ML19262A336

TMI-1 Cask Drop Evaluation.

ML19262A336
Person / Time
Site:	Three Mile Island
Issue date:	01/22/1976
From:	MPR ASSOCIATES, INC.
To:
Shared Package
ML19262A334	List: ML19262A333 ML19262A336
References
NUDOCS 7910260661
Download: ML19262A336 (28)

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MPR ASSOCIATES, INC. Ja.'ua ry 22, 1976 THREE MILE ISLAND NUCLEAR STATION UNIT NO.1 CASK DROP EVALJATION I

1

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1485 098 .r 1140 CONNECTICUT AVENus. N. V W AsHiNGToN. D. C. 2003' 202-659 2320

791026066/

M P R ASSOCIATES. INC.

TABLE OF CONTENTS I. INTRODUCTION II.

SUMMARY

III. PREsZNT CASK HANDLING SYSTEM IV. CASK DROP EVALUATIONS A. Transfer of Cask between Railcar and Top of "B" Spent Fuel Pool B. Transfer of Cask to and from Cask Loading Pit and Raising and Lowering Cask within Pit C. Transfer of Cask to and from Decontamination Pit and Raising and Lowering Cask within Pit i

1485 099

M PR ASSOCIATES. INC.

I. INTROD UC TION The purpose of this report is to summarize the results of an evaluation of the effects of postulated cask drop accidents at Three Mile Island Unit 1. This evaluation covers three main areas:

Evaluation of cask drop accidents during transfer of the cask between the railcar (elevation 301'-6) and the top of the "B" spent fuel pool (elevation 348'-0").

Evaluation of cask drop accidents during transfer of the cask to and from the cask loading pit and during raising and lower-ing of the cask within the cask loading pit.

Evaluation of cask drop accidents durin;; transfer of the cask to and from the decontamination pit and during raising and lowering of the cask within the decontamination pit.

The above evaluationa included consideration of the tollowing:

Integrity of spent fuel and spent fuel storage pool -- i. e. , can a cash be positioned near spent fuel such that it could be deflected into the spent fuel pool by a cask drop on the edge of the pool wall or by an eccentric drop caused by a break of the cask trunnion or lifting yoke on one side of the cask?

Integrity of safety sys' ems and equipment -- i. e. , in moving the cask to and from the es ik loading pit, and to and from the cask decontamination pit, does it pass over any systems and equipment important to safety which could be damaged by a cask drop accident?

Results of cask drop evaluations are summarized - Se ction l

II of this report. A description of the present cask har.dling system at TNI k

Unit 1 is given in Section III and detail results of the cask drop evaluatio$s 9

are presented in Section IV. Where the evaluations indicate corrective n[ea-I-1  :

1485 100

sures are required, the proposed plant modifications and ch.inges to plant crating procedures and Technica! Specification 3,11 are discussed.

I-2 1485 101

M P R ASSOCIATE" lNC, II.

SUMMARY

Evaluations have been performed to determine the effects of postulated cask drop accidents at TMI Unit 1. The evaluations included cask drop accidents during transfer of the cask between 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 trans-fer of the cask to and from the decontamination pit and raising and lower-ing of the cask within the pit. Cask sizes considered in the evaluation in-cluded small truck casks weighing ~ 25 tons up to large rail casks weighing up to the rated capacity of the fuel handling crane of 110 tons. Consider-ations were given to integrity of the spent fuel storage poci and spent fuel assemblies stored in the pool, and integrity of safety systems and equip-ment located below the cask transfer path. Results of these evaluations are summarized below.

During transfer of the cask between the railcar and the top of the "B" spent fuel pool, results of evaluations indicate that with the present cask handling system, 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 path. Accordingly, we plan to relocate one engineered safeguard circuit tray (containing two engineered safeguard cir-cuits) and to revise the cask transter path to take advantage of II - 1 1485 102

the physical separation that now exists between other trays so that single cas. drop accidents will not result in unacceptable damage to engineered safeguard circuits located below the cask transfer path. The specific details are discussed in Section IV. A of this report.

