ML18059A508
| ML18059A508 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 11/08/1993 |
| From: | Hillman C CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML18059A507 | List: |
| References | |
| LER-93-007-01, LER-93-7-1, NUDOCS 9311170023 | |
| Download: ML18059A508 (21) | |
Text
NRC Form 388 U.S. NUCLEAR REGULATORY COMMISSION 19-83) APPROVED OMB NO. 3160-0104 EXPIRES: B/31/86 LICENSEE EVENT REPORT (LERI FACILITY NAME Ill DOCKET NUMBER 121 PAGE 131 Palisades Plant olsjojojoj2jsjs 1 OF I 0 I 5 I TITLE 141 DEGRADATION OF BO RAF LEX NEUTRON ABSORBER IN SURVEILLANCE COUPONS - SUPPLEMENTAL REPORT 0
EVENT DATE 161 LER NUMBER l8J REPORT DATE 181 OTHER FACILITIES INVOLVED 18)
SEQUENTIAL MONTH DAY YEAR YEAR
> NUMBER i?. REVISION NUMBER MONTH DAY YEAR FACILITY NAMES N/A oj6jojojoj I
01 8 11 7 9 3 913 01 oI 1 011 ~ 1 0.18 91 3 N/A oj6jojojoj I
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR I: /Ch<<k OM,,,,,,,,,. of rM folJowingJ 11 IJ OPERATING N
I MODE 181 20.4021bJ
- 20.4061cJ 60.7311112JlivJ 73.711bl POWER LEVEL 110) I I
- 20.4061*111 JIii 20.4061*111 JliiJ -- 60.381cll11 60.381cll21 -- 60.7311112JM 60.7311112JlviiJ -- 73.711cJ OTHER !Specify in Abetroct
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20.40611JlllliiiJ 20.40611111 JIM 20.40611111JM
--x 60.7311112JliJ 60.731*112JliiJ 60.7311112JliiiJ LICENSEE CONTACT FOR THIS LER 1121
-- 60.7311112JlviiiJIAI
- 60. 7 311112JlviiiJIBI 60.731*112Jlxl below 8"d in Text, NRC Form 388AJ NAME TELEPHONE NUMBER Cris T. Hillman*
COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 1131 sARIEA1cl°~ I 1 I I 4 I - I s I 9I I 3 s 1 MANUF_AC* REPORTABLE MANUFAC* REPORTABLE
( ..
< x CAUSE SYSTEM COMPONENT TURER . TO NPRDS CAUSE SYSTEM COMPONENT TUR ER TO NPRDS
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I I I I I I I ............. I I I I I I I .
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n SUPPLEMENTAL REPORT EXPECTED 1141 ************* MONTH DAY YEAR EXPECTED YES Vf Y**, comp/ere EXPECTED SUBMISSION DATE!
rxi NO SUBMISSION DATE 1161 I I I ABSTRACT IUmit ro 1400 ~*** /.1., ._1,,..re1y flfreln . , . . . , , . , , . typewritten linl*l 1181 On August 17, 1993 the plant was in cold shutdown for refueling. A Boraflex surveillance coupon was removed from the spent fuel pool in ord~r to conduct a visual inspection, neutron attenuation test and a hardness test. While removing the coupon from the spent fuel pool, a dark debris cloud was observed in the spent fuel pool around the edges of the coupon. Upon removal of the sheet metal coupon cover, the Bora fl ex material was found to be approximately 90 percent disintegrated or missing. Additional coupons were removed from the spent fuel pool and examined; varying amounts of Boraflex material were found missing.
The cause of this event is unknown.
Corrective action will include performing blackness testing on the spent fuel pool racks. I
~311170023 931108 ,.,,
5 DR ADOCK 05000255
NRC Form 3HA U.S. NUCL:EAA REGULATORY COMMISSION lf-831 APPROVED OMB NO. 3160*<P0' EXPIRES: 8/31186 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE 1'1 SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant
- EVENT DESCRIPTION On August 17, 1993 the plant was in cold shutdown for refueling. A Boraflex surveillance coupon was removed from the spent fuel pool [DB] in*order to conduct a visual inspection, neutron attenuation test and a hardness test. Boraflex is the trade name of a boron impregnated, polymer-based sheet material that is utilized as a neutron absorber in the construction of spent fuel pool (SFP) storage racks [DB;RK]. The material was manufactured by Brand Industrial Services, Inc. The use of the Boraflex allows minimal center to center cell spacing in the SFP storage racks. The Boraflex is sandwiched between two strips of stainless steel sheet metal (refer to Figure 1 in Attachment 1).
