The first weld build-up repair has taken place at Canada's stricken National Research Unit (NRU) reactor, keeping the vital isotope-producing plant on schedule for a March 2010 restart.
| The NRU building at Chalk River (Image: AECL)
NRU operator Atomic Energy of Canada Ltd (AECL) has confirmed that the welding technique has been applied to the first of six areas of the inside base of the reactor vessel. The weld repair was carried out remotely, operating the specially designed welding equipment from a position about 30 feet (9.1 metres) away from the site of the repair. Non-destructive examinations of the repair are now under way to verify the quality of the weld, and preparations are in progress to conduct a repair at a second site.
The 52-year old Chalk River unit produces a major share of the world's medical isotopes but has been off line since the discovery of a minor leak of heavy water from its tank in May. The leak was a simple result of corrosion over the years, but its repair has required the draining of the tank and removal of all NRU's fuel. A lengthy remote inspection then revealed further areas requiring repair because of corrosion.
The repair work has necessitated the development of specialised tools to carry out the work, with operatives then being trained to use the equipment and qualification of the techniques being carried out on full-height mock ups of the NRU vessel constructed at the Chalk River site. The weld repair tool has been developed by Canadian company Liburdi Automation, which specialises in custom-made automated welding systems.
A range of isotopes used in medical applications are produced in nuclear research
|New operations leader at AECL
Ramzi Fawaz has been appointed as senior vice president, operations at AECL.
Fawaz has spent over 30 years in major projects in the oil and gas industries, predominantly with Royal Dutch Shell and according to AECL, has "extensive hands-on mega project management abilities" of which the Canadian company hopes to make full use.
reactors like NRU, but many medical isotopes only have a very short shelf-life so an extended outage of a major producer can quickly have a dramatic effect on supplies. Another major isotope producer - the Netherlands' High Flux Reactor (HFR) reactor at Petten - is due to shut down for lengthy repairs in February next year. The world's isotope suppliers are already planning ways to mitigate the expected shortfall in supplies when that happens, but both NRU and HFR are scheduled for closure within the next decade.
The timeline for the NRU repair project anticipates that once the repair phase is completed, it will take at least two months to return the reactor to service to allow time for refilling the vessel, refuelling the reactor, testing all the relevant systems, gaining regulatory approval and powering up, before isotope production can restart. Based on "the best evidence available," AECL currently anticipates that the NRU will return to service by the end of March 2010.