An Inspector’s Perspective On the Control Rod Drive Mechanism Housing Flaws At Palisades

Elba Sanchez Santiago
Materials Engineering Inspector
NRC Region III
 
Elba Sanchez Santiago is a Materials Engineering Inspector in the NRC's Region III.
Elba Sanchez Santiago is a
Materials Engineering Inspector in the
NRC’s Region III.

There has been a lot of interest lately in the flaws that were recently found in the control rod drive mechanism (CRDM) housings at the Palisades nuclear plant, near South Haven, Mich. I want to share my direct experience with the NRC’s thorough and independent evaluation of this issue.

First, some background. The control rod drive mechanism moves control rods inside the reactor to control the level of nuclear chain reaction. The housing is a metal tube around the control rod drive mechanism, which is connected to the control rod and prevents leakage of reactor water into containment.

According to a commitment made in 2012, the plant conducted inspections of 45 CRDM housings in this reactor and found flaws in 17 of them. Palisades committed to these inspections after the discovery of a crack in one of the housings resulted in a plant shutdown in 2012.

Because of my expertise as a materials engineering inspector, I was dispatched to Palisades after it shut down in 2012. I was to evaluate the plant’s response to the discovery of the through-wall crack. As a member of a special inspection team that further evaluated this issue, I reviewed the plant’s testing of eight additional CRDM housings and their corrective actions. Even though no other cracks were found, the plant committed to further evaluate the condition of the housings during the 2014 refueling outage.

I came to Palisades before the current outage started to evaluate the site’s inspection methodology, work procedures, tooling and personnel qualifications. When the examinations started, I observed some of the actual testing and evaluated the results. To date, there is no evidence of leakage resulting from the flaws. I will remain onsite providing oversight over the plant’s actions until the issue is resolved.

Since the issue first came to light in 2012, I have been working with a team of other inspectors and specialists in Region III and the headquarters office in Rockville, Md., to make sure we ask the necessary questions to understand the plant’s methodology and assessments, and independently verify the conclusions.

Our in-depth independent reviews will continue until the plant completes the necessary repairs and takes proper actions to make sure the CRDM housing flaws do not lead to a significant safety concern. The results of our inspections will be documented in a publicly available inspection report.