ML20043H149
| ML20043H149 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 05/31/1990 |
| From: | Belisle G, Burnett P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML20043H144 | List: |
| References | |
| 50-395-90-16, IEB-89-003, IEB-89-3, NUDOCS 9006220080 | |
| Download: ML20043H149 (9) | |
See also: IR 05000395/1990016
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UNITEG STATES
NUCLEAR REGULATORY COMMisslON
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Report No.:
50-395/90-16
Licensee: South Carolina Electric and Gas Company
Columbia, SC 29218
Docket No.:
50-395
License No.: NPF-12
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Facility Name:
V. C. Sunrner
Inspection Conducted: ' May 15 - 16, 1990
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Inspector:
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P
T. EfuFnett
Date pRjned
AccompanyingPersonnyl:,,G.A.Belisle
Approved by:
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G. A. BelislerUhief
Date Signed
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Test Programs Section
Engineering Branch
Division of Reactor Safety
SUMMARY
Scope:
This routine ' announced inspection addressed the areas of control of fuel
assembly o)erations in the spent fuel pool, response to NRC Bulletin 89-03,
Potential
Loss of Required Shutdown Margin During Refueling Operations, and
final' core 6 verification; examinations of used fuel- assemblies; control of
debris in the primary system; and fuel cycle 6 core analyses.
Results:
Management attention and initiatives in response to mislocation of_ four fuel
assemblies in the spent fuel pool were prompt and thorough.
The immediate
corrective actions were appropriate, and the completion dates for reviews of
potential. additional, long-term corrective actions are consistent with the
current schedule for-the next refueling. No violations of reactivity limits in
the spent fuel pool were created by the mislocations.
(Paragraphs 2.aand2.b)
Control of fuel assembly locations, during fuel loading into the core, to
preclude creating an unanalyzed critical array was addressed satisfactorily in
the fuel shuffle- procedure.
The loading of core 6 was verified to be correct
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by video examination of the completed core.
(Paragraph 2.c)
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Examinations of fuel discharged from core 5, using ultrasonic testing and
high-definition video, identified five-failed fuel pins.
No mechanism has been
positively identified for the failure. of one pin in a VANTAGE 5 fuel assembly.
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Failures of' the pins in other assemblies, without lower debris filters, are
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consistent with debris-induced fretting of the lower portion of the pin and
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subsequent secondary hydriding of the cladding. (Paragraph 3)
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Potential sources of debris in the reactor coolant system include material torn
from fuel assembly grids.
Control of material to avoid adding debris to the-
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reactor coolant . system, during the rece it removal of the bypass loops for
resistance thermometers and installation of thermal wells, appeared to be
adequate.-(Paragraph 4)
No violations' or deviations were identified.
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REPORT DETAILS
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1.
Persons Contacted
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Licensee Employees
- L. Cartin, Senior Engineer, Margin Management
- R. Clary, Manager, Design Engineering
- H. Donnelly, Senior Engineer, Regulatory Interface
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- B. Johnson, Supervisor, Core Engineering
- A. Koon, Manager, Nuclear Licensing
- G. Liu, Engineer Independent Safety Engineering Group
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- K. Nettles, General Manager, Nuclear Safety
- C
Price, Manager, Technical Oversight
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- J. Skolds, General Manager, Nuclear Plant Operations
- M. Williams, General Manager, Nuclear Services
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Other licensee employees contacted included engineers and office person-
nel.
NRC Inspectors
- L. Modenos, Resident Inspector
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R. Prevatte, Senior Resident Inspector
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- Attended exit interview on May 16, 1990.
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A list of acronyms and initialisms used in this report is given in the final
paragraph.
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2.
Fuel Handling Activities (60710)
a.
The fuel Mislocation Event
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The spent fuel pool is divided into three regions,1. 2, and 3.
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Region 1 is for the most reactive fuel, and all fuel from the reactor
is first unloaded into region 1 until burnup calculations are com-
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plete and a determination is made that allows movement into the lower
reactivity regions, 2 and 3.
