETA injection conditions shown in Table 2. Under the
ETA injection condition, magnetite solubility in the PWR secondary system was decreased comparedto the AVT condition.
Fig. 8 compares the FAC reduction rates under the AVT and ETA injection conditions obtained
from: solubility of magnetite (equation (25)) and the rotary disk test (equation (26)). RS ETA / AVT isbased on the model of FAC rate being proportional to magnetite solubility. In equation (25), CETA andCAVT are the magnetite solubility under the ETA injection condition and AVT condition, respectively.

139

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

From the results of the magnetite solubility calculation, FAC rate is expected to be lowered fromabout 0.1 to 0.3 by ETA injection. RRETA/AVT was evaluated by the FAC rate measured from therotary disk test described in section 3.2. In equation (26), JETA and JAVT are FAC rates of the ETA
injection condition and AVT condition. Regarding the SG and condensate pump, RRETA/AVT differs
remarkably from RSETA/AVT.

C ETA
C AVT
J
RRETA / AVT = ETAJ AVTRS ETA / AVT =

(25)
(26)

22.LP-Preheater drain4
21.LP-Preheater drain3
20.LP-Preheater drain2
19.LP-Preheater drain1
18.HP-Preheater drain
17.MSR drain
16.LP turbine5
15.LP turbine4
14.LP turbine3
13.LP turbine2
Component 12.LP turbine1
11.HP turbine2
10.HP turbine1
9.SG
8.HP-Preheater
7.Dearater out
6.Dearater in
5.LP-Preheater4
4.LP-Preheater3
3.LP-Preheater2
2.LP-Preheater1
1.Condensate pump

ETA
AVT

Two phase

0

2

4

6

8

10

12

Solubility of magnetite, ppb

Fig. 7

Calculated magnetite solubility under ETA and AVT conditions in the PWR secondary system

140

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

22.LP-Preheater drain4
21.LP-Preheater drain3
20.LP-Preheater drain2
19.LP-Preheater drain1
18.HP-Preheater drain
17.MSR drain
16.LP turbine5
15.LP turbine4
14.LP turbine3
13.LP turbine2
Component 12.LP turbine1
11.HP turbine2
10.HP turbine1
9.SG
8.HP-Preheater
7.Dearater out
6.Dearater in
5.LP-Preheater4
4.LP-Preheater3
3.LP-Preheater2
2.LP-Preheater1
1.Condensate pumpRotary disk test
Solubility of magnetite

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

FAC reduction rate, RSETA/AVT and RRETA/AVT

Fig. 8Comparison of FAC reduction rates obtained from solubility of magnetite (equation (25), greenbars) and the rotary disk test (equation (26), pink bars)

4. Discussion
4.1. Model calculations of the PWR secondary system
Model calculations were carried out regarding evaluation of the PWR secondary system waterchemistry. The evaluation was based on the mass balance calculation taking into consideration thethermal decomposition constant of hydrazine in the SG and the liquid-vapor distribution coefficient ofvolatile substances in the SG and MSR which were determined by parameter fitting. The calculated
and measured water chemistry showed a good correlation as noted earlier (Fig. 2), and water chemistryof the PWR secondary system is considered to be able to provide an evaluation with sufficientaccuracy.
Fig.9 compares pH, FAC rate and magnetite solubility under the ETA injection and AVT
conditions. As seen there and in Table 2, the pH at each component under the ETA injection condition
increases compared to the AVT condition. The ETA injection is considered to be effective forincreasing the pH value of the PWR secondary system. Furthermore in the two phase condition suchas at the SG , the concentration of ammonia, which is used to adjust the pH, is decreased under the
AVT condition, while the concentration of ETA, also used for pH adjustment, is increased under the
ETA injection condition as shown in Table 2. The behavior of pH adjustment compounds in the PWR
secondary system differs depending on the actual compound used such as ammonia and ETA. The
water chemistry of the PWR secondary system can be changed dramatically by changing waterchemistry of the feed water. It is important to understand the effect of water chemistry change.

141

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

Fig. 9pH, FAC rate and magnetite solubility under ETA injection and AVT conditions

