ML18059A437

LER 93-004-01:on 930630,fuel Rod Failed & Loss of SNM Discovered Following Refueling Operations.Caused by Core Shroud & Fuel Assembly Interface Problem.Fuel Assembly Insps Increased & Failed Fuel Response Plan Implemented

ML18059A437
Person / Time
Site:	Palisades
Issue date:	10/14/1993
From:	Hillman C CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
Shared Package
ML18059A436	List: ML18059A435 ML18059A437
References
LER-93-004, LER-93-4, NUDOCS 9310190062
Download: ML18059A437 (8)

Text

NRC Form 366 U.S. N.UCLEAR REGULATORY COMMISSION~,

19*831 APPROVED OMB NO. 3160-0104 EXPIRES: 8/31 /86 '

LICENSEE EVENT REPORT ILER)

FACILITY NAME 111 DOCKET NUMBER 121 PAGE 131 Palisades Plant I I I I I I I

.0 5 0 0 0 2 5 5 1 I OF I 0 8:

TITLE 141 FUEL ROD FAILURE AND SUBSEQUENT LOSS OF SPECIAL NUCLEAR MAT.ERIAL DISCOVERED FOLLOWING REFUELING OPERATIONS - SUPPLEMENTAL REPORT ,

EVENT DATE 161 LER NUMBER 161 REPORT DATE 161 OTHER FACILITIES INVOLVED 181 SEQUENTIAL

• REVISION FACILITY NAMES MONTH DAY YEAR YEAR NUMBER NUMBER MONTH DAY YEAR N/A 939j3 old4 011 N/A THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR l: (Ch<<k,,,,. or"""9of1M following/ 1111 OPERATING POWER MOOE 191 I

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CAUSE SYSTEM COMPONENT TUR ER TO NPROS CAUSE SYSTEM COMPONENT TUR ER TO NPROS 1* .I I I I I I I I I I I I I . ':*::~

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I I I I I I I I I I I I I SUPPLEMENTAL REPORT EXPECTED 1141 MONTH DAY YEAR

'l EXPECTED YES Vf y ... com~oto EXPECTED SUBMISSION DATE!. ;i NO SUBMISSION DATE 1161 I I I ABSTRACT IUmit to 1400.,,.coa, i.e.. epprr>1ti,,..toly fifteen aing~.,,.c* typewritten lin ..I 116)

On june 30, 1993, at approximately.2300. hours, while draining the refueling cavity in preparation far* re~attaching the reactor head to the reactor vessel, an object located in the reactor cavity tilt pit exhibited contact dose rates of approximately 7000R/hr.

A review of a remote camera inspection video tape led to the postulation that the object was a piece of fuel rod.* Further remote camera inspection of the tilt pit resulted in the discovery of three additional pieces of what appeared to be a fuel rod. Subsequent investigation determined that fragmented pi.eces of failed fuel rod S-15 dislodged from fuel assemb.ly 1-024 during refueling operations.

• The failure of the fuel rod was caused by a' core shroud and fuel assembly interface problem that resulted in the wear and failure of a single fuel rod. The damaged fuel rod became dislodged from the _fuel a~sembly during refueli~g operations.

Corrective action for this event includes increased. f~el assembly inspections, inspection of the core shroud during the next full core offload, Cycle 11 core redesign incorporating stainless st~el rods in selected fuel assemblies, limiting the use of the standard bi-metallic fuel assembly design to four cycles or less; continued periodic reactor noise analysis, procedure changes, and implementation of the Failed Fuel Response Plan.

9310190062 931014  ;

PDR ADOCK 05000255 S PDR I L.

NRC Form JeeA U.S. NUCLEAA REGULATORY COMMISSIO" 19*831 APPA0\/£0 OMB NO. 3160-0104 EXPIRES:. 8131186

.LICENSEE EVENT REPORT llERI TEXT CONTINUATION FACILITY NAME 111 . OOCKE'T NUMBER 121 LER NUMBER Ill S£QUEHT1.Al '11£\/ISION YEAA NUMBER NUMBER Palisades Plant o 6 *5 0 0 *O 2 .5 5 9 3 - 0 0 4 - O. 1 0 2 0~ 8 :

EVENT DESCRIPTION On June 30, 1993~ at appr~ximately 2~00 h~urs, ~hil~ draining the refueling cavity in preparation for re-attaching the reactor head .to the reactor vessel, radiological dose rates in the reactor cavity near the t n t pit [OF] exceeded the dose rates typically experienced during previous similar refueling cavity draining evolutions. At the time of the event the reactor head was in place over the reactor vessel resting on shims.