While removing the coupon from the spent fuel pool, a dark debris cloud was observed in I the spent fuel pool around the edges of the coupon. Upon removal of the sheet metal coupon cover, the Boraflex material was found to be approximately 90 percent disintegrated or missing. Five additional coupons were removed from the spent fuel pool I and examined; varying amounts of Boraflex material was found missing.
Boraflex surveillance coupons are not part of the SFP storage racks, but rather are I placed in the SFP to be examined and tested periodically to judge the condition of the Boraflex in the SFP storage racks. The first coupon removed on August 17 was being tested to fulfill a five year surveillance interval commitment made to the NRC. In a similar manner to that in the surveillance coupons, the Boraflex in the spent fuel pool storage racks is contained in a stainless steel wrapper. The wrapper assembly is then attached to the walls of the storage cells of the storage racks.
There are two types of coupons at Palisades (refer to Figure 1): Full length coupons and short set coupons. Some full length coupons have the Boraflex bonded .to one side of their sheet metal wrapper; in others, the Boraflex is not bonded. Four of the five coupons removed for testing were full length coupons and the other was a short set coupon. Three of the full length coupons had Boraflex bonded to the sheet metal.
Material lost from the full length coupons varied from 38 percent to an estimated 90 percent. All of the Boraflex material in the short set coupon was retained. The Boraflex material .in the full set coupons was from a different batch of material than that used in the short set coupons.
Neutron attenuation testing performed on the Boraflex material remaining in the surveillance coupons showed no loss of boron areal density, within measurement tolerances, from the original condition. There was no thinning of the remaining material.
NRC Form 3HA U.S. NUCLEAR REGULATORY COMMISSIO" lf-831 APPROVED OMB NO. 3160-010' EXPIRES: 813I186 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE'"
SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant o I s Io Io Io I2 Is Is 913 - o I o I1 - o I1 ol 3 oF o Is CAUSE OF THE EVENT The cause of the event is unknown at this time. Known contributors to the degradation of Bora fl ex are:
- 2. Gamma flux which causes changes in the material characteristics of the base polymer resulting in hardening and embrittlement~
- 3. Chemical exposure of the boric acid environment in the SFP may lead to deterioration or erosion.
ANALYSIS OF THE EVENT An analysis of the present spent fuel pool storage configuration was completed to ensure there was no possibility of a criticality occurring in the spent fuel pool under worst case conditions. The analysis conservatively assumed there was no Boraflex present in the storage racks and no boron in the spent fuel ~ool ~ater.
Further analysis by the manufacturer of the spent fuel pool storage racks, Westinghouse, has been completed. The Westinghouse results, and the results of in-house analyses are provided in Attachment 1, the interim results of the Palisades Boraflex Program.
Westinghouse was contracted to determine whether the licensing design basis requirement of a 5 percent shutdown margin was being met, assuming no Boraflex remained in the storage racks and no boron existed in the spent fuel pool water. A burnup versus enrichment curve provided in the analysis reported that the fresh fuel enrichment equivalency requirement for spent.fuel stored in the SFP racks containing Boraflex had dropped from the technical specification value of 1.5 to 1.0 weight percent. Some assemblies that were in Region II racks did not meet this lower enrichment equivalency.
Using the results of the Westinghouse analysis, a CASM0-3 based analysis was completed to identify the highest reactivity assemblies in Region II. As a result, the 23 most reactive assemblies were moved from the Region II racks and replaced with assemblies which met the new burnup versus enrichment curve. Westinghouse then completed a KENO-Va based calculation considering the most reactive assembly after the 23 spent fuel assemblies had been removed. The calculation showed Ken to be below 0.95 (0.947 including uncertainties) with no credit taken for Boraflex or soluble boron.
