How to generate create table script without primary and foreign key in Oracle
You could try the following:

set pagesize 0
set long 90000 

exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,'STORAGE',false);
exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM, 'CONSTRAINTS',false);
exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM, 'REF_CONSTRAINTS',false);

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


This should result in the DDL without any indexes and foreign keys.

Reference: 


docs.oracle.com
dba-oracle.com