Re: Chapelcross fuel incident - follow up question

["julian ginniver" <julian.ginniver@lineone.net>]

Bjorn,

    I recently read a report in a newsletter published by the NUclear

Installations Inspectorate in the UK with a little more detail on the

incident.  In addition there is some (although not a lot) more information

on the news section of the BNFL web site (www.bnfl.com).



It would appear that 12 of the fule rods (elements) fell a distance (approx

80' I think) down a fuel chute.  3 of the fuel rods were damaged during the

incident.  I not sure of the exact plant design but from descriptions I am

assuming it is not very dissimilar to the later commercial stations.  One

description I have read refers to the location where the rods were found as

"on top of the gamma gate" I have to admit that I not sure what this is .

The others suggest that the rods "fell" down the discharge chute and into

container (skip) in the fuel pond.  At the magnox station that I have worked

at in the past, fuel was discharged from the fuelling machine down a

discharge chute and into a skip in an area of the pond called the acceptance

bay.  This was normal practice.  The fule chute was simply a transfer tube

that allowed the fuel to move from the reactor block and into the pond.  The

height of the starting point of the tube in the reactor block was 75' and

the fuel ended up in the acceptance bay (receipt area) of the pond at

approximately ground level.  In the pond the fuel was stored in these skips

for a minimum of 90 days (to allow of the decay of Radio-iodines and other

short lived fission products thus reducing the heat loading during

transport, possible doses to the public from a release of radio-iodines

during an transport accident and large releases of radio-iodines within the

reprocessing plant).  The fuel rods would then be transferred in the skip

(each skip containing up to 200 rods) for transport to the reprocessing

plant at Sellafield.  The outlet of the discharge chute was below water

level.  If the fuel rods did end up in the pond then there was little change

of significant radiological exposure of personnel.  I'm not sure about any

release from the fuel rods when they were damaged.  Magnox elements are

composed of a solid bar about an inch in diameter encased in the MAGnesium

Non-OXidising cladding. hence the name.  Unlike light water reactor fuel

which is enriched uranium di-oxide in the form of ceramic pellets held

within a tube usually with an interspace pressurised with gas.  If the clad

on this type of fuel rod is damaged it will result in the release of fission

product gasses which have built up in the interspace.  I'm not sure what the

result of a breach of cladding would have on a Magnox fuel rod.  What I do

know is, again at the plant where I used to work, there were problems with

damage to the fuel (which was believed to have occured after its removal

from the reactor that resulted in significant levels of Pu, Am, Cm in the

pond water.   This was made worse by problems with corrosion of the magnox

cladding in the ponds if, pond water quality was not maintained or  fuel was

stored for long periods due to problems at the reproccessing plant etc.  I

do not believe however that the damage to the fuel rods would have resulted

in significant doses to operators at the plant.  Any subsequent handling of

the damaged rods would have taken place below a significant amount of water

and in a manner consistent with normal fuel handling operations.



The NII in their news letter stated that there had not been any significant

radiation exposure as a result of this incident.



I hope this helps to clarify what you have already heard.



Regards

    Julian Ginniver





----- Original Message -----

From: "Bjorn Cedervall" <bcradsafers@HOTMAIL.COM>

To: <radsafe@list.vanderbilt.edu>

Sent: Wednesday, August 08, 2001 11:29 AM

Subject: Chapelcross fuel incident - follow up question





> Please pardon me if I missed something:

>

> Is it correct that three fuel rods were damaged and that no radioactivity

> was released? If not - what is the most accurate description from a

> radiological point? Was anyone exposed due to the incident?

>

> Bjorn Cedervall    bcradsafers@hotmail.com

>

>

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