ML090140289
| ML090140289 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 07/16/2008 |
| From: | Ross Telson Reactor Projects Region 3 Branch 4 |
| To: | Thorp J Office of Nuclear Reactor Regulation |
| References | |
| FOIA/PA-2009-0026 | |
| Download: ML090140289 (13) | |
Text
John Giessner From: Ross Telson-Sent: Wednesday, July-1 6 2008-i 2:21,-PMi' To: Johr-Th-0orp Cc: Kent Wood; Thomas Herrity; Mahesh Chawla; John Ellegood; John Giessner; Robert Lerch; Frank Tran; Mark King; David Pelton'
Subject:
ACE for CR-PLP-2007-03105.doc Attachments: -ACE-for CR-PLP-2007-03105.doc
- John, Per our discussion this morning, I've attached the Palisades Apparent Cause Evaluation (ACE) associated with the licensee's 7/30/07 corrective action document (CR-PLP-2007-03105) addressing a history of spent fuel pool fuel rack swelling that appears to date back to 1991 (highlighting is mine). The ACE provides useful background and contributed to licensee'testing discussed at today's 8:15 call following the licensee's preliminary indications (today) that the spent fuel pool fuel racks may have less neutron absorption ability than assumed in design analyses.
The residents (John Ellegood (SRI) and Jack Giessner) are following this issue and, in support of any generic review activities deemed necessary and appropriate by NRR, they will pass to Kent and Tom any significant additional insights as they develop. At this time, we have not identified any immediate safety concerns or questions that would warrant action beyond the licensee's administrative limits on SFP boron and ongoing "blackness" testing & data analysis.
Ross Telson (630) 829-9619 Chief, Branch 4 (Acting)
Division of Reactor Projects, Region III I
NUCLEAR NON-QUALITY RELATED EN-LI-119 REV. 7 lEn fergy MANAGEMENT
- .EJIL~Ii:: MANUAL INFORMATIONAL USE PAGE 1 OF 12 Apparent Cause Evaluation (ACE) Process Condition Report Number: Assigned Department:
CRPL4007036- System Engineering (Reactor)
PROBLEM STATEMENT: (The WHAT) (see Procedure step 5.4[2](a))
~Note-. rhis event was previously evaluated per C-PLP-2007-03 105 GA -00001. CbARS
~subsequently diected that a lower tier pparent cause evaluation be performed.,
Du-ig fuel huffle. in' theSpeniitu P~fLool (SrP)'on 07/3i7/iO7, the ISIpI eInt Fuel HaInd -lng Machin-(SFH-M) wa~s unable to lift assembly S35 from NUS rack location R-~12. A hoist overload occurred as soon as the assembly lift was attempted. Alignment was re-verified and the lift attempt was repeated per procedure SOP-28 with the same results - auto stop on overload.
This SFP fuel shuffle was being performed to prepare for new fuel receipt. As there were adequate space available without this move, the move of S35 from R-12 was aborted and the remaining staging moves were completed.
Does this ACE report require an Equipment Failure Evaluation (EFE)? EL Yes 0 No (See procedure steps 5.4 [2](b) and 5.5)
IF Yes, THEN complete Attachment 9.7 Equipment Failure Evaluation AND attach in PCRS IF No, THEN an EFE analysis is not required.
Was an HPER assigned & performed for this CR? El Yes 0 No (See procedure step 5.4 [2](b))
IF Yes, THEN ensure results of the EN-HU-103 HPER are discussed in the Event Description.
EXPLANATION OF PROBLEM: (the HOW) (see Procedure step 5.4[2](c))
NUS Rack Description The NUS.racks, also known-as.th* RegionI racks, cossi'sts of 422 storage wn intalled
'"gecells "a in 19771o increase SFP st"orage capacity. A rack assembly consists of a rectangular array of storage cans with a minimum 10-1/4 inches center-to-center spacing of the fuel assemblies. Each cell is approximately 12 feet in length with an inside square cross sectional length of 8.56 inches.
