Can reducing Boric acid concentrations extend the life of fuel assemblies?

[Rofida]

Hi,
do you think that reducing Boric acid concentrations at the begin of the cycle would extend the like of the fuel assembly?

 

[gmax137]

Do you think that is true? I think it would help us answer your question, if you explain why you think so?

 

[Astronuc]

do you think that reducing Boric acid concentrations at the begin of the cycle would extend the like of the fuel assembly?

What life limiting condition would one expect to address?

Note that the question involving boric acid would apply to PWR fuel, since BWR fuel is not exposed to boric acid in the coolant. Furthermore, BWR fuel has much the same technical limits as PWR fuel, given the same cladding metallurgical structure.

 

[Rofida]

Do you think that is true? I think it would help us answer your question, if you explain why you think so?

thank you!
i will explain it little further.
some materials are being avoided to be used as reactors materials because of their higher neutron absorption cross sections (example: iron based alloys as fuel cladding materials) although they have many other good properties, my question is, can we use such materials and reduce their neutron penalties through reducing neutrons absorption by Boron via controlling its concentrations to be a little less?

 

[gmax137]

Boron is added to PWR coolant to compensate for excess reactivity in the fresh fuel. Using the soluble boron for this allows the operators to slowly reduce the boron concentration during the fuel cycle, as the fuel burnup accumulates.

In other words, the initial boron concentration is not an outside factor that the operators have to live with, rather it is a deliberately determined value that results from the core and fuel design.

At the end of a fuel cycle, the boron concentration may be reduced to a very low value or even zero. Once the concentration gets to zero, continued operation requires the operators to reduce coolant temperatures to maintain criticality. This is referred to as "Taverage coastdown."

 

[anorlunda]

my question is, can we use such materials and reduce their neutron penalties through reducing neutrons absorption by Boron via controlling its concentrations to be a little less?

If you want to innovate in nuclear engineering, you'll have to considerably broaden your considerations of side effects and your list of quality metrics.

There are lots of smart people in the world. That makes it almost impossible to have a bright idea for improvement of anything that has not been explored before.

Perspiration, not inspiration is the surest road to success.

 

[Rofida]

thank you!
the second line of your answer is the incentive behind my posted question.

 

[nuclearsneke]

Hi,
do you think that reducing Boric acid concentrations at the begin of the cycle would extend the like of the fuel assembly?

Actually, i am studying questions of fuel lifetime extension right now. If you want fuel to be utilized longer, you may be interested in use of thorium-based fuel as it builds up u233, a fissile material, and also produces less transuranic waste. However, u233 has gradually lower delayed neutrons fraction and this fact makes reactor control a little bit harder.
Another way is to increase fuel enrichment, but not further than 19.9% wt, albeit this path is not feasible since you load more fuel and its burnup is very unlike to be higher than the case of lower enrichment (Burnup ~ lifetime and ~1/mass of fuel) .
And the last but not least, one may try increasing diameter of fuel to get longer fuel lifetime but burnup makes it not feasible (again).

 

[Rofida]

Actually, i am studying questions of fuel lifetime extension right now. If you want fuel to be utilized longer, you may be interested in use of thorium-based fuel as it builds up u233, a fissile material, and also produces less transuranic waste. However, u233 has gradually lower delayed neutrons fraction and this fact makes reactor control a little bit harder.
Another way is to increase fuel enrichment, but not further than 19.9% wt, albeit this path is not feasible since you load more fuel and its burnup is very unlike to be higher than the case of lower enrichment (Burnup ~ lifetime and ~1/mass of fuel) .
And the last but not least, one may try increasing diameter of fuel to get longer fuel lifetime but burnup makes it not feasible (again).

thanx for this answer
its very informing