4.2. Evaluation of wall thinning rate due to FAC by rotary disk test
Regarding measurement of wall thinning rate due to FAC by the rotary disk test, it is thought tohave been measured successfully because fish-eye type wear was observed on the specimens (Fig. 4);
such wear is commonly seen for FAC in this test. In Fig. 4, the surface appearances of the posttest
specimens are different, depending on water chemistry and temperature condition. The degree ofoxide film peeling of the specimen surface under the ETA injection condition is less than that underthe AVT condition, so that the inhibitive effect of FAC due to ETA injection can be seen. Furthermore
under the AVT condition, the degree of oxide film peeling of the specimen surface at 142ºC is more
remarkable than at the other temperatures, so that the effect of temperature can be seen, although it isnecessary to pay attention to the fact that water chemistry is slightly different.
Comparison of the wall thinning rates of the rotary disk test between ETA injection and AVT
conditions indicates that the wall thinning rate due to FAC under the ETA injection condition islowered to a fraction of the value under the AVT condition except at the SG and condensate pump as
shown in Fig. 5. At the SG and condensate pump, the wall thinning rate due to FAC under the ETA
injection condition is nearly the same as under the AVT condition. As shown in Fig. 9 and Table 2,each pH value at the components of the PWR secondary system is increased by ETA injection; theinhibitive effect on FAC rate by ETA injection can be seen for some components, but the degree of the
FAC inhibitive effect is a fraction at most, and it is not a sufficient enough effect to allow neglect of
the FAC. On the other hand there are components where the inhibitive effect cannot be seen despite
the increased pH. Therefore maintenance of carbon steel components is considered to be necessary
after ETA injection.
In order to consider why the inhibitive effect of the FAC rate differs among components, the FAC
rate measured by the rotary disk test was organized by pH and is shown in Fig. 10 and was organizedby temperature and is shown in Fig. 11. In Fig. 10, the FAC rate measured by the rotary disk test does
not show a simple decrease at high pH, some small FAC rate data like for the SG under the AVT
condition are seen. It is considered that FAC rate is not controlled only by pH but also by atemperature effect. Fig. 11 has a bell- shaped temperature dependency for FAC rate. The peak of the
FAC rate is at about 180ºC under the AVT condition and over 220ºC under the ETA injection
condition. Under the ETA injection condition, the peak of its FAC rate shifts to higher temperature. It
should be noted that no inhibitive effect of FAC rate is seen for the SG at 274ºC with ETA. Also no
inhibitive effect of the FAC rate is seen for the condensate pump at 33ºC with ETA, and it isconsidered the reaction rate is very small due to the low temperature.

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T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

1
ETA
AVT

FAC rate, g/m2/h

0.8

0.6

0.4

SG
Condensate
pump

0.2

0

5

6

7

8

9

10

pH at operating temperature

Fig. 10

pH dependency of measured FAC rates

1
ETA
AVT

FAC rate, g/m2/h

0.8

0.6

0.4

SG
Condensate
pump

0.2

0

0

50

150

100

200

250

300

Temperature, ºC

Fig. 11

Temperature dependency of measured FAC rates

4.3. Evaluation of wall thinning rate due to FAC based on magnetite solubility
As shown in Fig. 7, the magnetite solubility in the PWR secondary system is decreased under the
ETA injection condition in a range from a fractional amount to one order of magnitude compared to
the AVT condition. The reduction of wall thinning rate by ETA injection is expected considering thatthe model of wall thinning rate due to FAC is proportional to the magnetite solubility.
But comparing the FAC reduction rates of the expected value from the calculated magnetite
solubility and the measured value from the rotary disk test, it is seen that FAC rates of the SG at hightemperature and the condensate pump at low temperature measured by the rotary disk test do notshow the reduction expected from the calculated magnetite solubility even though some of the othercomponents showed a good correlation (Fig. 8). This result is considered to show the limitation of143

T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

adopting the model of wall thinning rate due to FAC which is proportional to the magnetite solubility
at high and low temperature components.
Fig. 12 shows the relationship between calculated magnetite solubility and measured FAC rate ofsection 3.2. While the observed tendency for the FAC rate is to increase due to increasing magnetite
solubility, some low FAC rate data such as for the condensate pump are observed regardless of themagnetite solubility being high under the AVT condition. The reason for the low FAC rate for thecondensate pump regardless of the high magnetite solubility is considered to be the small reaction rate
due to the low temperature. And therefore the calculated FAC rate is high due to high magnetite
solubility, but the measured FAC rate is small due to the small reaction rate at low temperature. And
one of the reasons for the low FAC rate for the SG (which is at a high temperature) is considered to be
the change the magnetite dissolution reaction due to the changing oxide film property [11] at hightemperature.

1.0
AVT

FAC rate, g/m2/h

0.8

ETA

0.6

0.4

0.2

SG
Condensate pump

0.0

0

1

2

3

4

5

6

Solubility of magnetite, ppb

Fig. 12

Relationship between calculated magnetite solubility and measured FAC rate

5. Conclusion
For the purpose of evaluating the effect of ETA injection on FAC rate, at first a water chemistryevaluation of the PWR secondary system under AVT and ETA injection conditions was made bymodel calculations, then FAC rate measurements of some components of the PWR secondary systemwere made by the rotary disk test, and finally the FAC reduction rate evaluation was carried out frommagnetite solubility calculations. The following findings were obtained.
(1) The PWR secondary system water chemistry can be evaluated with suitable accuracy by themass balance calculation taking into consideration the thermal decomposition of hydrazine in the SG
and the liquid-vapor distribution of volatile substances in the SG and MSR.
(2)Because behavior of the PWR secondary system water chemistry varies drastically with thechemical substances present and the components of system, it is necessary to know the effect of waterchemistry on each components of PWR secondary system when changing the water chemistry.
(3) ETA injection is effective to increase pH of the PWR secondary system.
(4) The inhibition effect on FAC rate was observed for almost all components of the PWR

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T. Fukumura/ Effect of Ethanolamine Injection on Wall Thinning Rateof PWR Carbon Steel Components

secondary system in the rotary disk test under the ETA injection condition, but ETA injection was not
sufficient to allow neglect of the FAC.
(5) There were some components which had a small FAC rate inhibition effect for the ETA
injection condition in the rotary disk test, such as the low temperature condensate pump and hightemperature SG.
(6) There is a limitation to adopting the model of wall thinning rate due to FAC which is
proportional to magnetite solubility for high and low temperature components of the PWR secondary
system.

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