ML20128D814
| ML20128D814 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 01/29/1993 |
| From: | Jeffrey Jacobson, Replogle G, James Smith NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20128D673 | List: |
| References | |
| 50-461-93-02, 50-461-93-2, GL-89-10, NUDOCS 9302100234 | |
| Download: ML20128D814 (14) | |
See also: IR 05000461/1993002
Text
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U.
S. NUCLEAR REGULATORY COMMISSION
REGION III
Report No.:
50-461/93002(DRS)
Docket No.:
50-461
License No.:
HPF-62
Licensee:
Illinois Power company
_
500 South 27th Street
Decatur, IL 62525
Facility Names
clinton Power Station
Inspection Ats- Clinton site, clinton, IL 61727
Ir.spection conducted:
January 4-15, 1993
Inspectors:
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M te ials and Processes Section
Insoection Summary
Insoection conducted durina Januarv 4-15, 1993 (Recort Ran_
50-461/93002fDRS))
Areas Insoected:
Announced safety inspection of-the licensee's-
response to Generic Letter (GL) 89-10',_ " Safety-Related Motor-
Operated Valve (MOV) Testing and" Surveillance" (2515/109).-
Results - No violations were identified.
The licensee demonstrated strengths in the following areas:
Probabalistic risk assessment (PRA) techniques were used to
-identify the MOVs_most important to safety.
These MOVs were
given the highest priority in the program.
The program reflected significant management attention and-
the coordination between the different participating
departments was excellent.
The trending program for-the evaluation offMOV. failures and.
test results was, excellent.
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Inspection Summary
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The licensos demonstrated weaknesses in the following areast
A schedule that outlined the testing of MOVs was not in
place at the time of the inspection.
The corrective actions taken in response to the failuro of
MOV 1SX173B (June 1990) were weak.
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TABLE OF CONTENTS
EAGE
1.
Persons contacted.
1
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2.
Inspection of the Clinton Program Developed in
>
Rosponse to Generic Lotter 89-10
1
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1
a.
Background.
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b.
Supplomont 3 to Gonoric Lotter 89-10.
1
. . . . . .
c.
Generic Lotter 89-10 Program Review .
2
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(1)
Scope of the Generic Lottor Program.
3
. . . .
(2)
Design Basis Reviews .
3
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(3)
MOV Switch Settings.
4
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(4)
Design Basis Differential Pressure and Flow
Testing.
5
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(5)
Periodic Verification of MOV Capability.
6
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(6)
Schedule
6
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d.
Associated Programmatic Reviews .
6
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(1)
Design Control for Thormal Overload
Protection . .
6
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(2)
Maintenance.
6
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(3)
Training .
7
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(4)
MOV Failuros, correctivo Actions and
Tronding .
7
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(5)
Diagnostics and the Evaluation of Test Data.
10
(6)
Walkdown .
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3.
Licenseo Self Assessment .
-11
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4.
Exit Mooting .
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DETAILS
1.
Eersons Contacted
Illinois Power Comoany (IP)
- J. Perry, Senior Vice President
- R. Bhat, Supervisor, Mechanical Design
- J. Cook, Vice President and Manager
- R. Frantz, Licensing Engineer
- J. Langley, Director Design and Analysis, Engineering
- J. Miller, Manager, Nuclear Systems Engineering
Department
- K. Moore, Director, Plant Technical Staff
- R. Phares, Director, Licensing
- J. Puzauskus, Project Manager, Generic Letter 89-10
- J. Sipek, Supervisor, Regional Regulatory Interface
U.
S.
Nuclear Reculatory Commission (NRC)
- P. Brochman, Senior Resident Inspector
- F. Brush, Resident inspector
- D. Pickett, Project Manager, NRR
- Denotes those attending the exit meeting on January 15,
1993.
2.
Insnection of the Procram Developed in Resnonse to Generic
Latter-(GL) 89-10 (2515/109)
a.
Backaround
A previous inspection of the Clinton GL 89-10 program
was conducted on October 7 through 11, 1991.
Due to
the lack of sufficient progress towards program
development at that time, a second inspection was
scheduled.
This report details the results from the
second inspection,
b.
Suoulement 3 to GL 89-10
During the first GL 89-10 inspection, NRC inspectors
identified four Supplement 3 motor-operated valves
(MOVs) as having marginal capabilities.
