ML19344A922

Forwards Responses to 780517 Ltr Re Control of Heavy Loads Near Spent Fuel

ML19344A922
Person / Time
Site:	Vermont Yankee
Issue date:	07/07/1978
From:	Moody D VERMONT YANKEE NUCLEAR POWER CORP.
To:	Office of Nuclear Reactor Regulation
Shared Package
ML19344A923	List: ML19344A922 ML19344A924
References
REF-GTECI-A-36, REF-GTECI-SF, TASK-A-36, TASK-OR WVY-78-63, NUDOCS 8008220591
Download: ML19344A922 (11)

Text

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VERMONT Y AN KEE NUCLEAR POWER CORPORATION SEVENTY SEVEN GROVE STREET ,

RL'TL AND, YE R >t O NT 05701 REPLY TO:

ENGINEERING OFFICE TURNPIKE RO AD WESTBORO, M ASS ACHUsETTS 01581

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THIS DOCUMENT CONTAINS WY 78-63 P00R QUAUTY PAGES IMS G.6.8.1 July 7,1978 United States Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Office of Nuclear Reactor Regulation Ref e rences: (a) License No. DPR-26 (Docket No. 50-271).

(b) Safety Evaluation by DOL, USAdC, with the matter of VYNPC da ted June 1, 19 71.

(c) Letter VYNPC to US AEC dated July 23, 1973.

(d) Letter VYNPC to USNRC dated December 30, 1975.

(e) Safety Evaluation of Amendment No. 29 dated January 28, 1977.

(f) Letter USSRC to VYNPC dated May 17, 1978.

Enclosure:

(A) VYNPC Responses to NdC Requests.

Subject:

Control of Heavy Loads Near Spent Fuel in response to ref erence (f), the Vermont Yankee Nuclear Power Corporation (VYNPC) wishes to provide the following information.

As part of the original saf ety evaluation (Reference (b)), VY hTC investigated the consequences of accidentally dropping a fuel shipping cask into the spent fuel pool. The results of that investigation disclosed that the- bottom of tne pool would lose its water tight integrity making it difficult to maintain adequate shielding and cooling of the stored spent fuel. In addition, a toppling f all could conceivably damage some stored s pe nt fuel.

As a method of preventing any load drop occurrence, VYNPC modified tL reactor building crane, converting it into what later became known as a " single failure proof" crane. Preliminary design concepts were submitted to the NRC in Reference (c), and af ter resolution of certain NRC coacerns, 87XBEtos7 s.

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the modification ~ was ins talled at Ver: ant Yankee. A detailed description, Reference-~(d), was submitted with final NRC approval received via Ref erence

-(e).

Following receipt of your request for information, Reference (f),

telephone conversations with Jaces A. Long of your staf f provided additional clarification. Our response to your request for -information is included as Enclosure A.

Very truly yours, VERMCNT YANKEE NUCLEAR POWER CDRPORATION j

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- 1g D. E. Moo Mar.ager of Operations

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. ENCLOSURE A 4 VfNPC Responses to NRC Requests s -

- Question No. 1

. Provide a diagram which illustrates the physical relation between the reactor core, the fuel transfer canal, the spent fuel storage pool and the set down, receiving or storage areas for any heavy loads moved on the refueling floor.

Response

The attached diagram illustrates the relationship between the reactor core, spent fuel storage pool and the set down, receiving and storage areas for various heavy components moved during refueling. Vermont Yankee has no fuel transfer canal. The fuel is coved from the reactor vessel well through a refueling gate directly into the spent fuel pool.

4 It can be- readily seen that in no instance is heavy load movement across either the spent fuel storage pool or the open reactor vessel required.

Question No. 2 l Provide a list of all objects that are required to be moved over the reactor core (during refueling), or the spent fuel storage pool. For each object listed, provide its approximate weight and size, a diagram of the movement path utilized (including carrying height) and the f requency of movement.

Response

, In the course of preptring the reactor for refueling, the following equipment is removed and moved directly to its respective laydown position

in the following sequence.

1.- The reactor shield plugs, the pool plugs, and the refueling slot plugs.

2. The 'drywell head.

3. :The reactor vessel head insulation.

- 4. The reactor vessel head (at this point in the process the reactor vessel is open and the steam dryer-separator package is exposed.)

5.. Next the dryer assembly is removed and stored in the storage pool.

The personnel basket is' lowered into the vessel and the steam line e -- , . , . . , _ , "_ . . . , _ . . _ . __ _

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plugs installed. The steam separator is still in place and the reactor .

core is not exposed. At this time, a light metal trough called the " Cattle I' Chute" is placed on the reactor pool floor under the path taken by the fuel -

moving from the vessel to the storage pool. This trough tends to catch any crud f alling f rom the fuel bundle as it moves through the water toward '

the storage pool and f acilitates reactor pool cleanup.

