ML19340E983
| ML19340E983 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 01/14/1981 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8101160445 | |
| Download: ML19340E983 (13) | |
Text
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NSits NORTHERN STATES POWER COMPANY uin u sanou s. us u u s. ora.. oi January 14, 1981 Director of Nuclear Reactor Regulation U S Nuclear Regulatory Commission Washington, D C 10555 Prairie Island Nuclear Cenerating Plant Docket No. 50-282 License No. DPR-42 50-306 IPR-60 Supplemental Information - License Amendment Request Dated January 31,.1980 Attached is the second set of answers to questions sent to L 0 Mayer from R A Clark on November 5,1980, concerning the Prairie Island NGP Fuel Storage Facility modification. The first set of answers to the Chemical Engineering and Effluent Treatment Systems Branches was sent on November 21, 1980.
Attached are the answers to Auxiliary Systems Branch (ASB) questions 1,3,4, and 6, and Structural Engineering Branch (SEB) questions 1,2,and 5.
ASB No.2 and 5 and SEB No. 3,4, and 6 thru 12 answers are expected to be submitted later this month.
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l L 0 Mayer, PE l
Manager of Nuclear Support Services 1
LOM/TMP/bd cc: J G Keppler C Charnof f i
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Attn: J W Fe rman NRC Resident Ins pector I
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ATTACHMENT TO JANUARY 13, 1981 LETTER AUXILIARY SYSTEMS BRANCH (ASB)
QUESTION ASB 1:
Exhibit 8 item 5.6B and drawings NF 39208, NF 39211, NF 39212 and NF 39213 indicate that a fuel pool enclosure surrounds the two spent fuel storage pools and the new fuel pit. Provide the following information:
a.
Describe and discuss the limitations this structure imposes on the handling of all leads that pass through or are handled within the enclosure when using the large oven-ead crane.
RESPONSE ASB la:
Load handling by the auxiliary building crane is restricted by the spent fuel pool enclosure. A north-south path is provided through the enclosure over the #1 Spent fuel pool. This path consists of a 9'-0" vide doorway on each side of the enclosure centered on a 3'-6" wide slot in the top of the enclosure.
Figure 8 Exhibit A, of the January 31, 1980 license amendment request identifies the slot in relation to the doorway. The enclosure restricts the height a load may be lif ted inside the enclosure.
Ihe width of a load which can enter or pass through the enclosure is also restricted.
QUESTION ASB lb and ic:
b.
Describe the overnead cranes protective devices which will limit the bridge, trolley and Faist motions when handling loads within the fuel pool enclosure in order to be assured that the load or load carrying members do not contact the fuel pool enclosure.
i c.
Describe the features of the overhead crane which precludes the j
possibility of "two blocking" while the lower load block passes over the fuel pool enclosure or demonstrate that the structure will I
withstand the impact of a dropped lower load block.without failing or creating secondary missiles.
RESPONSE ASB lb and Ic:
When using the auxiliary building crane for handling loads through and within the fuel pool enclosure operating restrictions are observed. Only trained, experienced, plant personnel will be allowed to operate the crane.
Because of the ilmited dimensions of the access slot, there is a possi-bility of the crane block or cable hitting the side. To prevent this from occurring:
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o During this modification, a spring loaded cover will be installed over the crane control buttons for east-west movement. This will prevent inadvertent east-west crane movement.
o Experienced riggers will be employed to direct the trolley movement.
i o The crane will be moved in only one direction at any time.
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f o The crane lower load block will be kept above the top of the enclosure by the use of predetermined length slings.
The occurrence of any load hitting the enclosure ceiling is also prevented by using a predetermined cable length.
The upper travel limit switch will stop the crane before the load approaches the enclosure ceiling.
The occurrence of two blocking is only a concern when the crane is used for lif ting loads from inside the enclosure, e.g.,
removal of existing storage racks during modification; to prevent this occurrence:
o The crane will be modified to have a second (backup) upper travel limit switch.
o One crane limit switch will be tested each day before the crane is used inside the enclosure and the backup limit switch will be tested monthly during the period of the modif icat ion.
QUESTION ASB Id:
Identify, describe and provide the weights and principal dimensions of all loads aside from those associated with this modification that must pass through the fuel pool enciesure during the modification program in order :o accomplish repair, maintenance or replacement of equipment with a the building.
