Hydrogen Water Chemistry (HWC) has been successfully employed to mitigate the IGSCC of BWR internals over the past decade, However, the use of elevated levels of feed water hydrogen in the BWR results in high operating dose rates due to N16 partitioning into the main steam. Recent studies have shown that the presence of noble metals on reactor internal surfaces, by alloying or by various spray techniques could significantly reduce the hydrogen demand necessary to achieve the IGSCC protection potential of-230 mV(SHE) without the operating dose rate increase.

A simpler method of applying noble metal on to reactor internals involve the addition of a noble metal compound into reactor water to cause deposition of noble metal from solution onto surfaces. This noble metal chemical addition (NMCA) technology has been successfully used in numerous laboratory tests to produce a "noble metal like" surface on three of the major structural materials, Type 304 SS, Inconel 600 and Alloy 182, used in the nuclear industry. The success of this technology has been tested using constant extension rate tensile (CERT) tests, crack growth rate (CGR) tests and electrochemical corrosion potential (ECP) response tests. The NMCA technology has successfully decreased the ECP of surfaces below -230 mV(SHE), prevented crack initiation and mitigated crack growth rates in stoichiometric excess hydrogen in simulated boiling water reactor (BWR) environments. The NMCA treatment of surfaces has drastically lowered the hydrogen demand necessary for IGSCC protection of the materials tested, with no identified side effects including no adverse effects on zircaloy fuel cladding materials.

This paper describes the performance of the first NMCA treated BWR over a 12 month period. The paper will also describe the application of NMCA technology to internal components of the BWR by employing the reactor coolant water as the medium of transport for depositing noble metal on in-reactor surfaces. The paper will also describe results obtained during the process application, the plant response to low hydrogen after NMCA treatment and the plant performance in maintaining low ECPs during the fuel cycle. The benefits of the application of NMCA technology to the operating BWR fleet will also be highlighted.

Subject
Water, Intergranular stress corrosion cracking, Boiling water reactors, Hydrogen concentration, Recirculation, Metal surfaces, Reactors, Noble metals, Outages, Rods, Flanges, Feedwater, Hydrogen
Keywords:
intergranular stress corrosion cracking, noble metal chemical addition, electrochemical corrosion potential, hydrogen water chemistry
© 1998 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).
1998
Association for Materials Protection and Performance (AMPP)
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