Unsellable items

You don't need to do anything special. They are included in your accounts as a cost, so that's fine.

They are no longer included in your accounts as turnover, but you will not be issuing a sales invoice for them either, so that is also fine.

It is simply a smaller margin between your purchases of trade goods and your sales of products. But that is fine, part of that margin is simply that things break from time to time.