NukeWorker Forum
Career Path => Outages => Topic started by: Ksheed on Apr 10, 2012, 09:24
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What's the hangup with North Anna's Outage?
Submitted by NUCBIZ on April 2, 2012 - 22:17
by Bob Meyer ©
North Anna reportedly had a fuel assembly stick to the upper internals. North Anna is in day 22 of its outage and may be delayed due to a dangling spent fuel. The same incident happened in a French Plant, Graveline August 9, 2009. The rod was recovered September 3, 2009. To date, the NRC has not released any information that they have sent a special team for additional oversight. Fuel handling accidents have the highest offsite doses of any accidents in most nuclear plants.
A special tool should have arrived at North Anna from Europe, there is only one tool to handle this incident.
Many plants used Graveline’s corrective actions and captured them in their Fuel Handling and Upper Internals Movement procedures. Fuel assemblies not located directly under specified UI location due to stack up of tolerances could cause alignment pins to deflect into "S" holes in the fuel assembly’s top nozzle. This happened at Byron in 1993. Indian Point and Byron (1990) had damage to alignment pins on upper internals due to impact with storage stand. There is also potential for debris in the fuel assembly top nozzle or even manufacturing defects in the top nozzle. Detailed inspection of the Fuel Assemblies top nozzles must be performed to ensure no burrs or galling in the alignment holes which could interact with the Upper Internals alignment pins.
Westinghouse Fuel Spec procedures have been revised which required loading pattern to prevent stack up of tolerances which would allow this issue to occur.
Lower core plate inspection prior to fuel load ensure no debris which could affect proper seating of fuel assemblies. Tricastin Nuclear plant had debris fall off the refueling bridge and impacted fuel assembly seating.
With the high seismic activity, leaving the spent fuel assembly hang partially in the core risk would appear large. It would be interesting to see how the risk was managed for the week it has been stuck.
The French issue was caused by FME. The issue at NA may be caused by the seismic activity that rocked the Washington area last year.
Look at your FSAR and find out how many curries are in the fission gap gasses of a spent fuel element.
This is a good example of a bad day for the nuclear industry!!!
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