The final disposal plan for low and intermediate level decommissioning metal waste from Olkiluoto Nuclear Power Plant in Finland is to pack them in concrete boxes and place these boxes into bedrock silos. This metal waste consists of mainly carbon steel. For safety evaluation it is necessary to be able to estimate the corrosion rate of carbon steel for an extensive time period. Therefore a long term field exposure to measure quantitatively the corrosion rate of carbon steel in the environment simulating the final repository conditions was started in the bedrock in 1998. Besides carbon steel, the corrosion of zinc coated steel, a material for rock bolts of the repository, and that of pure zinc was investigated in the same ground water positions.

In oxygen free water the corrosion of carbon steel is very low, unless the water is acidic or there is microbiological activity on the surfaces. In these cases, increased corrosion rates of carbon steel have been detected and in the latest measurements the corrosion of zinc had clearly increased as well. DGGE (Denaturing Gradient Gel Electrophoresis)-technique was used to compare the diversity and similarity of predominant bacterial populations on the surfaces of carbon steel and zinc specimens.

In this paper the corrosion exposure results after 33 months and 136 months immersions of carbon steel as well as results from 113 months immersion of zinc and 92 months immersion of zinc coated steel are presented. The site tests are ongoing and further sampling will be done.

Subject
Coated steel, Steel surfaces, Water, Materials, Corrosion rate, Corrosion detection, Oxygen, Carbon steel, Immersion, Deposit corrosion, Zinc, Samples, Sampling
Keywords:
carbon steel, zinc, localized corrosion, repository conditions, microbiologically influenced corrosion
© 2012 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2012
Association for Materials Protection and Performance (AMPP)
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