Estimate the frequency of handling each of these loads. Describe all features of the load handling system for these operations, including devices such as slings, yokes and other devices interposed between the hock and the load in detail suf ficient to enable the staff to conclude that the potential for a load drop is extremely small.
RESPONSE ASB Id:
At this time it is not anticipated that any heavy loads other than those associated with the modification will need to be handled in the fuel pool enclosure during the modification program. However, if it is necessary to handle such loads they will be handled in accordance with the requirements of Technical Specification 3.8.B.l.
QUESTION ASB 3:
In regard to the heavy load handling operations required to accomplish the proposed spent fuel pool expansion program, provide the following information:
a) Describe the 15 con temporary crane and rigging to be employed in this modification in sufficient detail as to enable the staff to arrive at a finding that either: (1) the potential for a load drop is extremely small, or (2) for each area addressed, the following evaluation criteria are satisfied:
i.
Releases of radioactive material that may result from damage to spent fuel based on calculations involving accidental dropping of a postulated heavy load produce doses that are will within 10 CFR Part 100 limits of 300 rem thyroid, 25 rem whole body (analyses should show that doses are equal to or less than 1/4 of Part 100 limits);
ii. Damage to fuel and fuel storage racks based on calculations involving accidental dropping of a postulated heavy load does not result in a configuration of the fue. such that k is "If larger than 0.95; iii. Damage to the spent fuel pool based on calculstions of damage following accidental dropping of a postulated heavy load is limited so as not to result in water leakage that could uncover the fuel, (makeup water provided to overcome leakage should be from a borated source of adequate concentration if the water being lost is borated); and iv. Damage to equipment in redundant or dual safe shutdown paths, based on calculations assuming the accidental dropping of a postulated heavy load, will be limited so as not to result in loss of required safe shutdown functions.
RESPONSE ASB 3a:
The 15 con temporary crane that was used in the last fuel rack modifica-tion, will be used again during this modification.
It is a doable leg gantry type unit with an overall height of 24' - 0" and a span of 30' - 0",
fabricated from structural steel shapes. The crane has a single hook with a live load capacity of 30,000 f.
Vertical and horizontal (north / south) hook travel will be by an electric motor drive. Horizontal (east-west) crane travel on the fuel handling bridge rails will be by hand. Crane operation in all cases will be controlled by trained, experienced, NSP plant personnel walking alongside the unit.
Crane assembly and disassembly, and movement of the crane sections in and out of the fuel building, will be done using the Auxiliary Building Crane. Crane assembly and disassembly will be done in the area of Pool 1.
Crane sections being moved into and out of the fuel building will be transported with no more than 6 inches clearance above the pool cover when
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fuel is present in pool 1.
The 15 ton temporary crane will be used primarily for the transfer of both new and existing fuel racks into and out of the fuel pools. A rack lif ting rig will be used to move the new racks into the fuel building and fuel pools.
This lif ting rig will be used to handle the racks inside the pool enclosure at all times. Four hooks on the lif ting rig are inserted below the rack upper grid to lif t the rack. A lifting rig will also be used to remove the existing racks, except for one rack where slings must be used.
Both rigs were built with a factor of l
safety of 10.
i The rigging to handle heavy loads associated with this modification eye the covers will have an overall factor of safety of 10.
l Whsn fu21 is storsd in Pool 1, no rccks or temporary cecna parts will bo moved above that pool unless the protective cover is in place. This cover has been analyzed for the drop of a fuel rack. For each of these cases it has been shown that the cover will withstand the load drop without failure.
The crane will not be used in the area of Pool 2 when fuel is present in Pool 2.
The potential for a load drop is small.
In addition, the pool covers will protect the fuel from potential drops of racks or temporary crune parts. Thus the four evaluation criteria are satisfied.
QUESTION ASB 3b:
Describe the 125 ton Auxiliary Building cask handling crane and rigging to be employed in this modifiction in sufficient detail as to enable the staff to arrive at a finding that either: (1) the potential for a load l
drop is extremely small, or (2) for each area addressed, the following i
evaluation criteria are satisfied:
i.
