From NUREG-1022 section 4.2.3 ENS Notification Retraction
If a licensee makes a 10 CFR 50.72 ENS notification and later determines that the event or condition was not reportable, the licensee should call the NRC Operations Center on the ENS telephone to retract the notification and explain the rationale for that decision. There is no set time limit for ENS telephone retractions. However, because most retractions occur following completion of engineering and/or management review, it is expected that retractions would occur shortly after such review. A retracted ENS report is retained in the ENS database, along with the retraction. See Section 2.8 for further discussion of retractions.
From NUREG-1022 section 2.8 Retraction or Cancellation of Event Reports
An ENS notification may be retracted via a followup telephone call, as discussed further in Section 4.2.3 of this report. A retracted ENS report is retained in the ENS database, along with the retraction.
Sound, logical bases for the withdrawal should be communicated with the retraction or cancellation. (Example 3 in Section 3.2.4 of this report illustrates a case in which there were sound reasons for a retraction. The last event under Example 1 in Section 3.2.6 illustrates a case in which the reasons for retraction were not adequate.) For reports that were submitted as a result of an operability determination, the retraction or cancellation should discuss why the operability determination was revised, as well as its impact on the associated reporting criteria (e.g., system operability was never lost, the limiting condition for operation (LCO) was always met, completion times were never exceeded, etc).
RIS 2005-20, Revision 1 provides guidance on operability determinations.