Darlington refurbishment achieves new milestone

Removal of the final calandria tube insert at Ontario Power Generation's Darlington unit 2 yesterday marks the completion of an important step in disassembly of the Candu reactor as it undergoes refurbishment.

Removal of the final calandria tube insert (CTI) at Ontario Power Generation's (OPG's) Darlington unit 2 yesterday marks the completion of an important step in disassembly of the Candu reactor as it undergoes refurbishment.

Inside Darlington 2's reactor vault during CTI removal (Image: OPG)

Calandria tubes sit in the reactor's core, each housing a pressure tube containing nuclear fuel bundles. They are secured at each end by a CTI, a metal ring which forms a mechanical seal.

A new production planning tool used during CTI removal allowed the work series to be completed early, OPG said. The tool involved a process map including timed durations for each of the steps in the process, including removing the components, placing them in flasks, transferral to waste containers, and returning the flasks back to the unit. These maps are now being used in subsequent work series, the company said.

"The result was like clockwork since we understood every discrete step of the sequence including the impact of speeding up or slowing down one step and the impact on the rest of the steps," the Darlington Refurbishment Team's Perrik Le Dreff said.

Completion of CTI removal means the extraction of the calandria tubes themselves can now begin. After this, the reactor will undergo inspections before it is rebuilt.

Darlington 2 is the first of the plant's four Candu units to undergo refurbishment in a phased CAD12.8 billion (USD9 billion) project which is scheduled for completion by 2026. Refurbishment of Darlington unit 2 formally began on 14 October 2016 after six years of planning, and will take some 40 months to complete. The project passed the halfway mark on 15 February. Refurbishment of unit 3 is scheduled to begin after completion of work on unit 2 to allow the implementation of lessons learned.

Researched and written
by World Nuclear News