ML19344A916
| ML19344A916 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/31/1978 |
| From: | Herbein J METROPOLITAN EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19344A915 | List: |
| References | |
| REF-GTECI-A-36, REF-GTECI-SF, TASK-A-36, TASK-OR GQL-0147, GQL-147, NUDOCS 8008220586 | |
| Download: ML19344A916 (34) | |
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METROPOLITAN EDISON COMPANY susswiser or se seast ?t. etic uritiries conocnar c.
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TELEPHONE 215 - 929-3601 POST OFFICE BOX 542 READING, PENNSYLVANI A 19603 January 31, 1978 GQL 0147 gj'!y.t,.
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.r'o Director of Nuclear Reactor Regulation g
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R. W. Reid, Chief C
OS Operating Reactors Branch No. k 9- %
576u U. S. Nuclear Regulatory Commission Washington, D. C.
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Dear Sir:
Att" ',/
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Cperating License No. DPR-50 Docket No. 50-289 Cask Drop Analysis Additional Infor=atien In response to your letter of August 18, 1977, and per our letter of November 22, 1977 (GQL 1622), enclosed please find the subject additional information.
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J. G Herbein Vice President-Generation JGH:RJS:cjg Enclosure
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THREE MILE ISLAND NUCLEAR STATION UNIT 1 CASK DROP ANALYSIS ADDITIONAL INFORMATION The Cask Drop Evaluation for Three Mile Island Unit 1 (TMI-1), enclosed 1.0 with your February 14, 1976 letter, states:
(1) "During transfer of the cask to and from the deccntamination pit and raising and lowering of the cask within the pit, results of evaluations indicate that with the present system, cask drop accidents could possibly result in unacceptable damage to engineered scfeguard circuits, spent fuel pool coolant pipes, and cooling vater pipes to the spent fuel pool coolers. Met-Ed is currently evaluating possible plant modifications and changes to operating procedures to correct this situation," and (2) "When the location for cask decontamination operations is selected, the specific plant modifications and changes to operating procedures and technical specifications that are required vill be described to NRC. Until such time, the present cask decontamination pit vill not be used."
The discuss _on supporting the proposed changes to the Technical Specifications transmitted by your letter of September 21, 1976 states that as a result of your studies, it is now proposed to relocate the cask decontamination area in the shaded area shown in Figure 3.11-3 of your September 21, 1976
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2 submittal. Further, FSAR Figure 1-3 shows that the Unit 1 temporary new fuel storage area is located parallel to the transporter railroad tracks and could be in the path of the spent fuel cask as it travels to and from the Unit 1 decontamination area as well as the corresponding vork stations in Unit 2.
It is expected that an inconing empty shipping cask will be moved frem the transporter to the decontamination area for cleaning before being moved to the loading pit. For the Unit 1 loaded cask, it is possible that it vill be moved from the cask storage and loading pit across the railroad tracks and again over the temporary new fuel storage area to the decontamination area for decontamination before being loaded on to the transporter.
To enable us to continue our review and evaluation of the cafety implications of the Unit 1 proposed changes, once the shipping cask and transporter has entered the Unit 1 building for the offsite shipment of fuel from either Unit 1 or Unit 2, we vill require the following additional information.
QUESTION Provide one drawing showing the relative location of the following areas 1.1 of Unit 1:
(i) the new fuel storage areas; (ii) the spent fuel storage pool; (iii) the spent fuel cask storage and loading pit; and (iv) the specific location of the cask decontamination area.
RESPONSE-The requested information is shown on Figure 1.
3 To further clarify these areas, the following figures have been revised:
~
l Figure 1-3 M -1 FSAR (1) " Temporary New Fuel Storage l
Rack" changed to " Receiving /
Shipping Area."
l I
(2)
" Spent Fuel Cask Storage Area" changed to " Spent Fuel Cask Storage & Leading Pit and Decontamination Area."
Figure 1 h M -1 FSAR (1) " Decontamination Pit" chaaged to
" Decontamination Pit (Not Used)."
(2)
" Spent Fuel Cask Storage" changed to " Spent Fuel Cack Storage & Loading Pit and Decontamination Area."
Figure 9-18 'IMI-1 FSAR (1)
" Temporary New Fuel Storage Rack" changed to " Receiving /
Shipping Area."
(2)
" Shipping Cask Area" changed to
" Spent Fuel Cask Storage &
Loading Pit and Decontamination i
Area."