A cell consists of two concentric~ 18Iinch Ty'pe 3-4sanessee aswt 4 neutron abso-rber pjate~s in,;talled i) the annular qlVpb~etween the cas The top andth~e bo6ttom of the twocan~swere
- Enferoy NUCLEAR MANAGEMENT NON-QUALTY RELATED EN-LI-I 19 REV. 7 MANUAL INFORMATIONAL USE PAGE 2 OF 12 Apparent Cause Evaluation (ACE) Process closed by welding aspacer between the two cans on either end. Originally the design called for' the annulus to be water tight, but cell wall swelling due to internal gas production from gamma exposure necessitated the drilling of 3/16 inch vent holes in the upper region of each cell.
The neutron absorber plates were manufactured by Carborundum. The manufacturing process bonded B4C powder in a carbon matrix through a sintering process producing a hard cerarmic like material. The absorber is 50% 134C by volume with the remainder being carbon and voids..The
'absorber was fabricated into 0.21 inch thick plates. A number of these plates were inserted in the annular space.
History of NUS Rack Stuck Fuel Assemblies Currently there are ten. identified stuck fuel assemblies in the SFP NUS rack. The following list identifies the ten assemblies currently classified as stuck.
Assembly Cell Date In Discovered Condition Report K65 K-4 10.05/1990. 01/22/19,91 D-PAL-91-0015, C-PAL-95-0343 K04 1-3 09/23/1992 03/11/1994 D-PAL-94-0078 K1 6 N-4 09/23/1992 04/20/1995 C-PAL-95-0357 C141 F-1I1 09/23/1992 04/13/2001 C-PAL-01-1392 B19 H-12 09/23/1992 04/14/2001 C-PAL-01-1417 B66 Q-1 8 04/13/2001 01/19/2003 CAP032988 C139 U-8 07/17/1988 11/22/2003 CAP038744 Q34 1-10 04/15/2001 10/03/2004 CAP044237 Q31 1-9 04/12/2001 04/15/2006 S35 R-12 10/03/2004 .. 07/30/2007 CR-PLP-2007-031 05 During the Cycle 7 offload in 1988 it was not possible to insert a fuel assembly in cell G-1 9. G-1 9 has not been used a storage location since this occurrence.
During Cycle 9 core reload on January 22, 1991, fuel assembly K65 could not be extracted from cell K-4 under a maximum load of approximately 2500 lbs utilizing the Spent Fuel Handling, Machine (SFHM). The overhead crane was used to apply a load of 3400 lbs to the assembly without any detected. Fuel assemblies are normally extracted with little or no resistance (e.g.,
SFHM load cell reading; :1400 Ibs).
Also during Cycle 9 reload, there were problems extracting fuel assembly L06 located in cell Q-8.
An applied maximum load of approximately 2500 lbs was required to remove fuel assembly L-006.
Fuel assembly L-006 was subsequently lowered and raised in an alternate storage location with no high SFHM load cell indication. Presently, cell Q-8 is not used to store fuel. These two events were documented in D-PAL-91-015.
During UT inspections for dry fuel storage on March 11, 1994, fuel assembly K04.could not be fully extracted from cell 1-3 using a maximum load of approximately 1750 lbs. The overload limit was reached with the fuel assembly approximately two feet out of the storage cell. The fuel assembly would not lower using normal procedures. The assembly was lowered back into the cell
NUCLEAR NON-QUAUTY RELATED EN-LI-119 REV. 7
`Entpry MANAGEMENT MANUAL INFORMATIONAL USE PAGE 3 OF 12 Apparent Cause Evaluation (ACE) Process using the weight of the fuel assembly to overcome the binding forces. This event was documented in D-PAL-94-078.
Fuel assembly K16 was found to be stuck in cell N-4 on April 18, 1995, during a fuel shuffle to support the offload during the 1995 refueling outage. The overload was set at 1535 lbs. The fuel assembly did not move using the maximum force of 1535 lbs. C-PAL-95-0343 was written to document and capture all of the stuck fuel assembly events.
