What factors determine the length of fuel cycles in nuclear reactors?

[tony.almeda]

1- i have a proplem to understand the meaning of the once & twice burned fuel,
and why we use when we going to simulate the whole core

2- is there a specific formula for the IFBA radius,

 

[Astronuc]

Once-burned fuel = fuel with one cycle of operation
Twice-burned = fuel with two cycles of operation

What does one mean by IFBA radius?

IFBA fuel has a coating of ZrB₂ on the periphery of the fuel pellets. It depletes during the first cycle.

Fuel assemblies are often scatter-loaded in a checkerboard pattern, although modern core designs may have fresh fuel loaded side-by-side with the appropriate reactivity hold-down (IFBA or IFBA+BPA). Fresh and once-burned fuel are set in-board and twice-burned are placed on the periphery.

 

[tony.almeda]

but what is the length of each cycle(once burned& twicw burned) for PWR or IRIS reactor

 

[gmax137]

but what is the length of each cycle(once burned& twicw burned) for PWR or IRIS reactor

Cycle length can vary, and is established by the utility company operating the plant. Typical PWR cycle is 18 months, though some run 24 months. In the old days most (?) ran 12 months. It's an economic decision that has as much to do with timing the outages relative to the other power stations in the utility's system, as the physics.

 

[Astronuc]

but what is the length of each cycle(once burned& twicw burned) for PWR or IRIS reactor

Like gmax137 indicated, it's variable, and it depends on the particular operating philosophy of the utility.

More or less, cycle length is whatever one wants it to be - subject to some technical constraints.

Many BWRs and many of the moderately rated PWRs (usually 14x14 and 15x15 fueled plants) have adopted 24 month cycles. Some utilities have opted for high capacity 18-month cycles.

High duty PWR plants with 16x16 and 17x17 fuel run 18-month cycles, but one plant runs 19-20-21 month cycles due to their rather unique circumstances.

Besides efpd, capacity factor (CF) and outage length, other factors for consideration include batch size, enrichment and burnable poison loading (reactivity hold-down).