ML17037C523

Letter Submitting Report Describing Proposed Change for NMP Unit 1 on Access Platform Be Added to the Refueling Bridge Structure to Expedite Refueling Operation and Also Enhance Safety

ML17037C523
Person / Time
Site:	Nine Mile Point
Issue date:	01/11/1973
From:	Brosnan T Niagara Mohawk Power Corp
To:	O'Leary J US Atomic Energy Commission (AEC)
References
Download: ML17037C523 (16)

Text

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MOHAWK 300 ERIE BOULEVARD, WEST SYRACUSE, N. Y. 13202 January 11, 1973 Mr. John F. O'eary, Director OI gI,IIi<~~73 I gag W ~rg@pal Directorate of Licensing United States Atomic Energy Commission Washington, D. C. 20545

Dear Mr. O'eary:

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RE: Nine Mile Point Unit No. 1 Docket 50-220 The attached report describes a proposed change for Nine Mile Point Unit No. 1 in accordance with paragraph 50.59 of 10CFR Part 50. It is proposed that an Access Platform be added to the refueling bridge structure to expedite the refueling operation and also enhance safety.

The platform will aid in the removal and replacement of the drywell and reactor vessel'heads. It will also'aid in the washing of the reactor cavity walls.

This modification has been reviewed and approved by the Site Operations Review Committee and the Safety Review and Audit Board.

I

. Brosnan Vice Presi ent and Chief Engineer TJB/.

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0 I. Introduction The Access Platform to be added to the refueling bridge structure will serve the following functions:

1. Removal and replacement of drywell and reactor pressure vessel heads and also the steam separator assembly.

2. Washing of reactor cavity walls At the present time the above operations are carried out as follows:

1. Access is by means oF portable ladder to the drywell and reactor vessel head levels.

2. Wall washing is accomplished by a man standing on a portabl'e ladder using a hose.

The addition of this platform will expedite the refueling operation and also will enhance the safety with which the above are carried out.

The Access Platform (as shown in Figure 1) for the Station consists of a main platform section with extendible sections at each end; two telescoping tube assemblies which attach the Access Platform to the refueling bridge structure; and two winch hoists, each of which can raise the Access Platform. With the extendible sections fully retracted, the overall length of the Access Platform is'18 feet (excluding any wall cleaning equipment). With the platforms fully extended the overall 1ength of the Access Plaform is 36 feet. This length per-mits access of the walls of the reactor cavity at the greatest width. The design characteristics of the Access Platform are summarized in Table l. Wall-washing assemblies are mounted on the extendible platforms and can be positioned and locked at any point on the curved section of the extendible platform railing.

The high pressure spray nozzles are mounted on a vertical manifold assembly which will maintain the nozzles perpendicular to the v>all and at the distance requi red for'fficient cleaning.

Modifications to the refueling bridge structure will be made to obtain smooth bridge operation. These modifications include:

1. Floating the wheels on one platform truck to eliminate wheel binding caused by leg spread.

2. Replacement of'he existing walkway with a significantly stiffer structure, so as to afford better distribution of loads due to addition of Access Platform.

3. Replacement of existing bridge dirve torque rods with sti ffer torque tubes, eliminate wind up associated with current rods.

Some additional modifications to the refueling bridge structure are required to make it suitable for the addition of an Access Platform. These involve the ad-dition of knee braces at each end of the upper structure, the addition of winch hoist mounting structure, the addition of a horizontal brace on each end frame, and the addition of decking above the monorail. beam bracing to provide access to the platform components.

FIGURE 1 125 TON HOOK 375>-0" TRAVELING BRIDGE CRANE GIRDE 125 TON HOOK-MAX. ELEV 25 TOH HOOK BOTTOM OF CRANE BRIDGE-ELEV. 368'-l-l/2" 6'/2 HIHCHES 6 PULLEYS SHOWN SHADED TOP ELEV 362' TON AUXILIARYHOIST SERVICE CABLE FOR HOIST.

OTTOH OF FESTOONED LOOP ELEV.

363'-6-1/2'OP OF EXISTIHG REFUELIHG BRIDGE STRUCTURE-ELEV.

356' 5" NEW, STRUCTURAL MEMBERS AND NEll HECHANISH TO ACCOHODATE ACCESS PLATFORM ARE SHOWN SHADED.

EXISTIHG REFUELINE BRIDGE 5'IRUCTURE BOTTOM OF PLATFORM IH "U POSITION-ELEV. 344'-0" 8

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REFUELING SEAL PLATFORM, .a 315' 4 I/8" 'LEV.

NOTE: THIS SKETCH IS NOT TO SCALE BUT IS PROPORTIONED TO CONVEY AH IDEA OF THE ACCESS PLATFORM INSTALLATION> OPER-ATION AND THE CONTAINMENT L'~ ~ ~ BUILDING CONDITIONS.

Kl ACCESS PLATFORM FOR ADAPTION TO REFUELING STRUCTURE

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TABLE 1

1. LOAD CAPACITY Main Platform 50 lbs/sq. ft. or a concentrated load of 2000 lbs. of personnel and/or equipment.

Extension Platform 600 lbs. for each extension platform.

2. 'IFT/STROKE Lift 29 feet. {In the full "up" position the Access Platform is 4 feet above the refueling floor to permit unrestricted operation of the refueling bridge structure.)