. U.S. NUCLEAA AEClUl.ATOAY COMMISSION AP!'ROVEO OMB NO. 3160-0104 I
tt-831 EXPIRES: 8131186 ~
'1 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION F4CIUTY NAAllE 111 DOCKET NUMBER 121 lER NUMBER 131 P40E 141 SEQUENTIAL REVISION YEM NUMBER NUMBER Palisades Plant
- olslololol2lsls 913 - olo I 7 - o I 1 014 OF oIs I Following the relocation of the 23 most reactive fuel assemblies and the completion of the KENO-Va analysis, an additional CASM0-3 based analysis was performed~ Reactivity equivalencing using CASM0-3 shows that all fuel assemblies currently located in the Region II racks have a*reactivity less than or equal to the assembly considered in the KENO-Va analysis.
Until the results of blackness testing on the SFP racks are known, no fuel assemblies will be moved into the Region II racks unless they either meet the new burnup versus enrichment curve with no Bora fl ex or are shown by reactivity equi va 1enci ng* to be 1ess reactive than the most reactive assembly considered by in the KENO-Va calculation.
Based on the results of these analyses, the temporary requirement for daily sampling and analysis of SFP Boron has been discontinued. Prior to discontinuing the daily sampling and analysis, the action was discussed with the Palisades NRC Senior Resident Inspector.
Safety Significance Subcriticality in the spent fuel pool, at greater than 5 percent, is assured by the presence of over 1720 ppm of boron in the water. The licensing design basis assumes a 5 percent subcriticality margin with rto boron in the pool water and a minimum storage rack spacing. Based on the results of these analyses, assuming no Boraflex remained in the storage racks and no boron existed in the spent fuel pool water and the present configuration of spent fuel in the Region II storage racks, the greater than 5 percent subcriticality margin licensing design basis is being met.
CORRECTIVE ACTION Corrective action for this event includes:
I. Notifying the operating staff of the possible deteriorated condition of the Boraflex and making them aware not to dilute the spent fuel pool boron concentration below the plant administrative limit of 1800 ppm.
- 2. Corrective action to perform qaily sampling and analysis of the spent fuel poo 1 boron concent.r..at ion was performed unt i1 the ana 1yses described in Attachment 1 *were completed. *
- 3. Analyses to determine subcriticality in the spent fuel pool have been completed and are described in Attachment 1.
- 4. Determining the condition of the Boraflex neutron absorber material in the spent fuel pool storage racks. This activity is expected to occur following the loading of additional spent fuel storage casks in 1994.
NRC Form 388A U.S. NUCUNI REOUl.ATORY COMMISSION 19-831 ,._OVED OMS NO. 3160-0104 EXPIRES: 8/31116 LICENSEE. EVENT REPORT (LERI TEXT CONTINl,IATION FACILITY NAME 111 OOCKET NUMBER 121 LER NUMBER 131 PAOE 141 SEQUENTIAL REVISION NUMBER NUMBER Palisades Plant olslolololilsls I - 0 I I - ~ I I OF 0 I ADDITIONAL INFORMATION Refer to NRC lnformat ion Notice 93-70: "Degradation of Bora fl ex Neutron Absorber Coupons."
A detailed description of our analyses and results are provided in Attachment I to this LER.
Palisades Boraflex' Program
Background
Boraflex TM is a boron impregnated, polymer-based sheet material. This material was utilized as a neutron absorber in the construction of the Palisades Region II SFP racks to allow for smaller cente*r-to-center cell spacing. Industry experience and testing has raised long-term concerns with the durability of BoraflexTM when utilized for this particular application. To quantify and evaluate any degradation, an action item, AIR A-NL 92-225, was initiated to track actions associated with our NRC commitment PW081688A. This commitment required placement of Boraflex' surveillance coupons (see figure 1) for ease of material testing. Below is an outline of the steps to be taken to address this commitment.
Current Couoon Status A total of 12 BoraflexTM coupons were .available in one of the following three locations:
- 1. Store room - replacement coupons of original condition.
- 2. SFP long term - coupons placed between SFP racks containing assemblies with > 1 year decay time prior to placement in Region II racks.
- 3. SFP accelerated - *coupons placed between SFP racks containing assemblies which were placed in Region II (credit for burnup region) shortly after discharge from core ( 1 to 2 months).
Additionally, the coupons are one of the following three types:
- 1. Short coupon set - full .. length specimen holder with a total of 24 1 " x a
- 4. 5 n placed in rows of 3 each equally spaced along the length of the specimen holder.
- 2. Full length bonded - full length specimen holder with a 6" x 128" BoraflexTM sample bonded to. the specimen holder in a manner consistent. with that used to manufacture the Region II rack cells.
