ML19344A924
| ML19344A924 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 07/20/1978 |
| From: | Moody D VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19344A923 | List: |
| References | |
| REF-GTECI-A-36, REF-GTECI-SF, TASK-A-36, TASK-OR WVY-78-68, NUDOCS 8008220592 | |
| Download: ML19344A924 (10) | |
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VERMONT YANKEE NUCLEAR POWER CORPORATION SEVENTY SEVEN GROVE STREET RuTuxo, VERMONT 05701 G.6.8.1 REPLY T O:
ENGINEERING OFFICE TURNPlKE RO Ao July 20, 1978 WESTBORO, M ass ACHUSETTS O1581 TELEPHONE 617 36 6-9 0 l t EVY 78-68 Supersedes WVY 78-63 United States Nuclear Regulatory Commission Washington, D. C.
20555 Attention: Offic'e of Nuclear Reactor Regulation
Reference:
(a) License No. DPR-28 (Docket No. 50-271)
(b) Safety Evaluation by DOL, USAEC, with the matter of VYNPC dated June 1, 1971.
(c) Letter, VYMPC to USAEC, dated July 23, 1973.
(d) Letter, VYNPC to USNRC, dated Dece=ber 30, 1975.
(e) Safety Evaluation of Amendment No, 29 dated January 28, 1977.
(f) Letter, USNRC to VYNPC, dated May 17, 1978.
(g) Letter, VYNPC to USNRC, dated July 7, 1978 (WVY 78-63).
Dear Sir:
Subject:
Control of Heavy Loads Near Spent Fuel Your letter, Reference (f), requested additional information concerning movements of heavy loads near spent fuel.
In return, VYNPC submitted a detailed response, Reference (g). We have since learned of a significant computer error which resulted in a tajor portion of another facility response being substituted in the final printout of Enclosure A to Reference (g).
In light of this problem we intend that this letter supersede Reference (g) in its entirety.
VYNPC, as part of the original safety evaluation, Reference (b),
investigated the consequences of an accidental shipping cask drop into the spent fuel pool. The results of that investigatica revealed that the bottom of the pool would lose its water tight integrity, thereby, making it difficult to taintain adequate shielding and cooling of the stored spent fuel. Furthermore, a toppling fall could conceivably damage some stored spent fuel.
~ The reactor building crane was codified, converting it into what later became knoun as a " single failure proof" crane, to prevent any load drop occurrence. Preliminary design concepts were submitted to the NRC in Reference (c), and following resolution cf further NRC concerns, the modification was installed at Vermont Yankec. A detailed description, Reference (d) was sub=itted, which ultimately rcceived NEC approval via Reference (e).
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United States Nuclear Regulatory Commission July 20, 1978 Attn: Office of Nuclear Reactor Regulation Page Two Enclosure A provides the information requested in Reference (f),
as clarified by celephone conversation with Mr. James A. Long of your staff.
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION 1
4 D. E. Mo dy Manager of Operations RHG/kg w
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ENCLOSURE A VYNPC Responses to NRC Requests Question No. 1 Provide a diagram which ' illustrates the physical relation between the reactor core, the fuel
- rans fer canal, the spent fuel storage pool and the set down, receiving or storage areas for any heavy loads moved on the refueling floor.
Res pons e -
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 trans fer canal. The. fuel is moved from tne reactor vessel well through a refueling gate directly into the spent fuel pool.
It can be readily seen tnat in no instance is heavy load movement across either the spent fuel storage pool or the open reactor vessel required.
Question No. 2 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, pivvide its approximate weight and size, a diagram of the movement path utilized (including carrying height) and the frequency of movement.
Res pons e In the course of preparing the reactor for refueling, the following equipment is removed and moved directly to its respective laydown position in tne 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 anc 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
- plugs installed. The steam separator is still in place and the reactor core is not exposco. 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 storage pool. This trough tends to catch any crud f alling from the fuel bundle as it moves through the water toward the storage pool and facilitates reactor pool cleanup.
6.
The steam separator is unoolted and removed to its laydown position in the storage pool as the water level is slowly raised.
1' 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 exposed. Following Step 7, the reactor is ready for movement of fuel.
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 infrequent and conducted in accordance with special procedures which were generated prior to the task.
When the fuel movement is completed, the reactor components are reassembled in the reverse order to that described above.
