ML19337A284
| ML19337A284 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 09/03/1980 |
| From: | Baynard P FLORIDA POWER CORP. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| TAC-42266, NUDOCS 8009090442 | |
| Download: ML19337A284 (5) | |
Text
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Florida Power C O A 7 0 4 a 7 $ 0 84 September 3, 1980 File:
3-0-3-a-3 i
Mr. Robert W. Reid Branch Chief Operating Reactors Branch #4 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Subject:
Crystal River Unit 3 Docket No. 50-302 Operating License No. DPR-72 NRC Letter Dated July 1,1980 Requesting Additional Information on Fuel Assembly Holddown Springs j
Dear Mr. Reid:
By letter dated July 1,1980, you requested additional information on i
Fuel Assembly Holddown Springs for Crystal River Unit 3.
This letter responds to questions of the subject letter.
4 Should you have any questions concerning this subject, please contact this office.
Very truly yours, FLORIDA PCWER CORPORATICN Pa
. Sa rd Manager Nuclear Support Services i
Baynard(WO4)D1-1
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- r STATE OF FLORIDA i
COUNT?:0F PINELLAS P. Y. Baynard ' states that-she is the Manager, Nuclear Support Services.
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Department.of Florida Power Corporation; that she is _ authorized on the part of said company to sign and file with the Nuclear Regulatory Com-mission the information attached hereto; and that all such statements made and matters set forth therein are true and correct to the oest of her knowledge, information and belief.
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/ (f. Y.]B(ynard Subscribed and sworn to before me, a Notary F blic in and for the State and County above named, this 3rd day of September,1980.
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Notary Public Notary Public, State of Florida at Large, My Commission Expires: June 8, 1984 PYB/MAHNotary(DN-98)
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FLORIDA POWER CORPORATION RESPONSES TO NRC QUESTIONS ON HOLD 00WN SPRINGS
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Question 1:
.(If the reactor'~ ts down for refueling and the reactor 4
vessel head is off)
Examine all fuel assembly holddown N,
springs -in the core and in the spent fuel pool _.and report jh
- the number - and extent of damage - on the springs and i
affected assembly components.
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Response
.A total of 233 fuel assemblies in the core attd ~ spent fuel pools 'were examined using remote video equipment..This represents all of the fuel previously used for power operation.-
One broken holddown spring was found.
No
.other damage was observed on any other assembly or compo--
4 nent.
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. Question 2:
Provide _a discussion of the safety significance of opera-7[
ting with one or more broken springs 'in the core.
Your discussion should include, but not necessarily be limited to the' following:
d a.
Assume the holddown spring is broken, provide an estimate of the flow conditions under which the assemblies would be levitated.
(Provide the value of the force required ito lift the assembly, the flow conditions under which that force would be supplied, the' number of coolant pumps that would be in operation under such conditions, and the schedule of C
reactor operations under which such conditions might have been achieved.)
Contrarily, demonstrate the margin between the assesmbly weight and the calculated maximum applied. lift-off force, if there is such margin.
Response
An analysis was perfomed for Crystal River 3 assuming 112% design flow and no spring holddown force at the con-dition of 100% power, and also at a condition of 500*F
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isothermal.
The latter condition represents the fourth reactor coolant startup temperature.
Holddown require-ments are greatest at the lower coolant temperature.
At this limiting condition no fuel assemblies in control rod locations are expected to lift.
Open core locations re-quire from -23 ~to '+ 81 lbs. of holddown force to. prevent lift.
All broken springs observed in B&W units to date have retained at least 100 lbs. of litt force.
Thus it is not expected that fuel -assemblies with broken holddown springs will experience lift.
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Question b:
Have any loose assembly parts (i.e.,
broken springs, pieces of cladding) been observed anywhere in the primary system?
Describe your methods for loose part detection.
Are there installed noise detectors. capable of detection i
of broken springs, pieces of cladding, or vibrating 3) assemblies?
Response
There has been' only one instance of a loose assembly part at CR-3.
In March of 1978 a burnable poison rod assembly worked its way frun its nonnal position in the core to the upper tubesheet area of B-0TSG.
This incident has been previously -reported in detail to the NRC.
For this particular loose part event our loose parts monitoring system was able to detect the presence of parts in the steam generator.
The single broken holddown spring found at CR-3 was not considered to be a loose part.
The presence of two spring ~ parts would not have been detectable with the LPMS.
The LPMS used at CR3 was designed, installed and tested by B&W.
It employs strategically placed accelerometers coupled with signal conditions.
Output in the control room consists of.tlarm modules, meters, audible indica-tion and connection to a real time spectrum analyzer.
the system is fully described in B&W's Reactor Diagnostic System Instruction / Technical Manual NSR-109.
The installed loose parts monitoring system has a minimum sensitivity of detecting a.25 lbm part impacting with an energy of.5 ft-lbf. This threshold energy level permits the detection of significant impacts in the RCS.
How-ever, not all loose parts or internal component failures (i.e. broken holddown springs) will reach this energy level.
Furthermore, the background noise level at some locations tends to mask out potential loose part indica-tions.-
Therefore, each case of a loose assembly part will be slightly different depending upon type of fail-ure, impact energy level, locatien and background noise level.
CR-3 neutron noise systems, which is also described in B&W document NSR-109, is capable of detecting and indicating core internals movements.
To date there has not been indication of any assembly movement.
Question c.
Have there-been any ' excore or in-core neutron detector indications of levitatcd assesmblies?
Describe the ex-pected reactivity effects that would result from lift-off or reseating of assemblies with broken holddown springs.
What. efforts are.being utilized to detect loose assem-blies by either nuclear or mechanical monitoring devices?
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Response
There have been no indications of levitated asssemblies I!
by. either the in-com or excore neutron detectors.
As described in the response to 2a, asssemblies are not ex-pected to experience lift under any operating conditions; therefore, reactivity effects would not be_ expected.
Il Methods for detecting internals movement am described in
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the msponse to 2b.
g Question d:
Have there been any observed indications of lateral re-positioning of loose assemblies?
Describe the methods used to detect lateral asssembly motion. Described under 2a, assemblies are not expected to experience lift there-fore lateral repositioning effects are not expected.
Response
There have been no indications of loose assemblies or lateral repositioning of any kind.
Methods of detecting internals movement are described in the msponse to 2b.
As described under 2a, assemblies are not expected to experience lift, therefore, lateral repositioning effects are not expected.
Question e:
(i) Describe the degree of " worst-case" m::chanical damage that would be expected as a result of movement of a
" loose' assembly (one with a broken spring) against adjacent asssemblies, core baffle, or other core compDnents.
(ii) Discuss the results of flow tests or other experi-ments that have provided measurements of axial or lateral vibratory motion of an assembly after lift-off or that would otherwise support the response to Q 2.e(1).
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Response
As described under 2a, movement of an assembly with a broken spring is not expected.
As a
- result, no mechanical damage would be expected.
Question 3:
Provide a description of the cause of the failures and corrective action to reduce *5e likelihood of future failures at your facility.
Response
The spring failure at Crystal River 3 was caused by metal fatigue which is thought. to have propagated from a very small crack in the spring.
Attention to the possibility for this type of failure will reduce the likelihood for this type of failure in the future through improvements in spring requirements.
l Baynard(WO4)D1-1,
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