- 3.
- Full *length unbonded - identical to above except that BoraflexTM sample was not bonded to specimen. holder.
At least one of each type of coupon is in each of the three sample locations.
A total of five coupons have been removed for testing.
Page 1
Degradation Mechani.
Three prime contributors(1) to the degradation of Boraflex' are:
- 2. Gamma flux - leads to changes in the material characteristics of the base polymer. Primary c.oncern is hardening/embrittlement.
- 3. Chemic~I exposure - boric acid environment of SFP may lead to BoraflexTM edge deterioration/erosion.
Scope of Testing*
In order to adequately evaluate the Boraflex' coupons for known modes of degradation, the following testing program was implemented:
- 1. Visual inspection upon removal with emphasis on the following:
o Length, width and thickness measurements o Discoloration o Cracking o Flexibility o Edge deterioration o Erosion
- 2. Neutron attenuation o Determi.nation of actual 8 10 concentration per square cm.
- 3. Material hardness o Informational testing.
Evaluation Method To adequately assess the performance of Boraflex, relative to assumptions made in the Region II SFP rack criticality analysis, two parameters are of key interest:
- 1. Boron areal density
- 2. Physical size and condition (1 )An Assessment of Boraflex Performance in Spent Nuclear Fuel Storage Racks EPRI NP-6159 .
December 1 988 Page 2
In order to gain r.esentative samples, covering a r . e of gamma exposures, a total of five Surveillance coupons were removed. These represent different bonding techniques as well. Specific type and placement
,information is shown in Figure 2.
Method of Testing Boraflex TM surveillance coupons were removed from the SFP on 8-17-93 and 8-19-93. Figure 2 maps the particular coupons removed. Dl,Jring coupon removal, a dark, cloudy material was seen spilling from the sides and bottom of the full length coupons. The severity of this cloudiness appears to be directly proportional to the amount of BoraflexTM material missing from the individual coupons.
Initial visual inspections were conducted for the full length coupons. These inspections were performed following coupon removal and prior to coupon shipment. Anomalies are noted in Table 1, Visual Results column.
Physical size of the Boraflex coupons was determined by measuring the remaining portion of the Boraflex material and comparing to the original dimensions for a percentage of material lost. This was performed at University of Michigans' Ford Reactor facility by CPCo personnel. Results are presented in Table 1 .
Shore A hardness testing was performed on coupon 7705G. A variety of locations were tested again .by CPCo personnel. Results are presented in Table 1.
Boron areal density was calculated from neutron attenuation data obtained by.
University of Michigan personnel. U of M procedure NRC-007 Revision 3 was utilized. For the full length coupons, a total of seven neutron attenuation measurements were taken for each coupon. These were performed at approximately 16" intervals alo'ng the length of each coupon. For the short .
set, a total of 16 measurements were taken, two at each of the eight sample
- locations. Average 8 10 density, of remaining material, is presented in Table 1.
Actual attenuation and* corresponding 8 10 density *is presented in Table 2, along with the corresponding material thickness, as this information was utilized in the boron areal density calculation.
- Lastly, to quantify the cumulative gamma* dose received by each coupon, a Northeast Technology Corporation, Lotus 1-2-3 template was utilized.
Specifics of input data are detailed in engineering analysis EA-BWB-93-01.
Resulting gamma exposures are also presented in Table 1 .
Interim Conclusions/Actions Potential Implications Based on the significant degradation of the surveillance coupons, the integrity of the actual rack Boraflex~ should be considered as suspect until such time as rack blackness testing can be performed. This inference is contradictory to industry experience related to BoraflexTM degradation but represents a conservative approach. Also in favor of normal rack Boraflex TM degradation, is the SFP silica level. Although a spike was noted earlier in the. year, most likely due to recycled boric acid additions to support MSB (Multi-Assembly Storage Basket) loading, silica levels are in the range of 1 to 4 ppm (Refer to SFP Boron/Silica graph). This is somewhat elevated but within the range of other plants also utilizing BoraflexTM type racks (Refer to Table 4). Additionally, the short set coupons showed almost no degradation whatsoever, beyond the anticipated embrittlement. Of the BoraflexTM which remained in the full length coupons, no thinning or loss of boron areal density was noted. These factors tend to suggest that it is likely that the rack BoraflexTM is still reasonably intact.