During transfer of the cask to and from the cask loading pit, results of evaluations indicate that with the present cask trans-fer path, a cask drop on the edge of the pool vcall could result in the cask being deflected into the "B" spent fuel pool. Ac-cordingly, we plan to revise the cask transfer path to the cask loading pit so that the cask will be tipped in a direction away from the "B" spent fuel pool in the event of a ce sk drop on the edge of the pool wall. The revised cask transfer path to the cask load-ing pit is discussed in Section IV. B.

During transfer of the cask to and from the decontamination pit and raising and lowering of the cask within the pit, results of eval-uations indicate that with the present system, cask drop accidents could possibly result in unacceptable damage to engineered safe-guard circuits, spent fuel pool cooling pipes, and cooling water pipes to the spent fuel pool coolers. Met Ed is currently eval-uating possible plant modificatior.s and changes to operating pro-cedures to correct this situation. In addition, the possibility of decontaminating the cask in a new location is also being evaluated.

Until these additional evaluations are completed, the irCTnt de-contamination pit will not be used.

1485 II - 2

In summary, it is concluded that the plant modifications and changes in operating procedures and technical specifications dis-cussed in this report are reas.onable and practical for an existing operat-ing plant and will provide an acceptable cask handling system at TMI Unit I with regard to plant safety considerations.

II - 3 1485 104

M P R ASSOCIATES, INC.

III. PRESENT CASK HANDLING SYSTEM The cask handling system at TMI Unit 1 is described in Sec-tion 9. 7 of the FSAR and shown in Figure III-1 of this report. The sequence of major cask handling operations is as follows:

The empty spent fuel shipping cask enters the auxiliary building at elevation 301'-6" by railcar or truck depending on the particu-lar cask.

The cask is upended and lifted to the top of the "B" spent fuel pool (elevation 348'-0") using the 110-ton capacity fuel handling crane.

The cask is lowered into the cask loading pit located in the south-west corner of the "B" spent fuel pool. Spent fuel assemblies are placed in the cask by the fuel storage handling bridge. The loaded cask is then removed from the pit.

The loaded cask is moved to the decontamination pit.

The loaded cask is lowered into the decontamination pit, decon-taminated, and then removed from the pit.

The loaded cask is moved to and placed on the railcar or truck for transport to a spent fuci reprocessing plant or storage facility.

An automatic travel interlock system is administrative 1y imposed whenever the fuel handling crane is used to transport loads in excess of 15 tons and confines the crane bridge and trolley horizontal mo-I tions to the shaded area shown in Figure III-2. The height of the cask i i

lower surface is administrative 1y maintained at less than 1 foot above the top of the spent fuel pool walls (elevation 348'-0"). [

III - 1 ,

1485 105

O The bottom of the cask loading pit is constructed of rein-forced concrete to bedrock and thus is designed to withstand the impact of a dropped cask (maximum drop height ~ 44 feet). Likewis e , the 5-foot wide walls of the "B" spent fuel pool are constructed of reinforced con-crete to bec ock and are also designed to withstand the impact of a dropped cask (maximum drop height ~ 1 foot). The 1. 5 foot wide east wall of the cask loading pit is constructed of reinforced concrete to bedrock. Neithe r the bottom of t' "B" spent fuel pool, the bottom of the decontamination pit, nor the floor slabs at elevations 348'-0", 33: i" 30 5'- 1",

, and 301 '-

6" have been designed to withstand the impact of 1 iropped cask.

III - 2 1485 106

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M P R ASSOCIATES, INC.

IV. CASK DROP EVALUATIONS Results of cask drop ei aluations and proposed plant modifi-cations and changes to operating procedures and technical specifications where the evaluations indicate corrective measures are required are de-scribed below. The cask drop evaluations cover the following major areas:

Transfer of the cask between the railcar and the top of the "B" spent fuel pool.

Transfer of the cask to and from the cask loacing pit and rais-ing and lowering of the cask within the pit.

Transfer of the cask to and from the decontamination pit and raising and lowering of the cask within the pit.

