sql_variant data are truncated

I try to create a new table ‘Table_1’ in SQL Server 2008 and add a field ‘f1’ of type sql_variant, then try to invoke the following SQL statement to insert a value to ‘f1’, as follows:

Insert into [Table_1] values(cast ('0x71FFA0D03B75068C7E8778734DD0BE82BEDBC246412B8CFA307F70F0A754863295AA5B68' as nvarchar))

However, after the insert, I try to open the ‘Table_1’, I find the inserted value is truncated as

‘'0x71FFA0D03B75068C7E8778734DD0’

What is the problem?

Thanks