6. . The steam separator is unbolted and removed to its laydown position in. the storage pool as the water level is slowly raised.

7. Once the water level in the reactor well is equal to the spent fuel storage pool level, the fuel pool gates are removed to their storage position on the north wall of the pool.

Until Step 6 is complete, the fuel in the reactor vessel is never of fuel.

exposed. Following Step 7, the reactor is ready for movement In the course of moving fuel between the spent fuel pool and the reactor vessel, no heavy equipment is moved over the vessel or the stored fuel except the refueling platform itself.

Upon occasion, special inspections or repairs in the reactor vessel require the use of a light weight aluminum in-vessel service platform.

In conjunction with this operation lead wool blankets for shielding are hung by slings from the vessel studs. These unusual operations are inf requent and conducted in accordance with special procedures which were generated prior to the task.

When the fuel movement is completed, the reactor components are reasseculed in the reverse order to that described above.

Thi4 sequence of events is provided to illustrate that no heavy loads are ever carried over the open reactor vessel. In addition, crane operating procedures specifically prohibit the movement of heavy loads over ,

the stored spent fuel.

Question No. 3 What are the dimensions and weights of the spent fuel casks that are or will be used at your facility?

Response

Reference (d) points out that no spent fuel shipping cask has yet been chosen and no description is available. The capacity of the crane is now 110 tons, ana the vertical clearance between the hook in its upper position and the reactor operating floor is approximately 24 feet. These

. provide the weight and size limits of any cask that could ultimately be cnosen. Prior to using any cask, a description of'the cask and its lifting fixture will be submitted for approval as required by Reference (e).

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M Ques tion No. 4 Identify any heavy load or cask drop analyses perforned to date f or your facility. Provide a copy of all such analyses not previously submitted to the NKC s taf f.

, - Res ponse d

Cask drop analyses were perforced by the Nuclear Scrvices Division of the Yankee Atomic Electric Company and are retained in the files. The results of these analyses led to the single failure proof crane modification.

Ques tion No. 5 Identify any heavy loads that are carried over equipment required f or the saf e shutdown of a plant that is operating at the time the load is moved. Identify what eq uipment could be affected in the event of a heavy load handling accident (piping, cabling, pumps, etc.) and discuss the ,

f easibility of such an accident affecting this equipment. Describe the basis for your conclusions.

Response

Vermont Yankee is a single reactor plant, consequently, the movenent of heavy loads associated with refueling will only occur when the reactcr

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plant is shut.down. Although no fuel shipments are postulated for the near

' . f uture, the plant design is such that fuel shipments could be made when the reactor is operating. It is the opinion of VYNFC that the single failure proof crane described in Reference (d), ef fectively answers the concern about dropping a ' fuel shipping cask anywhere in the reactor building. As a result, no ' additional accident analysis has been performed.

- question No. 6 If heavy loads are required to be carried over the spent fuel storage j

pool or fuel transfer canal at your facility, discuss the feasibility of a handling accident which could result in water leakage severe enough to uncove r the spent fuel. Describe the basis for your conclusions.

. Response a

The normal- path of a ' fuel shipping cask as shown in Reference (d) i does not pass over 'the . stored spent fuel or the reactor vessel. The narrative description explains how rail s tops are provided to prevent the

inadvertent passage of a fuel cask over the stored spent fuel. Heavy weights associated with ref ueling such as shielding blocks, reactor head, and drywell

', cover loca tion. are not- carried over the fuel pool on the way to their laydown Reactor internals go directly to the separator storage pool.

As a result, no handling accident which would result in water leakage e

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sufficient to uncover the spent fuel needs consideration.

Question No. 7 Describe any design features of your facility which affect the potential for a heavy load handling accident involving spent fuel, e.g.,

utilization of a single failure proof crape.

Response

The single failure proof crane .is described in detail- in Reference (d).

Ques tion No. 8 Provide copies of all procedures currently in ef fect at your facility for the movement of heavy loads over the reactor core during refueling, y the spent fuel storage pool, or equipment required for the safe shutdown of a plant that is operating at the time the move occurs.

Response

VYNPC does not move heavy loads over the open reactor vessel during refueling or over the spent fuel storage pool at any time. Complete refueling procedures are available at the plant for your inspection. Since Vermont Yankee is a single unit plant, it is assumed the last statement does not apply.

Question No. 9 Discuss the degree to which your facility complies with the eight (8) regulatory positions delineated in Regulatory Guide 1.13.

Res pons e:

Regulatory Position 1 The spent fuel storage facility (including its structures and equipment except as noted in paragraph 6 below) should be designed to Category 1 seismic requirements.