A. Transfer of Cask between Railcar and Too of "B" Soent Fuel Pool

1. Results of Evaluations Transfer of the cask between the railcar (elevation 301'-6") and the top of the "B" spent fuel pool (elevation 348'-0") requires that the cask be handled over engineered safeguard circuits located be-low the floor slabs at elevation 301'-6" and 305'-1" and along the south and west walls of the "B" spent fuel pool. Engineered I

safeguard circuits are also located in the air intake tunnel. Lop cations of the above mentioned engineered safeguard circuits N.

are shown in Figures IV-1 ana IV-2.

Since the floor slabs at efe-i vations 301'-6" and 305'-1" are not designed to withstand the impact IV - 1 148510k

4 of a dropped cask, the engineered safeguard circuits located i low these floor slabs as well as the engineered safeguard circuits located along the south and west walls of the "B" spent fuel pool are subject to damage in the event of a cask drop accident. As shown in Figures IV-1 and IV-2, both red and green engineered safet tard circuits are involved. (Note: Engineered safeguard and reactor protection circuits are color coded as follows: Red -

redundant channel A; Green - redundant channel B; Yellow - re-dundant channel C; Blue - redundant channel D; Multicolored (e. g. ,

red / green) - interconnections between two redundant channels. )

The following criteria have been established to determine the ac-ceptability of damage to engineered safeguard circuits as a result of cask drop accidents.

A single cask drop accident should not be permitted to dam-age engineered safeguard circuits of more than one color.

Damage to any number of circuits of the same color is ac-ceptable as long as circuits of another color are not affected.

Damage to multicolored circuits (e. g. , red / green) along with darnage to circuits to one of those two colors is accept-able since the multicolored circuits are protected intercon-nections between two redundant channels.

These criteria ensura that no more than one channel of engineered redundant safegu2rd systems could be damaged by single cask drop accidents, .c that the safety function can still be carried out by the undamaged channels.

A review of Figures IV-1 and IV-2 indicates the following possible a reas of ccncern: 1485 110 IV - 2

A cask drop in the west end of the cask receiving area could result in damage to the green engineered safeguard circuits in tray T 54 along with the red engineered safeguard cir-cuits in trays 167, 577, and 757. Howeve r, at the we st end of the cask receiving area, there is sufficient separation be-tween the green erigineered safeguard circuits in trays T-54-15, 318, and 955 and the red engineered safeguard circuits in trays 167, 577, and 757 to prevent a single cask drop accident from damaging both of these green and red cir-cuits at the same time.

A cask drop in the east end of the cask receiving area could result in damage to the green engineered safeguard circuits in trays T 54, T-54-15,166, 756, and 850 as well as the red engineered safeguard circuits in trays 167, 577, and 757.

Based on the above evaluation of cask drop accidents during trans-fer of the cask between the railcar and the top of the "B" spent fuel pool, it is concluded that corrective measures are required.

?. . Corrective Measures The following corrective measures will provide reasonable assur-ance that ; ingle ca k drop accidents during transfer of the cask between the railcar and the top of the "B" spent fuel pool will not damage engineered safeguard circuits of more than one color.

The green engineered safeguard circuit tray T-52-54 (con-taining two engineered safeguard circuits) will be moved from its present location below the railcar slab as shown in Figures IV-1 and IV-2 to run parallel and along with the green engineered safeguard circuit trays 166, 756, and 850 e.s ;hown in Figures IV-3 and IV-4.

During movement of the cask between the railcar and the top of the "B" spent fuel pool, the cask will be restricted to the transfer path shown in Figures IV-3 and IV-4. Administra-tive procedures and visual aids will be used to control the cask to the prescribed path. Administrative procedures will also be used to ensure that the cask lifting yoke is oriented in the north-south direction during this transfer ope ration to reduce the possibility of tipping of the cask in the east direc-tion due to an eccentric drop accident.

1485 111 IV-3 - .

9

Administrative procedures will be used to umit the height the cask lower surface is raised above the tcp of the "B" spent fuel pool to 6 inches maximum.

Techni.a1 Specification 3.11. 3 will be modified to reflect the above.

3. Results of Structural Calculations Calculations have been performed to determine structural dam-age to reinforced concrete floor slabs and watts located below the transfer path shown in Figures IV-3 and IV-4. These calcula-tions included cask drops over the railcar slab at elevation 301'-

6", the north and south walls of the railcar slab, and the flocr slab at elevation 305'-1". Results :f these calculations arc sum-72aiTrp b : low.