Releases of radioactive material that may result from damage to spent fuel based on calculations involving accidental dropping of a postulated heavy load produce doses that are well within 10 CFR Part 100 limits of 300 rem thyroid, 25 rem whole body (analyses should show that doses are equal to or less than 1/4 of Part 100 limits);
ii. Damage to fuel and fuel storage racks based on calculations involving accidental dropping of a postulated heavy load does not result in a configuration of the fuel such that k is larger "I
than 0.95; iii Damage to the spent fuel pool based on calculations of damage following accidental dropping of a postulated heavy load is limited so as not to result in water leakage that could uncover the fuel, (makeup water provided to overcome leakage should be from a borated source of adequate concentration if the water being lost is borated);
and iv. Damage to equipment in redundant or dual safe shutdern paths, based on calculations assuming the accidental dropping of a postulated heavy load, will be limited so as not to result in loss of required safe shutdown functions.
RESPONSE ASB 3b:
The Auxiliary Building crane has two hoists:
- 1) main hoist - 125 ton capacity and 2) auxiliary hoist-25 ton capacity.
The auxiliary hoist which will be used for this modification consists of a steel drum, powered by a 50 hp motor through an enclosed gear train, one solenoid operated brake, one eddy current brake, a sheaved load block with a single-type hook with safety latch, and equalizing sheaves. The hoist has a 12 part, 9/16" 302 stainless steel cable with a working load safety factor of 5.
The total travel of the hook is 97' 10" to a maximum elevation of 78810".
The power unit, drum, and equalizing sheaves are located on the trolley.
The crane will be controlled remotely by trained, experienced, NSP plant personnel.
The 25 ton hoist will be used to:.--
1.
Tecasfsr the existing fual recks from insida the fual pool enclosure to a decontamination area outside the enclosure.
2.
Transfer the new fuel racks from outside the fuel pool enclosure to a location inside where the 15 ton temporary crane can handle and ins tall them in the pools.
3.
Move the sections of the 15 ton temporary crane in and out of the fuel pool enclosure, and assist in the assembly and disassembly operations.
Rigging to handle heavy loads associated with this modification over the covers will have an overall factor of safety of 10.
The potential for a load drop is small.
In addition, the pool covers will protect the fuel from potential drops of racks or temporary crane parts. Thus the four evaluation criteria are satisfied.
QUESTION ASB 3c :
With the aid of drawings, describe the travel path that will be followed 3
in installing and removing the 15 ton temporary crane and the storage racks.
Identify all equipment, essential in the safe shutdown of the reactor or employed to mitigate the ceasequences of a load drop which is beneath, adjacent to or otherwise within the area of influence of the dropped load along the entire travel paths.
RESPONSE ASB 3c:
Referring to Figure 6 of the January 31, 1980 License Amendment Request Exhibit A, the 15 ton temporary crane and fuel racks will be brought into the building at the south-west corner.
This equipment will be raised through the access opening in that area to the floor at elevatica 755' - 0" (elevation at the top of the fuel pool). Equipment may be located temporarily on this floor outside of the access opening. Equipment l
will be moved directly into the enclosure through the 9' - 0" doorway on j
the south side of the enclosure. The temporary crane may be stored north l
of the fuel pool enclosure at times during the modification, f
l There is no equipment which is essential in the safe shutdown of the reactor located beneath, adjacent to or otherwise within the area of influence of a dropped load along this travel path.
QUESTION ASB 3d:
In the load handling operations involving the spent fuel pool covers, indicate and describe the load handling equipment and rigging that will l
be employed as well as the sequence and frequencies of these operations in order to complete the spent fuel pool modifications.
RESPONSE ASB 3d:
The spent fuel pool covers are placed into position and removed using the Spent Fuel Pool Bridge crane. Two trolleys will be placed on the Bridge crane. Rigging extends down from each hook and engages at each end of the pool cover to handle each section. The bottom edge of the cover is never lifted more than six inches above the floor. When the cover is moved l
above pool 1, the north and south ends of the cover will extend past the I
edge of the fuel pool and over the floor at all times.
This will ensure that even if a cover section is dropped, it will land on the floor and will l
not drop into the fuel pool.
In addition, each of the two trolleys used is l
capable of supporting the entire weight of each cover section. !
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The modificction plcn cells for the covers to be removsd (nd rapisced only one time during the operation while fuel is stored in the pool.
QUESTION ASB 3e:
It is noted that pool cover analyses provided during the last spent fuel pool modification program were intended to show that the covers were adequate to:
i.
Withstand the drop of previously installed racks from a height of six inches provided it drops in a non-tilted orientation.
ii. Withstand the drop of the previously installed racks from a height of three inches if it drops in a tilted condition.
iii. Withstand the resulting dynamic loading if the previously installed racks are not lowered onto the covers at a lowering speed in excess of 2 feet per minute.
iv.
