require builder returning false in rails 3

I am upgrading my rails application from rails 2.3 to rails 3.1. I am using builder like this

b = Builder::XmlMarkup.new :target => @data, :indent => 2

this works in rails 2.3 but not in 3.1.

Also, when i try to execute require 'builder' from rails console it works in rails 2.3 but says false in rails 3.1

Can anyone help. Thanks.