Many boiling water nuclear reactors (BWRs) throughout the world have applied the NobleChemTM (or noble metal chemical addition: NMCA) process just before end-of-cycle shutdown or during a mid-cycle shutdown to mitigate the stress corrosion cracking (SCC) of structural materials in BWRs. The first Online NMCA (OLNC) plant demonstration was successfully completed during the summer of 2005 while the reactor was in power operation. When injected into BWR environments, the noble metal particles deposit on Type 304 stainless steel surfaces and reduce the corrosion potential, which decreases the propensity for SCC. Very fine noble metal particles are formed and able to potentially deposit inside the crack and maintain catalytic surfaces in the critical regions inside the crack. This paper discusses the effect of various environmental factors that control the size and distribution of noble metal particles on the surface during injection of the noble metal salts, and highlight the benefits associated with the Online NMCA process.

Subject
Water, Intergranular stress corrosion cracking, Boiling water reactors, Metal surfaces, Reactors, Noble metals, Crevices, Molar ratio, Oxide surfaces, Cracks, Corrosion potential, Stress corrosion cracking, Hydrogen
Keywords:
BWR, Noble Metal Chemical Addition (NMCA), On-Line NMCA (OLNC), ECP, IGSCC
© 2007 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).
2007
Association for Materials Protection and Performance (AMPP)
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