Support the previously installed racks provided that they are placed on the cover such that a minimum clearance of 5 inches is maintained between the nearest edge of the legs of the racks and the outside edge of the cover.
In regards to the above qualifications, update the analysis for this modification and provide the following (1) a discussion which demonstrates that the loads being handled during this modification program cannot be dropped onto the covers from heights which will cause the cover or covers to fail, (2) a discussion which demonstrates that loads being handled at the maximum safe carrying height above the covers will only drop in the non-tilted orientation or that the covers can also withstand the resulting eccentrically applied dynamic loads resulting f rom tilted dropped loads and (3) that the covers can withstand, without failure, all load drops at any point along the length of travel of the loads over the covers.
RESPONSE ASB 3e:
The rigging used to handle heavy loads associated with this modification l
above the fuel pool cover will have a predetermined length such that the l
bottom of the load will not be more than six inches above the pool cover.
The use of this predetermined length rigging will ensure that the loads cannot be dropped onto the cover from a height which would cause the cover to fail.
The covers are capable of withstanding the drop of a load in either a tilted or non-tilted position. This concern is fully addressed in the response to Structural Engineering Branch Question 4 (to be submitted later).
QUESTION ASB 3f:
Indicate the weight of the heaviest rack currently in the spent fuel storage pool and the weight of the heaviest proposed rack.
RESPONSE ASB 3f:
The heaviest rack currently in the storaga pool (8 x 8 rack) weighs 12.4 tons.
The weight of the heaviest proposed rack (7 x 8 ) is 10.8 teas. l 1
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QUESTION ASB 3g:
Describe the handling equipment and rigging utilized in removing and installing these racks in suf ficient detail as to enabis the staf f to conclude that a load drop is extremely small.
RESPONSE ASB 3g The Auxiliary Building Crane and the 15 con temporary crane will be used to handle heavy loads associated with this modification. These cranes and the associated rigging are discussed in responses ASB 3b and 3a, respectively.
The covers will protect the spent fuel in the event of a load drop.
QUESTION ASB 4:
In accordance with Section IV (4) of the enclosure to NRC letter dated April 14, 1978, describe and discuss the maximum uplift forces available
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from the load lif ting devices spanning the spent fuel pools and the adverse consequences if they should be applied to the free standing unanchored fuel storage racks.
Further, verify that the specific loads i
and load combinations are acceptable and conform wwith 3.8.4-II-3 of the Standard Review Plan.
l RESPONSE ASB 4:
Af ter '.neta11ation of the fuel racks and insertion of fuel in the new racks, the Spent Fuel Pool Bridge Crane will be used for handling fuel and other ':omponents stored in these racks. The hoist has a 6000-pound capacity.
The load imposed on the spent fuel rack has been conservatively assumed to consist of simultaneously applied 7000 pound vertical and 3500 pound horizontal forces. As described in the January 31, 1980 License Amendment Request, Exhibit C, the resulting stresses are within the allowable limits.
Since the postulated load is less than the rack weight and since the racks are not bolted to the floor, no loads will be imposed on the pool floor.
The specific loads and load combinations are acceptable and conform with 3.8.4-II-3 of the Standard Review Plan.
QUESTION ASE 6:
Provide the rollowing information individually for the Fuel Transfer Canal Pool No. I and No. 2:
i a)
Free Volume l
b)
Volume of Fuel Racks including Absorber Materials f
c)
Volume of a Typical Fuel Assembly d)
Volume of Water at Nominal Level RESPONSE ASB 6:
The requested information is presented below:
TransferCana[lume(hT V
oo 1 Pool 2 a)
Free Volume (1) 16,294 14,228 33,308 b)
Rack Volume Not Applicable 473 1,139 l
c)
Fuel Assembly Volume (3)
Not Applicable 1,063 2,576 d)
Water Vclume (2) 16,294 12,692 29,593 1
4 It should be noted that the volume of water used in the thermal calcula-tions for this modification igncred the presence of fuel and fuel racks in the pool. This is conservative, since the heat capacity of the fuel and fuel rack materials is substantially higher than for water on a volume basis. Although water has a high heat capacity per pound, its relatively low density of fsets this when, as in this case, the heat capacity per unit volume is the item of concern.
(1) This is the total water volume at normal water level ignoring the presence of fuel and fuel racks.