This sequence of events is provided to illustrate that no heavy j ~
loads are ever carried over the open reactor vessel.
In addition, crane operating procedures specifically prohibit the movement of heavy loads over tne stored spent-fuel.
Question No. 3 4
What are tne dimensions and weights of the spent fuel casks that are or will ce useo at your facility?
Res po ns e Reference (d) points out that no spent fuel shipping cask has yet been chosen and no description is available. Tne capacity of the crane is now 110 tons, anc 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 chosen. Prior to using any cask, a description of the cask and its lifting
' fixture will be subaitted for approval as required by Reference (e).
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Ques tion No. 4 -
Identify any heavy load or cask drop analyses performed to date for your f acility. Provide a copy of all such analyses not previously submitted to the NRC staff.
Response
Cask drop analyses were performed by the Nuclear Services 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 for the safe shutdown of a plant that is operating at the time the load is moved.
Identify what equipment could be.af fected 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.
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Response
1 Vermont Yankee is a single reactor plant, consequently, the covement of heavy loads associated wita refueling will only occur when the reactor plant is shut cown. Although no fuel shipments are pos tula ted for the near future, the plant design is suen that fuel shipments could be made when the reactor is operating.
It is the opinion of VfN?C that the single failure proof crane described in Reference (d), ef fectively answers the concern about dropping a fuel snipping 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 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.
Res ponse,
The. normal path of a fuel shipping cask as shown in Reference (d) does not pass over the storea spent fuel or the reactor vessel. The narrative cescription explains how rail stops are provided to prevent the inadve rt e nt passage of a fuel cask over the stored spent fuel. Heavy weights associated with refueling such as shielding blocks, reactor head, and drywell cover are not carried over the fuel pool on the way to their laydown location. Reactor internals go directly to the separator storage pool.
As a result,- no handling accident which would result in water leakage
sufficient to uncover the spent fuel needs consideration.
Ques tion No. 7 -
Describe any design features of your facility which af fect the potential for a heavy load handling accident involving spent fuel, e.g.,
utilization of a single failure-proof crane.
Res po ns e The single failure proof crane is described in detail in Reference (d).
Question ho. 8 o
Provide copies of all procedures currently in ef fect at your facility for the movement of heavy loads over the reactor core during refueling, the spent fuel s torage pool, or equipment required for the safe shutdr.n of a plant that is operating at the time the move occurs.
Res po ns e VYNPC does not move heavy loads over the open reactor vessel during refueling or over the spent fuel storage pool at any t ime.
Comple te refueling procedures are available at the plant for your inspection. Since Vermont Yankee is a single unit plant, it is assumed the last state =ent does not apply.
Question No. 9 Discuss the degree to which your facility cocplies with the eight (8) regulatory positions delineated.in Regulatory Guide 1.13.
Response
Regulatory Pos ition 1 The spent fuel s torage facility (including its structures and equipment except as noted in paragrsph 6 below) should be designed to Category I seismic requirements.
Res pons e:
The' spent fuel storage facility is locatea 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 Pos ition 2 -
The facility should be designed (a) to keep tornadic winds and
s missiles generated by these winds from causing significant loss of watertight integrity of the fuel storage pool and (b) to keep missiles generated by tornadic winds from contacting fuel within the pool.
4 Res pons e:
Tne reactor building containing the fuel pool was designed and built to meet the requirements specified in (a) but since the reactor building i
above the level of the refueling floor is a steel frame covered with corrugated metal siding, no additional missile protection as suggested in
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(b) above is provideo.
Regulatory Position 3 Interlocks should be provided to prevent cranes from passing over stored fuel (or near stored f 31 in a manner such that if a crane failed, the load could tip over on stored 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 minimize the need f or bypassing such interlocks.
Res po ns e :
The reactor building crane is the only crane with capacity for nandling heavy loads which pass over the spent fuel pool.
Reference (d) describes tne mechanical rail stops which prevent a cask from being inadvertently moved over s tored spent fuel. This feature provides an additional safeguard to the redundant load bearing components of the " single f ailure proof" crane.
