ML19347A480
| ML19347A480 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 04/03/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19347A478 | List: |
| References | |
| NUDOCS 7904190369 | |
| Download: ML19347A480 (10) | |
Text
I mA Kigg
'JNITED STATES j
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'4 NUCLEAR REGULATORY COMMiss10N WASHINGTON. D. C. 20555
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i SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 57 TO FACILITY OPERATING LICENSE NO. DPR-3 YANKEE ATOMIC ELECTRIC COMPANY YANKEE NUCLEAR POWER STATION (YANKEE-ROWE) t DOCKET NO. 50-29 Introduction By application dated February 7,1979 (Proposed Change No.158, Supplement No. 3) and additional information provided by letter dated l
March 5,1979, Yankee Atomic Electric Company (the licensee) requested an amendment to Facility Operating) License No. DPR-3 for the Yankee v.
Nuc.Nr power Station (Yankee-Rowe.
The amendment would change the provisions of the Technical Specifications to permit moving a temporary gate and shielding panels over the spent fuel pit for implementation of the licensee's proposed modifications to upgrade the spent fuel pit.
In addition, the amendment would delete permission for moving the gate support brackets and shielded work platform over the spent fuel pit, since these provisions are no longer required.
Discussion To accomplish the installation of the proposed permanent features, a temporary gate will be installed to divide the pit roughly in half.
This will permit dewatering, decontamination and construction in a portion of the storage pool while spent fuel is stored in the other portinn.
Shield panels and concrete shield plugs will be installed j
to reduce radiation exposure in the work zone. The licensee has proposed technical specifications to allow moving the temporary gate l.
and the shield panels. The licensee also proposed that the provisions in the technical specifications, allowing the gate support brackets F
and the shielded work platform to be moved over the spent fuel pit be deleted.
This is no longer necessary since the work requiring these provisions has been completed as authorized by Amendment No.
51, dated October 6,1978.
Our Safety Evaluation supporting Amendment No. 51 describes the licensee's proposed overall program for upgrading the spent fuel storage facility, indicates our consideration for. authorizing specified phases of the program, and describes the bases for our approval of the completed preparatory work.
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In the February 7,1979 application and the March 5,1979 submittal, the licensee provided detailed information on the preposed modifications which would involve:
(1) installation of a stainless steel liner in the spent fuel pit, (2) installation of a full width division wall with 2
gate across the north end of the pit, (3) installation of spent fuel
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rack support fixtures on the bottcm of the pit, (t) provisions to enlarge the enclosed area of the spent fuel pit buildia, (5) installa-tion of a temporary gate in the existing gate support brackets, (S) installation of shielding between the spent fuel and the temporary gate, and (7) addition of a redundant pe,r to the spent fuel pit cooling systes and associated piping modificatfor s.
The defined surfaces of the spent fuel pit w'11 be lined with 1/t inch thick type 30t stainless steel plates. Widths and lengths have been selected consistent with handling and installation restrictions and to minimi:e in-pool construction time. A division wall will be erected across the full width of the pool in the north end to allow dewatering of the fuel transfer area without affecting the fuel storage area.
This will allow access for repair of the fuel transfer equipment
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and fuel transfer chute and will provide capability fer cask handling whien is to be reviewed in the future. A slot in the center will be used for transporting fuel from the fuel transfer side to the fuel storage side. A fuel transfer gate would be provided to close off this opening when required.
During erection of the liner and division wall, spent fuel rack support fixtures would be installed.
The function of these fixtures is to transfer loads from the spent fuel racks through the liner and onto the c:ncrete structure.
Part of the fixtures are to provide capability for future expansion of spent fuel storage capacity.
The supports for future
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racks would be completely separate from the present spent fuel racks.
However, en cc=pletien of the installation, grating wculd be placed above the existing spent fuel racks to provide additional protection against a fuel handling accident.
The licensee indicated that the modification to the Spent Fuel Pit Euilding would provide more floor area to accorredate changes to the spent fuel pit cooling system. The addition to the Spent Fuel Pit Building would be erected adjacent to the existing building, the new walls and roof would be connected to the old east wall, and then the cid east wall w0uld be removed. This additional space would also
- rovide inside work space during the in-pool construction to minimi:e removal of the building roof natches.
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j The proposed temporary gate to be installed in the pit consists of two pieces which, when joined, form a wall 34-feet high dividing the pit into two parts.
The manner of installation would be similar to the method used to install the temporary gate support brackets. The bottom section would be lifted with the yard crane and moved to the enclosure building central hatch without passing over stored spent fuel.
