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152

ENSI Erfahrungs- und Forschungsbericht 2011

3.6. Pt concentration on the

specimen surface

Table 3 shows the Pt concentration measured on

the specimens from Tests 1 and 2. Although no

Pt particles were discovered in the SEM analysis

(apart from the pre-oxidised specimens of Test 2),

a very low but clearly measurable amount of Pt

has been detected on the surface of all specimens

using LA-ICP-MS. The Pt concentration was found

to be homogenous over the 120 measurement

points across the front and back side of each spe-

cimen. However, the uncertainty level marked in

the table amounts up to 50 %, mainly caused by

the calibration curve recorded at higher concent-

rations.

In spite of the high level of uncertainty, a clear

trend in Pt concentration between Tests 1 and 2

and also between the non pre-oxidised and pre-

oxidised specimens can be seen. The specimens

of Test 1 have less Pt deposited on the surfaces

than the ones from Test 2. This could be due to

the higher Pt injection rate in Test 2 resulting in a

higher Pt concentration in the high-temperature

water (Table 2). This result is also confirmed by the

more pronounced reduction of the ECP during Pt

injection in Test 2 (see Section 3.4). In case of both

tests, the non pre-oxidised specimens revealed lo-

wer Pt concentrations than the pre-oxidised. This

might be explained by the different size distribu-

tion of the oxide crystals, such as bimodal struc-

tures, leading to a higher surface roughness and

therefore more effective Pt deposition behaviour.

3.7. Summary

In a sophisticated high-temperature water loop

facility at PSI two experiments were performed in-

vestigating the Pt deposition behaviour under si-

mulated BWR conditions at two different (extre-

mely low) Pt injection rates and with differently

pre-treated coupon specimens. Taken together all

observations from the ECP measurements, SEM

and LA-ICP-MS analyses, these first tests show that

a more effective Pt deposition, resulting in a lower

ECP and therefore better protection against SCC,

could be achieved using a higher Pt injection rate

(corresponding to a higher Pt concentration in the

high-temperature water). Pre-oxidation of the spe-

cimens seems to additionally increase the Pt con-

centration on the specimen surface. Due to the

preliminary character of these results no further

conclusions can be drawn at this stage.

A more detailed analysis of the surface/oxide film

structure (e.g., using TEM) is necessary to get a

more conclusive picture of the Pt distribution on

stainless steel. Experiments with higher amounts

of Pt (closer to plant OLNC application conditions)

and different injection rates are underway to con-

firm the results and to get better insights into the

Pt deposition behaviour and processes behind. An

example image from such a test is shown in the

following sub-chapter.

3.8. Example image of a specimen

with higher Pt particle density

A SEM micrograph of a specimen from the latest

experiment, where a higher amount of Pt has been

injected into the high-temperature water loop

(665 µg) is shown in Figure 4. In contrast to the

first two tests (see above) a rather high density of

small Pt particles with a size distribution ranging

from 12 to 20 nm (15 nm in average) can be ob-

served on the oxide crystals. The analytical investi-

gation of this test (together with other compara-

ble tests) is still ongoing and conclusive results are

expected soon.

4. National collaborations

The collaboration and technology transfer on the

national level takes place within the Swiss nuclear

Test 1

Pt concentration [ng/cm

]

Test 2

Pt concentration [ng/cm

]

Non pre-oxidised Pre-oxidised Non pre-oxidised Pre-oxidised

10 ± 3 17 ± 6 11 ± 5 19 ± 6

Table 3:

Pt concentration on the

surface of specimens from

Tests 1 and 2, determined

by LA-ICP-MS.

1 2 ... 149 150 151 152 153 154 155 156 157 158 159 ... 303 304

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