I
k (3)
" Decontamination Pit Area" changed to " Decontamination Pit Area (Not Used)."
QUESTION To adequately evaluate the potential for unsafe conditions occurring in 1.2 Unit 1 following a cask drop accident at any point along its revised path of travel between the transporter, the newly located decontamination area, and the spent fuel cask loading pit, superimpose the travel paths of the shipping cast for Unit 1 and 2 vithin the Unit 1 building on the drawing requested above.
- RESPONSE, The travel path of the shipping cask for Unit 1 and 2 within the Unit 1 building is shown on Figure 1.
QUESTION Verify that the path of travel of the spent fuel cask from the transporter 1,3 to the Unit 2 building has not changed due to these proposed changes or describe, discuss and demonstrate that no safety related consequences could result from these changes.
' RESPONSE 9
The path of travel of the spent fuel cask from the transporter to the Unit 2 building remains as shown in the 'IMI-2 FSAR, Volume 8, Section 9.1.h.2.2.
See Figure 1.
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5 Therefore, there are no changes to evaluate for safety related consequences.
QUESTION ~
1.4 Assuming the engineered safeguard circuit trays have been relocated as proposed in Figures IV-3 and IV h (February 14, 19T6 submittal) and a cask drop accident occurs such as to disable one of the two separated Provide the engineered safeguard trays when the reactor is at power.
following information:
Describe, discuss, and demonstrate that the single event (cask drop),
(a) at any point along its path of travel, will not initiate another event that potentially could prevent a safe reactor shutdown or prevent adequate spent fuel cooling. Your analysis should assume a single failure in the systems associated with the rema,ining intact engineered safeguards tray or other essential systems but may include use of non-safety grade equipment. Where possible, reference the appropriate Figures in the FSAR which show the location of threatened equipment.
RESPONSE
The engineered safeguard cable raceway system in the vicinity of the spent fuel cask handling path is separated and constructed so as to preclude damage The raceways to more than one redundant safeguard channel for any single failure.
are separated and contained within two protected areas so that a postulated cask drop accident would not simultaneously damage redundant engineered safeguard The simultaneous occurrence of an open or short circuit in the protected
, channels.
redundant engineered safeguard cable is highly improbable and not considered credible.
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6 Additionally, we have analyzed the postulated cask drop and have concluded that this accident will not initiate another event that could preclude a safe reactor In addition, IEEE Trial-Use shut-down or prevent adequate spent fuel cooling.
Standard Criteria for Safety Systems for Nuclear Power Generating Stations, August 15, 1977 IEEE Std. 603-197T Paragraph h.3 Single Failure Criterion, does not require an analysis that would " assume a single failure in the systems associated with the remaining intact engineered safeguards tray." A postulated cask drop is a design basis event and in itself is considered a single failure; therefore, the engineered safeguard system in not required to sustain a second single failure.
Per the Cask Drop Evaluation, February 14, 1976 item h page IV-9 it is concluded that the " changes described" will provide reasonable assurance that cask drop accidents during transfer of the cask to and from the cask loading pit and raising and lowering of the cask within the pit vill not result in the cask falling into the "B" spent fuel pool. This means that there can be no damage The only to the mechanical equipment of the spent fuel pool cooling system.
mechanical portion of the spent fuel pool cooling system that could be damaged is that portion of the h" line (for filling and partially emptying the spent fuel cask storage and loading pit) that penetrates the liner of the west wall of Since the only function of this pipe is to fill and partially empty the pit.
the spent fuel cask storage and loading pit, no damage whatsoever is incurred to the spent fuel cooling system.
QUESTION 1
1.h(b) In reference to the criteria that will be followed in making the modifications, the following statement is made " Damage to multicolored
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7 circuits along with damage to circuits associated with one of those colors is acceptable since the multicolored circuits are protected interconnections between two redundant channels." Provide further clarification which demonstrates that the protected interconnections between two redundant channels will provide adequate protection in the i
event of:
(a) any open circuit, (b) any short circuit and (c) any short circuit between any two conductors that could develop as a result of a cask drop accident, and thereby provide assurance that no more than one channel of redundant engineered safeguards system, or reactor protection system could be degraded er disabled, i
i
RESPONSE
There is only one multi-colored circuit in the vicinity of the cask travel area.
This circuit provides an interlock to the reactor building emergency cooling unit This circuit is run in conduit through the area of a postulated cask drop fan.