Inveistigation ofthese first three stuck assemblies.(K65, K04, and K16) and the Kfirssto blwcked cels lead to anpparent cause that the stuck f~uel assemnblies are a result of fuel assembly to cell wal ineato u ocell wall sw~elling. The swelling is a result of prsuizto ofthe nua
§pace because of radiatilon~ ihduced gas generation thiat lacks a vent path.ý There are significant differences between the original group of stuck batch K assemblies and blocked cells identified in the earlyl1990's and the next four events. The three K assemblies were discovered to be stuck relatively soon after they were discharged, when they were still producing considerable heat and radiation. They had similar discharge assemblies placed in adjacent cells such that the cell walls were exposed to relatively high radiation levels and thus had high gas generation rates.
'Conversel~y, 141, B19, B9'6~,andC139 were all discharged fromff Cycle 1 andwere producing reaive__lo radiation fields at the time they were discover~ed to be stuck. C~141 B19, n 6 were-mo into the egion nea the soth ti.*t pitgate on 9/23/1992 aftercooling for al"most 1 years. They ?emaine eundiseturbeduntiltApril 2001 when C141anld B19 we discvered to b stuck. B66 was successfully moved from K-13 to Q-18 with no problems identified. In fact, 39 of 41 Cycle 1 assemblies were successfully relocated from the area near the south tilt pit gate. Due to dose issues, this region is only accessible for moving irradiated fuel when the south tilt pit is flooded, such as during a refueling outage. Prior to September 1992, this region was typically unoccupied except during refueling outages in which the full core was off-loaded. Therefore, the cell walls in this region have been exposed to lower than average lifetime radiation fields (and gas generation rates). Cell U-8 is not within this south tilt pit gate region and has been occupied since 1983. In fact, assembly C139 has been in cell location U-8 since 7/17/1988, had not been disturbed in over 15 years prior to being discovered to be stuck.
Assemblies Q34 and Q31 were discharged in April 2001 (EOC 15) to the NUS rack near the south tilt pit gate. At that time, a large group of discharge assemblies were placed in this region. Q34 and Q31 were undisturbed for three and a half or five years respectively before they were discovered to be stuck.
,itis,suspected that the vent hole of cells with stuck fuel assemTiblies may be plugged o were mis-
,drilled during installation. The racks were initially farctd ihu vent holesbut the need$ for inag prior tointallaionin the SFP. The vent holes were drilled prior to installation but records from the vent hole drilling project are inconclusive as to the precise location of the vents, The vent holes of the cells containing stuck fuel assemblies cannot be examined since the holes are covered by the assemblies. Probing of G-19 and Q-8 vent holes revealed that these vent holes were plugged, but did not determine the reason for the plugging.
2 NUCLEAR NONQUALTY RELATED EN-LI-119 REV. 7
_Ente- gy MANAGEMENT MANUAL INFORMATIONAL USE PAGE 4 OF 12 Apparent Cause Evaluation (ACE) Process History of NUS Rack Blocked Cells In addition to the stuck assembi~es tree empty cells M-, 0-8 and G-1 a identified as blocked.
.CellM-7 was reenty disco*vered to be. boked.on 8/27/07. These cells are administratively controlled and not used for fuel storage because of past problems encountered while extracting or.
inserting fuel assemblies. Cells M-7 and Q-8 are now used to store items with smaller cross sections than fuel assemblies.
taer inspections of ~cells Q-9 2and G-1 9 have revealed an inward ~distortion of the~ rinner cell wa~lls This would support the th~eory that the fuel assemblies. are stuck due to swellin~gofthe stora~ge ells in which they are store~d.
Puring March 1995, a specially designe todl wasused to probe the vent holes of QO-8 andG-1 9 The tool consisted of a 1/4 inch stainless steel welding rod attached to a Cam-Lock attachment. A camera was used to aid in probing the vent holes. The evolution was video taped. Camera inspection of the vent holes revealed a buildup of a substance at the vent hole. The probe was U to:sed break away the substance apparently blockingthe '*ent hole and once the probe scraped away enough of the substance, a large volume of gas was released. The gas was released in the form of small, fine bubbles. This scenario occurred with both vent holes. The operator was able to scrape enough of the substance from the vent hole of G-19 to insert the probe into the vent hole.
It was not clear how far into the vent hole the probe was able to penetrate. The operator could not remove enough material from Q-8's vent hole to enable insertion of the probe. The release of gas from each vent hole continued for approximately one hour. Also, theeblackcloudy material described earlier seepin~g from a cell vent hole was also capturedi on video tape during the evolution.