Potential Contributing Factors Several factors which could contribute to the accelerated degradation of BoraflexTM have been considered. Chemical reaction of the SFP water with the Boraflex TM was explored from the following perspectives:
- 1. pH of the SFP water
- 3. A past, inadvertent hydrazine addition to the SFP These factors were discussed with BoraflexTM experts within the industry.
The SFP pH typically ranges from approximately 4.8 to 5.2. Occasional spikes to near 7 .0 have occurred. Due to MSB loading activities, SFP boron levels have been relatively high, in the range of 2900 ppm, at times. Lastly, one inadvertent hydrazine addition to the SFP did occur, albeit some time ago.
None of these factors were considered to have a significant, adverse impact on the con.dition of BoraflexTM.
Another factor, which relates to our inability to correlate coupon data to rack performance as well, is the varying heat code and base material lot numbers associated* with the actual manufacture of the BoraflexTM sheet material. As shown in Table 3, three different heat codes were utilized in the manufacture of the rack and short coupon set BoraflexTM, while only one heat code, but two different lots of base material, were used in the manufacture of BoraflexTM. for the full length coupons. While this could be construed as significant, it is also necessary to consider that these lots were all manufactured in accordance with a certified QA program. As well, the composition al"'!d production of BoraflexTM is relatively simple and well within Page 4
the-realm of mod9 manufacturing technique~. Rela.e consistency among varying batches* can reasonably be relied upon. This leads to concluding that a manufacturing defect causing the gross degradation appears unlikely.
Mechanical construction differences do exist between the SFP racks and the surveillance coupons. , The racks were constructed by folding a 75 mil thick, 36" wide and approximately 146" long sheet of stainless steel into a 9" square box. The resulting seam was then welded. To each side of this box, a sheet of BoraflexTM was laid. Over this sheet, a.*20 mil thick, 8" wide and approximately 146" long sheet of stainless steel, stamped to form a 42 mil recess approximately the width and length of the Boraflex TM sheet, was laid and then tack welded in place along the sides. Spots of RTV were used to hold the Boraflex TM in place during this process. This was repeated for each of the four sides of the box. Series of these boxes were then arranged in a checkerboard fashion and welded again at the corners to form a rack. Open
- cells at the periphery were closed by a single sheet of 75 mil stainless steel with a BoraflexTM sheet enclosed in a similar manner(Refer to Figure 3).
Full length coupon construction is similar, however, two sheets of 20 mil stainless steel were utilized for closure. As well, the seams were closed via bolting. At the time of coupon construction, it was believed that this would approximate the rack conditions while allowing for inspection of the Boraflex TM without the use of destructive opening methods. The short sets were likewise fabricated except that only one full length sheet of stainless steel was utilized.
The groupings of three coupon strips were enclosed by a second 20 mil thick stainless steel sheet approximately 8" square. Each of these squares was
- bolted down using 8 .fasteners._ This is significant in that it appears, from visual inspections, as though a water-tight seal was formed around the short set coupon.
During removal of the full length coupons, a cloudy material was seen flowing from the sides and bottom of the coupon. This suggests that water was able to pass through the seams of the coupons. The composition of irradiated
- soraflexTM does reduce to mainly silica and boron carbide with time, silica being the primary binding agent as most of the polymer deteriorates. This water exchange through the coupon interior could easily carry away varying amounts of silica, depending on the rate of water exchange. Once the binding
. agents have been reduced, rapid degradati.on of the structure of the BoraflexTM
-logically follows. This is a possibility agreed upon by experts in the industry.
Due to the construction differences, the full length coupons are far more flimsy than the SFP racks. A rigid base is simply not afforded .. This likely resulted in more n open n seams on. the full length coupons, allowing for a higher than normal water exchange rate. This cannot be conclusively shown, however,* until a_ determination of the actual rack BoraflexTM condition is made:
For this, blackness testing is required.
Page 5
Comoensatorv- Action.
A conservative interpretation to the surveillance coupon data disallows Palisades to take credit for the Boraflex poison in SFP Region II. A CASM0-3 based analysis was completed determining the. k.., of the Region II racks when considered completely filled with the most reactive fuel in the racks at that time. The results are provided in engineering analysis EA-RDR-93-06 and show a k.., s .0.9855 with no Boraflex and 0.0 ppm Boron in the pool water.
