The swarf mostly built up in small, nice ridges straight under the gaps between the covers,
then there was a thin dust coat covering all over the cables in the 4' wide by 3' deep trench.
Reason for the even coating, was that there was a longitudinal flow of air dispersing the finer dust.

An ignition down there would probably have lead to a Zircaloy dust explosion,
(that also might have torched the ridges 6 feet apart, or blasted/ sucked those into the blast wave),
but certainly one heckuva flash and pressure wave along and out of the trench at both ends and thru the gaps.
The velocity of that blast wave, and if it would leave enough oxygen behind for a sustained fire has yet to be determined.
Sorta slitted "full-scale" recoilless rifle - "Would it really get trans-sonic?"
Guess the 6 x 4', 8" thick reinforced concrete covers would've stayed put, tho.

Risk assessment and consequence analysis wasn't very developed back then,
(even 4 years after Three Mile Island, but still 3 years before Chernobyl) as one of their cleaners asked me:
-"How would my film dosimeter badge protect me, if I get Uranium splashed (sic) in my face?"
I mentioned that (amongst some other H & S "anomalies" during my 6 month stint) to their Safety dept,
only to be transfered for "reasons of their staff's inconvenience and security", as my boss told me.