That will not work. Fractional_reserve is part of the name property.
Also, why are you dumping volumes from a file?
I don't see you connecting to a controller either.. How you are planning on executing this, That will determine how we can assist.
For example, what I would do
$hosts = gc c:\temp\filers.txt # list of filers
$hosts | % {
$Filer = $_
$c = connect-nacontroller $filer
$vols = Get-navol
$vols | % {
$volume = $_.name
if ((get-navoloption $volume | ? {$_.name -eq "fractional_reserve"}).value -ne 0)
{ set-navoloption $volume fractional_reserve 0
}
}
}