Response

The spent fuel storage facility is located within the reactor building and both are designed to seismic category 1. Details of this design are available in the Vermont Yankee FS AR.

Regulatory Position 2 1

The facility should be designed (a) to keep tornadic winds and 1

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missiles generated by these winds f rom causing significant loss of watertight integrity of the' fuel s torage pool and (b) to keep missiles generated by tornadic winds from contacting fuel within the pool.

Response

The reactor building containing the fuel pool was designed and built

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to meet the requirements specified in (a) but core is not exposed. At this time, a light metal trough called the " Cattle Chute" is placed on the reactor pool floor under the path .taken by the fuel moving from the vessel to the s torage pool. This trough tends to catch any crud f alling f rom the fuel bundle as it moves through the water toward the storage pool and facilitates reactor pool cleanup.

6. The steam separator is unbolted and removed to its laydown position in the storage pool as the water level is slowly raised.

o 7. Once the water level in the reactor well is equal to the spent fuel storage pool level, the fuel pool gates are removed to their storage position on the north wall of the ground level pool with a stainless steel liner so this calculated leak rate appears logical. Existing installed systems can easily cakeup a water loss of this magnitude.

The calculations are in our files and available for your review.

5. Identify any heavy loads that are carried over equipment required for the safe shutdown of a plant that is operating at the time the load is moved. Identify what equipment could be affected in the event of a heavy load handling accident (piping, cabling, pumps, etc.) and discuss the feasibility of such an accident affecting this equipment.

Describe the basis for your conclusions.

Response

lain Yankee is a single unit plant. Heavy loads associated with

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re ueling are never moved until the reactor is shut down. Reference (c) explains that the yard area crane does not pass over systems or equipment required for safety.

6. If heavy loads are required to be carried over the spent fuel storage pool or fuel transfer canal at your f acility, discuss the feasibility

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of a handling accident which could result in water leakage severe enough to uncover the spent fuel. Describe the basis for your conclusions.

Response

The yard area crane which spans the spent fuel s torage pool is equipped with crane travel interlocks to prevent its travel over the stored spent fuel as well as the fuel transfer canal. Examination of the drawings referenced in (1) above will show that the reactor containnent I

polar crane does not pass over the fuel transfer canal. During the movement of heavy loads associated with refueling in the containnent, the fuel transfer canal is isolated by a valve located.in the fuel building. Maine Yankee believes that the possibility of a handling accident which _ could result in water leakage severe 'enough to uncover the' stored spent fuel is extremely remote.

7. Describe any design features of your facility which affect the potential

- for. a heavy ~ load handling accident involving spent fuel, e.g.,

utilization of a single failure proof crane.

Response

Reference (d) describes- the codifications to the yard area crane to prevent a load handling accident involving spent fuel. Essentially, the use'of redundant brakes and redundant upper limit switches, in addition to overload and overspeed trips, minimize the probability of a heavy load handling accicent. Interlocks prevent crane travel over the stored spent fuel.

8. Provide copies of all procedures currently in ef fect at your facility for the novement of aheavy loads over the reactor core during refueling, the spent fuel storage pool, or equipment required for the safe shutdown

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of a plant that is operating at the tine the move occurs.

Response

Maine Yankee does not move heavy loads over the open reactor vessel during refueling. The response to request no. 2 above discusses t'c.e removal, storage and replacement of the reactor head and upper core internals.

The movement of these objects are covered in the overall refueline procedures which are on file at the plant and available for your review.

Heavy ' loads are not moved over the spent fuel storage pool so no procedures are required. Crnne bridge and trolley interlocks prevent inadvertent - travel over the ipent fuel.

9.. Discuss the degree to which your facility complies with the eight (8) regulatory positions delineated in Regulatory Guide 1.13 (Revision 1, Decenoer,1975) regarding Spent Fuel. Storage Facility Design Basis.

Regulatory Position No. 1 and 2

1. .The spent fuel storage facility (including its structures and equipment except as noted in paragraph 6 below) should be designed to Category I seismic requirements.

. 2. . The facility should be designed (a) to keep tornadic winds and missiles generated ' by- these winds from causing significant loss of watertight

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O integrity of the fuel storage pool and (b) to keep missiles generated 4 by tornadic winds from contacting fuel within the pool.

Response

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The(Maine Yankee FSAR states:

"The pool is designed to resist safely the hypothetical earthquake

. or tornado, as well as the applied loads 'of the water and fuel. In addition, the steel f raming above the pool is designed for earthquake and tornado to prevent it from f alling into the pool and damaging any fuel assemblies."

The fuel building above the pool is enclosed in corrugated metal siding and no additional protection against externally generated missiles damaging stored spent fuel is provided.