(2) This is the actual water volume at normal water level with all storage positions filled with fuel.
(3) The displaced volume of a single fuel assembly is 2.3 FT.
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O STRUCTURAL ENGINEERING BRANCH (SEB)
QUESTION SEB 1:
Provide details (discussion, sketches and schematics) of the rack base supporting structure, sliding surf aces, all gaps (clearance and expansion) of the rack struct tre, fuel handling system and fuel bundles.
RESPONSE SEB 1:
A sketch of the e tek base structure and the adjustable feet is given in Figure SEB l-1.
The base structure is composed of various sizes of l
f abricated box ' seams which are welded to box leg structures at each j
corner. The 4djustable foot screws are threaded into the heavy bottom l
plate of eacn leg. The screws then sit on a pad which rests on the fuel pool floor. This pad is free to slide on the pool floor.
There are presently anchor bolts at various locations en the pool floor.
These bolts were installed during plant construction to secure the original spent fuel racks. They will not be used for the present racks.
In order to mairt ain adequate clearance, some of these bolts will be cut off flush with ti.e ficor prior to installation of the new racks. At least 3.0 inches clearance will be maintained between any remaining anchor bolt and the fuel rack pads.
Figure SEB l-2 shows the clearances between the fuel cacks and the tuel pool walls.
The fuel racks are nominally designed to be ins:alled in contact with each other. Howeve r, to account for fabrication tolerances it is anticipated that some gaps of approximately 0.25 to 0.5 inch will exist between racks.
These gaps will reduce the rack to wall gaps shown on Figure SEB l-2.
However, the gaps will still be well in excess of the calculated sliding distance.
The inside dimension of each fuel storage tube is 8.27 inches.
The fuel outside dimension is 7.753 iaches.
This results in a total fuel to storage tube gap of 0.51 inch, which is equivalent to a 0.255 inch gap all around the fuel assembly.
The fuel storage tubes are located on 9.5 inch centers.
The outside dimension of each storage tube is 8.77 inches. Therefore, a gap of 0.73 inch exists between adjacent tubes. The tubes are maintained at this spacing by the upper and lower grid structures.
The fuel handling system is described in the FSAR Section 9.5.
The fuel bundles are described in Exhibit C of the January 31, 1980 license amendment request Table 3.3-1 page 3-6.
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QUESTION SES 2:
Indicate whether fabrication, installation and quality control of the spent fuel racks are in conformance with Subsection NF of the ASME Code.
If not, identify and justify the deviations.
RESPONSE SEB 2:
The fabrication, installation and quality control of the spent fuel racks will be in conformance with ANSI N4T.2 and applicable daughter standards.
QUESTION SEB 5:
Provide step by step general discussion on how the seismic ef fects on the racks have been considered.
Indicate, also, the justifications why the sliding analysis, stability analysis and seismic analysis are separate.
RESPONSE SEB 5:
The proposed racks are free-standing type racks. To assure the structural integrity of this type of rack under seismic loads, it is necessary:
a) to determine the stresses in various parts of the rack, b) to determine the maximum sliding distance and velocity, and c) to determine the factor of safety against overturning.
Even though these three parameters (stress, sliding and overturning) result from the same seismic event, and so are related, these were evaluated separately mainly to assure conservatism of results and, at the same t ime, to increase the confidence on the methodology.
This is explained in the following paragraphs:
Accurate seismic stress evaluation of a rack-like structure requires a detailed finite-element model as was used in the present analysis.
Also, to assure conservatism of the stress results, it was necessary to assume a non-sliding boundary condition, which is equivalent to infinite friction coefficient. This assumption was also necessary so that a linear analysis method could be used. From the consideration of computa-tional cost, it would have been quite impractical to use the same model for the nonlinear sliding analysis. Also, since the objective of the sliding analysis was to maximize the sliding velocity, the minimum friction coef ficient was assumed in this analysis.
This assumption of minimum friction coefficient would not have been conservative for the stress evaluation. Thus, to assure conservatism and accuracy of results, it was i
necessary to use two different analyses to compute the seismic stresses and the sliding velocity.
Overturning potential of the racks has been computed by an energy-balance method, but using the results from the sliding analysis.
Thus, the overturning evaluation is not a separate analysis in the true sense. Howeve r, to assure conservatism of results, overturning potential was computed using the maximum velocity obtained from the sliding analysis in which the minimum friction coefficient wss assumed. _