CREATE TABLE REF.MTHD_LKUP (
       MTHD_CD         VARCHAR2(4 BYTE) NOT NULL,
       MTHD_DESC       VARCHAR2(60 BYTE) NULL,
       CREATE_DT       DATE DEFAULT sysdate NULL,
       CREATE_USER_ID  VARCHAR2(30 BYTE) DEFAULT user NULL,
       UPDATE_DT       DATE DEFAULT sysdate NULL,
       UPDATE_USER_ID  VARCHAR2(30 BYTE) DEFAULT user NULL,
       DEACTV_DT       DATE NULL
);

Table created.

ALTER TABLE REF.MTHD_LKUP
           ADD (
  CONSTRAINT PK_MTHD_LKUP
 PRIMARY KEY
 (MTHD_CD));

Table altered.

GRANT SELECT, UPDATE, INSERT, DELETE ON REF.MTHD_LKUP TO INT;

Grant succeeded.

CREATE TABLE INT.SRVC_SPCL (
 SRVC_NAME                               VARCHAR2(60),
 SRVC_DESC                               VARCHAR2(150),
 SRVC_LONG_DESC                          VARCHAR2(250),
 MTHD_CD                                 VARCHAR2(4)
);

Table created.

ALTER TABLE INT.SRVC_SPCL ADD (
  CONSTRAINT FK_SRVC_SPEC_MTHD 
 FOREIGN KEY (MTHD_CD) 
 REFERENCES REF.MTHD_LKUP(MTHD_CD)
    ON DELETE SET NULL);
 REFERENCES REF.MTHD_LKUP(MTHD_CD)
                *
ERROR at line 4:
ORA-01031: insufficient privileges

grant references (MTHD_CD) on REF.MTHD_LKUP to INT;