The loss of this circuit through an open circuit could cause the loss accident.
of the Reactor Building cooling fan; a short circuit would definitely cause the loss of the fan control circuit and therefore the fan would be inoperable until minor modifications could be made. The consequences of the fan loss are minor (the requirements for this f'an are described in Section 6.3 of the FSAR) since this is the third redundant back-up to the Reactor Building Emergency Cooling System.
STATEMENT 2.0 It is stated in your submittal that:
G (1) the cask vill be handled above and adjacent to engineered safeguard equipment; (2) the floor slabs are not designed to withstand the impact of a dropped cask; (3) cask sizes considered in the evaluation included small truck casks weighing approximately 25 tons up to the large rail casks weighing up to the rated capacity of the fuel handling crane of 110 tons.
QUESTION Based on the most adverse combination of cask drop conditions, at all points 2.1 along its revised path of travel within the Unit 1 building, demonstrate by analysis that sufficient design margin exists to enable the_ staff to conclude that, for the specific shipping casks considered, the resulting damage vill not preclude the facility's essential equipment (such as pumps, piping, valves,
and electrical trays) from attaining and maintaining a controlled, cold safe Where structures are found to withstand the impact of the reactor shutdown.
cask drop, present the input parameters assumed in the analysis including:
eask veight, cask impact area, drop height, drop location, and the assumptions regarding credit taken in the analysis for the action of impact limiters.
RESPONSE
The results of an evaluation of the effects of postulated spent fuel cask drop accidents at Three Mile Island Unit 1 are contained in the February 1h, 1976, sub-
+
9 mittal (Met-Ed letter GQL 0215 to NRC dated February 1h,1976).
Proposed
' technical specification changes to plant operating procedures during cask handling are contained in the September 21, 1976, submittal (Met-Ed letter GQL 12hh to NRC dated September 21,1976).
The evaluation included cask drop accidents during transfer of the cask be-tween the railcar and the top of the "B" spent fuel pool, transfer of the cask to and from the cask loading pit and raising and lowering of the cask within the pit, and transfer of the cask to and from the decontamination pit and raising and lowering of the cask within the pit. Thus, cask drop accidents were con-Cask sises considered sidered at all points along the revised transfer path.
in the evaluation included small truck casks weighing approximately 30 tons up to large rail casks weighing up to the rated capacity of the fuel handlin crane o
Considerations were given to integrity of the spent fuel storage of 110 tons.
pool and spent fuel assemblies stored in the pool, and integrity of safety sys-Results of the eval-tems and equipment located below the cask transfer path.
uation are summarized below.
During transfer of the cask between the railcar and the top of the "B" spent fuel pool, results of evaluations indicated that cask drop accidents at certain locations could possibly result in unacceptable damage to engi-neered safeguard circuits located in cable trays below the cask transfer Accordingly, Met-Ed has relocated one engineered safeguard circuit path.
tray (containing two engineered safeguard circuits) and revised the cask transfer path to take advantage of the physical separation that now existy between other trays so that single cask drop accidents vill not result in un-acceptable damage to engineered safeguard circuits located below the cask transfer path. The specific details are discussed in Section IV.A of the f
4
10 February lb, 1976, submittal and the September 21, 1976, submittal.
During transfer of the cask to and from the cask loading pit, results of evaluations indicated a cask drop on the edge of the pool well could result in the cask being deflected into the "B" spent fuel pool. Accordingly, Met-Ed has revised the cask transfer path to the cask loading pit so that the cask vill be tipped in a direction away from the "B" spent fuel pool in the event of a cask drop on the edge of the pool vall. The revised cask trans-fer path to the cask loading pit is discussed in Section IV.B of the Febru-ary lb, 1976, submittal and the september 21, 1976, submittal.
During transfer of the cask to and from the decontanination pit and raising and lowering of the cask within the pit, results of evaluations indicated that cask drop accidents could possibly result in unacceptable damage to engineered safeguard circuits, spent fuel pool cooling pipes, and cooling water pipes to the spent fuel pool coolers. Accordingly, Met-Ed has de-cided not to use the present cask decontamination pit. The cask will be decontaminated in the cask loading pit and transferred to the receiving /
shipping area.
Results of additional evaluations indicate that during transfer of the cask over the receiving / shipping area on the 305'-1" elevation, south of the railcar slab, cask drop accidents could possibly damage green engineered safeguard circuits located in the air intake tunnel. To do this, the cask would have to penetrate two floor slabs at elevations 305'-1" and 293'-0" as shown in Figure IV-2 of the February 1h, 1976, submittal.
