ML19343C680
| ML19343C680 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/23/1981 |
| From: | Shaw H Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17193B241 | List: |
| References | |
| NUDOCS 8103250022 | |
| Download: ML19343C680 (5) | |
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t UNITED STATES OF AMERICA i
NUCLEAR REGULATORY COMMISSION
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In the Matter of
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Docket Nos. 50-237
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and 50-249 i
COMMONWEALTH EDIS0N COMPANY
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(Spent Fuel Pool Modification)
(Dresden Station, Units 2 and 3)
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j SUPPLEMENTAL TESTIMONY OF HORACE K. SHAN ON FUEL CHANNEL B0 WING i
I am employed as a Senior Mechanical Engineer, Division of Licensing, Office i
of Nuclear Reactor Regulation, United States Nuclear Regulatory Commission.
A statement of my professional qualifications is attached to this testimony.
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Introduction The-purpose of this testimony is to present the results of the NRC review of Applicant's testimony concerning potential interference resulting between surfaces where certain fuel assemblies ~with large total deformations (bulge i
d plus bow), which are to be stored in certain minimal-size storage locations within the proposed Dresden spent fuel racks.
Description The Dresden Nuclear Power Plant Units 2 and 3 have proposed a spent fuel rack modification to accomplish high density spent fuel storage. New racks will l
l be of 9x11-and 9x13-array configuration and will be fabricated by spacing l
stainless steel tubes at specific pitches. Because of the tolerances permitted in the fabrication process, dimensional deviations in the pitch would develop; some storage locations will'be smaller than others.
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810s260 O N
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. i Spent fuel assemblies are deforced. During nor al reactor oceration, r.eutron flux tends to produce bewing of the fuel channel box and pressure differential across channel walls induced by core coolant flow tends to procuce bulge deformation in fuel channels.
Concern has thus been raised as to the ;;ssiole interference between tne defor ed fuel assembly cnannel box and tne storage rack walls khat may develop during insertion or withdrawal of a defor e:: #uel assembly into or from a minimal-size storace location. Two possible inter-ferences have been identified.
The first possible interference may develop betw en the wall of the fuel channel in mid-scan where the total (bulge and bow) defor ation is at a maximur, and that of the storage location.
The second possible interference may exist at the top of a mininal size storage location where the lead-in clip further reduces the size of the opening. Our evaluation will assure the worst corbination of dimensional interferences.
Discussion The Cormonwealth Edison Company has reasured the inside dirensions of so e storage location openings. Measure ents taken from four 9xil array racks currently stored in the Dresden facility indicated that only one storage rack location measures less than 5.74".
The reasured dimension is 5.729" with an accuracy of 1 0.01".
Efforts were also made to reasure 1735 channel sides.
The total (bulge and bow) deformation found was not rore than 0.15" and 0.2" respectively for 86' and 94.5% of all the channel sides ceasured. Only 15
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' sides have total deformations greater than 0.3".
The greatest total deformation reading was foJnd to be 0.43" (once) and the next greatest reading was found to
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be 0.39" (once). With the conservative assumption that the centrally situated channel with the greatest total deformation is in the smallest storage location,
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i maxiaum interferences of 0.25" may exist at the mid-span of the channel, and t
l 0..cJ" may exist at the lead-in Clips.
Forces required to overcome drag t
3used by these interferences were estimated conservatively to be 310 lbs.
and 200 lbs., respectively.
Fuel assemblies are inserted into storage locations by their own weights.
Since each fuel assembly weighs 680 lbs. and will produce about 600 lbs.
l gravitational force even when it is fully submerged in water, there should F
i be no other force required to insert the worst deformed fuel assembly into the -smallest storage location. No extraordinary loadings will be experienced.
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by the load handling system.
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To withdraw this fuel assembly from the storage location, however, the handling
~ system must produce forces to overcome the gravitational force caused by the i
' weight of the fuel assembly as well as the drag force caused by the inter-i ferences. The maximum force is thus estimated to be 1190 lbs. This is well-L I
within the capability of. the handling system. Analyses also indicated that i
stress level caused by this loading is below design for all components in r
the handling system. The structural integrity of the storage racks and fuel
. i, assemblies werefalso checked and found to be within the design capabilities.
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. Drag forces will be proportionally greater if actual interferences should be greater than the assumed figures. However, assuming the total deformation is 0.50" instead of 0.43" drag force will increase to 409 lbs. instead of 310 lbs.
Even this unlikely deformation will not change the analytical results substantially.
The Dresden facility currently is or shortly will be irple-menting the following procedures:
a.
Channel boxes manufactured using a new heat treatment and fabrication process resulting in more dimensional stability for these channels will be used.
b.
A screening process which will eliminate channels with large total deformation from further service.
c.
An operating procedure which describes actions to be taken in case a fuel assembly is stuck in a storage location.
Conclusion l
Based on the above evaluation, it is the conclusion of the NRC staff that the concern raised regarding interference developed between walls of fuel l
assemblies and storage locations within the proposed Dresden spent fuel l
racks does not represent a safety problem.
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HORACE K. SH4W Professional Experiences:
Senior Mechanical Engineer, UStiRC, 1974-present Specialist-Research, Member of Technical Staff, Atomics International Div., Rockwell International Corp., 1965-1974 Consultant, Private Practice, 1964-1965 Project Engineer, Johnson and Johnson, 1955-1964 Design Engineer, Koppers Company, 1952-1955 Research Fellow, University of Washington, 1949-1950 Plant ".agineer, Chinese Petroleum Corp., 1945-1948 Staff Engineer, Tzu-Yu Iron and Steel Works, 1943-1945 Educational Backcround fiational Central University, China, BSME,1943 University of Washington, Seattle, MSME,1950 Registered Professional Engineer in Illinois