try with the option :
readsize

The READSIZE parameter lets you specify (in bytes) the size of the read buffer. The default value is 65536 bytes; however, you can specify a read buffer of any size depending on your system.

In the conventional path method, the bind array is limited by the size of the read buffer. Therefore, the advantage of a larger read buffer is that more data can be read before a commit is required.

For example:

sqlldr scott/tiger control=ulcas1.ctl readsize=1000000