From Oracle FAQ
NCLOB (National Character Large Object) is an Oracle data type that can hold up to 4 GB of character data. It's similar to a CLOB, but characters are from the national character set.
In 12c, the storage limit is extended to (4*1024*1024*1024-1) * CHUNK size given in the LOB STORAGE clause defining the LOB (database block size by default).
CREATE TABLE t1(c1 NCLOB); INSERT INTO t1 VALUES( N'any nchar literal' );