Since CASM0-3 has not been accepted as a criticality code and the result did not*show compliance to design basis commitment of k 11tts0.95 Westinghouse, the rack manufacturer, was contracted to do a separate analysis. Daily SFP Boron sampling was begun to give sufficient notice of any dilution trends assuring a safe configuration under all credible situations. Westinghouse delivered a conservative Burnup vs. Enrichment curve to ensure a k 11tt below ANSI Standard 0.95. The reported fresh fuel enrichment equivalency dropped .
from the Tech. Spec. value. of 1.5 to 1.0 w/o. Many assemblies presently in Region II racks did not meet this lower enrichment equivalency.
At this point anoth_er CASM0-3 based analysis was completed showing the highest reactivity assemblies in Region II. An ordered ranking of these assemblies is reported in engineering analysis EA-RDR-93-07. The 23 most reactive assemblies were moved from the Region II racks and replaced with assemblies which meet the Burnup vs. Enrichment curve provided by Westinghouse. Westinghouse then completed a KENO_Va based calculation considering the most reactive assembly after the 23 had been removed. K11tt was shown to be below 0.95 (0.947 including uncertainties) with no credit for Boraflex' or soluble boron taken. A description of the calculation is found in Westinghouse's Region II criticality report titled "Criticality Analysis To Support Current Fuel Storage in the Palisades Region 2 Spent Fuel Racks with no Boraflex Panels". Reactivity equivalencing using CASM0-3 as reported in engineering analy~is EA-RDR-93-07 shows that all fuel assemblies currently residing in the Region II racks are of reactivity less than or equal to the assembly considered in the Westinghouse analysis. Until the results of Blackness testing are known, no fuel assemblies will be moved into the Region II racks unless they either meet the Burnup vs. Enrichment curve with no Boraflex' or are shown by reactivity equivalencing to be less reactive than the most reactive assembly considered by Westinghouse in their KENO Va calculation. At this time, daily SFP Boron samples are no longer necessary.
i A Safety Review was completed and attached to EA-RDR-93-07. The Analysis shows that remaining in. a condition where no credit is taken for Boraflex' panels in the Region II racks does not increase the probability or consequences of either accidents or malfunctions of safety related equipment.
No previously unanalyzed accidents or malfunctions are introduced and the margin of safety is not reduced.*
Pa.ge 6
Long-term Action In order to determine the actual condition of the SFP rack Boraflex TM, blackness testing of the racks is required. This involves placing a neutron source and four neutron detectors into individual fuel cells to map the presence/absence of neutron absorbing material. For this testing to be effective, the blackness testing service provider recommends that background gamma radiation levels be below 20R/hr. Higher radiation levels le~d to detector saturation which precludes neutron count rate monitoring.
SFP rack backgro*und gamma radiation levels were measured utilizing an underwater dose rate meter. Results are shown in Figure 2. These show that to reduce background radiation levels below 20R/hr, fuel assemblies can be no closer than 3 to 4 cells away, in all directions. As a minimum, an approximately 7x7 area would need to be cleared of fuel assemblies to allow for 'testing the center cell. Given only 13 non-occupied fuel locations, this is simply not possible at this time.
To compensate for the delay in blackness testing, the fuel assemblies in the SFP were re-.arranged to remove the most reactive assemblies from Region II racks and replace them with lower reactivity assemblies. The resultant ~tt is
~ 0.95 as outlined previously. This assures a safe configuration during all
- credible scenarios, including dilution to zero ppm boron concentration, without relying on credit for BoraflexTM. Silica levels continue to remain well within the range of other facilities. utilizing BoraflexTM racks. As silica level is an indicator of BoraflexTM degradation, this is the best indicator that our rack BoraflexTM degradation is likely consistent with that experienced by others.
Given the current safe configuration, low SFP silica levels, mechanical design differences between coupons and racks, it appears reasonable to align rack blackness testing such that it coincides with the dry fuel storage loading effort, scheduled to commence spring of 1994. This will open additional fuel locations in the SFP to allow for blackness testing of a representative number of fuel locations without requiring excessive fuel movement to reduce background radiation levels. Any further actions with respect to this issue, will be based on the actual condition of the rack BoraflexTM.