Typical dose rates at the floor level of the refueling cavity ne.ar the tilt pit (elev.

625-feet) are 200-300 mR/hr; however, during this event the dose rate on the refueling machine bridge (elev. 649;feet) was 700 mR/hr with no water in the tilt pit. A~ object located on the tilt pit floor (elev. 610-feet).; exhibited contact dose rates of approximately 7000R/hr.

• The refueling cav-ity was immediately evacuated and the radiol6gical conditions assessed. Approximately two feet of water was added to the tilt pit to provide shielding. Prop~~ radiol-0gical postings and boundaries were established, and access to the containfuent area was controlled. At the time of the event the reactor was in a refueling mode. There was no radiological release to the environment as* a .result of this event, and there were no personnel exposures that exceeded either 10 C~R Part 20 limits .or CPCo administr*tive limits .. This event had no adverse effect on the health and safe.ty of the *public.

A remote ~amera inspection of the tilt pit ~ai.conduct~d and a cylindrical Object approximately five (5) feet in length and approximately fou~-tenths (0.4) i~ch in diameter was identified. It was suspected that the -Object was a piece *of a*fuel rod

[AC]. On July 1, 1993 the NRC was notified of the possibility of a fuel rod in the reactor cavity.tilt pit.

• Further remote camera inspection of the tili pit resulted tn the identification of three more pieces of what appeared to be a fuel rod. The* total length of all four pieces was* estimated to be about 12 feet. A review of the video tape.*from the remote camera inspection of the thre~ additibnal objects revealed that one of the pieces had an end cap and the serial number was visible. Based on the serial number, it was determined that*the fuel rod came from'fu~l assembly 1-024 which was in the reactor core. The 1-024 fuel assembly had been removed from the reactor during refueling, taken to the tilt pit, rotated_l80 degrees and returned to its core position~

In response to these de~~lopments, CPCo formed .a project.team to develop an action plan for recovery of the fuel rod pieces from the tilt pit, recovery of the damaged fuel assembly from the reactor core, and analysis of the entire event. *

• On July .4, 1993 the:three fUel rod fragments*were retrieved and relocated to storage baskets in the tilt pit. It was determined th~ fourth piece was not a fuel rod fragment and tt was not recovered.* By July 6, 1993 a plan.had be~n *developed and.

approved by the Plant General.Manager and the NRC for the recovery of fuel assembly I-024 from the reactor <ore. The reactor head was removed and placed on the reactor head stand. Preparatio~s were then made to remove the Upper Guide Structure (UGS) from the reactor v.essel. During the lift ._of the. UGS, the load cell readout indicated a load *I.:

greater than anticipated. A remote camera i~spection of the underside of the UGS

• confirmed that a fuel assembly still in its core position was being lifted with, the UGS. The UGS lift was halted and the containment was evacuated. An Unusual Event was

NRC F0tm 3HA .

U.S. NUCLEAA REOUL..*.-l'ORY COMMISSION 19*831

. APPflOVEO OM.B 0jO. 3160-010*

' EXPIRES: 11311116 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME f1 I. OOCll;ET NUMBER 121 LER NUMBER 131

• PAOE l'I SEQUENTIAL REVISION YEAA NUMBER NUMBER Palisades Plant Q 5 Q Q Q 2 5 5 9 3 - Q Q . 4 - Q 1 Q 3 OF Q 8 declared at 2254 hours0.0261 days <br />0.626 hours <br />0.00373 weeks <br />8.57647e-4 months <br /> on July 6, 1993 .. Ther~ was no radiological release to the environment as a result of the lifting of a fuel assembly with the UGS, and there were no exposures that exceeded either 10 CFR Part 20 limits or .CPCo administrative li~its.

The lifting of a fuel as~embly with.the UGS had no adverse effect ori the health and safety of the public.

A.closer examination of the location of the fuel assembly attached to the UGS indicated that the fuel assembly was attached to. the UGS in a location where fuel assemblies had been stuck to the UGS on two previous occasions. (See.LERs 88015, dated October 3, 1988 and 92017, dated March 30, 1992.} All reactor vessel work was stopped pending recovery of the fuel assembly stuck to the UGS. Containment integrity was established by closing the equipment hatch and routine work activities in the containment were suspended. Procedures_ w~re then developed for the recovery of the stuck fuel assembly.