During the
second inspection, the NRC inspectors verified-that
modifications were planned for the subject MOVs during
the fall of 1993.
The MOV modifications were based on a relatively
conservative valve factor (0.5) and stem friction
coefficient (0.2).
However, the differential pressure
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(dp) used in the calculations included significant flow
losses.
The calculated dpa were 836 paid for reactor
core isolation cooling (RCIC) valves 1E51-F063 and
F064, 1014 psid for reactor water cleanup (RWCU) valve
1G33-F001, and 683 psid for RWCU valve 1G33-F004.
The large calculated flow losses were made possible
because of the long distance between the valves and the
location of the postulated breaks.
For example, the
break for the RCIC valves was at a point in the piping
which was estimated to be approximately 175 feet from
the valves.
The inspectors were concerned because the
approach was not consistent with the spirit of GL 89-10
in that a worst case break might be considered to be
immediately downstream of the valves and not at a more
distant location.
Nevertheless, the licensee did not
consider the closer breaks to be within the licensing
basis of the plant.
As a result of the NRC concerns, the licensee performed
an evaluation and determined that the valves could
perform their design basis functions based on a worst
case dp of 1128 paid for the RCIC valves and normal
reactor pressure for the RWCU valves if a less
conservative valve factor of 0.4 and stem friction
coefficient of 0.15 were assumed.
For the Clinton
plant, the use of ncrmal reactor pressure, in lieu of
the first relief valve setpoint pressure, appeared to
be justified because tha main steam isolation valves
would not receive an isolation signal during the
accident (reactor pressure would not increase).
The
inspectors considered the licensee's analysis to be
adequate, for the interim, since the less conservative
valve and stem friction coefficients have been used at
other nuclear power stations.
This issue will be
reviewed during a future inspection when more specific
information is known about the behavior of these
valves.
c.
GL 89-10 Prqgram Review
Probabalistic risk assessment-(PRA) techniques were
used to identify the MOVs most important to safety.
Fifty-two MOVs were identified as having a potentially
high impact on safety and were given the highest
priority in the GL 89-10 program.
The inspectors
considered the applied use of PRA to be a strength.
Significant resources were dedicated toward completing
the program.
Additionally, communication between the
various participating groups appeared to be good and
the staff coordination appeared to be excellent.
The
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NRC inspectors considered the increased management
attention and staff coordination in the area of MOVs to
be a strength.
(1)
Scope of the GL Procram
The scope of the program was reviewed and found to
be acceptable in the previous Part 1 inspection.
At that time, there were 231 MOVs in the GL 89-10
program.
Since that time, only one Mov was
removed from the program and justification for-
removal appeared to be acceptable.
(2)
Desian Basis Reviews-
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(a)
Differential Pressure Reauirements
The. inspectors reviewed Clinton Nuclear
Engineering Standard ME-03.00 (" General
Guidelines for performing Bounding Valve
Differential Pressure Analysis"), Revision 3,
dated December 18, 1992. - The procedure
described the methodology to be used to
determine the design basis dp for each MOV-
and appeared to be acceptable.
(b)
Reduced Voltaae capability
Tne' degraded voltage calculations did not
incorporate the use of locked-rotor current
as specified in.the GL, but used a less'
conservative current from the motor torque-
curves.
Although the approach did not appear
to-be consistent with the licensee's current
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commitments, the NRC inspectors did not
pursue issuing a Noticelof Deviation because
- the NRC staff was evaluating the
acceptability of alternative approaches to
degraded voltage calculations.
However, when
- this issue is reviewed during-a future
-
inspection the: licensee -will be -expected to
comply.with the docketed commitments.
The inspectors were concerned about theTlack-
of conservatism used in determining the
appropriate motor current for the
calculations.
- For example,-additional margin
to account for the inaccuracies in-the motor
curves.was not. included.
The-licensee also
failed to account for the difference between
the nominal motor curve voltage.(typically
460V) and.the actual voltage applied to~the
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motor.
Since a given motor would generate a
different curve for a different applied
voltage, a motor impedance change would be
expected and would affect the calculations.
Additionally, the calculations assumed that
the locked rotor current power factor would
apply.
However, under high loads, at less
than locked rotor conditions, the power
factor is typically higher and would result
in a lower calculated motor terminal voltage.
Cumulatively, the oversights may cause the
calculated motor terminal voltages to be
unrealistically high.
The licensee agreed to
address the NRC inspectors' concerns.
