ML20245H755
| ML20245H755 | |
| Person / Time | |
|---|---|
| Issue date: | 05/05/1988 |
| From: | Israel S NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| References | |
| TASK-AE, TASK-T805 AEOD-T805, NUDOCS 8905030508 | |
| Download: ML20245H755 (4) | |
Text
__
AEOD TECHNICAL REVIEW REPORT UNIT:
N/A TR REPOP.T NO.: AE0D/T805 DATE: May 5, 1988 DOCKET NO.: N/A LICENSEE:
N/A EVALUATOR / CONTACT:
- 5. Isr."1 NSSS/AE:
N/A
SUBJECT:
INSIGHTS FROM SIGNIFICANT EVENTS IN 1987 donMARY A review of 1987 licensee event reports (LEPs) provisionally rated category I or category 2 by the ROAB screening process indicates that deficiencies in design, fabrication, and installation caused about half of the events. Similar observations were made for the 1986 LERs rated significant. About half of these deficiencies were detected by licensee programmatic reviews er followurs to other events. These results illuminate the benefits of inservice inspection programs, licensee inititted reviews, and random probing.
DISCUSSION The AECD staff provisionally rated approximately 180 licensee event reports (LERs) as category 1 or 2 events in 1987. Both categories identify significant events, except that category I connotes a higher sense of urgency in agency response. These events reflect serious degradation of the plcnt operation tecause of multiple component failures, pipe failures, recurring failures in single trains of safety grade equipment, etc.
For this review, causal factors of AEC1 significant events were roughly evaluated and grouped into five categories:
(a) equipment failure, (t-)
design, fabrication, or installation (DFI) errors, (c) personnel errors, (d) maintenance errors, and (e) administrative errors. Each event was asssigned to only one category. based on the reviewer's judgement. The subjectivity associated with this process blurred the demarcation among administration, personnel and maintenance errors and between equipment failure and DFI and maintenance errors.
Percentage of events associated with each facter are shown in Figure 1.
Design, fabrication, and installation errors acccunt for 50 percent of the significant events similar to observations made for 1986 significant events.
These events were fairly evenly distributed among the plants except for four sites which had more then five events apiece in this category. Of these four plants, two were shutdown for extended periods of time and have extensive corrective actions programs onging. Problems with fire protection, equipnent qualification, air systems, fuse coordination, motor operated valves (V0Vs),
NPSP in safety systems were some of the issues covered in these LERs. Equip-ment qualification problems, fire protection problems, and POVs probitms, which are the subjects of long-term programs in the industry, accounted for about 25 p(rcent of the events in the CFI category.
g503o$og 5
OR og-t Poc
(
R O
S R
R R
O E
R T
L R
E E
N N
E A
N C
C O
N IF S
A R
N I
E E
N 7 P
T G 8 N
I
_md S9 IA 1
M g$M 2 -k R
Y ON
&K
=2 M.
F I
mbv f
S S
nM=g!
S ST R
=
R RN O
O
=
OE R
k R
TV R
N R
=
-[
CE E
E l =C
=-
A N
b E
t V
=
F O
s I
L TI
&= T I
T A
A A
L R
S L
T A
S U
T K
A S
h N
i L~-
I C
N M
/
D 1
N E
A O
R U
E T
L I
R A
I C
A U
F I
R G
B T
IF A
N F
E
/
M N
P G
I U
IS Q
E E
D
~
Examination of the LEPs in this category indicates that about half were specifically captured by licensee programmatic reviews or follow-ups to other events. Because serendipity plays such a large role in discovering these l
" hidden" deficiencies, the licensee must maintain constant vigilance and probing to ferret out latent problems that may not otherwise be detected.
Another large fraction ( one-third) of the DFI events were identified as the result of external stimulus, e.g., vendor reports, NRC notices and bulletins, and NRC inspectors. Many of these discovery mechanisms are mandated by l
license requirements and normal ongoing regulatory activities.
Included in 3
this category are safety system function inspections which are indepth probes of selected systems at selected plants.
Finally, about 20 percent of the flaws were discovered by the licensee investigation of related events--either equipment failures or maintenance activities.
Topics associated with about 50 percent of the DFI events are reflected in previous AE0D studies, NRC information notices, etc., while about 15 percent are poter.tial topics for new AE0D studies.
One would expect that most of the significant events would have been noted previously.
In a mature industry, older issues should have been resolved, especially those involved with design oversights. Because of changes in the AE0D screening, the trend in the number of events in this category is indeterminant although this was also a major category in the 1986 events.
The remaining causal factors noted in Figure I were almost equally divided.
Uncertair; ties introduced by the screening process blur the relative contribu-tions of each of them. Maintenance has received considerable industry attention recently and valve problems are a major contribution to this category. The high interest in valves may bias the process so that everyone is sensitive to valve events.
Potential common mode failures are a major concern with maintenance and one significant event in this category dealt with a potential common mode condition--blockage of a drain (inadequate maintenance) which could cause water backup and damage to redundant systems. Another event was particularly noteworthy--plugged strainers in a diesel generator fuel line is a potential common mode situation under different circumstances or different plant design.
Tnus, equipment failures provide valuable insights to plant improvements that reliability assurance programs can harvest.
Personnel errors consisted of improper component tagout during test and mainten-ance, improper sampling, improper steam generator tube plugging, etc. --
situations where the an operator was an active participant in the plant evolu-tions. One event, the undetected loss of 20 percent of the primary system inventory was similar to the Three Mile Island accident in nature, not outcome.
This suggests that old lessons / issues should be revisited to minimize repeating significant events. The importance of this category may be understated because the reporting process may not be sensitive to marginal operator performance until it exceeds a very high threshold. Thus, important precursor events may not be observeble.
Pandom equipment failure is to be expected.
Pipe cracks, circuit card failures, and loss of offsite power are significant, but unavoidable events.
-4 Administrative errors such as missed surveillance, long-term misalignment of systems, poor procedures, mis-coordination among personnel, QA problems, etc.,
reflect poor supervision / management. Mistakes can be minimized but not avoided, so adequate independent verification is imperative to operating a safe plant. The small number of events in this category provides some confi -
dence that should be tempered by the possibility that poor working habits involved in benign events may be overlooked or go unreported.
Taking a broad overview of these assembled events, electrical and mechanical problems are about evenly represented as are component versus system level issues. Three subcategories stuck out, each with about 10 percent of the events: valve problems, equipment qualification problems, and ac power problems (which are station blackout issues).
CONCLUSION The distribution of the events into different subcategories does not suggest a specific area to concentrate further effort to improve plant safety, except possibly the design, fabrication, and installation area. Despite the uncer-tainties in the relative importance of the different causal factors shown in Figure 1, DFI is a dominant contributor. Since these problems may go undetected by the normal plant routines unless a particularly severe event challenges a safety component / system, it is important to maintain programmatic reviews such as safety system function inspections and feedback programs sponsored by the vendors INP0, and NRC. The diffuse nature of the problems requires careful screening and sensitivity to capture important precursors and feedback the insights to the operating plants.
l l
l l
l
)
_ _ - - _ _ _ _ _ _ _ _ _ - - - _ _ _ _