Stuck Assembly S35 Discussion Cell R-12 has been used extensively. See table below for the occupancy history of cell R-12:
Assembly Date In Date Out XF67 04/09/81 10/09/85 H62 12/26/85 06/13/88 K22 03/10/92 09/23/92 G22 09/28/92 05/07/93 L36 06/26/93 04/13/95 N34 11/01/96 02/12/99 S47 10/09/99 11/02/99 (New Fuel) 018 11/02/99 02/22/01 T15 03/02/01 04/12/01 (New Fuel)
C111 04/12/01 11/24/03 Cl11 11/24/03 02/11/04 C111 02/11/04 07/19/04 V40 08/27/04 10/03/04 (New Fuel)
S35 10/03/04 Note that the multiple moves for assembly C111 were for UT and visual exams prior to placing
'e!i!n(r~iil NUCLEAR MANAGEMENT NON-QUALITY RELATED EN-LI-119 REV. 7
........ y MANUAL INFORMATIONAL USE PAGE 5 OF 12 Apparent Cause Evaluation (ACE) Process C111 in Dry Fuel Storage.
No problems were noted on the move sheets of recent moves (018, T1 5, C 11, and V40) out of R-12 prior to placing S35 into R-12 in 2004. As a EOC 17 discharge assembly, S35 was producing relatively high radiation fields. S35 was a thrice-burned assembly with a Cycle 17 burnup of 16022 MWd/MTU and a total discharge burnup of 44145 MWd/MTU. Therefore, S35 was generating a relatively high radiation field, but not exceptionally high compared to other discharge assemblies. All other EOC 17 discharge assemblies have been successfully moved from their initial SFP discharge location. This includes several assemblies with higher burnup and Cycle 17 power than S35.
The high radiationieldsand resulting -gasgen nrat ue! ithis blocked. Manyicels in the NUS racks havebeen exposed to n s with s*tuck assemblies with noadverse effects observd. It is most likely that vent holes for cell R-12 have become plugged, for if the vents had been. mis-drilled during fabrication, it is likely that an earlier assembly, L36, N34, or 018 would have become stuck when they were discharged to R-12.
Operating Experience These- events do not appearto be como to th~erest ofthinuryhahveN acs contai*ingCarbun Queries of the industry have not revealed other stuck assembies. One
'possible explanation fo~r this is thiat other plants' NUS racks have largrvn oe.Tevn oe
,at~Calvert Cliffs are approximately 1/2 inch, while the venthoesat ge Palisades 3/ The nchft e hoes precursor to a stuck assembly is plugging ofthe vent hole, a 3/16 vent hole would be easier to plug than a larger vent hole.
EDF (Fac)ddidct htte aeosre the swelling phenome~non iwith their NUS rack~s and attributed it to water logging of the B, aes This information cotait U etn o ter saturation effects, TheNUS testi results predicted, that exposure to waterwould cause mEiniml [swellingof theapanIels. f Signifcant Event Report 1381, "Swelling ofB14 C Poison Plates i Fuel Rack",' was addressed in
'ACE0032f11for assemibly C1 39. In the SER, off gassing of the absorber is blamed for swelling of the ~racks at Kewauinee. Kewaunee's racks are niot ven~ted. The' Conn~ecticut Yankee plant is, mention'ed as having a similar problem, olved by venting their racks.
grqaI densitytermined that t Ujoadtngwas _4% l vaIuq. vatisaaes does not have coupons for the NUS rack. Palisades does not have a vent hole in the bottom of the cell which creates a flow path.
NUCLEAR NON-QUALITY RELATED EN-LI-1I19 REV. 7 MANAGEMENT
.... ..... MANUAL INFORMATIONAL USE PAGE 6 OF 12 Apparent Cause Evaluation (ACE) Process Carborundum Test Report CB078-299 describes test conditions for the coupons that are more severe than actually encountered during use in the racks. For example, the test coupons were immersed in a circulating fluid during irradiation that does not represent actual use in the racks.
