Prevent duplicate append - nothing unique

Help! I have been working on this all day and
cannot get my head around a solution....
I am running Access 2003.

I have created the following select query:

SELECT ScrapData.ScrapDate, ScrapData.PartNo, ScrapData.Description,
ScrapData.CostCtr, ScrapData.Value
FROM ScrapData
GROUP BY ScrapData.ScrapDate, ScrapData.PartNo,
ScrapData.Description, ScrapData.CostCtr, ScrapData.Value,
HAVING (((ScrapData.ScrapDate) Between
[Forms]![frmSelectCMCC]![FromDate] And [Forms]![frmSelectCMCC]!
[ToDate]))
ORDER BY ScrapData.ScrapDate;

called "qryPart1CM" from there, I have created
an append query to my countermeasure table:

INSERT INTO Countermeasure ( PartNo, Description, Cost, CostCtr,
WeekNo )
SELECT TOP 3 qryPart1CM.PartNo, qryPart1CM.Description,
Sum(qryPart1CM.Value) AS Cost, qryPart1CM.CostCtr, qryPart1CM.WeekNo
FROM qryPart1CM
GROUP BY qryPart1CM.PartNo, qryPart1CM.Description,
qryPart1CM.CostCtr, qryPart1CM.WeekNo
HAVING (((qryPart1CM.CostCtr)=[Forms]![frmSelectCMCC]![cboCC]))
ORDER BY Sum(qryPart1CM.Value) DESC;

Basically, each user responsible for a specific "CostCtr"
must enter countermeasures for Scrap data on a weekly
basis. The countermeasures are for the "Top 3" scrap
parts by value. I cannot open the form based on the
query as it is not updatable, so I thought I would run
an append query to a table and bind my form to it. However,
I need to prevent duplication to the "Countermeasure" table
and cannot figure out a way to create a unique field to accomplish
this.... Can anyone help?