ML23116A065
| ML23116A065 | |
| Person / Time | |
|---|---|
| Issue date: | 04/28/2023 |
| From: | Christian Araguas NRC/RES/DRA |
| To: | Raymond Furstenau Office of Nuclear Regulatory Research |
| Shared Package | |
| ML23116A064 | List: |
| References | |
| Download: ML23116A065 (3) | |
Text
April 28, 2023 MEMORANDUM TO: Raymond V. Furstenau, Director Office of Nuclear Regulatory Research Signed by Araguas, Christian FROM: Christian J. Araguas, (A) Director on 04/28/23 Division of Risk Analysis Office of Nuclear Regulatory Research
SUBJECT:
TRANSMITTAL OF THE ACCIDENT SEQUENCE PRECURSOR PROGRAM 2022 ANNUAL REPORT This memorandum transmits the Accident Sequence Precursor (ASP) Program 2022 Annual Report. The ASP Program assesses licensee event reports (LERs) at U.S. nuclear power plants to identify potential precursors to core damage. There were 135 licensee LERs issued in calendar year 2022. From these LERs, 111 (approximately 82 percent) were screened out in the initial screening process and 24 events were selected and analyzed as potential precursors.
The overall number of LERs and potential precursors remains at historical low levels.
Of the 24 potential precursors, 8 events were determined to exceed the ASP Program threshold and, therefore, are precursors. An additional two precursors were identified for a degraded condition where no LER was issued. Of the 10 total precursors identified in 2022, an independent ASP analysis was performed to determine the risk significance for 4 of these events, while 6 precursors were the result of greater-than-Green inspection findings. No significant precursors [i.e., conditional core damage probability (CCDP) or increase in core damage probability (CDP) greater than or equal to 10-3] were identified in 2022. In addition, no important precursors (i.e., CCDP or CDP greater than or equal to 10-4) were identified.
A review of the trends over the past decade (2013-2022) reveals statistically significant decreasing trends for all precursors and some precursors subgroups (e.g., initiating events, losses of offsite power, precursors at pressurized-water reactors, etc.). However, no statistically significant trends were identified for degraded conditions, precursors at boiling-water reactors, and emergency diesel generator degraded conditions during this same period.
Although the number of precursors identified in 2022 is the highest total in the past 5 years, this increase has not affected the decreasing 10-year trend in the occurrence rate of all precursors.
In addition, the number of LERs and potential precursors identified remain at historical low values.
Enclosure:
As stated CONTACT: Christopher Hunter, RES/DRA (301) 415-1394
R. Furstenau The ASP trends, along with the results of the ASP index, indicate that NRC oversight and licensing activities remain effective and that licensee risk management initiatives are not resulting in an increasing risk profile for the industry. In addition, there are no indications of increasing risk due to the potential cumulative impact of risk-informed initiatives and no new component failure modes or mechanisms were identified.
ML23116A064; Memo ML23116A065 OFFICE RES/DRA/PRB RES/DRA RES/DRA NAME CHunter CH MReisi-Fard MR CAraguas CA DATE Apr 26, 2023 Apr 26, 2023 Apr 28, 2023