~

A cask drop onto the railcar at elevation 301'-6" (Point A) would result in damage to the railcar slab and the red engi-neered safeguard circuits ir trays 167, 577, and 757 !ccat d directly below the portion of the railcar slab supporting the railca r. However, simultaneous damage to the green engi-neered safeguard circuits in trays 166, 756, 850 and T 54 also located below the railcar slab is considered improb-able since these circuits are located east of the extreme end of the railcar and in the air intake tunnel.

A cask drop onto the south wall of the railcar slab (Point B) would damage the wall itself, the railcar slab to the north of the wall, and the floor slab at elevation 305'-1" to the souh.

The floor slab at elevation 293'-0" above the air intake tunnel would remain intact. As a _ re sult, damage would probably occur to the red engineered safeguard circuits in trays 167, 577, and 757 located directly below the railcar slab at the point of impact. However simultaneous damage to the green engineered safeguard circuns in trays 166, 756, 850 and T-52-54 located below the railcar slab to the east of the impact point and the green engineered safeguard circuits in the air intake tunnel is considered improbable.

A cask d. onto the north wall of the railcar slab (Point C) would damage the wall itself and eithe r the railcar slab to the south of the wall or the floor slab at elevation 305'-1" to the north, depending on which way the cask tips after im-pact. The refore, simul ,

is damage to the red engineered IV 1485 112

safeguard circuits in trays 167, 577, and 757 located below

' the railcar slab and the green engineered safeguard circuits in trays T-52-54, 166, 756 and 850 located beloc the floor slab at elevation 3058-1" is considered improbabic.

A cask drop onto the floor slab at elevation 305'-1" (Point D) would result in damage to the floor slab. The physical sep-aration between the geen engineered safeguard circuits in tra.ys T-54-15, 318, and 955 located along the south and west walls of the B spent fuel pool, and the red engineered safe-guard circuits in trays 167, 577, and 757 located below the floor slab at elevation 305'-1" to the east of the impact point is such that simultaneous damage to botF these green and red circ-its is considered improbable.

4. Summa ry It is concluded that the plant modifications and changes in operat-ing procedures described above will provide reisonable assurance that cask drop ace lents during transfer of the cask between the railcar and the top of the "B" spei.t fuel pocl will not result in un-acceptable damage to engineered safeguard circuits located below the transfer path.

B. Transfer of Cask to and from Cask Loadine Pit and Raisinc and Lowering Cask within Pit

1. Results of Evaluations With the present interlock system on the 110-ton fuel handling crane (see Figure III-2) two transfer paths to and from the center of the cask loading pit are possible.

Approach in the north direction over the south wall of the "B" spent fuel pool, or Approach in the east direction over the west wall of the "B" spent fuel pool.

IV - 5 1485 113

A cask drop on the edge of the south wall of the "B" spent fuel pool would tip the cask northward towards the gate of the cask loading pit. This gate is not designed for such an impact load.

Therefore, it is considered unlikely that this gate would prevent the cask from falling into the "B" spent fuel pool after impact with the gate.

A cask drop on the edge of the west wall of the "B" spent fuel pool would tip the task eastward towards the east wall of the cask loading pit. While cs1culations indicate that the east wall may be strong enough to withstand the impact of the cask without gross structural fsilure, as shown in Figure l'/-5, th mamentem and locadon of the center of gravity of the cask at impact are such that it cannot be shown with a reasonable degree of certainty that the cask would not fall into the "B" spent fuel pool after impact.

A cask drop into ohe "B" spent fuel pool is considered unaccept-able since it could result in damage to spent fuel assemblies stored in the pool and to the bottom of the spent fuel pool. There-fore, based on the above evaluation of cask drop accidents during approach to the cask loading pit, it is conclu '_ed that corrective measures are req tired.

2. Corrective Measures The following corrective measures will provide reasonable as-surance that a cask drop accident during transfer of the cask to IV - 6 1485 114

and from the cask loading pit will not result in the cask subse-quently falling into the "B" spent fuel pool.