On July 8, 1993 the fliel *assembly, .while still in its ~ore position, was successfully removed from the UGS and placed on the reactor vessel core support plate. The UGS was then lifted without further incident and was placed in its storage location in the

. reactor cavity. The fuel assembly that was lifted with the UGS was then moved to the spent fuel pool for examination. Also on July 8,_1993, an NRC Augmented Inspection*

I.

Team (All) arrived at Palisades to investigate the broken fuel rod.found in the reactor cavity tilt pit, the lifting of a fuel assembly ~uring removal of the UGS, and other recent issues. **

On July ll, 1993 fuel assembly 1-024 was removed from the reactor core. Prior to removal from the reactor core, fuel assembly 1-024 had been visually inspected to ensure that additional fuel rods would not be damaged during removal from the reactor core. The visual inspection of fuel assembly 1-24 while it was in th~ reactor core was.

accomplished by removing an adjacent fuel assembly and an adjacent control rod. Prior to removal, it w~s noted th~t.the upper end piece of the failed fuel rod was still contained within the uppermost spacer grid of the 1-0~4 fuel ~ssembly. During the removal of the 1-24 fuel assembly from the reactor core, this piece of fuel rod dropped from the fuel assembly and landed on top of another fuel assembly tieplate in the core.

The piece that had fallen from fuel assembly 1-024 was retrieved from the core and was stored with the other three fuel rod pieces. The 1-024 fuel assembly was subsequently relocated to the spent fuel pool, along with the pieces of damag~d fuel rod, where inspections by CPCo personne 1 and the fue 1 vendor could be conducted. .*

Inspection of the 1-024. fuel assembly and the broken fuel rod have bee*n completed.

Inspection of.the reactor core and lower vessel area for loose fuel pellets, other debris, and'other indications of fuel damage bas been completed. The results of these inspections were used t~ determine a root cause for the failur~ of fuel assembly 1-024 I.

and to develop corrective actions associated with this event. *

• This event is reportable to the NRC in accordance with 10CFR50.73(a}(2)(ii} as an event wherein a principal safety barrier (i.e., fuel cladding) was seriously degraded.

'*I NRC f0tm 3&8A U.S. HUCLEAA REOUL.ATORY COMMISSlO" lf.831 Al'PflOVEO OMB NO. 3160~104  :

. EXPIRES: 1131.116 LICENSEE EVENT REPORT ILER) TEXT CONTINUATION FACILITY H.AME 111 OOCKET HUMBER 121 LEA NUMBER 131 PAOE 141 SEQUENTIAL REV1SION YEM HUMBER

• NUMBER Palisades Plant olslololol2lsls 913 - oIo 14 - 0 11 014. OF o1s I i

CAUSE OF THE EVENT The failure of the fuel rod from fuel assembly 1-024 .was caused by a core shroud and

. fuel assembly interface problem that resulted in the wear and fail~re of a single fuel rod.

This event involved the failure of a principal safety barrier (fuel cladding) and is considered a failure of equipment important to safety.

ANALYSIS OF THE EVENT Fragmented pieces of failed fuel rod S-15 from fuel assembly 1-024 were found in the reactor side tilt pit following th~ initial draining of the re~ctor cavity near the end of Cycle IP refueling outage. Based on inspections of the failed fuel assembly, fragmented fuel rod pieces, and the core shroud corner location where fuel assembly 1-024 was located, the following conclusions have been made:

1. The fuel rod was failed and severely damaged during Cycle 10 operation;

2. The upper *portion of the fuel rod and the associated corners of spacers 6 through 9 were rubbing against the core shroud during Cycle 10 operation.

3. A circumferential break in Span 9 e~isted on the failed rod during Cycle 10 operation. This is *believed to be due to secondary hydriding. The initial primary failure is believed to have originated in Span 5 or 6 due to rod fretting against the core shroud.

4. The rod was peeled from the fuel assembly while being handled over the reacto~

side tilt pit during the initial ~nd of Cycle 10 core fuel shuffle.*

5. As the rod was peeled from the fuel assembly, it was broken into several pieces.

This peeling is believed to be the caus~ of damage to the corners of spacers 1 through 5 .

