A little wear is expected even on the most robust components in the harsh environment of a nuclear power plant. Recently, thermal sleeve wear issues at various penetrations were discovered during in-service inspections on multiple reactor vessel closure heads. The wear is attributed to contact between the thermal sleeve and the inside diameter of the control rod drive mechanism (CRDM) head adapter tube. Framatome has examined more than 70 units and has already repaired or replaced more than 20 thermal sleeves in plants globally, and our technology has been chosen by the largest utility in the world.

In 2018, a French utility posted a safety level 1 event with the possibility of a remnant of a thermal sleeve interfering with the control rod movement during startup at one of its plants. Evaluation of the condition verified that blockage may have been caused by a remnant of a thermal sleeve flange that had worn and become stuck in the CRDM nozzle. Wear magnitude was determined through thermal sleeve inspections and measurements. This particular plant had a replacement head operating at full power for less than 18 years. During a single refueling outage at this plant, Framatome replaced the thermal sleeve at the central position from the top, including CRDM removal/installation. The operation was performed successfully and the utility was satisfied. The utility decided to conduct examinations on all reactor vessel heads to identify, characterize and define strategy maintenance for those that may be affected during their next scheduled outage. Of the 58 examined, other reactor vessel heads at the utility’s additional European plants were impacted. In response to a safety level 1 event, Framatome is leading the industry in providing solutions for innovative measurement, inspection, and repair technologies to resolve wear issues to both the thermal sleeve flange and adapter.

Some sleeves wear more than others, and to keep the sleeves in use, we had to develop new, innovative mitigation techniques. Framatome has developed a technique that is flexible enough to be used in the CRDM nozzle guide tube (CRGT) and replace the sleeve, yet maintain the design functions of the thermal sleeve. The thermal sleeve electric discharge machine (EDM) tool removes the thermal sleeve from under the head. We have also developed a new thermal sleeve design that goes in from the bottom up – expands, pulls together, and then is welded – and performs just like an original sleeve. Additionally, Framatome has created a spacer product which is a preventative measure that acts as a compensator, and prevents the thermal sleeve from wearing. Our spacer is a permanent and long-term mitigation solution which is being tested and installed in 2020 at a European utility.

We’ve developed the industry’s most thorough solutions to address thermal sleeve wear issues and extend the operating life of plants worldwide. Now utilities can better manage thermal sleeve wear with tailored solutions that allow shorter, more predictable outages and reduced maintenance cost. Our international collaboration, breadth and depth of tooling, and preventative options provide in-service inspection, mitigation, and repair solutions for all plant operators. We consistently develop cutting-edge technologies and improve upon strategies for extending plant operating life.