'ahen snipping casks are not being moved, the stops can be retracted to allow trolley movement along the crane bridge. This allows. the use of the auxiliary hoist of the reactor building crane to move new fuel f rom shipping crates to inspection stand, to storage, and ultimately j
to the pool wnere it is then handled by the lesser capacity fuel handling c ra nes. Additionally, when fuel handling is not in progress such as during refueling preparation, movement of the crane trolley along the full length of the briage is required. Examination of the attacheo drawing will clearly explain this requirement. At this time, movements of heavy loads over the
. pool is prchibited by administrative ' control. No interlocks are provided.
Regulatory Position 4 A controlled leakage building should enclose the fuel pool. The
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building should be equipped with an appropriate ventilation and-filtration system to limit the potential release of radioactive iodine and other radioact ive ma terials. The building need not be designed to withstand extremely high winds, but leakage should be suitably controlled during 4
refueling operations. The cesign of the ventilation and filtration system should be based on the assumption that the cladding of all of the fuel rods
4 in one fuel bunale might 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 Storage Facility for Boiling and Pressurized Water Reactors" (Safety Guide 25).
Response
The spent fuel storage pool is entirely within the reactor building which is equipped with an appropriate ventilation system to limit the release of iodine and other radioactive subs tances. This system is described in detail in the Vermont Yankee FS AR.
The system design is based on the assumptions stated above.
Regulatory Position 5 The spent fuel storage facility should have at least one of the following provisions with respect to the hanaling of heavy loads, including the refueling cask:
Cranes capaole of carrying heavy loads should be prevented, preferrably a.
by design rather than by interlocks, from moving into the vicinity 4
of the pool; or b.
Cranes should be designed to provide single-failure proof handling of heavy leads, so that a single failure will not result in loss of capability of the crane-handling system to perform its safety function; or The fuel pool should be designed to withstand, without leakage that l
c.
could uncover the fuel, the icpact of the heaviest load to be carried by the crane from the maximum height to which it can be lifted.
If this approach is used, design provisions should be cade to prevent the crane, when carrying heavy loads, from moving in the vicinity of stored fuel.
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Response
The single failure proof crane described in Reference (d) meets the requirements of Sb.
Rgilatory Position 6 Drains, permanently connected mechanical or hydraulic systems, and other features that by maloperation or failure.could cause loss of coolant that would uncover fuel shoulc not be installed or included in the design.
Systems for maintaining water quality and quantity should be designed so
- that any maloperation or failure of such systems (including failures resulting frou the Sale Shutdown Earthquake) will not cause fuel to be
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uncove red. These systems need not otherwise meet Category I seismic requirements.
Response
The spent fuel storage pool and the fuel pool cooling and 4
demineralizer system is described in detail in the Vermont Yankee FS AR.
No inlets, outlets or drains are provided that might permit the pool to be drained to a level belev 10 feet above the top of the active fuel.
Regulatory Position 7 j
Reliable and frequently tested monitoring equipment should be provided to alarm both locally and in a continuously manned location if the water level in the fuel storage 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
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High and low level detectors are provided which monitor the water level in the spent fuel pool and alarm in the main control room. Area radiation monitors (ARM) are placed strategically throughout the reactor building with.at least one in the area of the spent fuel pool. ARM's trip both upscale and.'own and alarm in the main control roco. A detailed d
description of this sys tem is given in the Vermont Yankee FS AR.
Automa t ic f
actuation of the filtration system is initiated by a high radiation level in the building ventilation system.
Regula tory Pos ition 8 -
l A seismic Category I makeup system should be provided to add coolant I
to the pool. Appropriate redundancy or a backup system for filling the pool from a reliable source, such as a lake, river, or onsite seismic Category 1 water-storage facility, should be provided.
If a backup system 4
is used, it need not be a permanently installed sys tem.
The capacity of the makeup systems should be such that water can be supplied at a rate detennined by consideration of the leakage rate enat would be expected as the result of damage to t'.e fuel storage pool froa the dropping of loads, I
f rom eartnquakes, or frca missiles originatin; in high winds.*
- The'staf f is considering tne development of additional guidance concerning
-protection against missiles that. might be generated by plant-failures such as turbine failures.
for the present, the protection of the fuel pool agains t,such missiles will be evaluated on a case-by-case basis.
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Response
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1 Normal makeup to the pool is provided from the seismic Category I condensate storage tanks oy the condensate transfer syste:n which is not designed to meet 'the requirements of seismic Category I.
Means are available to make up.to the pool from the Connecticut River using the fire systen or the seismic Category I service water system. The expected leakage rate from missiles has not been calculated.
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