Regulatory Position No. 3 ,

3. Interlocks should be provided to prevent cranes from passing over stored

. fuel (or near stored f uel in a manner such that if a crane failed, the load could tip over on storec fuel) when fuel handling is not in

, progress. During fuel handling operations, the interlocks may be bypassed and administrative control used to prevent the crane from carrying loads that are not necessary for fuel handling over the stored fuel or other prohibited areas. The facility should be designed to cinimize the need for bypassing such interlocks.

1 kesponse:

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. Electrical ; terlocks are provided to prevent the crane from passing over the store; spent fuel at all times. Bypassing the interlocks is not required during fuel handling operations.

,Fegulatory Position No. 4

4. A controlled leakage building should enclose the fuel pool. The

! building snould be equipped with an appropriate ventilation and filtration system to -limit the potential release of radioactive iodine

! and other radioactive materials. The building need not be designed to withstand extremely high winds, but leakage should be suitably controlled during refueling operations. The design of the ventilation and filtration system should be based on the assumption that the

cladding of all of the fuel rods in one fuel bundle night be breached.

The ' inventory of ' radioactive caterials available for leakage from the building should be based on the assumptions given in Regulatory Guide 1.25, " Assumptions Used for Evaluating the Potential Radiological Consequences of a Fuel Handling Accident in the Fuel Handling and

, Storade Facility for Boiling and Pressurized Water Reactors" (Safety Guide 25).

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Response

The Maine Yankee fuel building is equipped with a ventilation / filtration sys tem to limit the release of radioactive iodine and other radioactive ma te rials. The system design is based on the assumptions of regulatory position C.4 of Regulatory Guide 1.13.

Regulatory Position No. 5

5. The spent fuel storage facility should have at least one of the following provisions with respect to the landling of heavy loads, including the ref ueling cask:

a. Crancs capable of carrying heavy loads should be prevented, preferrably by design rather than by interlocks, from moving into

, the vicinity of the pool; or

b. Cranes should be designed to provide single-failure proof handling of heavy loads, so that a single failure will not result in loss of capability of the crane-handling system to perform its safety tunction; or

c. The fuel pool should be designed to withstand, without leakage that could uncover the fuel, the impact of the heaviest load to be carried by the crane from the maximum height to which it can Se lifted. If ' his approach is used, design provisions should be made to prever% the crane, when carrying heavy loads, fron moving in the vicinity of stored f uel.

Response

The results of the analysis performed for a cask drop into the spent fuci storage pool, described in response number 4 above, show that the leakage resulting will be easily within make-up capability and the fuel will not be uncovered. The yard area crane spans the fuel storage pool, however, and is presented f rom traveling over the fuel by crane travel interlocks.

Regulatory Position No. 6

b. Drains, permanently connected nechanical or hydraulic systems, and other features ti.at by maloperation or failure could cause loss of coola nt that would uncover fuel should not be installed or included in the design. Systems for maintaining water quality and quantity should be desJd ned so that any maloperation or f ailure of such systems (including f411ures resultind from the Safe Shutdown Earthquake) will not cause fuel to be uncovered. These systems need not otherwise meet

. Category I seismic requirements.

6.

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Response

The Maine Yankee fuel storage pool meets these requirements. The re g are no drains installed in the pool. Examination of Section 9.8 and its associated flow diagram in the Maine Yankee FS AR shows that the l suctions for the skimmer punps, the cooling pumps, and the purification pumps, are all taken from the upper three feet of the fuel pool water. .

Piping is ins talled to pump out the pool but its use requires the deliberate manual installation of a blind flange.

Redulatory Position No. 7 ,

7. Reliable and f requently tested monitoring equipment should be provided l to ala ra both locally and in a continuously nanned location if the water level in the fuel s torage pool f alls below a predetermined level or if high local-radiation levels are experienced. The high-radiation-level instrumentation should also actuate the filtration system.

Response

High and low level detectors are provided which alarm in the control roon. Radiation uonitors are provided which alarn locally and in the main control room. The ventilation filtration system is not initiated by a high radiation signal.

Regulatory Position No. 8

8. A seiscic Category I makeup systen should be provided to add coolant to the pool. Appropriate redundancy or a backup system for filling the pool f rou a reliable source, such as a lake, river, or onsite seisaic Category I water-storage facility, should be provided. If a oackup system is used, it need not be a pe rmanently installed system.

The capacity of the makeup systems should be such that water can be supplied at a rate determined by consideration of the leakage rate tnat would be expected as the result of damage to the fuel storage pool f rom the dropping of loaos, f rom earthquakes, or f rom missiles originating in high winds.

Response

Makeup to the spent fuel storage paal is provided f roa the charging and volume control system. The connecting piping is not seismic Category I. Additional makeup capability is available from the condensate storage tank or the fire system via hoses. The available capacity of each of these systens greatly exceeds the expected leakage rate, i

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