Maybe we're just playing it wrong, but we have yet to have righteous fury come up like like this.
Just to confirm, it only comes up when you roll a 10 on one of the damage dice, and it allows you to add another damgage dice right, that also has the same effect if it rolls a 10, I'm at work right now, so my books not handy.
No, what your group is doing is how Righteous Fury is played from DH. In Deathwatch, upon rolling a 10 the player makes another attack roll (or not if attacking a Xenos). If the second attack roll hits, the player makes another damage roll that is exactly the same as the first damage roll.
For example, the damage roll for a bolter is 3d10+5, dropping the lowest die. If a 10 is rolled and RF is confirmed, then the player rolls another 3d10+5. If a 10 is rolled again, then roll another 3d10+5; etc, etc. etc.
A lot of players/DM have house ruled RF in DW to have the same effect as RF in DH.