Extension Platform Stroke 9 feet.

3. OPERATING SPEEDS Lift/Lowering Speed 40 fpm.

Extension Platform Travel 20 fpm.

Speed

4. DIMENSIONS Main Platform 156" long x 33" wide.

Extension Platform 30" long x 33" wide.

5. CONTROLS Access .Platform Controls Two control consoles: One is located on the Access Platform; the second is located on the refueling bridge structure. A selector switch determines which station is in control. Each console controls Access Platform operation, refueling bridge structure bridge motion, and extension platform operation {retraction only).

Extension Platform Each extension platform has a control console to Controls control extension/retraction motions.

6. INTERLOCKS - Up/down travel limit switches

- Cable overload interlock

- Slack cable interlock

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TA8LE 1 (Cont'd)

- Extension/retraction travel limit switches

- Extension platform travel interference switches

- Access Platform travel interference switches

7. SAFETY FEATURES Control system interlocks Dual hoist cables (each cable has a safety factor of 10 over its nominal load)

Each hoist is capable of raising the Access Platform at reduced speed for a limited time period .(maximum of 2 to 3 minutes for motor operation with full load).

NOTE: Single hoist capabili,ty is provided only to permit raising the Access Platform out of the reactor cavity in the event of a failure of one hoist winch and/or the associated controls.

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III. Structural Anal sis Analyses have been performed to determine the effect of adding the Access Plat-form to the refueling bridge structure. These analyses investigated the response of the refueling bridge structure to static and dynamic loadings, using a finite element computer code FEABL. The FEABL program allows very detailed modeling of the platform structure and calculates the deflections, translation, bending moments, and loads for each structural member defined by the model. For the Nine Nile Point refueling bridge structure, the model consisted of 109 individual members interconnected of 71 model points. The Access Platform loads were applied to. the refueling bridge structure at the locations where the telescoping tube assemblies would be attached. In the initial analysis it was assumed that only the monorail hoist beam carried the loads even though the columns were also attach-ed 'to the"refuels'ng bri.dge structure walkway. Six cases were analyzed for both static and dynamic loading (three fuel hoist trolley locations at tHo walkway load conditions). The maximum deflection occurred for the case in which the hoist and walkway loads were concentrated at the center of the platform span. This assump-tion was made because the existing walkway is a relatively limber structure. The results of the analyses indicated that the monorail beam deflection for the sever-est loading case was approximately 1.6" producing a maximum stress of 14,000 psi which is below the maximum allowable stress of 22,000 psi for the beam. However, this stress value is above the design value that is normally used for structural design (approximately 12,000 psi for Type A36 steel when a design safety factor of 1.85 is applied).

Therefore a re-analysis was performed with the Access Platform loads distributed-between the monorai 1 beam and the new walkway in-a manner whi'ch will keep the stress levels in both structures well below the A36 steel design value of 12,000 psi. The new walkway will be 2 feet wide and much stiffer than the old 3 feet.

wa'1 kway.

The structural analysis also established the'leg spread that occurred for different static and dynamic loadings with the access platform installed'he maximum change in leg spread (less than 0.75 inches) will be accommodated by the floating wheel design which provides for a lateral motion of one (1) inch. With the wheels of one truck free to move laterally, the change in leg spread produced by the shift-ing or changing refueling platform loads cannot cause "crabbing" as the refueling bridge structure moves along the rails. Consequently smoother bridge operation will be obtained.

r It has been calculated that the refueling bridge structure will not tip due to the deceleration forces produced by a sudden stop from the maximum operating speed of 20 fpm. If a sudden stop of the access platform produced deceleration lift lift forces in excess of 0.104 g a maximum of 3 to 4 inches could occur. To insure that the wheels will not off the tracks to the point where the clear the track, the platform trucks will be extended about 4 feet on the wheel'ims equipment storage pit side. Clearance between the tru'ck extension and the floor (or rail) will be controlled to limit the wheel lift. This extension also guar-antees that the refueling bridge structure will not tip for the design horizontal seismic force of 0.4 g.

IV. ~5f A Use of the Access Platform will generally enhance the safety of refueling oper-ations by simplifing access to all areas of the reactor head cavity. Operational analyses have been made which assure that the addition'f this equipment will not

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woa f~A1 i ( i d) create-interferences of any kind; eg: there will be no interference with the refueling grapple which is on the opposite side of the refueling bridge structure.

Double winches and hoist cables are employed so that failure of one would not cause an accident. Each hoist is capable of raising the platform at reduced speed. Travel interference interlocks are also provided to prohibit motion of both the access platform and the refueling bridge structure, thus providing ad-ditional operational safety.

They are as follows:

1. Prohibit outward motion of extendible, section contacted.

if an obstruction is 2,. Prohibit raising or lowering, of the platform depending on condition.

3. A signal from either 1 or 2 above prohibits motion of the refueling bridge structure.

A guality Assurance Program is established in accordance with the Ninth Supple-ment to the FSAR and ANSI 45.2. A guality Control program is also being carried out by Niagara Mohawk to ensure that the system meets Niagara Mohawk's Class I requirements as outlined in the FSAR. Therefore, the addition of the Access Platform will be consistent wi th the design of the present refueling bridge struc-ture.

To assure proper operation the platform will be shop tested before delivery to the field and will be pre-operationally tested at the site before use during actual refuelings.

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