This
issue will be reviewed during a future
inspection.
The worst case grid voltage used in the
calculations was not always based on the
under-voltage relay setpoint as recommended
in the GL.
However, the licensee had-
compensatory measures in place to account for
the differences in the values.- Additionally,
five percent was deducted from the calculated
motor terminal voltages to account for future
electrical load changes.
Since the added
conservatisms appeared to bound the above
noted discrepancies, the inspectors
considered the licensee's approach to be
acceptable.
This issue will be reviewed
during a future inspection.
The degraded voltage calculation for DC MOVs
only included tne resistance value for one
thermal overload (each circuit contains two
thermal overloads).
In response to the
finding, the licensee re-performed the
calculations, incorporated the appropriate
number of thermal overloads and determined
that no significant cafety c">ncerns resulted
from the error.
The corrective actions
appeared to be acceptable.
(3)
MOV Switch Settinas-
Switch setting calculations and the setting of
switches were performed in accordance with
approved procedures.
Switch settings were
recorded in a controlled document and appeared to
be acceptable.
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The stem friction factor and valve factor assumed
in the thrust calculations woro 0.2 and 0.5,
respectively.
To support the relatively
conservative factors, the licensee planned to
perform approximately 130 modifications to improve
the capability of the MOV population.
Margin to account for the degradation of the MOVs
was not included in the torque switch settings.
Since torque switches were normally set
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immediately after maintenanco, additional margin
to account for the degradation in performance that
will occur over the specified maintenance period
may be necessary.
Typically, the stem friction
factor will increase over the time interval and
will, in effect, decrease the thrust available to
close a valvo at torque switch trip.
The licenson
agreed to perform an evaluation of this issue and
stated that appropriate changes to the switch-
setting methodology would be made.
Margin to account for the load sensitive behavior
was not included in thrust calculations.
Additional margin may nood to be added-to envelop
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this effect, when applicable.
The licensco
planned to change the switch setting methodology
when more information about the phenomena was
known.
(4)
Desian Basis Differential Pressure and Flow
Testing
MOVs found to have the capability to support a
valve factor of 0.5 and a stem friction
coefficient of 0.2 were-considered to have
substantial capability and would not be subjected
to design basis testing.
Although the approach
appeared to be consistent with the licensee's
current commitments, the NRC inspectors were
concerned because recent design basis testing at
other facilities has shown that this approach may
not be bounding.
In response to the inspectors'
concerns, the licensco-agreed ~to refine the
methodology and consider categorizing the valves
into groups.
The methodology would then be shown
to be bounding for each group.
If.the approach
could not be shown to be bounding for a given
group then design basis testing would be
considered for these valves.
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(5)
Ecriodie Verification of MOV Canability
The plan for puriodic verification of MOV
capability included static diagnostic testing of
MOVs on an interval consistent with the GL
recommendations.
The NRC inspectors informed the
licensco that without adequato justification,
static testing was not an acceptable method of
periodic verification because of uncertainties in
the performance of MOVs under static and design
basis conditions.
The licenson was considering extending the
periodic verification interval for some valves and
exempting ether MOVs from the testing altogether.
This approach was not consistent with
recommendations mado in the GL or the licensco's
current commitments.
The licensco agreed that any
chango in the current approach, of a less
conservative nature, would require justification.
This issue will be reviewed during a future
inspection.
(6)
Schedula
A schedule that specifies the testing of MOVs was
not in place at the time of the inspection.
The
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licenseo did plan to perform design basis testing
on MOVs within a time framo consistent with the
GL.
However, most of the testing would have to be
performed in one refueling outage.
Due to the
largo number of valves that may require testing,
completion of the program within the recommended
schedule would be difficult.
The lack of a test
schedule was considered to be a weakness.
d.
Associated Programmatic Reviews
(1)
Deslan Control for Thermal overload Protection
At the time of the inspection, thermal overloads
were intended to be bypassed for all accident
conditions but were active for normal operations
and test conditions.
The methods for sizing
thermal overloads appeared to be acceptable.
(2)
Maintenance
The NRC inspectors reviewed Clinton maintenance
procedures to evaluate the adequacy of the
,
maintenance program.
The program only required
checking the lubrication on valve stems on an 18
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month interval and did not require stem cleaning
and re-lubrication.
The inspectors were concerned
because visually checking the lubrication may not
identify all forms of degradation.