The actual rack use is sealed encapsulation with only the small vent hole as a possible exposure point to pool water. The actual condition should substantially reduce any dissolution or washout of the B4C material.
The evaluation of CAP032988 (B66) identified one partially related event from Vermont Yankee in 2001, which involved contact between the fuel channel fastener and their new BORAL racks. For BWR fuel, the bundle is contained in a channel and the head of a fastener that secures the channel to the bundle protrudes slightly above the surface of the channel. Given the tight tolerances of their new SFP racks, Vermont Yankee encountered a few cases of interference. As their racks are constructed with BORAL, swelling of the cell wall, as has occurred at Palisades, is not an applicable mechanism.
APPARENT/CONTRIBUTING CAUSE(S): (the WHY) (see Procedure step 5.4[2](d))
The apparent cause of S35 being stuck in NUS cell R-1 2 is the result of fuel assembly to cell wall interaction due to cell wall swelling. It is most likely that vent hole for cell R-1 2.has become plugged.
Contributing Cause A contributing cause for the pressure buildup within the NUS racks is the vent hole size, location, and blockage vulnerability.. Originally purchased without v~ent holes, the NUS racks were field.
modified at the Palisades site. Poor documentation exists as to the hole size (dra~wing specs called forO0..19" diameter holes), location, and verification that the holes were actually drilled in all of the cells. A mis-boceted hole could result in the hole be~ing drilled into solid material, preventing venting of the sandwich material. A hole diameter of 0.19" seems to be disputed in several previous corrective action documents, with hole variability identified as a noticeable difference between cells. Only one small hole is intended to vent all four sides of a cell, a potential problem if cell tolerances limited exchange of gasses between cell walls, or the single hole becomes blocked.
An earlier corrective action document noted that an internal pressure of 4 to 5 psi was sufficient to cause wall swelling of the thin wallepd cell, sufficient to cause the wall to contact the fuel assembly.
NUCLEAR NON-QUALIY RELATED EN-L,-119 REV.7
' 'Enterovi MANAGEMENT MANUAL INFORMATIONAL USE PAGE 7 OF 12 Apparent Cause Evaluation (ACE) Process EXTENT OF CONDITION: (see Procedure step 5.4[2](e))
With respect to the mechanical impact on the fuel assemblies due to the swelling of rack cell walls; the cell walls will primarily contact the guide bars, grid straps, upper and lower tie-plates with only minimal contact force on peripheral fuel rods. The guide bars in particular, unique to Palisades fuel, provide protection from contact.
Cooling flow through the affected SFP rack cells is expected to be minimally impacted.
The SER for the NUS racks evaluated the unlikely event of foreign material blocking cooling flow in one or more fuel assemblies. This analysis showed the maximum clad temperature would be less than 250 OF, considerably less than the minimum clad failure temperature of over 1000 OF. Swelling of the rack walls would not impede cooling flow inlet located at the bottom of the cell. Contact of a fuel rod to the stainless steel wall would still provide adequate heat transfer.
FF h-e__m niost ole- b un k6nc6nw ditio n ass 0c Iatedw it h SFP Kegion)I ra Ck swe IIin is wit -
'respect to the criti~calityan'alysis impgct jthat would resut fr~fom alossQr reconfiguration 61 Palisades spent fuel pool water has been routinely tested for Total Organic Carbon (TOC),
and the levels are very low (< 0.2 ppm) and stable, indicative of minimal loss of material.
Note TOC sampling was not initiated for B4 C condition monitoring, rather since TOC will break down into corrosion forming constituents in the PCS, SOER 82-13 recommends TOC analysis on all systems that can come in contact with the PCS. Also, oil or grease may get into the pool from machinery used around the pool, such as the crane. TOC is monitored in the SFP to ensure high TOC water does not enter the PCS. Additionally, the testing on Kewaunee coupons supports that no significant loss of material is occurring.
An extensive evaluation was completed by Palisades in support~~of the Condition Report evaluated in C-PAL-95-0343. This included input from the 134C manufactu~re~r,the
ýP~brucu Cmgy.Sm ofte general conclusions ofthreota:
" There was visible idence of nun ematerialleaching through the venthold. This ould represent a Small. loss f material. However, because the vent holes are near the tops of the cells and the amount of observed material is small, the'impact of any B4 C material loss is expected to be very slight.