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in position, the piece would be lowered onto support beams which rest on the pit walls.
With the first section supported on the beams, the second piece would be transported to the center roof hatch without passing over the fuel and lowered into position. While the second section is suspended from the crane hook, the pieces would be bolted together.
Then the full gate would be raised off the beams and lowered its final position.
The gate would eventually be removed by raversing the installation process.
The gate weighs approximately 14.1 tons and would be lifted using the 15 ton auxiliary hook, with redundant lifting cables to protect agai4)?
j failure of a sling.
When the pieces are joined, they will be lifted with the 75 ton main hook, again using redundant cables.
Sealing around the perimeter of the installed gate would be by redundant con-tinuous inflatable seals mounted on the support bracket.
Each seal has its own pressure regulator, check valve, and alarm so that loss of plant compressed air or loss of one of the seals would not cause gate seal failure.
The horizontal joint between the gate sections has a compressible seal for watertightness.
The bottom gate section has fittings provided for pumping off leakage collected in the space between the peripheral pneumatic seals.
Fittings are also provided for filling and draining the bottom core.
Before shipment to the site, the gate sections will be pressurized to verify watertightness.
There are two independent barriers to leakage between the bracket plate and the concrete.
No seal is required on the south side of the bracket as the liner will serve this function When the north end of the pit is dewatered.
The licensee stated that, because the spent fuel will be stored : lose to the temporary gate, it is necessary to redute the radiation leval on the dry side of the pool. The spent fuel must be positioned as far from the gate as possible and graded so the newest fuel is farthest from the gate. As cuch shielding will be placed between the fuel racks and the gate as is possible. By using a 10-element rack next to the north wall when the spent fuel is in the north end, the first row of cavities can be emptied, providing an additional ll-inch distance and a significant reduction in radiation.
Finally, the construction nust proceed cuickly so that the number of spent fuel bundles in the pool is minimi:ed.
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4-I The licensee has taken measurements of radiation close to the spent i
fuel in the pit. The radiation level on the dry side of the temporary gate is conservatively estimated to be 10 to 20 R/hr; therefore, it i
i will be necessary to provide three tenth-value layers of additional shielding between the spent fuel and gate. The shielding used will be steel cased lead panels providing 4.75 inches of lead. Each panel weighs approximately 9.5 tons and would be lifted using the 15 ton l
auxiliary hook with redundant cables. The panels will be positioned without being moved over the stored fuel.
The licensee stated that removing fuel from the first row, using the 4
- shield panels, and flooding the core of the lower gate section will provide enough shielding to lower the radiation to less than 20 mR/hr.
Concrete shield plugs which weigh less than a spent fuel assembly would also be placed in the empty first row cavities. Since these will be directly in front of the closest fuel bundles, they will further reduce radiation, but the actual reduction cannot be accurately estimated. The licensee stated that a survey will be taken and additional l
shielding placed on the dry side as required to eliminate any radiation zones higher than 20 mR/hr.
The licensee indicated that the final effort to reduce radiation level i
depends upon the construction schedule.
Completion of the. preliminary work authorized in October 1978 will shorten the overall schedule so j
the liner installation can be completed before the April 1980 refueling 1
outage. This will reduce radiation levels because there will be 36 less irradiated fuel elements in storage when the north end is dewatered, which would result in an extra 22 inches between the stored fuel and the gate.
The cooling system would be permanently changed to support the various construction phases. The major change would be the addition of a second pump to be installed on the roof of the new fuel vault in the space provided by the addition to the spent fuel pit enclosure building.
The present pump would be moved to the new fuel vault roof and the suction and discharge of the two pumps would be cross-connected to enable either one to take suction on either end of the pit.
The licensee indicated that the heaviest loads presently allowed over the e
spent fuel pit are the spent fuel racks which weigh up to 6.3 tons.
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The shielding panels and temporary gate sections will weigh in air approximately 9.5 and 14.1 tons, resoectively, and 8.6 and 4.5 tons i
in water.
The licensee further indicated that movement directly over stored spent fuel is prohibited and that all handling will be in accordance with approved written procedures.
To provide further i
assurance against a handling accident, redundant slings and lifting eyes are to be used on the gate sections and shielding panels.
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5-The licensee has assessed the ability of the pool to retain water in the unlikely event a component is dropped from the crane. Based on conservative conditions, the limiting concrete pentration was stated by the licensee to be 15 inches which would not perforate the 36 inch thick floor slab.