.6. A total of six fragmented rod ~ieces were found. The entire length of the failed rod has been accounted. for; however, approximately three feet of partial circumferential cladding (1/3 to 1/2 circumference) remains missing. *

7. The missing partial cladding is believed to have worn or broken away during Cycle 10 operation. One to three cladding shards may exist that are equivalent in size to one of the shards found (which was one~foot long, about 90 degrees circumference, and worn down by the core shroud). *

8. Approximately five feet of fuel, 213 pellets, is missing from the retrieved fragmented rod pieces~

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NRC Form 388A 111*131 . "*" """. . ""~"" """"" 'l AP9110VEO OMB N*O. j 1&0-01 O*

EJl:PIRES: 8131 /H LICENSEE EVENT .REPORT (LERI TEXT CONTINUATION FACl~ITY NAME 111 OOCKET NUMBER 121 . LEll NUMBER 131 . PAGE l'l SEQUENTIAL REVISION*

NUMBER NUMBER Palisades Plant 0 5 0 0 Q 2 5 5 9 3 - 0 Q 4 - Q 1 Q .5 OF Q 8 Root Causes That Are Considered Likely*

• A core shroud and fuel assembly interface probl~m is considered the likely proximate cause. The root cause(s) must still.be determined coriside~ing potential contributing.

factors~

Root causes being considered~

1. Shroud distortion due to operating conditions.

2. Shroud distortion due to loose or broken bolting.

3. Misalignment between the UGS and the core support barrel.

4. The problem may have always *existed from :the original as-built conditions; however, the add~tion of some ~ontributing factors caused the I-024 failed rod

.event. * *

• Contributing factors being considered:

1. Fuel assembly I-024 was in the car~ five ~ycle~.

2. Minor damage *on fuel assembly 1-024 may have existed from a handling event.

3. Fue.l assembly I-024 had loose spacer grids.

4. Increased PCS flow due to the steam generator replacement after Cycle 9.

5. Crire bar~el vibration changes.

6. Localized PCS flow changes* due to introduction of (HTP) High Thermal Performance fuel assemblies.

7. Fuel assembly* bow. *

8. -~uel assembly twist.

Six of the above contributing factors 1, 3, 4, 5, 6, and 7 are considered key factors to be specifically addressed for operation of CycJe:11 and future cycles. Contributing factor 2 was addressed to some extent during the root cause analysis. Refueling equipment was *inspected for damage or snag hazards to verify no generi.c handling damage issue existed. Contributing factor 8 may have some subtle contribution with respect to how a fuel assembly interfaces with its surroundings; however, fuel assembly twist was a minor contributor to the failed rod event since the fuel assembly's upper and lower tie pl~tes are held in position by the Upper Guide Structure lower alignment plate and the lower core support plate, respectively. *Any fuel assembly* twist would tend to be reduced or eliminated due to the tight positioning tolerance provided by the alignment ins and ali nment holes. *

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\ J NRC Fotm 3HA 19*8ll

.* "' """"' "'~'"' """""'"\.1i\*

.. *APPROVED OMS )jo. l160~10*

EXPIRES: 8131186 LICENSEE EVENT REPORi: (LERI TEXT CONTINUATION FACILITY NAME.11) oocic:t; NUMBER 121 LER NUMBER 131 PAGE 1'1 SEQUENTIAL REVISION YEAR NUMBER NUMBER

,1 Palisades Plant 0 5 0 0 0 2,. 5 5 9 *3 - 0 *4 - 1 8 l 0 0 0 6 OF 0 Disposition of Missing Material

• Material "missing from fuel assembly 1-024 and failed fuel rod. S-15 is suinmarized as: . 'I Mi ss.ing Cladding SJ .gr~ms Missing Pellets 938 grams Missing Insulator Disk 2 grams Missing Spacer Pieces (not quant Hi ~d, see below)

A total ~f six fra~mented rod.pieces were found and ~etrieved. The entire length of the failed fuel rod has been accounted for; however; :approximately three feet of*

partial circumferential cladding (1/3 to 1/2 cir,cumference) is missing. The missiryg partial cladding is believed to have worn away during Cycle 10 operation at least to some extent. We believe that o~e to three cladding shards may exist that aie

• equivalent in size to one of the shards. retrieved (which was one-foot lon*g, about 90 degrees in circumference, and apparently .worn away by interaction with the core shroud). The missing cladding shards may have broken intb smaller ~ieces.

Approximat~ly five feet of fuel pellet material is missing from the retrieved fragmented fuel. rod pieces. Remedial corre~tive action with.respect to accountability and ~mpact of. the missing fuel is ~iscussed in our September 30, 199~ letter.

• In addition to the missing fuel rod material~ spacer material is'mtssing fro~ the damaged corner of fuel ~ssembly I-024. Most of the-missing material consists of small portions of the side plates in the area of the failed.fuel rod. A very small amount of internal strip material and one lantern spring from, spacer 9 are als.o *missing.