- The Carborundum Company reviewed the data and concluded that the black material is very likely a boron compound but notes that boronleachability over time is relatively low, although there is no test data to document leaching over a, 10-15 year time span.
There are no vent holes at the base of the racks. Thus, a slow discharge of degraded B4 C material, with its inherent loss of reactivity hold-down, is not considered a credible scenario.
In addition, the locations of the vent holes are below the upper tie plate, but slightly above the active fuel region. Therefore, if the all the interior B4 C above the vent were to leak through the holes, there would be an insignificant amount of reactivity hold-down degradation in the active fuel region.
Because Palis~ades ~does not hiave rack material surveill~anc copons, Palisades has requested su pporting information from the Kewaunee pliant, whli~chLuses a sim~ilar B4C rack design and which has an *acyl7surveillanceplan.
Kewaunee responded by stating that other than some possible B4 C dust leakage and some observed chipping (most likely due to the effects of handling), there was no visible degradation of the B4C material. However, as Kewaunee does not.test for brittleness, they were unable to confirm that B4 C would not degrade under long-term temperature and radiation exposure. Therefore, ft reasonable and~conservative to assume at least some _d~egree' of B14p degradation over time.
As noted above, there are no vent holes at the rack base to permit egress of degraded 134C. As th (ohyorer~main i their oiginal configuration, we can conclue.
hacks that, exept for the swollen~ racks, the B4C remains in place., For the swollen rack locatiornes, ito psonceivable tohconsiderkaeB4C "slumapingeffecwitn whichthe degraded neutron absorber, notwin powdered form, sinks tocaliyer levelsinstide the racks, as would a liquid.Realistically, the mnaxim~um amo~unt of slumnping would reduce the absorb~er height, to no lowerthan approximately 80% of its original position.
Howyever beca~useslum~ping to tat degree culd remov~e neutr~on absorber function in the v~ery top of the affected rack loaios En~tergy has elected to proma. cri~ticality assessment, considering the potential for B47C loss anid crediting SFP boron concentraton to compensate.
Criticality Assessment In order to provide assurance that k-effective was remaining within the limits of design basis assumptions, Entergy has completed a criticality assessment, with SEP boron Th gcriioit onIFe l iti alt Calc lati ns, t~he criicalgit an alysi th ofe cis rde(AORl Crly R akA racks fromd the AOR. The6 MONK comipujter code, ~use~d prreviously for the criticality
'analysis, is no longer available. Therefore , the racks were mo deled using th~e CASMO serieso.f modeling codes which are compatible with the rack model used by MONK.
CASMO-4 was used for the calculated criticality values, and the model was confirmed to agree well with the original CASM 0-3 analysis for the normal condition. i~ evr isnot licensed to ue CASMO for design bas~is calcuatiorn'.tiethrefore, the resultsthat,-
tollow must be considered as an asesmn,.utal.fr......y eeriatorather Assumptions associated with the criticality assessment are as follows:
" The model assumes the entire Region 1 is filled with new fuel enriched to 4.95 w/o U-235, as noted in Technical Specification 4.3.1
" The model takes no credit for B4 C reactivity holddown. In other words, it assumes complete degradation of all neutron absorber and its replacement in the gap by B4 C off-gas. This is an extremely conservative position, but is retained as it (1) provides a more straightforward model and (2) bounds the current conditions;
" Because the U-235 enrichment is a nominal one, several cases were repeated for an actual enrichment of 5.00 w/o, which is the nominal value of 4.95 w/o U-235 plus a manufacturing uncertainty of 0.05 w/o;.
" In order to establish the most conservative conditions, an additional case was run with the gap filled with water instead of gas'.
WThe code was rn o a variety of SF Pboron concentrations. Themos~t.sign ific n't of these aWre 1720 ppm, whichis the minimumsSeP boron concentration required by the Palisades Technical Specification3.7.15 and 2550apm, which is the I R. 9 refueling boron concentration. 2550 ppm is also a procedural minimur for normal operation in Modes 1-4, required to ensure core subcriticality after a design basis seismic event. For normal operation in Modes, 5 arnd 6, a procedural minimum SFP boron concentration of 1800 ppm is specified.'