The licensee has evaluated the off-site consequences of a massive
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failure of spent fuel in the unlikely event a heavy load is acciden-tally dropped on a loaded spent fuel rack. Assum.ing all the fuel presently in the pit is damaged, the resultant thyroid dose calculated by the licensee is 0.34 rem and the whole body gamma dose is 0.05 rem.
g During the construction work a pool cover would be placed over the
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storage area of the pool to prevent accidental entry of tools or debris into the water.
The licensee indicated that all pieces making up the pool cover weigh less than 900 pounds and will be installed in accordance with approved written procedures. This cover will be the same one used during installation of the center roof hatch which was completed as part of the preparatory work.
Evaluation The licensee has described the structural and material features covering the design, fabrication and installation of the proposed stainless steel liner in the spent fuel pit, the division wall with gate in the pit, the spent fuel rack supports, the extension of the existing fuel pit superstructure, and the temporary gate.
The liner would be designed to provide a leaktight membrane in the fuel pit storage area.
The design conforms to-ASME Section III, Division
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2, " Code 'for Concrete Reactor Vessels and Containments".
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to deadweight and hydrostatic loais, a thermal load has been imposed l
corresponding to a 150 F maximum bulk pool temperature.
No loads are imposed on the liner by equipment or structures in the pool, as all loads are transmitted directly to the concrete by special anchors.
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The division wall will be designed in accordance, as applicable, with AISC Manual of Steel Construction, 7th Edition (1970), ACI 318-77, i
. " Building Code Requirements for Reinforced Concrete" (1977) and ASME Section III, Division 2, " Code for Concrete Reactor Vessels and Contain-ments" (1977).
Load combinations are based on criteria outlined in NPC Standard Review Plan 3.8.4, "Other Seismic Category I Structures." The F.;
loads considered are deadweight, hydrostatic and thermal with an additional bm.
lateral load capacity to allow for anticipated seismic requirements.
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6-The supports for future spent fuel storage racks are completely separate from the existing storage racks.
However, on completion of the installation, grating would be placed above the existing spent fuel racks to provide additional protection against a fuel handling accident.
The grating and supports will be designed to resist the impact of a fuel bundle dropped from 11 feet above the existing storage racks.
The design of the support fixtures conforms to the AISC Manual of Steel Construction, Seventh Edition,1970. Analysis for dropped fuel bundle permits plastic deformation but limits distortion to prevent contact with the spent fuel rack. An allowance for lateral strength has been included in anticipation of seismic requirements.
The temporary gate will be designed to resist deadweight and hydrostatic loads in accordance with AISC Manual of Steel Construction, Seventh Edit ion, 1970.
Loads on the gate will be transmitted to the concrete by the gate support bracket which has been installed as.uthorized in Amendment No. 51.
Prior to placing the bracket, a field test was per-formed in the pit. A test plate of the same thickness, width and material was mounted on the pit wall using anchor bolts of identical size and material as on the bracket, placed in the same bolt configuration, i
In the test, the test plate was lifted incrementally to twice the allowable design loading.
Inspection indicated that the bolts still maintained anchorage. This test acceptably confirmed the adequacy of the bracket anchors.
The gap between the bracket plate and concrete was filled with an epoxy grout. The licensee has determined that the epoxy compound will not introduce harmful concentrations of halides into the spent fuel sterage pit either through radiation induced degradation or the leaching of contaminants.
Nevertheless, as indicated in our Safety Evaluation supporting Amendment No. 51, we requested the licensee to provide additional information to document long-term compatibility of the epoxy compound with the pit environment.
The licensee performed a detailed investigation of the grout composition and reported the results of this investigation in a letter dated October 18, 1978. Results indicate that there are no heavy metals present which could affect the pit water chemistry. There are no chlorinated compounds other than in trace quantities (less than 0.3%) originating from the resias used in the formulations.
There are no fluorides.
The only sulfur compound is barium sulfate which is insoluble in water. There is no observable leaching of chemicals nor formation cf gases during the cure of any of the products. Assuming the release of all chlorides in the grout into the pit water, the licensee estimated that the chloride content of the pit water would rise less than i ppm. We agree with the licensee that this change in pit water chemistry is insignificant and would not have any long-term adverse effects on the integrity of the pit or the stored spent fuel.
In addition, this estimate is conservative since any release of chlorides would be gradual and concentrations would be reduced as the pit water is continuously passed through a demineralizer.