The present cask transfer path to and from the cask loading pit will be changed to the revised path shown in Figure IV-6.

Interlocks on the bridge and trolley will be used to restrict the cask to a path width of 6 inches. Administrative procedures will be used to ensure that all lateral movements of the cask are performed at slow bridge and trolley speeds.

Administrative procedures will be used to limit the height the cask lower surface is raised above the top of the "B" spent fuel pool walls to 6 inches maximum.

Administrative procedures will be used to ensure that the cask lifting yoke is oriented in the east-west direction during this transfer operation. The purpose of orienting the yoke in the east-west direction is to reduce the pos sibility of tipping the cask in the north direction (i. e. , towards the gate on the ncrth side of the cask loading pit) during approach to and insertion c,f the cask into the cask loading pit.

Technical Specification 3. I1. 3 will be modified to reflect the above.

The main reasons for following the revised transfer path shown in Figure IV-6 are summarized below.

Results of calculations indicate that the cask should be stable if dropped onto the 5-foot wide south wall of the "B" spent fuel pool provided (a) the height the cask lower surface is raised above the wall is limited to 6 inches or les s, and (b) the center of gravity of the cask is limited to a 6-inch wide path located along the centerline of the wall. The above ca'.culations in-cluded both straight and eccentric drops of the cask.

During travel in the north-south direction, the cask should be stable if dropped over a portion of the path as shown in Figure IV-6, even though the center of gravity of the cask is located inside the cask loading pit. If the cask is dropped over the un-stable portion of the path down in Figure IV-6, the direction of tip will be generally westward towards the 5-foot wide west wall of the "B" spent fuel pool. In this event, local crushing of the concrete wall underneath the cask of several inches is expected due to the impact of the cask. However, this amount of local crushing would not affect the gross strength of the wall and should prevent the cask from rolling along the wall to a point IV - 7 1485 115

where it could then fall into the "B" spent fuel pool. Onc e the cask clears the edge of the south wall of the "B" spent fuel pool, the direction of tip will be directly towards the west wall of the "B" spent fuel pool and there will be no ten-dency for the cask to roll along the wall and fall into the "B" spent fuel pool after impact.

During travel in the east-west direction, the cask will eithe r tip directly towards the west wall of the "B" spent fuel pool as described above, or drop into the cask loading pit. As in-dicated previously, the bottom of the cask loading pit is con-structed of reinforced concrete to bedrock and thus is designed to withstand the impact of a dropped cask.

3. Results of Structural Calculations Calculations have been performed to determine the structural adequacy of the walls of the "B" spent fuel pool and east wall of the cask Icading pit as a result of postulated 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. Results of thes' calculations are summarized below:

A cask drop onto the 5-foot wide south and west walls of the "B" spent fuel pool will result in local crushing of the con-crete wall at the top. The gross strength af these walls, which are constructed of reinforced concrete to bedrock, is not a'fected by this amount of local crushing at the top.

A cask drop onto the east wall of the cask loading pit will result in local crushing of the wall of less than 1/2-inch at the top. The gross strength of this wall, which is also con-structed of reinforced concrete to bedrock, is not affected by this amount of Ic. cal crushing at the top. The east wall has 'aeen analyzed for the vertical and horizontal reaction loads due to a cask tipping accident on the edge of the wall.

Results of these calculations indicate the wall is structurally adequate for the maximum applied reaction loads.

During cask insertion into or withdrawal from the cask load-ing pit, the lateral and angular motion of the cask produced by an eccentric drop accident coull cause the cask to impact the sides of the cask loading pit. By orienting the cask lift-ing yoke in the east-west direction, these impacts are limited IV - 8 1485 116

to the east and west walls of the pit. For these impacts, the

1. 5-foot wide east wall is controlling. For the maximum im-pact load, the deflection of the east wall is calculated to be

~ 1 inch which is ~ 10 times the elastic deflection of the wall.

Gross structural failure of the wall for this deflection is not expected for the following reasons:

p (1) The wall has a very low reinforcement ratio (i. e. , the ultimate strength of the wall is limited by the strength of the steel reinforcement instead of the concrete) which re-sults in good ductility. Results of calculations indicate the maximum calculated impact energy of the cask is less than one-half the strain energy capability of the wall.

