ML20037A438
| ML20037A438 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 08/01/1975 |
| From: | Stello V Office of Nuclear Reactor Regulation |
| To: | Goller K Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001140866 | |
| Download: ML20037A438 (2) | |
Text
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Docket Nos.: 50-270/287
'I I373 l
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Karl R. Coller, Assistant Director for Operating Reactors, RL -
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. OCONEE 2 & 3 CORE LIPI POTENTIAL WITH HIGUER CORE PRESSURE DROP (TAR-1636)
Plant Name: Oconee Units'2 & 3 Docket Fos.: 50-270/237 Responsible Branch in Project Leader:. ORB-1, C. Tranmell l
Technical Review Branch Involved: Reactor Systems Branch Core Performance Branch-Review Status: Complete In accordance with the request from R. A. Purple to F. Schroeder dated June 2, 1974, the Reactor Systeas Branch and_ Core Performance Branch have reviewed the reports which vere encicsed with the request.
In Duke Power Company's letter of 1:ay 23, 1975, a discussion was submitted on the results g
of flow cciturements for Unit 2.
Avalueof111.5~percentofdesigniflow was observed as conpared to a predicted minimum flow at which lift could occur of 112.1 percent design flow; 'therefore, the predicted lift flow rensins greater than ucasured coolant flow.. In addition, a test designed.
t to determine whether or not fuel assembly lift is ~ occurring was conducted fn Unit 2 at both full flow and partial flow conditions. The licensee has stated that the test procedure was capable of verifyink core lift within
~+0.25 inches and that no movement was detected. The licensee has also indicated that no anonalies have been detected by the loose parts. monitoring systems currently in use on Units 2 and 3.
Since predicted core lift for Enit 3 is 115.1 pere'ent design flow, with neasured core flow of approximately j
112.4 percent, core lift is also not expected in Unit 3.-
j For the foregoing reasons, it is concluded that the high reactor coolant; flow does not constituta an unsafe condition. Nevertheless, the ~ 1icensee.
~
I has considered the nechanical, thernal-hydraulic, and nuclear consequences of operation with reactor coolant flow exceeding the core lift point..The licensee's analysis indicates that, should fuel assembly lift occ'ur, reseating of these lif ted assenblies during flow-reducing transients could potentially add reactivity of 0.1 percent Ak/h to the system. Ue agree with the estinate of 0.1 percent Ak/k as the :*aximum amount of reactivity that could be inserted. The effect of a sudden fasertion of this reactivity upon' core:
1 power is a " prompt jump" in power followed by a power rise with a 1ong5
~
(%60 seconds) period. The'11censee has re-analyzed the'4-pump'coastdown:
g and locked-rotor transients to evaluate the potential consequences.of such
/
a' reactivity insertion. Effects were shown to be less severe fo'r the' case N
vhich assumed assembly 111ft because the higher core flow allowed si higher
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initial DNB ratio at' the~ onset of each transient.thereby compensating.
I for the higher peak neutron power reached during the transient.-
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Should lif t occur, benic mechanical integrity and geometry will beinain-
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i tained since:
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The height of the pad which is used to locate the bottom of the v.
fuel assembly during loading and which' engages tho'biitton' plate of the assembly in sufficient to prevent lateral'movmant.
2.
Out-of-pile flow testa in a Babcock and Vilcox hot test loop e&
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showed no axini chattering notion when flow lifted the[asse:nbly.
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Oconce 1 post-irradiation inspect, ion of.the fuel atLthe'end of.
a cycle service showed no observable frotting on fuel rods at spacer finger spring locations.
-high as 109% of design flow.
Flow van reported to W as?
a The licensee has examined the potential effects of core lift upon the '.
&ms w:n :.
re=aining events in the FSAR and concludes that the increased flow' rat'sJ.
a would not cause an increased probability of occurrence of any*accidenti previously analyr.ed in the Oconce ESAR, nor would safety margissibe t
i reduced.
Consideration was also given to the'poss.ibility_of d"poition l
of the core flow bypassin' g a lifted ~ elament; however, the' licenses" con /
vould offer less resistance than the existing flow'jathlbro
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l assembly.
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9p-Although the foregoing evaluation indicates that we do not believe;r.
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thehighreactorcoolantflowconstitutesanunsafecondition7fradeoca that" dictates that an increased fuel surveillance program be adopted [diiring?
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each outage for Oconee Units 2 and 3.
f5C As a~ minimum., this surveillance)?
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chould include an examination and evaluation of the followinglitenst a's,-1.
r Fuel assembly position prior to removal.
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a ; 73 1
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g Holddown spring force and permanent deflection.
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Fuel rod fretting at spacer locations.
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Vear in the fuel assembly pad on the lower core plate.- y)
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a Anonalics observed, both in the above surveillance p
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to TR for further review.:
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