A search for !Jlissing material was performed in the core location where fuel assembly I-024 resided. The bottom of the reactor vessel under the core support plate, the top

.of the core, the r~act6r cavity iilt pit, the transfer tube, and the spent fuel pool side south tilt pit were also inspett~d.

• The.missin~ partial claddin~ was:not located.

Three small pieces of spacer side p~ate fu~terial were located on the core shroud and on the core plate, and were retrieved using the ~ormal ~acuuming equipment. It is

• possible that' .other missing spacer pieces and small cladding pieces were retrieved during the several. tilt pit, reactor cavity fl*oor, or core region vacuumings that.took pl a.ce during the refueling outage.

Some spacer .and cladding materi~l has nof'.*been found; If this material. still resides

• within the primary coolant system, the 'potential exists for fuel rod fretting after the primary coolant pumps are returned to service. The impact of fuel **rod fretting will be

• mitigated since 136 of the 204 total fu~l assemblies incorporate a debris resistant design.

Additionally, it is recognized that d~bris i~ the PCS *ha~ the potential td affect PCS*

r internal components such as valve i nt'erna 1s. and steam. generator tubes.* The majority ~f j

NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION 11*831 APPROVED OMB NO. 3160-010' EXPIRES: 8/31 /86 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 ' DOCKET NUMBER 121 LER NUMBER 13) PAGE 1'1 SEQUENTIAL.

• REVISION YEAR. NUMBER NUMBER*

• Palisades Plant Q* 5 Q Q Q 2 5 5 9 3 - Q Q 4 - Q *1 Q 7 OF Q 8 .

the 5~ gram~ (0.12 pounds, plus.a slight additio~ due to spacer material) of missing non-fuel material is zircaloy. The missing material will cause little fretting wear against stainless steel or Inconel components. The effect of the missing 53 g~ams of material on other components, such as valve internals, is considered to be minimal based on previous experience at Palisade~.

CORRECTIVE ACTION Corrective action for this event includes:*

I. Inspection of a minimum of four fuel* assemblies in the shroud corner locations every refueling outage.

2. Performing a detailed inspection of th.e core* shroud after the next core offload.

3. Attempting to retrieve the as-built drawings and documentation of clearances between the core shroud and the fuel assembl*ies.

4. Limitiri~ the use of the standard b\-metallic fuel assembly design to four cycles

• or less.

5. Continued inspection of the High Thermal Performance spacer grid assemblies to confirm they meet their de~ign.

6. For Cycle 12, implement the planned shield fuel assembly design*, or configure

. *-burned fuel assemblies placed in the shroud corner positions such that the fuel assembly bow .is oriented toward the core and away from the shroud.

• 7: Continued pe.riodic reactor noise *analysis utilizing the ex-cor'e neutron detectors.

In additio~, 16 "L" fuel assemblies ~ill b~.used in the Cycle 11 .co~e design and will be located in the baffle corner locatiQns. The 16 "L" fuel assemblies have 14 fuel rods replaced by .oversized stainless stee1 rod_s . . Eight of the stainless steel rods are oriented in the corner of th~ *fuel assembly which interfaces with th& shroud corner to mitigate the consequences of a potential fuel assembly failure similar to that -

experienced by the 1-024 fuel assembly. The* other three corners of each assembly have two stainless steel rods each.

Miscellaneous further correcti~e actions iricl~de:

1. Incorporating the lessons learned from this event into the fuel performance monitoring procedures~

2. Evaluating the need to perform supplemental noise monitoring during Cycle 11 utilizing externally mounted vibration monitoring equipment.

3. Implementation of the Failed Fuel Response Pla~ to monitor future fuel failure.

) NRC Form 399A U.S. NUCLEAA REGUl.ATORY COMMissio ..

19*831 APl'llOllED OMB NO. 31&0-<l104

[)(PIRES: 813118&

LIC.ENSEE EVENT REPORT I (LERI TEXT CONTINUATION FACILITY NAME Ill DOC II.ET NUMBER 121 LER NUMBER 131 SEOUEHTIAl REVISION YEM NUMBER NUMBER Palisaqes Plant 0 5 0 0 0 2 5 5 9 .3 - 0 0 4* - 0 1 Q 8 OF Q 8 ADDITIONAL INFORMATION

• A. detailed description and the results of the* root cause analysis for this event are contained-in a letter from Consumers Power Company to the NRC dated' September 30, 1993 .

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