Since the resulting damage would be limited to one redundant system, the possible danage
11 is considered acceptable in accordance with the criteria established in Section IV-A of the February 1h, 1976, submittal.
The railcar slab at elevation 301'-6" and the operating floor slab at elevation 305'-1" (refer to Figures IV-3 and IV h of the February 1h, 1976, submittal) located below the revised cask transfer path are not designed to withstand the impact of a dropped cask. Therefore, in the cask drop evaluation, the engi-neered safeguard circuits located in trays below these floor slabs are assumed The to be damaged in the event of cask drop accidents over these floor slabs.
specific circuits that could be damaged are identified in Section IV-A of the February 14, 1976, submittal. As discussed in the February 1h, 1976, sub-mittal, the revised cask transfer path and the plant modification to relocate one entire engineered safeguard circuit tray provide reasonable assurance that single cask drop accidents over the floor slabs at elevations 301'-6" and 305'-1" will not result in damage to more than one redundant channel of engi-neered safeguard circuits. This vill assure that the resulting damage vill not preclude the facilities' essential equipment from attaining and maintaining a controlled, cold, safe reactor shutdown.
The bottom of the cask loading pit is constructed of reinforced concrete to bed-Maximum rock and thus is designed to withstand the impact of a dropped cask.
drop height is approximately hh feet. Likewise, the 5-foot vide valls of the "B" spent fuel pool are constructed of reinforced concrete to bedrock and are also designed to withstand the impact of a dropped cask. Maximum drop height is approximately 1 foot (FSAR Section 9.T.1.1.).
The 1.5-foot vide east vall of the cask loading pit is also constructed of reinforced concrete to bedrock.
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Additional calculations have beer performed to determine the structural ade-quacy of the east vall of the cask loading pit as a result of postulated cask drop accidents. As indicated in Section IV-B of the February 14, 1976, submittal, a cask drop on the east vall of the cask loading pit will result in local crushing of the vall of less than 0.50-inch at the top. The gross strength of the east The east vall has been vall is not affected by this amount of local crushing.
analyzed for stability or buckling due to the cask impact load and the vertical and horizontal reaction loads due to a cask tipping accident on the edge of the Results of these calculations indicatr the vall is structurally adequate vall.
for the maximum applied impact and reaction loads.
Input parameters for the above analyses are summarized below.
Assumed impact Drop W
Hei@t Drop Location eight Area i
Co sidered in2 in tons NFS-4 30 660 - Balsa 6
Center of 5'-0" wide south wall of "B" spent 77 - Steel fuel pool and center of i
-6" wWe east waH of NLt 1/2 30 855 (2) 6 cask loading p,it.
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IF 300 75 814 (3) 6 i
IF 400 110 1134 (3) 6 (Proposed) i 3959 (2) 6 NLI 10/24 110
. (1) Total impact area of the bottom of the cask. The impact area on the l'-6" east wall is Dia of Cask x '.'.'idth of East Wail Total Impact Area x Projected Area of Cask Bottom (2) Impact area of cask bottom plate without impact limiters.
_(3) Impact area of the impact fins.
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13 For the NLI 1/2 and NLI 10/2h casks, the impact limiters were assumed to be removed from the cask, i.e., no credit was taken in the analysis for the impact For.the IF 300 and IF h00 (proposed) casks, no credit was taken limiters.
The actual for the energy absorption characteristics of the impact limiters.
impact area of the impact fins 16cated on the cask bottom plate was used in the For the NFS h casks, credit was taken for the balsa wood impact analysis.
limiter which is an integral part of the cask bottom plate.
Two additional areas of the structure found to withstand the impact of the cask drop within the Unit 1 building are discussed in Section IV.A.3 of tne February h, 1976 submittal (Points B and C). For these areas the input parameters assumed in the analysis are:
110 Tons a.
Cask Weight Point Impact b.
Cask Impact Area hk'-0" c.
Drop Height Direct hit on to the North d.
Drop Location and South vall of the rail-car slab, at Elevation 305'-1".
None Credit for Cask Impact Limiters e.
QUESTION Demonstrate that following a cask drop accident the cask will not tip, 2.2 roll, or impact on Unit 1 temporarily stored new fuel in a manner which wou1d lead t; a criticality accident.
In particular, state a maximum
~
1h credible value for the multiplication factor (K,ff) following such a cask drop accident considering the effects of any possible reduction in fuel spacing, with the introduction of neutron moderating material (aqueous foam, water from ruptured pipes or fire-fighting apparctus, etc.).
