Q.rhubarb
Is there anything you can use to spray the grass around rhubarb plants that will not kill the rhubarb?

The safest way would be to remove the grass manually and then you can mulch the plants to keep weeds and grass down.
These links may help you.
https://www.gardeningknowhow.com/plant-problems/weeds/how-to-kill-grass-naturally-kill-unwanted-grass-in-your-yard.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/vegetable-weed-control.htm