CANDU REPLACEMENT | COVER STORY
Left:
OPG overhauled the turbine generator and is installing new digital turbine controls as part of the Darlington refurbishment programme
basically doing a retube, removing and replacing the pressure tubes, the calandria tubes and feeder pipes which is where all the nuclear reactivity occurs. We also looked at the rest of the systems and did a component condition assessment to see what systems needed to be replaced to support the 30-year extended life of the asset.” Work is progressing on the Primary Moisture Separator replacement on two of the steam generators, for example, although the majority of the steam generators do not need to be replaced even after 30 years: “The steam generators at Darlington were in very good condition,” Rose notes. Similarly, although the output of the plant will not change as a result of the refurbishment programme, some systems are being improved where that is appropriate: “We are upgrading our turbines in terms of the control system and we’re doing maintenance work on those. We’re not replacing any blades but we are replacing the stator in a couple of cases. We also have some safety upgrades to make and balance of plant items too such as electrical systems and some piping work,” Rose says.
The design of the CANDU reactor requires replacement of the pressure tubes and calandria tubes at the midlife stage. “That mid-life for Darlington was at about the 230,000 effective full power hour level, but of course you can’t change all four units on one day. We started Unit 2 early at about 180,000 hours so that when we got to the last unit it was within its range of needing to be replaced. This mid-life refurbishment is a design requirement and depending on the unit that midlife could be at different full power hours before it needs to be refurbished,” Rose explains.
Learning by doing Almost unique among nuclear projects, the Darlington reactor replacement programme is not only on budget but it is ahead of time too. Rose puts this remarkable outcome down to both the detailed multi-year planning but also assiduously applying learning from one unit to another: “A lot of learnings came from the work on Unit 2. The team tracked about 3,000 different learnings, some very minor learnings where we updated procedures to make it easier, more efficient, safer or better quality, for example,” he says. He explains the challenges of translating even the most
thoroughly laid plans into the actuality of on-site action and the necessity of maintaining a dynamic approach to major infrastructure projects like reactor replacement. “The first time you do anything you have great plans laid out but once you get into those and the reality of the job face, it doesn’t work exactly as you had planned. The teams learned lessons and learned them in real time. It might be things like adjusting the parameters of the welding machines to
optimise the welds of these feeder pipes onto the headers which is a significant component of our work. Learnings from how to do the welding of the feeders on Unit 2 made it more efficient for the subsequent units,” Rose says. One of the key issues was a change to the conceptual
team structure to create a more cohesive unit between OPG staffers and third-party contractors. Rose says: “One of the large learnings was the ‘one team’ concept. When we started Unit 2 we approached it in a traditional EPC way where OPG was the general contractor and we had a vendor who was the EPC.” He continues: “We found out during the process of doing Unit 2 that instead of having our team doing oversight it made a lot more sense for us to be an integrated team. So, we integrated the OPG oversight team with the vendor team into this one team concept. You didn’t know who was working for what company and, quite frankly, it didn’t matter. It was all about the team working together on a common goal to accomplish the refurbishments on time and on budget.” Rose emphasises the importance of the shift from the
traditional EPC model to one of an integrated project delivery model as a key component of the successful outcome.
In addition, the OPG approach also meant having the
courage to change the model for CANDU replacement. Rose explains: “There were other things we learned on unit 2, for example we removed the pressure tubes first and then the calandria tubes in series. That’s the way the 10 refurbishments before us had all been done. But during Unit 2 when we started to think about some possible efficiency improvements one of our engineers brought forward this idea of removing both the pressure tube and calandria tubes together. It’s faster and in fact it’s safer because you have less transports of the pressure tubes from the reactor to the waste stream. In Unit 3 we removed both of them together and it saved us over 30 days on the schedule and it’ll save at least that on Units 1 and 4, too. That investment ultimately saves 90 days on the schedule, which is quite a bit of money when you think about the cost of all the people working on this project, the capitalised interest and so on.”
Tooling and testing Devising a new procedure to take out the pressure tube and the calandria at the same time was a combination of changing the process but also developing new equipment and a new device. All those changes had to be qualified too. As Rose says: “Modifications to the tools, to the procedures, to the work that was happening on the face – in nuclear every task is qualified so we have to have procedures,
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