During the morning of April 23, 1990,
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while performing fuel bundle / fuel rack position verifications to
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confirm the fuel was properly positioned for reloading the core, the
licensee determined that two bundles that should have been in region
1 were in region 2 and region 3.
In addition, two other bundles were
conservatively mislocated.
They were in region 1 and should have
been in regions 2 and 3
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The SFP region burnup requirements, in MWD /MTV, are 34,546 and
14,804, for regions 3 and 2 respectively.
Fuel assembly G35, which
was incorrectly placed in region 2, had a burnup of 17,623 MWD /MTV and
did not violate the region 2 exposure requirements.
Fuel assembly
G28 had an exposure of 18,287 MWD /MTV and did violate the region 3
exposure threshold, when placed there. The design basis for region 3
is that k-effective will be less than 0.95 with one unexposed, 4.25
w/o U-235, fuel bundle optimally located within it, with a SFP boron
concentration of 2000ppmB. The actual boron concentration in the SFP
was over 2000 ppmB and the initial enrichment of G28 was 3.79 w/o
Hence, there was no criticality concern at that time.
However, the failure of the material and administrative controls was
of concern.
After reviewing completed procedures and fuel movement data sheets,
the licensee concluded that a transcription error, rack location
18-23 was written down as 18-33, led to moving a region 1 fuel
assembly to region 3.
The concomitant error was that the bundle in
18-23, which was destined for region 3, was left in region 1.
The
source of the second error was less certain.
The bundle in 11-25
should have been moved from region 1 to 2.
Instead, the bundle in
10-25 was picked. -The licensee speculated that the crane was mis-
indexed or the index mark misread. Again, the concomitant error was
that the bundle in 11-25 was left in region 1.
Two hours after the mislocations were identified, all fuel bundles
were verified by the licensee to be in their proper locations. The
immediate corrective actions were to install a chalk board in the SFP
area, so that rack positions could be written for all concerned to
see and verify when a fuel assembly was selected for movement, and to
require that manual changes to the fuel transfer forms receive
independent verification,
b.
Inspection Activities
The inspector toured the SFP area and observed the index marks for
both the bridge and the hoist,
indexing of the bridge appeared to be
unambiguous.
There are two sets of numbered index marks for the
hoist on the bridge railing. Those on the horizontal surface are for
the fuel racks without neutron absorbing material.
Numbered index
marks for the racks with neutron-absorbing material built in are on
the vertical surface of the railing and are prefixed with a P.
It
does not seem likely that an attentive operator would misindex the
hoist, and a miscommunication error seems the more likely source of
the second mislocation error.
The inspector reviewed the Off-Normal Occurrence Report and two Core
Engineering reports, one on consequences and one on corrective
actions, which were issued shortly after the April 23, 1990, event.
In addition, the Material Transfer Forms in use at the time of the
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fuel mislocations were reviewed.
These documents adequately
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described and evaluated the event.
The event was also addressed in MRB
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Meeting- 90-06 on May 8,1990.
At the end of the meeting, the MRB
issued the following open items related to this event:
90-06-04: Evaluate the ability to identify region 1 in the SFP by
color coding or other possible means for physical identifi-
cation. (Due date: July 31, 1990)
90-06-05: Identify long term corrective actions and incorporate these
findings into procedures to address both verbal and physi-
cal communications during the movement of fuel.
This
should address both SFP transfers as well as core trans-
fers.
(Due date: July 31, 1990)
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90-06-06: Evaluate the indexing iocated in the fuel handling bridge
crane (on the railing.' for possible human factor improve-
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ments.
(Duedate:
prior to refueling 6)
90-06-07: Core Engineering personnel involved in this event are to
provide a " lessons learned" training session to personnel
in their department.
(Due date: June 10, 1990)
90-06-08: Review the numbers of hours worked by Core Engineering
personnel and evaluate the desirability to add contract
personnel during future outages.
