UPDATE on single column on a heap with 1.2B rows

Hi,

I have a table with 1.2Billion rows of data.  It's currently a heap and around 300GB in size (un-partitioned).

I'm trying to do a blanket UPDATE on the entire table on one of the columns by using a statement like:

UPDATE table SET column1 = column1 + '-' + CAST(column2 as varchar(10))

Column1 is varchar and column2 is int so I need to cast column2 to varchar to allow concatenation.

I run the update but the translog has grown to 200GB and it still growing, the tempdb is now around 100GB.  The query is still running, is not blocked etc.

I thought that because the UPDATE did not have a WHERE clause then the table being a heap may not matter, is this the case?

Can anyone point me in the right direction of some help with this UPDATE please?

Thanks