How to generate create table script without primary and foreign key in Oracle
This will do the trick :

EXEC dbms_metadata.set_transform_param (dbms_metadata.session_transform,'STORAGE',false);
EXEC dbms_metadata.set_transform_param (dbms_metadata.session_transform,'TABLESPACE',false);
EXEC dbms_metadata.set_transform_param (dbms_metadata.session_transform,'SEGMENT_ATTRIBUTES', false);
EXEC dbms_metadata.set_transform_param (dbms_metadata.session_transform,'REF_CONSTRAINTS', false);
EXEC dbms_metadata.set_transform_param (dbms_metadata.session_transform,'CONSTRAINTS', false);

SELECT DBMS_METADATA.GET_DDL('TABLE','table_name','schema') FROM DUAL