This maximum credible value should include reflective effects from structural concrete and any other moderating materials near the Provide the assumptions made in the analyses and the resulting fuel mass.
safety margins which support your conclusions.
RESPONSE
As shown on Figure 1, the area south of the railroad track is no longer New fuel vill be receipt designated as a temporary storage area for new fuel.
inspected in this area and then vill be transferred to the new fuel storage racks shown in Figure 1 or to the spent fuel pools. No new fuel will be pe mitted in the Therefore the questioned receiving / shipping area during cask handling operations.
impact of an accident on Unit 1 temporarily stored new fuel cannot occur.
QUESTION For each of the spent fuel shipping casks that will be handled, demonstrate 3.0 that the crane hoist will not subject the various cask trunnions and handling yokes, considered in your evaluation, to excessive deceleration loads under the following assumptions:
(1) the cask is near its upper limit of travel; (2) the cask is being lowered at its maximum speed as defined by the hoist controls; and (3) the crane experiences a loss of power thereby causing the hoist mechanical load brake and the solenoid
15 brake to automatically set.
Ac ordingly, in tabular form for each cask, provide the following information:
tle static factors of safety of the cask handling yoke, the cask (a) trunnions and the weight of cask; (b) the maximum lowering speed as defined by the hoist controls; and (c) the results of dynamic analyses which demonstrate that the cask
- unnions and herdling yoke have sufficient design margin to preclude theff failure due to the deceleration loads created by the hoist b* eses.
RESPONS1 The static The considered casks are in conformance with 10 CFR 5 T1.3(c).
factor of safety of the cask handling yoke and the cask trunnions is 3.0 We maximum lowering speed as based on the yield strength of the material.
defined by the hoist controls is 5 feet per minute.
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load
. Dynamic analyses have been performed considering*that the decelerat on hypothesized in Items 3.0 (1), (2) and (3), is absorbed by the crane hoist reeving between the take-up drum / upper block and the main block in its highest position. The results of these analyses are:
16 Cask Weight (Tons)
Dynamic Load Factor of Safety On Yield 1.1 3 + 1.1 = 2.7 110 1.1 3 + 1.1 = 2.7 75 25 1.2 3 + 1.2 = 2.5 These results are conservative as no credit is taken for the mechanical portion of_the crane acting as an energy absorber.
demonstrate that the cask trunnions and handling yoke have sufficient The result' design mar an to preclude their failure due to the deceleration loads created by e
the hoist brakes.
QUESTION h.0 It has been noted that the bases provided 'in your September 21, 1976 submittal for Iten 3.11.2 of the revised Technical Specifications has omitted reference to FSAR Figure 9-18A entitled " Fuel Handling Building Crane Key Interlock System Limits". Provide a revised Figure 9-18A showing the new key interlocked limits of travel of the crane.
Further, the basis for the present Technical Specification states that in the "unlikely event of a load drop accident, there would be no possibility of this resulting in any damage.....".
The proposed corresponding statement in the revised Technical Specification basis states there "would be less possibility." Describe, discuss and clarify the purpose of this revision and the potential equipment and structures iny'olved.
17
RESPONSE
FSAR Figure 9-18A will be revised showing the naw key inteilock limits This will be accomplished by substituting Figure 1 of travel of the crane.
for 9-18A. Additional details are also shown in Figures IV h and IV-6 of the February 1h, 1976, submittal.
L The substitution of the phrase "would be less possibility" for "would be no possibility" in the revised Technical Specification was editorial in nature and was not to be construed as a revision in itself potentially affecting equipment and structures. The appropriate phraseology shall be "would be no possibility" as was previously stated in the original Technical Specification.
QUESTION 5.0 Since the keyed interlock limits of crane travel only applies when the' load being handled exceeds 15 tons, provide the following information regarding the system acceptability when there is a load of 1h tons on the crane hook, and it is over the stored spent fuel when "two blocking" occurs (i.e., the upper limit switch fails and the lower hoist block contacts the lower block). Demonstrate that either (a) the resulting radiolor'"al release will remai: within acceptable limits should the lower load block and hook drop and impact on the stored spent fuel; or (b) the lower load ~ 1ock and hook will not drop shculd "two blocking" (In the latter case, the analysis should take into account the occur.
peak stall torque of the hoist motor plus the kinetic energy of the hoist motor plus the kinetic energy of the hoist power train and motor when the hook is being raised at its maximum rated speed as allowed by
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18 the control system).