(Due date:
prior to
refueling 6)
These action items reflect appropriate management concern for the
event and for preventing a recurrence,
c.
Refueling for Com 6
Refueling was controlled by REP-107.002 (Revision 4), Core Shuffle,
and the completed copy of the procedure was reviewed by the inspec-
tor, with no procedure deviations or deficiencies identified.
The
arocedure contains steps to control temporary storage of fuel assem-
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) lies both in the core and in the SFP.
No temporary arrays are
allowed in the core.
If- a change in loading sequence is required to
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box in a location to guide in a bowed fuel assembly, only the fuel'
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assemblies assigned to the locations are used for the boxing in.
These changes to the procedure satisfy requested actions I and 2 of
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NRC Bulletin No. 89-03.
The licensee stated that use of a device called a shoe had eliminated
the need for boxing in during the most recent refueling,
ibe shoe
fits into a grid position adjacent to the assembly to be insulled
and guides the bottom nozzle into place during the last few incias of
travel.
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The inspector reviewed portions of the video tape made of the core
verification following refueling.
Definition of the fuel assembly
numbers on the tape was excellent for even twice-burned fuel; thus,
there should have been no difficulty in confirming the assemblies
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were properly located.
There was no narration on the tape; so it
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could not be used alone to verify proper loading. The independently
verified data sheets, filled out dt.'ing the video inspection, did
confirm that the core was loaded according to design.
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In reviewing procedure REP-107.002, the inspector noted that the
source of the final core design loading is not identified or clearly
documented in the procedure.
This administrative control is neces-
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sary because core design can and has changed up to the time reloading
begins.
The correct loading design was used in cycle 6 as a result
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of individual initiative rather than procedural control. The licen-
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see agreed additional procedural control was necessary and issued an
internal tracking number to assure the necessary revision was per-
formed prior to the next refueling.
No violations or deviations were identified.
3.
Fuel Pin Examinations (60710)
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Five failed fuel pins have been identified in four fuel bundles.
Using
the licensee's terminology, two fuel pins were identified as fully failed
by UT.
Two other were identified as suspect (failed in the licensee's
judgement) by UT.
The fifth failure was in a VANTAGE- 5 fuel assembly
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(G08), which passed UT examination, one of three times, but later HDTV
inspection showed to be blistered, a sign of hydriding.
The VANTAGE 5
fuel has debris filters at the bottom.
Hence, the blisters may be from
primary hydriding.
(Primary hydriding means the water or hydrogen source
entered the fuel pin during the manufacturing process.) This fuel bundle
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was -reconstituted, with a solid SS rod replacing the fuel rod, and . reload-
ed into core 6.
The licensee is continuing discussions with the UT
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inspection vendor regarding the failure to positively identify the VANTAGE
5 pin as failed.
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The inspector viewed the HDTV video tapes of the VANTAGE 5 assembly.
The
blisters were clearly defined by the imaging system and were observed
below grids 7, 6, and 4.
This distribution of blister locations is
different from other hydriding failures observed by the inspector.
In the
other cases the hydriding effects were all at or near the top of the fuel
pins.
The blisters were about 3/16th inch in diameter.
In the two cases-
in which there was an obvious hole in the clad, the hole was about 1/16th
inch in diameter.
The lighting and depth resolution did not permit visual
confirmation that the clad was fully penetrated.
The third location
appeared as only a raised area on the cladding with a different metallur-
gical structure from the cladding.
There was no visible evidence of
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During the inspection, the licensee received word by telephone from the
fuel vendor that a review of the manufacturing records for the pin in G08
did not reveal any problems in the manufacture of the pin.
The inspector
is not convinced that the pin damage did not originate on the outside of
the cladding rather than the inside.
The licensee agreed to keep the
inspector Informed of the results of any further inspections or evalua-
tions of that fuel pin.
The remaining four failures were in older fuel. Two were in adjacent pins
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in the same bundle, which makes debris induced fretting failure, with
secondary hydriding, the most likely failure mode.
