Caple AUF900 Manual de usuario descargar pdf (Pagina 152)

150

ENSI Erfahrungs- und Forschungsbericht 2011

and outlet (dissolved oxygen (DO), dissolved hyd-

rogen (DH),

k, T, p, flow rate, etc.) were recorded

continuously. Four coupon specimens (two pre-

oxidised and two in «as received» state) were ex-

posed to the high-temperature water in the au-

toclave, whereas one of them («as received» sta-

te) was electrically connected with a wire for ECP

measurement. The ECP of this specimen, of the

autoclave and the redox potential (Pt sheet) were

measured vs. a Cu/Cu

O ZrO

-membrane refe-

rence electrode. BWR conditions were simulated

with high-purity water at a temperature of 280 °C

and pressure of 90 bar. For HWC conditions, a

mixture of H

and O

was adjusted (stoichiomet-

ric excess of H

). The Pt compound (Na

Pt(OH)

)

was injected through ion-chromatography tubing

into the inlet water stream by an Eldex high-pres-

sure dosing pump after one week of pre-oxidation

(«t = 0»). Following several pre-tests, two compa-

rable tests were performed injecting the same to-

tal amount of Pt at two different Pt injection ra-

tes. Compared to plant OLNC applications, injec-

tion rates as well as the total amount of Pt injec-

ted were much lower in these tests. Three days af-

ter the Pt injection was finished, the experiments

were shut-down. The major test parameters can

be seen in Table 2.

3.3. Analytical techniques

The microstructural investigations were performed

using a Zeiss scanning electron microscope (SEM)

equipped with a field emission gun and X-ray

energy dispersive spectrometer (EDS) from EDAX

for chemical analyses. A secondary electron detec-

tor was used to investigate the oxide layer topo-

graphy, whereas a back scattered electron detec-

tor was used to identify Z (chemical) contrast ac-

ross the oxide layers.

The Pt concentration on the surface of all speci-

mens was measured by Laser Ablation-Inductively

Coupled Plasma-Mass Spectrometry (LA-ICP-MS).

Front and back side of the specimens were abla-

ted using a UV laser ablation system, coupled to

a sectorfield ICP-MS instrument (Element 2, Ther-

mo Fisher Scientific, Bremen, Germany). The la-

ser system is a quadrupled Nd:YAG laser delive-

ring a beam of 266 nm wavelength [15]. Analy-

ses of Pt on the specimens were carried out using

a point analysis mode. The Pt standards used for

the calculation of the Pt concentration on the sur-

face of the specimens are homogenous thin films

of Pt with a layer thickness of 0.14 and 1.4 nm on

SiO

substrate. The layer thickness corresponds to

0.3 and 3 μg/cm

3.4. Effect of Pt injection rate on

the electrochemical corrosion

potential

Figures 2a and 2b show the course of the speci-

men, autoclave and redox potentials during Tests

1 and 2, respectively. The small fluctuations of the

potential curves are due to short interruptions of

the Pt injection (e.g., change of the Pt injection so-

lution) and due to water sampling. Just before the

Pt injection the specimen potentials of both tests

were in a comparable range at about -200 and

Experiment designation Test 1 Test 2

Experiment duration [h]

477 305

Pressure [bar]

90 90

Temperature

autoclave

[°C]

280 280

Mass flow rate

inlet water

[kg/h]

10 10

Water chemistry Inlet Outlet Inlet Outlet

Molar ratio (DH/DO)

DH [ppb]

DO [ppb]

Conductivity [µS/cm]

4.6

258

0.055

0.070

4.9

244

0.055

–

0.060

Pt conc. of solution [ppb]

9.7 9.6

Pt injection period [h]

207 40

Pt injection rate [µg/h]

0.24 1.20

Nom. Pt conc. in water [ppt]

24 120

Total Pt injected [µg]

48.6 47.9

Table 2:

Summary of the major

test parameters during

the two experiments.

1 2 ... 147 148 149 150 151 152 153 154 155 156 157 ... 303 304

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