is.na() replacing all values instead of na ones

I have dataframe tr which contins around 1700 rows. I am trying to replace Type column values wherever they NA with string "None".

I do a quick count to check how na's I have in my Type column.

na_count= tr[which(is.na(tr$Type)),]

na_count contains 8 records.

Now I replace all the NAs with "None" using

ifelse(is.na(tr$Type),tr$Type<-'None',0)

The above command is replacing all the 1700 rows with None instead of just the 8. I'm not sure why that is happening.