No violations or deviations were identified.
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Control of Debris in the Reactor Coolant System (92705)
Other than the usuoi steam generator inspections, tube plugging, and
hot-end tube peening, the licensee had not performed any significant
primary side maintenan:e to introduce debris during previous outages.
However, with four pin failures possibly attributable to debris-induced
fretting, the licensee has attempted to characterize the current condition'
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of the RCS.
The licenseo has identified some debris in the RCS, with one
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piece, apparently, from a intermediate fuel assembly grid strap.
HDTV
inspection of fuel removed from cycle 5 showed that grid straps on four
fuel assemblies had received some damage.
On three, the damage, although
visible, did not appear extensive to the inspector, and all fuel pins were
still supported by the straps in the area of damage.
Two of the assem-
blies were reinserted in cycle 6.
The fourth assembly, 001, had part of
grid 6 totally missing to the extent that five pins were unsupported by
it.
That assembly was not scheduled for any further use.
The licensee
stated that their review of fuel handling records from previous cycles did
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not reveal any problems, such as hoist overload, with D01.
One of the activities completed during the current outage was the removal
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of the RTD bypass manifolds from the pri. nary loops, and the installation
of thermal wells directly into the loops. This work had the potential for
introducing debris into the RCS.
The inspector reviewed WCAP-12189, RTD
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Bypass Elimination Licensing Report for V. C. Summer Nuclear Station
( April .1989) and the completed work package.
In addition,- the inspector
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interviewed the licensee's proje:t engineer for the work.
Cleanliness and
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debris control appeared to be adequate to preclude the entry of fuel
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cladding threatening material into the RCS.
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No violations or deviations were identified.
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5.
Core Analyses for Cycle 6 (92705)
By letter dated May 3, 1990, the licensee informed the NRC that in per-
forming final calculations for the Reload Safety Evaluation Report for the
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Virgil C. Sumer Nuclear Station, Cycle 6
the licensee had discovered
that the calculated boron worth for operating modes 3 and 4 were more
negative than those previously assumed in the boron dilution accident
analysis.
The licensee's imediate corrective, to use shutdown margin
curves more conservative than TS Figure 3.1.3, was acceptable.
The
inspector attempted to learn through discussions with the responsible
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personnel the reason for the seemingly late discovery of this problem.
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From discussions with Core Engineering personnel, the inspector learned
that redesign of the cycle 6 core became necessary when management made
the decision t) terminate cycle 5 about 80 EFPD earlier than planned. The
short notice placed the redesign work on the critical path of activities.
Nevertheless, the design process received all scheduled interim reviews,
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but the problem was sufficiently subtle that only the final, in-depth
review could identify it.
The proposed, long-term corrective action of
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placing the shutdown margin curves (now TS Figure 3.1-3) in the Core
Operating Limits Report would focus sufficient attention on this problem
to assure it is addressed early in the design cycle in the future.
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Other documents reviewed in the inspection of this area included:
a.
Startup Physics Package for the V. C. Summer Nuclear Power Plant,
Cycle 6.
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b.
Cycle 6 Core Operating Limits Report (Draft dated May 7, 1990).
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No violations or deviations were identified.
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ExitInterview(30703)
The inspection scope and findings were summarized on May 23, 1990, with
those persons indicated in paragraph 1 above. The inspector described the
areas inspected and discussed in detail the inspection findings.
No
dissenting comments were received from the licensee.
Proprietary material
was reviewed in the course of the inspection, but is not included in this
report.
7.
Acronyms and Initialisms Used in This Report
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effective full power days
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HDTV
high defirition television
ISEG
Independent Safety Engineering Group
Nanagement Review Board
metric tons of uranium
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MWD
megawatt days
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ppmB
parts per milliol boron
-RCS
Reactor Enginsering Procedure
resistance temperature device
spent fuel pool
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stainless steel
TS-
Technical Specifications
ultrasonic testing
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