Control Strategies for a Purified Water System at a Nuclear Generating Station

Developing an Effective Practical Solution

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Client

A large nuclear generating station (NGS) in North America.

Scope of work

Corrosion of a stainless steel liner was detected in the irradiated fuel bay (IFB) at a nuclear generating station. IFB leakage due to corrosion cannot be tolerated because of the danger of radiological release into the environment. Large numbers of bacteria were found, and associated with sediments at the bottom of the IFB.

Microbiologically influenced corrosion (MIC) may have played an important role in the corrosion process at this station because corrosion was occurring in locations distant from the welds, i.e. areas where there were unlikely to be crevices. Corrosion product analyses by Kinectrics revealed the presence of bacteria that have been implicated in the corrosion of stainless steels.

A strategic approach

Kinectrics developed a strategic approach for an effective solution to eliminate the source of the corrosion.

1. An optimum dose of hydrogen peroxide, to be used as a biofouling control measure, was determined in lab experiments.
2. A program for the addition of hydrogen peroxide in the IFB at regular intervals was initiated

3. Stainless-steel coupons immersed in the de-ionized water of the IFB at the NGS were monitored for biofouling and biocorrosion.

Evaluation and results

After a two-month period, coupons were analysed for viable and non-viable micro-organisms before and after the hydrogen peroxide treatment. There was a significant reduction in viable bacterial counts (approximately 90%) after treating the IFB water with hydrogen peroxide.

After 7 and 12 months, coupons were again retrieved from the IFB before and after the hydrogen peroxide treatment. Biofilm analysis of coupons revealed that there was a significant reduction in bacterial counts (more than 90% reduction) on coupons that received the hydrogen peroxide treatment.

The coupons were analysed for the presence of bacteria and corrosion products after 67 months. General fouling bacteria were detected; however, the numbers were not greater than those observed on coupons that were immersed in IFB water for 7-12 months. MIC bacteria were almost absent. Corrosion products, such as sulphur for sulphate-reducing bacteria, were present in negligible quantities.

Direct cost-effective benefits

The annual or semi-annual hydrogen peroxide treatment of the IFB was successful in controlling MIC at very little cost after 6 years of operation. However, regular treatment must be maintained to control microbial fouling and MIC in the future.

For more information, contact

Dev Jain, 416.207.6000 x6536, dev.jain@kinectrics.com

Allan Jarvine, 416.207.6000, 5785, allan.jarvine@kinectrics.com