Refuelling outages

Approximately 25—30% of a reactor s fuel is removed and replaced during plaimed refueling outages, which normally occur every 12 to 18 months. Spent fuel is highly radioactive because it contains by-products from nuclear fission created during reactor operation. A characteristic of these radioactive materials is that they gradually decay, losing their radioactive properties at a set rate. Each radioactive component has a different rate of decay known as its half-life, which is the time it takes for a material to lose half of its radioactivity. The radioactive components in spent nuclear fuel include cobalt-60 (5-yr half-Hfe), cesium-137 (30-yr half-Hfe), and plutonium-239 (24,400-yr half-Hfe). 

R10, also in a refueling outage is for additional test and maintenance after some dccav < if the residual heat. 

Interconnecting of all the new systems, connections to new cabling and to existing plant equipment. This includes temporary connections required because of step-by-step implementation of the Project during three or four refueling outages. 

In all studies, a normal refuelling outage has been examined. Shutdowns for maintenance or other puiposes have not been considered so far. 

Closed circuit television equipment is used for general surveillance and for the examination of core restraint structures. Normally 2/3" newvicon cameras are used but for increased sensitivity 1" cameras can be employed. The cameras are modified on-site to be gas-cooled and to permit manipulations between the core and the pressure vessel. All the reactors are surveyed during their annual refuelling outages and no noticeable lens darkening has been encountered even after several hours continuous operation. 

Preventive Maintenance (major part carried out during refueling outages)... 

One with a total duration of 16 days from breaker to breaker considering the Normal Refueling Outage. Such a Normal Refueling Outage includes most of the preventive maintenance tasks except those concerning the safety trains, which are realized in power operation, (see Fig. 6)... 

FFTF was designed for a cycle of 102 days of operations and 28 days for refueling. In a refueling outage, typically one-third of the reactor core would be replaced. This included 24 driver fuel assemblies, 6 control rods, 12 reflector assemblies, and 2 closed-loop test assemblies. 

Withdrawal schedules may be modified to coincide with those refueling outages or plant shutdowns most closely approaching the withdrawal schedule. The two standby capsules are provided in jg the event they are needed to monitor the effect of a major core change or annealing of the vessel, or to provide supplemental toughness data for evaluating a flaw in the beltline. 

NOTE Schedule may be modified to coincide with those refueling outages or... 

Overall plant availability goal greater than 90 percent considering forced and planned outages. Objectives for unplanned reactor trips less than one per year. Objective for a refueling outage free of major problems is completion in 17 days or less (breaker to breaker). 

On-power refuelling, to eliminate the need for refuelling outages... 

Spent fuel blocks are removed and replaced with fresh fuel blocks during periodic refueling outages. 

Whether the components are sourced from other facilitates or manufactured within, when the final assembly is complete, the fuel is ready to be shipped to a nuclear power plant and inserted into a reactor during a scheduled refueling outage. Fuel fabrication facilities used for commercial power reactors are large, industrial-scale manufacturing... 

A partial core offload info the SFP which becomes filled to capacity with the partial core offload. This scenario covers a sfandard refueling outage where only the assemblies to be discharged are transferred to fhe SFP. 

An abnormal full core offload (full core plus a partial core offload) into the SFP into the spent fuel which becomes filled to capacify with the abnormal full core offload. This scenario covers a shutdown of fhe reactor and transfer of the entire core soon after a previous refueling outage. 

Five-year core life and pull-and-replace core module reduces costs associated with refuelling outages. 

All accessible areas of the core are inspected regularly during refueling outages with special attention now to core shroud. 

FW nozzle being regularly inspected in each refueling outage and no cracks were found. 

Reactor head studs and reactor recirculation pump casing studs are inspected ultrasonically every refueling outage and their threads are examined visually. No degradation has been observed. 

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