Null Value To Return 0

When the SSN field is null I would like this query to return : 000000000, is this possible and if so could you show me how? Thanks

SELECT
[CASEHEADS RECEIVING NON WELFARE MONEY].IVA_MEMBER_ID AS [IVA #],
[CASEHEADS RECEIVING NON WELFARE MONEY].MEM_SSN AS SSN,
Sum([CASEHEADS RECEIVING NON WELFARE MONEY].AMT_DISBURSE) AS AMT,
[CASEHEADS RECEIVING NON WELFARE MONEY].DT_DISBURSE AS [DATE] INTO [CASEHEADS RECEIVING NON WELFARE MONEY TBL2]

FROM [CASEHEADS RECEIVING NON WELFARE MONEY]

GROUP BY [CASEHEADS RECEIVING NON WELFARE MONEY].IVA_MEMBER_ID, [CASEHEADS RECEIVING NON WELFARE MONEY].MEM_SSN, [CASEHEADS RECEIVING NON WELFARE MONEY].DT_DISBURSE
ORDER BY [CASEHEADS RECEIVING NON WELFARE MONEY].IVA_MEMBER_ID;