Furthermore,
poor lubrication on unaccessible areas, such as
the stem nut area, may go undetected.
For
example, volve 1SX173A failed to stroke during a
routine surveillance.
Although the stem appeared
to be well lubricated during the subsequent Valve
Operation Test and Evaluation System (VGTEC) test,
the calculated stem friction coefficient was 1.0,
t'hich was substantially higher than the 0.1 to
0.17 values typically seen on well lubricated
stems.
In response to the NRC concerns, the
licensee changed the applicable procedure to
require the cleaning and lubrication of stems on-
an.38 month interval.
A specific schedule for the overhaul of MOVs did
not exist.
The need for overhaul was based on
preventive maintenance _and trending results.
This
practice may be def!cient because degradation of
MOVs at other nuclear plants was not identified by
preventive maintenance or diagnostic equipment.
Furthermore, degradation which contributed to the
failure of two Clinton MOVs (1SX173A and 1SX173B,
extensive disc guide wear) could have been
detected during an overhaul but would not have
been detected during routine maintenance or static
diagnostic testing.
The NRC inspectors encouraged
the licencee to consider the establishment of a
periodic overhaul frequency.
(3)
Training
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The NRC inspectors discussed the Clinton Station
training practiceu with licensee personnel and
reviewed training outlines and records.
No
concerns were identified in this area.
(4)
MOV Failures. Corrective Actions and Trendina
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The trending program for evaluation of maintenance
problems and MOV test results was excellent.
The
program covered an expansive range of data and
appeared to trend all the known trendable
parameters.
The inspectors considered the
trending program to be a strength.
Corrective actions taken in response to the
failure of valve 1SX173B (shutdown service water
(SX) pump minimum flow valve)'appcared to be
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inadequate in that the licensee failed to take
actions to preclude a similar type failure which
occurred involving the sister valve (ISX173A) in
August 1992.
In June 1990, valve 1SX173B failed
to complete its stroke during a surveillance test
of the SX system.
After the failure, a root cause
evaluation was not performed.
However the
licensee's staff indicated that the valve may have
been used to throttle flow (not a recommended use
for a gate valve) and the throttling was believed
to be the root cause for the damage which was
observed during the December 1990 inspection of
the valve.
Steps to address similar degrcdation
which may have existed on-the sister valve were
not taken.
After concerns about the licensee's corrective
actions were raised by the NRC inspectors, the
licensee performed an evaluation and determined
that the failure of the second valve was not
safety cignificant for the following reasons.
(a)
If the valve failed to perform its safety
function (establish a minimum flow path for
the SX pump), an annunciator would have
alerted control room operators of-the valve
failure.
(b)
An alternate minimum flow path l existed
(through the RHR heat exchanger) and could
have been established in a short time period.
The worst case response time was estimated to
be 10 minutes.
(c)
The pump manufacturer was contacted and a
representative confirmed that the pump could
have performed its safety function if it were
run at " dead-headed" conditions for the first
10 minutes.
Based on the evaluation performed by the licensee,
the inspectors agreed that the safety consequences
of the valve failure were minimal.
However, the
inspec ors considered the licensee's failure to
e
'take cbrrective actions to preclude the failure of
the-sister valve 1SX173A to be a weakness.
The root cause evaluation, completed to address
the 1SX173A failure, did not consider all
contributing factors to the event and corrective
actions were not timely (documented in Condition
Report No. 1-92-08-006, " Valve 1SX173A Destroyed
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Itself in a Manner similar to 1SX17'20', dated
August 6,
1992).
For example, the cause of the
valve failure was determined to be the horizontal
orientation ot the valve which resulted in a high
valve factor (0.6).
Additionally, a contributing
factor was an unexplainably high stem friction
f actor (1. 0) that was observed during diagnostic
testing - the stem lubrication, at the time of the
testing, appeared to be in good condition and was
only six months old.
The inspectors were
concerned with the evaluation because it failed to
consider, as a contributing factor, the valve's
apparent usage for throttling flow.
Corrective actions, in response to the failure of
1SX173A, were not always timely.
For example, to
address potential generic implications that were
associated with other horizontally mounted valves
in the plant, the plan was to wait for the plant's
evaluation of NRC Information Notice (IN) 92-59
(" Horizontally Installed Motor-operated Gate
Valves"), to identify other similar valves prior
to taking additional corrective actions.
