Fi Pocock, Alice Richardson, Claire Allen and Charlotte Barras are all injured while Amber Penrith and Sarah Beale are taking a break from the game.
Street is planning to blood a host of fresh faces from the under-20's and believes they will show no fear when they make the step up.
"Our plans for the Six Nations are going really well despite the injuries we've got from the World Cup and we can't wait to get back into action," said Street.
"We will miss all of the players who aren't going to be available but from what I've seen of those that have come in they are desperate for an opportunity to show what they can do at senior level.
"And I know a lot of the home nations have suffered a lot of retirements so we aren't really sure what we are going to come up against.
"Last season we had all sorts of information on the players we were going to play against but we won't have that this time."
Street and his staff haven't seen their team in competitive action since the defeat to the Black Ferns.
But after arranging a post-Christmas blow-out for 30 players last weekend, Street is convinced his side are in good shape to defend their crown.
"We got the girls together last weekend for a training meet-up and organised a proper 15 v 15 game for them," added Street.
"To say it was hard-fought would be an understatement and they really threw themselves into it - no-one held back at all.
"We also trained them pretty hard last week and I've had quite a few messages about aching bodies this week.
"It was good to get back together again and we're all determined to put the World Cup behind us and hopefully retain the Six Nations again."