With these considerations in mind, the results of the criticality assessment are as follows Results are in units of k-inf, which is criticality in infinite array, and bounds (i.e. is always greater than) k-effective:
- 1. The k-inf for Region 1, crediting a 1720 ppm boron concentration in the SFP, is below 0.98. [calculated CASMO value was 0.97914]
- 2. The k-inf for Region 1, crediting an 1800 ppm boron concentration inthe SEP, is below 0.98. [calculatedvalue was 0.97202, linearlyinterpolatedbetween two calculated CASMO values]
NUCLEAR NON-QUALITY RELATED EN-LI-1 19 REV. 7 MANAGEMENT
....... MANUAL INFORMATIONAL USE PAGE 10 OF 12 Apparent Cause Evaluation (ACE) Process
- 3. The k-inf for Region 1, crediting a 2550 ppm boron concentration in the SFP, is below 0.92. [calculated CASMO value was 0.91044]
- 5. These conclusions remain valid if the gas within the rack is replaced by unborated water.
- 6. Increasingenrichment from 4.95 w/o to 5.00 w/o U-235 results in a slight increase in k-inf, across a range of 0.0015 to 0.0027.
ACTIONS COMPLETED (See EN-LI-1 19 step 5.4[2](f))
APPARENT OR CONTRIBUTING CAUSE, ACTION COMPLETED OR EXTENT OF CONDITION ISSUE [note any Work Orders/Requests, ER'S,. other]
PROPOSED CORRECTIVE ACTIONS (See EN-LI-1 19 step 5.4[2](f))
APPARENT OR CONTRIBUTING CAUSE, CORRECTIVE ACTION DESCRIPTION Assigned Due OR EXTENT OF CONDITION ISSUE [note any Work Orders/Requests, ER's, other] Department Date Extent of Condition Issue Procedure changes to COP-27 and related System 12/5/07 procedures to maintain SFP boron at Engineering greater than 2550 ppm in all Modes rather (Reactor) than just Modes 1 through 4. This limit should be maintained at least until blackness testing can be performed.
Review of SFP boron sample history confirms SFP boron has been the maintained greater than 2550 ppm since
NUCLEAR
.* .......
- NON-QUALITY RELATED EN-LI-I19 MANAGEMENT EEig. MANUAL INFORMATIONAL USE PAGE 11 OF 12 Apparent Cause Evaluation (ACE) Process 5/25/03, so this limit does not appear to be unreasonable from an operational perspective.
Extent of Condition Issue Perform blackness testing on the NUS System 7/30/08 racks as was committed to in the License Engineering Extension SER Section 3.3.2.2.1 (Reactor)
Schedu~led completion date is 03/24/2011 or sooner. Ideal time to perform this testing would be after the 2008 DFS campaign when the maximum number of open spaces is available in the SFP.
Apparent Cause Issue Evaluate establishing a periodic System 4/30/08 maintenance activity to clean NUS cell Engineering vent holes, possibly involving low pressure (Reactor) flushing to loosen and remove vent hole blockage.
Apparent Cause Issue Evaluate value-added in establishing a System 6/30/08 periodic maintenance activity to implement Engineering the vendor recommendation contained in (Reactor)
NUS letter 8960-NUS-365, dated October 25, 1978 to perform periodic free path
.measurements in a representative number of storage cells This letter provided several options to perform these free path measurements, such as movement of fuel or a dummy assembly up and down within the fuel storage cell using a load cell to detect any measurable drag.
Apparent Cause Issue Evaluate methods for extracting stuck System 12/15/
assemblies. Engineering 2008 (Reactor)
TREND DATA:
Cause Codes:
Human Performance Causal Equipment Causal Factors (List O&P Causal Factor(s) (List all):
Factor(s) (List all) all):
EN-HU-103 not adopted by Palisades, thus a Human Performance Error Review not performed.
EFE Codes (see Procedure step 5.5 [51):
INPO PO&C codes: Failure Mode Codes:
ACE Evaluator (print Name): G.T. Wiggins