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___ _ We have reviewed the licensee's use of the following codes in the design and construction of the proposed structural modifications:
ASME Section III, Division 2. " Codes for Concrete Reactor Vessels and Containments", AISC " Manual of Steel Construction", Seventh Edition,1970, ACI 318-77 "Bifiding Code Requirements for Reinforced Concrete". The ACI 318-7) code has not yet been accepted by us.
ACI 318-71 is the last version of the Code approved by us.
The licensee's use of the 1977 version of the Code is limited to the concrete filler in the steel division wall.
The concrete in the i
division wall acts only as a filler and has no structural function.
For this particular application we conclude that the slightly different versions of the (approved) 1971 Code and the 1977 Code (not yet approved) can both be used without impairing the safety margins in the design and construction of the division wall.
In sunmary, based on our review of the detailed information presented by the licensee on the structural modifications we have determined t hat:
(1) all elements will be designed and constructed in accordance
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with Codes accepted by us, as discussed above, and the load combinations conform to the NRC Standard Review Plan 3.8.4 "Other Seismic Category I Structures", (2) conservative assumptions have been made on load magnitudes, and (3) the licensee has planned to carry out the work in accordance with a reasonable construction schedule. Accordingly, we have concluded that from a structural standpoint, the modifications
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described in Proposed Change No.158, Supplement No. 3, will not decrease existing safety margins and are therefore acceptable.
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We have evaluated the criticality aspect anociated with the movement of all spent fuel assemblies to one end of the pit before installing the temporary gate. After the planned rearr0ngement of the spent fuel, there will be some assemblies relatively close to the gate brackets.
When the gate is inserted into the brackets, the water in the spent fuel pool will contain the nominal refueling concentration of soluble bo ron.
A 3.2 x 10 ]so, the spent fuel racks in the pit will have a minimum of 2
boron ten atoms per square centimeter between every two adjacent stored fuel assemblies. Assuming that the gate, or a portica.
of it, is accidentally dropped before it is inserted into the brackets, it could crush the fuel racks.
However, in such an event the only way l
the k in the spent fuel could increase would be if the fuel assemblies were3u,hedtogetherwithoutdistortion.
It is unlikely that this would i
s happen, but in the event that it did the baron in the Boral plates and j.
the soluble boron in the spent fuel pool water would keep the k This is NRC's acceptance criterion for the naximun (worst case)eff < 0.C' calculated neutrcn multiplication factor in a scent fuel cool.
This 0.95 accectance criterion is based on the uncertainties asscciated with the calculational methods and provides sufficient margins to preclude criticality in the spent fuel cit. Assuming that the fuel asse :blies themselves were crushed
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and com; acted, the kg', would decrease due to the loss of the neutron oderating water.
._. We have concluded that all factors that could affect the neutron multiplication factor have been conservatively considered and that there is reasonable assurance criticality will not occur during the proposed modifications of the spent fuel pit.
We have also evaluated the adequacy of provisions for spent fuel cooling for implementing the proposed spent fuel pit modifications.
Using the method given on pages 9.2.5-8a through 14 (Residual Decay Energy for Light Water Reactors for Long Term Cooling) of the NRC Standard Review Plan, with the uncertainty factor, K, equal to 0.1 7
for decay timcs longer than 10 seconds, we calculate that the max peak heat rate in the pool prior to the next refueling is 1.0 x 10{ mum BTU /hr. The licensee has scheduled the pool modifications to be completed by the next refueling outage, scheduled for April 1980.
Assuming this heat rate in the pit and assuming the temporary gate is in place and one portion of the pit is dewatered, we calculate that the maximum possible rate s.' increase of the average temperature of the spent fuel pit water would be 1.80F/hr. Thus,itwougdtake
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33 hours3.819444e-4 days <br />0.00917 hours <br />5.456349e-5 weeks <br />1.25565e-5 months <br /> for the average temperature to rise from ambient 90 F to 0
the design temperature of 150 F without operating the spent fuel pit cooling system.
We find that this is sufficient time to make the final connections to the spent fuel pit cooling system as proposed by the licensee. We have also considered the potential consequences if a lcrge leak were to develop in the temporary gate seals.
In this case, the water level would be equalized over the whole pit with the water surface still seven feet above the tops of the stored fuel assemblies. Assuming continuous siphoning from any possible break in the pit cooling system during the modification work, the water level in the pit could not drop to less than five feet above the tops of the spent fuel.
