How do you break the runes? i don't see any option for that
All AW's share that one broken shards bar. Any forged rune from this bar is guaranteed to fit into the AW open when you forge it without breaking.
You go into any AW (I choose one I don't plan to build) and insert runes into the wheel, some of them will break. When the broken shards bar is full (10), close that AW, open the one you want the rune for and forge the rune. Rinse and repeat as necessary.
*Note: once the 'breaking runes' AW wheel is complete, the only way to get that wheel back to empty and able to be used again is to build it, wait until construction completes and then sell it. It will return to your inventory with an empty wheel.
Using GA (Golden Abyss) and ToS (Tome of Secrets) as examples (any AW's will work):
The GA is the one I want to build, I've placed all my GA runes and forged runes where I could and still need 3 runes to complete the wheel. I'm not planning to build ToS, but I have a lot of ToS runes. Go into ToS, insert runes, breaking some of them until the broken shards bar is full. Close ToS, open GA, forge rune. Repeat. Now, my ToS rune wheel is full, but I have more ToS runes and I still need one more rune to build my GA. Build ToS, then sell it (canceling the construction won't work). Open ToS, insert runes again. Once broken shards bar is full, close ToS, open GA, forge the final rune and build it.
Yes, it's clunky. But it works...