O&M

It’s a Small World

The "It’s a Small World" attraction at Disney World is iconic.

By Brian Schimmoller, Contributing Editor

The “It’s a Small World” attraction at Disney World is iconic. Its feel-good objective is to build awareness of the diversity of the human race and the value that can come from engagement with people that look, talk, and act differently.

This sense of global awareness is increasingly important to U.S. nuclear plant owners. What happens elsewhere can have impacts here, particularly as units age and materials issues emerge. Fukushima is the definitive example, but other recent issues highlight the importance of staying plugged into what’s happening around the world. Let’s look at two.

Baffle-former bolts are bolts that attach vertical core baffle plates to horizontal former plates in the core barrel of pressurized water reactors. The purpose of the core baffle is to direct coolant flow through the core and provide some lateral support to the fuel assemblies. To cool the baffle structure, a portion of the water flowing through the reactor vessel is directed between the core barrel and baffle plates in either a downflow or upflow configuration.

In early 2016, hundreds of degraded or missing baffle-former bolts were discovered during outage inspections at the Indian Point and Salem nuclear power plants. The issue appears to be limited to four-loop reactors with a downflow configuration and bolts made of type 347 stainless steel. The degradation is attributed to irradiation assisted stress corrosion cracking over years of operation.

Notably, such degradation was first detected in PWRs outside the United States in the late 1980s. The NRC communicated this overseas operating experience in 1998, and the industry adopted inspection and evaluation guidelines that included inspection of baffle-former bolts during the time when bolt degradation is most likely to appear. It’s not yet clear why the extensive degradation was not detected in a more timely fashion, but the NRC conducted a risk-informed evaluation and determined that the issue did not pose an immediate shutdown risk to the affected plants.

Indian Point 2 and Salem 1 replaced potentially degraded bolts with type 316 stainless steel bolts and were able to restart. The other U.S. reactors susceptible to this issue are accelerating scheduled inspections to examine their baffle-former bolts, and at least one – D.C. Cook – has replaced some baffle-former bolts. The NRC also is evaluating a generic industry communication.

The second issue with potential global repercussions involves investigations by French authorities into excess carbon levels in certain steel forgings and the potential falsification of quality assurance records. These investigations have rocked the French nuclear industry, forcing French utility EDF to take some plants off-line for additional inspection and analysis.

The carbon issue came to light in 2014 when excess carbon levels were found in the reactor vessel manufactured for the Flamanville EPR plant under construction in France. Excess carbon levels can affect the mechanical properties of steel, potentially rendering it more brittle. EDF has said that its latest tests of the Flamanville reactor vessel demonstrate its structural integrity, but the French nuclear authority ASN has not yet released its analysis of the test results.

Citing concerns about the extent of condition related to the excess carbon issue, ASN ordered the shutdown of 18 plants in France to allow more detailed analysis. ASN and EDF subsequently reaffirmed the ability of the plants to safely operate, and all have since returned to service.

ASN also is investigating suspected instances of falsified quality documents at Areva’s Le Creusot forge, dating back more than four decades. Thousands of documents are being reviewed to assess whether, and the extent to which, employees may have modified quality control data. As reported by the Financial Times, David Emond, head of Areva’s component manufacturing business, said that employees would sometimes round numbers up or down so they fell within technical safety limits. Emond noted that while 70 components with falsified documents had found their way into French nuclear reactors – and 120 into overseas power plants – no safety problems have so far been discovered.

The mention of those 120 overseas power plants highlights the global impact of this issue. The ASN actions in France prompted the NRC in early January to release a list of 17 U.S. nuclear reactors with parts from Le Creusot, although the agency does not see a need for plant shutdowns. In a blog post, NRC spokesman David McIntyre said, “We are confident at this time that there are no safety concerns for US nuclear power plants raised by the investigations in France. Our confidence is based on the US material qualification process, preliminary structural evaluations of reactor components under scrutiny in France, US material aging-management programs, our participation in a multinational inspection of Creusot Forge, and information supplied by Areva about the documentation anomalies.”

It’s often said that a nuclear plant issue anywhere is a nuclear plant issue everywhere. The issues described above bear truth to that adage. My apologies if the Small World song plays over and over in your head for the next week.

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