For additional information regarding BoraflexTM, contact:
Paul J. Kluskowski Plant* Reactor Engineer For additional information regarding criticality analyses, contact:
Guy C. Packard Physics. Design Supervisor Page 7
Table 1 Interim Results Coupon# Coupon Type Visual Results % of Boron-10 *Shore A y Exposure Material Areal Hardness Lost Density ..
(gm/cm2) 7709G Accelerated, '*' Most of boraflex Loss is Insufficient Insufficient 1.40 E 10 Full material was gone. estimated material material Rads length, Bonded Some sludge-like at 90%. present. present.
material in bottom area. No
- further eval.
7705G Long term, Full Approx. half of boraflex Loss was Average 92 to 99 was 5.92 E 9 length, Bonded was gone. Numerous measured density was the range at Rads cracks noted. Small at 50%. .00941 the top and amounts of sludge. middle. Near the bottom..
the range was 76 to 85.
7706G Long term, Full Approx. half of boraflex Loss was Average NA 5.95 E 9 length, Bonded was gone. Numerous measured density was Rads cracks noted. Small at 50%. .00912 amounts of sludge.
7712G
- Long term , Full Approx. one third of Loss was Average NA 6.26 E 9 length, boraflex was gone. measured density was Rads Un bonded Numerous cracks at 38%. .01000 noted. Small amounts of sludge.
Short set 1 Accelerated, Embrittlement was Loss was Average NA 1.47 E 10 Short length, noted. No loss or measured density was Rads Unhanded cracking. at0%. .00934 New Boraflex Shore A Hardness ranges from 80 to 88 Original criticality analysis assumed 8 10 areal density L.. 0.006 gms/cm 2
T abl e 2 A ttenuat1on Date Coupon ID Original Current ( 1 ) .. Original Current (2)
Thickness (In) Thickness (In) Neutron Neutron Attenuation Attenuation 7705G - 1 0.032 0.0315 .7193 .7316
-2 0.031 0.0306 . 7115 .7299
-3 0.031 0.0310 .7153 .7328
-4 0.032 0.000 . 7117 .2153
-5 0.031 0.000 .7134 .0955
-6 0.032 0.000 .7205 .1000
-7 0.031 0.000 .7157 .0993 7706G - 1 0.029 0.0295 .7112 .7177
-2 0.030 0.0295 .7106 .7143
-3 0.030 0.0293 .7117 .7180
-4 0.030 0.0305 .7073 .7223
-5 0.029 0.0310 .7044 .7274
-6 0.030 0.000 .7081 .0967
-7 0.030 0.000 .7101 .1188 7712G - 1A 0.032 0.0316 .7372 .7445
- 2A 0.032 0.0319 .7318. .7544
- 3A 0.032 0.0336 .7326 .7541
- 4A 0.031 0.0323 .7340 .7491
-.5A 0.032 0.0323 .7318 .7491
- 6A 0.032 0.0320 .7352 .7659
- 7A 0.031 *0.0320 .7283 .7469 GU70 1 0.025 0.0265 .7659 .7349
-2 0.025 0.0263 .7451 .7349 GU69 1 .0.024 0.0250 .7225 .7171
-2 0.024 0.0252 .7310 .7128 GU70 1 0.024 0.0258 .7256 .7209
-2 0.024 0.0259 .7231 .7209 GU71 1 0.026 0.0259 .7373 .7330
-2 0.026 0.0266 .7350 .7408 GU70-5-1 0.023 0.0261 .7272 .7246
-2 0.024 p.0250 .7283 .7191
Coupon ID Origin9 Current (1) Or ~I Current (2)
Thickness (In) Thickness (In) Neutron Neutron Attenuation Attenuation GU69 1 0.025 0.0260 .7358 .7281
. -2 0.025 0.0257 .7365 '.7299 GU70-7-1 0.024 0.0251 .7320 .7158 I
-2 0.024 0.0251 .7293 .7190 GU71-8-1 0.026 0.0270 .7399 .7412
-2 0.026 0.0254 .7442 .7341 J (1) Thicknesses for 7705G, 7706G, & 7712G were not taken in the same locations as originals but were measured in the closest pos~ible locations.
(2) Neutron attenuations for coupon 7712G were measured in locations where Boraflex was known to b~ present.