RESPONSE
Loads of lh tons'and less will be handled on the auxiliary crane trolley / block.
m "Two blocking" vill be prevented by the addition of a second limit switch.
This limit switch will provide a redundant means of stopping the crane block from exceeding its upper travel limit, i
QUESTION 6.0 In regard to the shipping cask crane which is shared by Units 1 and 2, it has been noted that the staff's Safety Evaluation Report for Unit 2, dated September 1976, contains the following statement "We find the fuel handling system to be acceptable for a cask not exceeding 70 tons in weight, and will condition the operating license accordingly until and i
unless the applicant justifies use of a larger cask."
Section 3.11.h of the Unit 1 Technical Specifications would permit the crane to handle loads up to 110 tons since it states " Loads in excess of hook capacity shall'not be lifted, except for load testing."
Describe and discuss any differences which exist between Units 1 and 2 as it relates to cask drop accidents. Further, the depth of detail provided should enable the reviewer to concur in the acceptability of 110 ton loads fer the crane when they are being handled in the Unit 1 facility.
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RESPONSE
The Unit 2 FSAR indicates that a cask tipping analysis has been performed for the proposed IF400 shipping cast which represents the maximum size and weight (%100 ton) of any cask under consideration.
It also states that any cask drop over the fuel handling bridge operating floor or the cask pool vill not result in damage to the The cask pool dimensions and spent fuel pool or other safety related components.
design vere based on the characteristics of the 70 ton General Electric cask, IF300.
However, a recent reanalysis has revealed that the Unit 2 fuel handling building is able to withstand a cask drop accident of weight equal to the capacity of the crane from a height of six inches.
2nd is, as a result, Unit 1 was analyzed in all respects for the larger size cas requesting licensing for the rated capacity of the crane.
Therefore, no difference exists between Units 1 and 2, with respect to cask drop accidents.
QUESTION Figure IV-3, (February lh, 1976 submittal) showing the modified cask transfer 70 path and new location for engineered safeguards tray, indicates that the railcar is located partially outside the building during those tines when the cask is Describe and discuss what means being lifted from and lowered onto the railcar.
will be provided to prevent the railcar position from being adversely altered during a cask handling accident, such that it spans both the red and green cable trays during a cask drop accident and thereby being in a position to potentially l
cause damage to both redundant portions of the engineered safeguards cable trays
RESPONSE
The detail cask handling procedures will require that the brakes on the cask
O 20 carrier, i.e., either the railcar or truck bed, be set and wheel chocks positioned prior to unloading or loading the spent fuel cask to prevent the ' carrier position from being adversely altered during a postulated cask drop accident. The procedures will also prohibit the cask carrier from being moved further into the building until the cask is removed from above the carrier.
QUESTION 3.) Since the rail car will be partially outside the building during cask handling operations, describe, discuss and demonstrate that there are no significant adverse safety consequences resulting frem having the heavy rolling door, shown in FSAR Figure 1-8, Section El - El, open during such operations involving the offsite shipmett of spent fuel Should from either Units 1 or 2 should a cask handling accident occur.
the open doors result in a potential hazard to public health and safety, describe your proposed corrective measures.
RESPONSE
i An analysis was performed to determine the radio. gical consequences at f
the TMI site boundary for a gross release of activity from a fully loaded fuel cask. The analysis is based en the following:
The accident is assumed to occur after the assemblies have cooled for a.
120 days, All of the rods in twenty assemblies are assumed to rupture as a result b.
of the accident.
21 The damaged assemblies are all assumed to be the highest povered assemblies.
c.
The inventory per assembly is determined by applying a radial peaking factor The inventory of an of 1.7 to the inventory of an average assembly.
average assembly is determined by dividing the core inventories of Table 15A-2 of the Unit 2 FSAR by the number of assemblies in the core.
All of the activity in the clad gap in the damaged rods is released d.
instantaneously to the environment.
The gap activity is based on Regulatory Guide 1.25 assumptions, i.e. 10 percent of the total noble gases other than Kr-85, 30 percent of the Kr-85, and 10 percent of the total radioactive iodine in the rods at the time of the accident.
