Documentação do Ubuntu diz
Brasero and K3B can't burn Blu-ray out of the box. In order to do so you have to install the cdrecord package from this PPA https://launchpad.net/~brandonsnider/+archive/cdrtools and in doing so you will be uninstalling wodim which is used by default and does not support BD-R media. See how to add a PPA.
Once you added the PPA, simply install cdrecord package as any other package.
Then you have to install K3b if you did not have it already installed and enable "Show advanced GUI elements" in the advanced settings.
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