Table 3 BORAFLEX LOT DATA Large Boron Carbide Lot Syl gard -170 Sylgard 170 Coupon ID No. *Elastomer Part A Elastomer Part B 7705 G 022688-1 ET028828 ET018832 7706 G 022688-1 . ET028828 ET018832 7707 G 022688-1 ET028828 ET018832 7708 G (1} 042585-1 ET028B25 ET018834 7709 G 042585-1 ET028825 ET018834 7710 G 042585-1 ET028825 ET018834 7711 G 042585-1 ' ET028825 ET018834 7712 G 042585-1 ET028825 ET018834 7713 G 042585-1 ET028825 ET018834 7714 G 042585-1 ET028825 ET018834 Large Coupon Material Heat Code: MA04 Spent Fuel Pool Rack Boraflex and Small Coupon Boron Carbide Lot Sylgard 170 Sylgard 170 Batch Number No. Elastomer Part A Elastomer Part B GU69 (2) 012986-1 EU095176 ET085250 GU70 012986-1 EU095176 ET085250 GU71 '*
012986-1 EU095176 ET085250 Repair Material Boron Carbide Sylgard 170 Sylgard 170 Lot. No. Elastomer Part A Elastomer Part B (2) 1021.85-1 ET085123 EP045964 (1) These coupons were repaired with Lot No. 042585-1, but it is not clear at this time if they were replaced or the original Lot No. 022688-1 coupons were repaired; * *
(2) Some Spent Fuel Pool Rack Boraflex Sheets were repaired with Lot No.
102185-1, but it is not clear at this time if the original sheets were repaired or replaced.
TABLE 4 Typical Silica Levels Facility % Cracking/Shrinkage SFP Silica Level 1 Unknown . 87 to 1. 25 ppm 2 Unknown 3.7 to 4.0 ppm 3 Unknown 4.4 to 6.0 ppm 4 'Ave 1.0% gaps 0.5 to 0.9 ppm 5 1. O to 1. 3% gaps 14 ppm 6 Unknown 7 ppm (1991) 7 2.8% shrinkage 1.0 ppm 8 Unknown 75 ppm 9 Unknown 0.6 to 1.4 ppm 10 < .34% 3.5 ppm 11 Unknown Unknown 12 No Indications 7.2 ppm 13 0.7 to 2.8% 2.2 ppm 14 Unknown 7.8 ppm 15 < 4.0% 2.8.ppm Facility names were withheld.
.Figure 1 Palisades Boraflex Coupon Types Boraflex material bolted between two sheet metal strips
- . Short set Full length
Figure 2 zw 11X11 RACK YW -REMOVED xw FOR LOADING uw MSB/CASK u
(])
u c
u 0 TW c _o 0
_o c
- J SW Dose Rates measured at rack mid plane _c _c
+-' +-'
CJ) CJ)
RW SOR/Hr c c
(]) (])
QW T~ > 500 R/Hr ~ 1----+---f.
- J u_
- J u_
- 15 R/Hr ~ ~
PW r-- '1""
Cl r-- r--
ow r--- r, NW > 500 R/Hr
- BA BA BA BA MW BL BL BA BA BA. BA LW BL BL KW 7711G Full length, unbonded BL ~ BL l---+---+~-l--+-~+----1----4---l--1-~+--J JW Short set 2, unbonded BL I BL l---+---+~-l--+-~+----1----4~-l--1-~+--J IW BL ~ BL
~+--~r-----i~-+---+-~-1---1------41---+---+~-1--+-~
HW BL I BL 1---+---1~-+---+~+--+-~+---+---l~-+--1r-----i~-+--+-~-1---1-----41---+-~~-+--1-~
GW 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 :30 29 28 27 26 25 Shading indicates coupon removed BL Lor1q- term Boraf lex Fuel location
~ Actual coupon location BA Acceh::-rated Boraf lex Fuel li..xation
Figure 3 RarK: construction Rack assembly method Detailed cell.view See. Boraf lex sheet ;;;:_
.detail rigt1t L. 075 11 S. Steel /
rl QJ QJ
/
Welded corner
+J
([)
([)
\Tuck 0 Folded corners
...____ welds for
/assembly N
~o for i
Open cell closure plate
SfP BORON AND SILICA
'10. 0 300
.0
.0 7.0
~ 260 E Q..
Q.. .0 Q..
---0-- BORON z C\I SILIC~
0
~ .0 0 0 en
'°
.0 220
.0 1.0