Atmospheric diffusion is calculated using a 0-2 hour dispersion factor e.
at the exclusion boundary of 6.1 x 10 h sec/m. This value is based 3
on Table 6.2-9c submitted in Amendment h8 to the FSAR for Unit 2 Isotopic releases to the atmosphere using these assumptions are summarized below:
Activity Released (curies)
Isotope 5 02+h Kr-85 9.T8+0 Xe-131m 3..T6-1 Xe-133 h.32+1 I-131 The resulting thyroid and whole body doses at the exclusion boundary are 13.5 and 0.016 Rem, respectively. These exposures are vell within the guidelines of 10CFR100. Since the calculations are extremely con-servative and were performed without taking credit for isolation of the I
22 cask loading area, no changes to facility equipment or Technical Specifications have been censidered.
QUESTION On Page IV h, of your February 1k, 1976 submittal, you state " Administrative 9.0 procedures will be used to limit the height the cask lower surface is raised above the top of the "B" spent fuel pool to 6 inches maximum".
Proposed 'fechnical Specification 3.11.3 also makes a related reference to aininistrative control of load elevation.
Clarify what vill be the carrying height of the cask bottom surface, with respect to fixed structurcs, at all points along the path of travel What of the spent fuel shipping cask while it is within the building.
are the measures, in addition to administrative controls, which could be incorporated to preclude cask drop heights exceeding the above carrying heights.
RESPONSE
Maximum height Maximum height over spent fuel pool valls will be six inches.
over 305'-1" floor vill be k3'-5".
These Presently there are structures that interfere with this travel scheme.
obstructions (a six inch curb, a few handrail posts and a fuel handling bridge stop) vill be removed during cask handling operations.
23 QUESTION Provide proposed Technical Specifications for crane rope inspection and 10.0 replacement and for assuring operability of the limit switches which restrict crane travel. Use the appropriate corresponding parts of chapter 2-2 of the American National Standards Institute ANSI B30.2 for guidance in preparing your response.
RESPONSE
Procedure 3010 outlines the frequent and periodic inspection of cranes at MI and is in accordance with ANSI B30.2 This procedure implements our legal requirements of Federal Register Par. II, Subpart N, Sec. 1910.179 of the Occupational Safety and Health Act and fulfills our commitment made in Amendment 50 of the MI-1 FSAR. Based on the above and since the IGC Standard Tech. Spec's do not require the above details, we feel that no technical specification is necessary.
t QUESTION The FSAR states "A Whiting automatic paddle-type limit switch is installed 11.0 for upper hoist limit to prevent "two-blocking" situations."
Describe the design features or procedures that vill be used to provide assurance that a single failure vill not defeat this protection against "two-blocking".
RESPONSE
"Two-blocking" is prevented on the fuel handling crane main hook by a paddl,e-
2h A screw-type switch type limit switch, and by Adminsistrtive control.
This svitch on the main hook is presently utilized as a lower lLnit switch.
Therefore, a will be modified to also function as an upper limit switch.
single failure in the system would still have redundant means of preventing "two-blocking."
QUESTION Provide a summary of the cask stability analysis when the cask is dropped on 12.0 the south wall of the "B" spent fuel pool for both eccentric and straight drop conditions."
RESPONSE
Results of the cask sttbility analysis when the cask is dropped onto the 5-foot vide south wall of the "B" spent fuel pool are presented belev for the eccentric drop condition. Results for the straight drop are less severe than the eccentric drop condition and therefore are not controlling.
The main elements of the cask stability analysis are sm=sarized below.
The cask bottom surface is assmned to be raised 6 inches above the top of the 1.
spent fuel pool vall and the cask center of gravity is assumed to be located 3 inches from the center of the 6-inch wide transfer path as shown in Figure 2a.
2.
The lifting trunnion or lifting yoke arm on one side of the cask is assumed to fail. This lets the cask drop straight down 3 to 5 inches (depending on the cask involvea, until the resulting slack in the syste= is removed, i.e.,
25 a straight line of action is established between the unfailed cask trunnion, the center of the lifting yoke and the cable drum as shown in Figure 2b.
At this point, the cable becomes tight.
As the cask continues to drop the load in the cable increases in direct pro-3 The eccentrically applied load reduces portion to the stretch of the cable.
the casks vertical velocity and imparts angular and lateral velocity ':o tne cask as shown in Figure 2c.
- able h.
Eccentric drop analyses indicate that the maximum force produced in the is about h tLaes the weight of the cask. At this load, the up until now unfailed cask trunnion or yoke arm is expected to fail. The cask then free falls with constant angular and lateral velocity as shown in Figure 2d until it impacts top of the south vall of the "B" spent fuel pool.
tu?
