control rod material 1

[Bob167]

Can anyone remember:

Were control rods made from (mild) steel with boron or boron carbide:-
a) as a surface coating
b) as particles within the iron microstructure ?

We are talking UK Gas-cooled reactors here -roughly 40 years ago

Perhaps your grandfather might have told you !!

 

[andyenergy]

The magnox stations have two types of control rods. Coarse control rods and automatic zone or sector control rods. Both are straight steel steel tubes baout 7.6 mm in diameter and 6.1 m long.

Coarse control rods have the highest neutron absorbing capacity and are termed black rods.These coarse rods contain boron steel inserts.

Sector control rods do not contain the boron steel inserts as they do not need to absorb neutrons as much and are used automatically during operation.

(Taken from Modern Power Station Practice) - I couldn't remember the precise details although I worked on them recently and some are still running.


Hope this is useful

Andy

 

[Bob167]

Thanks Andy,

That was extremely useful.
I have heard of black rods and grey rods but I didn't know they were two different types of rod ?

Do you know (roughly) how many of each ?
What form was the boron (carbide) in the black rods (solid B4C; surface coating on steel; carbide particles dispersed in a steel matrix ?

OR:
Do you have the book? or
Do you know author; publisher; date etc.?

Regards

Bob167

 

[andyenergy]

(From the book) typically an average sized (commercial as operated by the CEGB) Magnox reactor had 100 coarse rods separated in to four lifts with the core divided into 8 to 12 zones each with four additonal autocontrol rods.

A separate group of coarse rods provide additional shutdown capability againts unexpected or particular faults. These are the safety rods that drop automatically.

The grey rods you mention seem to be a separate group from the coarse rods and are used for radial trim of flux.

Unfortunately I do not know what the actual numbers of autocontrol rods are and the actual number is likely to have varied from design to design.

The boron inserts were I believe steel with high B content (up to 4%), not carbide or particles. The boron in the steelcontains boron-10 up to about 19% and it is this that is the neutron absorbing material.

The details come from British Electricity International, London, Modern Power Station Ptactice 3rd edition 1993, Volume J, Nuclear Power Generation.

I doubt there is much design info out in public space and it is likley that the above book is well out of print (a very specialist market).


Again, hope this was useful

Andy

 

[Bob167]

Thanks again Andy,

I will put your info together with the other stuff I've got and see if I can work-out what goes in the gaps.

I'll also ask our local library to source the book; they have managed it occasionally in the past.

I've been trying to get this information from site staff since before Christmas with little success (so much has been forgotten and so many records lost, destroyed or misplaced). Every question gets three contradictory answers !!!

Thanks again buddy, I owe you one

Regards,

Bob

 

[andyenergy]

Bob - found some more info.

I assume that you are talking about the earlier Magnox reactors, the later AGR reactors are very different and the moderation by control rods is very different.

Black rod - used for startup shutdown and safety.can be designed to absorb all of the neutrons that strike it and the inserts are 4% boron steel tubes within the outer steel tube. Cause a greater change in activity for a given movement.

Grey rods - mild steel cylinders used for radial flux shaping /T2 trimming. Absorb only a fraction of the incident neutrons. Grey rods can thus allow finer control when trimming a reactor.

The coarse, (bulk, black)rods are used to bring the reactor critical and raise power. About 30 of these bulk rods are secondary shutdown devices (frefall)and are held out of the core.

The sector (regulating zone grey) useed for fine temperarture control at load.

I'm almost out of easily available info now.

May I ask why you're interested?

Andy

 

[Bob167]

Thanks yet again Andy,

I am involved in proposals to dispose of some rods. The only original information we had was a drawing of a grey (mild steel) rod. We knew boron came into it somewhere and there were references (of unknown reliability) to boron carbide. I am fairly confident that we have a good picture of the situation now. So thanks very much for your interest and assistance,

Regards,

Bob