Therefore, regardless of the accident that might occur, we find that spent fuel will remain under water throughout the modification process and as long as the spent fuel assemblies are under water they will be adequately cooled.
The proposed changed features of the spent fuel pit cooling system will be designed to Codes and Standards that meet at least the l
original design requirements of the existing cooliag system. On l
this basis, we have concluded that the proposed spent fuel pit l
cooling system changes are acceptable and that the rpent fuel will be adequately cooled at all times during implementation of the spent fuel pit modifications in the manner propoied by the licensee.
The licensee has evaluated the consequences of an accidental drop i
of the shielding panels and temporary gate sections while suspended from the crane above the spent fuel pit.
This evaluation indicates that the 36 inch spent fJel ::it slab would not :;c ;,erforated frcm such a postulated accident-and that the water would be retained
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9 in the spent fuel pit. The licensee has used the same calculational method previously reviewed by us as indicated in our Safety Evaluation supporting Amendment No. 51. As before, we find these calculations to be reasonable and have concluded that even in the unlikely event that such an accident were to occur, the safety consequences would be acceptable. The use of redundant slings and lifting eyes provides additional assurance that a construction handling accident will not occur.
Nevertheless, we have considered the potential radiological consequences of the temporary gate and shielding panels falling or tipping into the part of the pit containing spent fuel.
The temporary gate and shielding panels are in sections with heights about half the depth of the pit.
If they fall or tip into the pit while they are being placed in the temporary gate support brackets, they could damage all the spent fuel in the pit.
The licensee has not presented an evaluation of the extent of damage to spent fuel for such an accident. However, if all the spent fuel in the pit has decayed at least 60 days, the potential consequences of dropping or tipping the temporary gate into the pit are well within the guidelines of 10 CFR Part 100 and are, therefore, acceptable. This
.J would also be true if 36 additional assemblies (a refueling) also with 60 days decay were added to the number of fuel assemblies I
presently in the pit.
Because all the spent fuel in the pit has decayed at least 150 days since the last refueling (October 21, 1979),
the potential consequences of this accident are less than one percent of the exposure guidelines of 10 CFR Part 100.
l We have reviewed the licensee's plan for installation of a liner, a division wall with gate and the rack support structure in the spent fuel pit with respect to potential occupational exposure.
The licensee estimates that the occupational exposure to do all the work in the pit would be about 80 man-rem.
We consider this to be con-i servative and as low as is reasonably achievable as discussed below.
l As stated in its letter dated March 5,1979, the licensee is moving l
the spent fuel as far as possible from the work area with the freshest spent fuel at the greatest distance.
He will clean the walls of the pit.
The licensee will place as many lead shield panels as possible between the spent fuel rack: and the temporary gate. The core of the l
lower section of the temporary gate will be flooded.
Concrete shield plugs will be placed in the empty cav' ties in the spent fuel racks near the gate.
In addition, the licensee is doing the const uction work in
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the ait before the next refueling outage when 36 fresh, pent fuel assemblies will be added to the pit.
The final phase if work after the temwrary gate has been removed involves the installiation of the rack su: port structure in the middle of the pit in the vicinity of the l
temcorary gate support bracket. This work will be accomolished by a diver since it cannot be performed with the temporary gate in place.
During this c eration the spent fuel in the pit will be olaced at octh er d s O f - t r.e cit a wa y fr r: the werk area. The licensee has iccksc at tre
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use of additional shielding during this operation but does not anticipate it will be needed.
The licensee stated, by telephone, that the shielded work enclosure, which we reviewed in our Safety Evaluation supporting Amendment No. 51 dated October 6,1978, cannot be used because of the nature of the work to be done by the diver. We have concluded that the licensee will take all reasonable measures to reduce occupational exposure during the proposed modifications.
In summary, based on our evaluation of the significant safety consideration associated with the fuel pit modifications, as discussed i
above, we conclude that the proposed changes to Technical Specification 3.9.7 are acceptable, because these changes do not affect the consequences of previous evaluations of postulated design basis accidents for the spent fuel pit.
Environmental Consideration We have determined that the amendment does not authorize a change in b
effluent types or an increase in total amounts of effluents nor an increase in power liiel and will not result in any significant environmental impate. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental ireact and pursuant to 10 CFR 151.5(d)(4), that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
Conclusion We have also concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety cargin, the amendment does not involve a significant hazards con-sideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commisson's regulations and the issuance of this amendment will F
not be inimical to the common defense and security or to the health and safety of the public.
Date:
April 3,1979
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