The angular and lateral kinetic energy of the cask at impact are determined 5
from the above model. Assuming all of this energy goes into increasing the potential energy of the cask, the amount the cask center of gravity is i
The cask is con-raised due to tipping is calculated as shown in Figure 2e.
sidered stable and vill not tip over if the cask center of gravity is on the stable side of the pivot point, i.e., to the right of the pivot point shown in Figure 5 Analyses were performed for three cask veights; 30-ton (NFS h and NLI 1/2),
75-ton (IF 300), and 110-ton (IF h00 - proposed, and NLI 10/2h).
Results ar' summarized below and show that all of the casks would be stable due to eccentric
26 1
drops from 6 inches or less.
Increase in Cask Cask Position Cask Velocity increase in Center of Gravity Cask at impact at impact Cask Center at which Cask Weight of Gr*VItY hecnmes Unstahle tons a x, in as, Deg ic, in/sec eRad/see ah, in ah
, in 30 1.88
.776 10.68
.077 0.50 3.05 75 2.08 1.85 11.80
.183 1.~10 2.92 110 2.22 2.58 12.6
.256 1.60 2.86 (1) includes maximum bridge travel speed = 50 fpm (10 in/sec).
QUESTION Show that the liner plate vill not tear if the east vall of the loading 13.0 Also discuss the effects pit deflects 1" as postulated in Section IV-3-3 on the fuel racks which are in contact with the east vall due to the '"
deflection.
RESPONSE
No credit is taken for the 3/16-inch liner plate in the analysis to determine the structural adequacy of the east vall of the cask loading pit for impact loads due to a postulated eccentric drop accident. Therefore, the conclusions stated in the February 14, 1976, subcittal stating that the deflection of the east vall is less than 1 inch and that gross failure of the east vall vill not occur are It is also noted that the 1-inch valid even if the liner plate locally tears.
vall deflection is calculated to cause a maximum strain in the liner plate of about 1.6 percent. This is well below the minimum elongation of the stainless
27 steel liner plate of 40 percent.
The 1-inch deflection reported in the February lb, 1976, submittal to the NFC is for a case where the cask impacts the l'-6" vide east vall of the cask load-ing pit following a postulated eccentric drop accident while raising or lowering the cask within the pit. The maximum calculated deflection of 1-inch occurs when the cask impacts the east vall at the top of the cask loading pit where the vall is considered as a cantilever since no credit is taken for support at the north end from the fuel transfer gate. At the elevation of the spent fuel stor-age racks, the east vall of the cask loading pit is much stiffer because it is supported at the north end, i.e., at this elevation the vall is no longer con-sidered a cantilever since the opening for the fuel transfer gate stops about 2.5 feet above the spent fuel storage racks. Hence, the deflection of the east vall of the cask loading pit at the elevation of the spent fuel storage racks due to cask impact loads is expected to be significantly less than 1 inch.
Additional analyses have been performed to (1) determine the deflection of the east vall of the cask loading pit at the elevation of the spent fuel storage racks due to cask impact loads on the side of the vall following a postulated eccentric drop accident, and (2) evaluate the effect of the deflection of the vall on the Results of these spent fuel storage racks that are in contact with the vall.
analyses are summarized below.
The maximum calculated deflection of the east vall of the cask loading pit at the elevation of the upper spent fuel storage rack supports is about 0.5 inch.
28 The maximum calculated impact load transmitted into the spent fuel storage rack suppcrts is about 320 kips. Assuming this impact load is carried by the three middle supports (out of a total of st. van), the maximum load per support is about 107 kips.
Thus, as a vorst case, the effect of the 0.5 inch deflection of the east vall of the cask loading pit could be to reduce the center-to-center spacing between fuel assemblies of two adjacent rows from 13.625 inch to 13.125 inch.
It should be noted that the above reduction ir. center-to-center spacing The center-applies only in the east-west direction of the spent fuel pool.
to-center spacing of fuel assemblies of adjacent racks in the north-south direction and center-to-center spacing of fuel assemblies within the individual racks is not changed.
Based on extrapolation of sensitivity studies performed in Metropolitan Edison Company Three Mile Island Nuclear Station Unit 1 " Spent Fuel Pool Modification Description and Safety Analysis", the calculated multiplication factor is less than 0.95 and therefore acceptable. It should be noted as with all previous analysis, no credit is taken for any boric acid concentration in the spent fuel pool water.
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