ML20315A396
| ML20315A396 | |
| Person / Time | |
|---|---|
| Issue date: | 11/18/2020 |
| From: | Lochbaum D NRC/NRR/DRO/IRAB |
| To: | |
| Tekia Govan, NRR/DRO/IRSB, 301-415-6197 | |
| References | |
| Download: ML20315A396 (37) | |
Text
Enhancing the Reactor Oversight Process Using Accident Sequence Precursor Insights Dave Lochbaum November 18, 2020 1
The NRC has administered an Accident Sequence Precursor (ASP) Program since 1979 as one of the lessons learned from the Three Mile Island accident.
2
An ASP is an event, an NRC inspection finding or plant owner identification of a degraded condition that increased the risk of reactor core damage by more than a smidgen.
Source: NRC March 2018 RIC Slide 2 3
Inputs to the ASP program are Licensee Event Reports (LERs) from plant owners about incidents and degraded conditions and NRC inspector findings of violations of regulatory requirements.
Source: ML112170424 4
895 ASPs thru 2017 98.7% of LERs screened out of ASP analyses The vast majority (98.7%) of LERs are screened out of the ASP analysis process because they involve very low risk.
Source: ML18130A855 5
Similarly, the vast majority of NRC inspector findings Source: Me involve violations having minor risk significance (97.9%).6
The NRCs annual reports for its ASP program from FY 2001 through FY 2019 were reviewed.
The reports for 2002, 2003, and 2015-2019 either did not explicitly identify degraded condition ASPs or did not specify the durations that degraded conditions existed.
7
This table is from the NRCs annual report for Fiscal Year 2001.
The ASPs for conditions that afflicted nuclear reactors for ten years or longer are highlighted in yellow.
Source: ML052700542 8
The NRCs annual ASP status report for FY 2004 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow. 9 Source: ML061920242
The tables for ASPs involving degraded conditions for 2005-2014 are in the Backup Slides.
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The vast majority (over 95%) of incidents and NRC inspection findings involve minor risk significance and are screened out.
The few incidents and findings evaluated under the ASP program (<
5%) have significantly higher risk.
Nearly one-quarter of these high-risk ASPs existed undetected at the plants for ten years or longer; sometimes way, way longer.
Source: Me 11
In other words, the Reactor Oversight Process FAILED to notice high-risk issues afflicting the nations nuclear power reactors for over a decade, until the issues self-revealed themselves or were finally found.
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Nearly one-quarter of the high risk incidents and inspection findings identified as ASP events existed for 10 years or longer. The NRC does NOT formally assess whether its existing agency programs should have detected these risks sooner?
Source: NRC March 2018 RIC Slide 3 13
I pointed out this situation to the NRC more than three years ago.
14 Source: ML16294A299 14
Finding at least some of the high-risk degraded conditions within 10 years is not overly optimistic.
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10 years is a common end-point for mandated inspection and testing intervals.
Source: ML032510128 16
10 years is a very common end-point for mandated inspection and testing intervals.
Source: ML11249A008 17
These ten-year inspection and testing programs do not mean that every inch of piping and every valve in the plant gets inspected and tested every decade; instead, they seek to ensure that vital components with safety roles are checked at least once per decade.
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The baseline inspection program of the ROP (i.e., the set of inspections that NRC conducts for every reactor) is based on a three-year cycle with each inspection getting performed at least once every three years. Thus, three-plus rounds are done every decade.
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The baseline inspection program audits a sample of items - not every item will get inspected in ten years.
And finite resources means that revising ROP to look at this means the ROP no longer looks at that.
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Nevertheless, formal evaluations of 10-year-plus ASPs for degraded conditions can either inform how the baseline inspection program picks its samples and how those samples are examined or confirm that the current program as-is provides the best focus on safety.
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The NRC should formally evaluate every ASP involving 10-year-plus degraded conditions to answer these questions:
- 1. Is the degraded condition within the scope of the baseline inspections?
- 2. If yes, which inspection procedure(s) could have found it and should they be revised to increase the odds of doing so?
- 3. If no, should inspection procedure(s) be revised to cover this area?
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In other words, refocusing the ROP to have inspectors spend less time cavorting in green fields and more time Source: Me 23 probing for high-risk conditions seems risk-informed.
BACKUP SLIDES 24
The NRCs annual ASP status report for FY 2005 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
Note that Kewaunee operated for decades with multiple afflictions. 25 Source: ML061920242
The NRCs annual ASP status report for FY 2006 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
26 Source: ML072070431
The NRCs annual ASP status report for FY 2007 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
27 Source: ML082240729
The NRCs annual ASP status report for FY 2008 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
28 Source: ML092190601
The NRCs annual ASP status report for FY 2009 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
29 Source: ML102100386
The NRCs annual ASP status report for FY 2010 without any conditions that afflicted nuclear reactors for ten years or longer. 30 Source: ML112170424
The NRCs annual ASP status report for FY 2011 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
31 Source: ML12220A606
The NRCs annual ASP status report for FY 2012 without any conditions that afflicted nuclear reactors for ten years or longer.
32 Source: ML13232A094
The NRCs annual ASP status report for FY 2013 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
33 Source: ML14230A102
The NRCs annual ASP status report for FY 2014 with conditions that afflicted nuclear reactors for ten years or longer highlighted in yellow.
34 Source: ML15188A101
35 36 37