(2) The deflection is local (i. e. , the whole wall is not de-flected 1-inch).

(3) The wall is lined with a 3/16-inch stainless steel liner.

This should prevent the ejection of large fragments of concrete from the wall into the "B" spent fuel pool.

4. Summa rv It is concluded that the plant modifications and changes to op-erating procedures described above 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 will not result in the cask falling into the "B" spent fuel pool.

C. Transfer of Cask to and from Decontamination Pit and Raisine and Lowerine Cask within Pit

1. Results of Evaluations During transfer of the cask to and from the decontamination pit, the present interlock system on the 110-ton auxiliary building claae restricts the cask to a 1-foot wide path located along the center of the 5-foot wide west wall of the "B" spent fuel pool as shown in Iv-9 34gq j)7

Figure III- 2. The cask lower surface is administrative 1y limited to a height of 1-foot above the top of the wall. Calculations indi-cate that a cask should be stable if dropped onto the 5-foot wide west wall provided (a) the path width is reduced to 6 inches, and (b) the cask lower surface is limited to o inches above the top of the wall.

Green and yel;c, v engineered safeguard cir .5, spenc fue' pool cooling pipes, and cooling water pipes to the spent fuel pool cocl-ers are located immediately below the decontamination pit. The bottom of the decontamination pit is not designed for a cask drop accident irto the pit. Therefore, the engineered safeguard cir-cuits , spent fuel pool cooling pipes, and cooling water pipes to the spent fuel pool coolers located below the pit are subject to damage in the event of a cask drop into the pit. In addition, re-sults of structural evaluations indicate that portions of the floor slab at elevation 305'-1" to the north and south of the decon-tamination pit may fail as a result of a cask drop into the pit.

Locateri below the floor slab at ... ation 305'- 1" are additional red engineered safeguard circuits to the north of the decontam-ination pit and additional green engineered safeguard circuits to the south. Therefore, these additional red and green engineered safeguard circuits could also be damaged by a cask drop into the decontamination pit.

iv - 10 1485 118

Based on the above evaluation, it is concluded that corrective measures are required with regard to potential damage to engi-neered safeguard circuits, spent fuel pool cooling pipes, and cooling water pipes to the spent fuel pool coolers as a result of postulated cask drop accidents during transfer of the cask to and from the decontamination pit and during raising and lowering of the cask within the pit.

2. Corrective Mea sures Corrective measures (i. e. , plant modifications and changes to operating procedurer and technical specifications) that would permit the present decontamination pit to be used in a manner such that cask drop accidents would not result in unacceptable damage to engineered safeguard circuits and spent fuel poc1 cocl-ing pipes are being evaluated by Met Ed. In addition, Met Ed is also investigating the possibility of decontaminating the cask in ,

locations other than the decontamination pit. Other locations being considered are the cask loading pit and a new location near the solid radwaste storage area at elevation 305'-1". When the

, location for cask decont mination operations is selected, the specific plant modifications and changes to operating procedures and technical specifications that are required will be described fo i

NRC. Until such time, the present cask decontamination pit wi: 1 W

not be used. 11

[

1485 119 .

IV - 11

NOTE:

ES/G = GREEN ENGINE- ~D 7EGUARD CIRCUITS ES/R = RED ENGINEERED SAF c. GUARD CIRCUITS E

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NOTE: ES/G CREEN E 4GINEERED SAF F UA P D CIP Ct;lTS '

ES/R . RED ENGINEERED SA) ECCAl<D CIACLITS

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i CASK IMPACT ON EAST WALL  !

FIGURE IV-5 1485 124

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LEGEND: NOTE 1. [.

TRANSFER PATH DIRECTION OF TIP FOR

d STABLE AREA - STATIC 3 ASIS CASK I ROPS IN UNSTABLE AREA (TYP) 1 i

TRANSFER PATH TO AND FRCM CASK LCADING PIT (E L. 3 4 8 '- 0 ")

FIGUR E IV-6 1485 125