However,
the due date for the evaluation of IN 92-59 was
June 1993, almost 1 year after the second known
failure.
The inspectors did not' con 91 der the
approach to be timely because several years might
expire before an adequate evaluation of the
generic implications reached completion.
Another example of untimely actions was the
response to address the unexplained high stem
friction factor.
The licensee planned to wait for
the GL 89-10 trending program to track the
information of interest.
The inspectors did not
consider this approach to be adequate because the
trending program was only recently established and
would only analyze test samples taken on an
approximate five year interval (the periodic
verification interval).
As such, this approach
would not identify the lubrication degradation
that previously occurred, on the 1SX173A valve,
over a six month period.
In response to the concerns raised by the NRC
inspectors, the licensee modified its corrective
action plans as follows:
(a). An attempt was made to identify other gate
valves used for throttling.
None were found.-
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(b)
All horizontally mounted gate valves were
identified prior to the end of the
inspection.
The licansee selected a sample
of the valves to test prior to the end of the
next outage.
Additional corrective actions
would be considered for this population based
on the results from the testing.
(c)
Plans were being developed to monitor the
degradation of the stem friction factor for
valve 1SX173A over the current maintenance
interval.
Methods under consideration
included monitoring of motor current as an
indicator of gross degradation and VOTES
testing.
The NRC inspectors considered the licensee's
revised approach to be acceptable.
(5)
Diacnostics and the Evaluation of Test Data
The program included the use of the VOTES
diagnostic equipment system during static and dp
testing.
The planned use of the diagnostic
equipment appeared to be acceptable.
The NRC inspectors reviewed procedures ME-05 (MOV
Performance Review Following Dynamic Testing"),
Revision 1, dated December 17, 1992 and ME-07
(" Engineering Evaluation of MOV Test Results"),
Revision 1, dated December 17, 1992.
Both
procedures provided instructions for the
evaluation of data from design basis testing.
Although the procedures appeared to represent a
good first attempt at evaluating test data,
improvements are needed.
The inspectors expressed
the following concerns to the licensee staff.-
(a)
Valve factors and motor capability were not
evaluated in the opening direction.
Since
opening requirements are often more limiting
than the closing requirements, it would be
appropriate to evaluate MOV capability in
both directions.
(b)
Pull-out forces were recorded but the running
loads were subtracted from the term prior to
comparing the values to valve and actuator
structural limits.
The pull-out forces
should have been compared to the structural
limits without subtracting the running load.
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(c)
Appropriate accuracy adjustments, in
accordance with recommendations from the
diagnostic equipment manufacturer, were not
made for data outside the specified
calibration range.
As a result of the
oversight, the actual pull-out forces may be
higher than originally documented.
(d)
The calculated valve factor was
inappropriately based on the thrust observed
at seat contact.
This point was not always
the highest thrust recorded during the stroke
of the valve.
For example, several MOVs
showed higher thrust readings prior to seat
contact.
As such, the calculated valve
factor was lower than the actual worst case
valve factor observed during the dp test.
The licensee agreed with the inspectors'
assessment of the procedures and planned to make
appropriate changes.
The inspectors considered the safety significance
of the procedural oversights to be minimal because
only four MOVs had been subjected to design basis
testing at the time of the inspection.
All the
MOVs appeared to have substantial margin.
(b)
Walkdown
The NRC inspectors performed a walkdown to observe
design basis testing on 1SXO96A as well ac the
general condition of other MOVs.
The inspectors
did not identify any significant concerns.
3.
Licensee Self-Assessment
The self-assessment program was acceptable, but narrow in
scope.
It thor 'aghly reviewed the areas covered,' identified
shortcomings, and provided a mechanism-for tracking
corrective action and for confirming closure.
However, it
was focussed primarily on the administrative portion of the
MOV program and did not encompass the range of programmatic
material normally reviewed by an NRC inspection of the GL 89-10 program.
Such expanded coverage is considered to be
essential because it provides an early opportunity for.the
licensee to obviate or mitigate program deficiencies.
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4.
Exit Meetina
The NRC inspectors met with the licensee representatives
(denoted in Paragraph 1) at the conclusion of the inspection
on January 15, 1993.
The inspectors summarized the purpose,
scope and findings of the inspection.
The inspectors also
discussed the likely informational content of the inspection
report with regard to documents or processes reviewed by the
'
inspectors during the inspection.
The licensee did not
identify any such documents or processes as' proprietary.
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