ML20037B646
| ML20037B646 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/02/1962 |
| From: | Wade I COMMONWEALTH EDISON CO. |
| To: | Lowenstein R US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8010270590 | |
| Download: ML20037B646 (12) | |
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t March 2, 1962 Mr. Robert Lowenstein, Director Division of Licensing and Regulation U. S. Atomic 2nergy Commission Washington 25, D.
C.
Jear Mr. Lowenstein:
Pursuan; to paragraph 3.a.(h) of License !?2-2, as anended, Connon-weal:n Idison Company roquesta tai; itas "3.
29 er7ina:iar of
':snimum '.ea e t er ?ror" of 3ection 2
?C'?I2 0 ??'_c ? c :1 ( a s redesi;nated pursuan; :o.imancmen; Jo. h of she appl ca: ton catec January :, 1962, for amendment af appendia a to
?2-2) ce anendad to read in 1 s antiretys "The maximum reactor power is defined as snat ther:21 power at whic: :ne saziaum nea; flu far any fuel rod is riacaed.
This uaminum hea; flux, saasd on calcula; ions an: 2 p a r i- ~ ~~
- cn;al da
- a, will nevar 2 :ssa th2 followin; values in 3;u/(hr)( sq f t):
Juel ?ype !
500,0CC
?;el Type ??-l :nrouin ??-u 395,000 Fuel Type ??-3 :nrough ??-9 330,000
~ " ' ' -
Juel Type ??-10, 11, and 12 640,000 s
"The perk rated heat flux and resulting rated power ar A than set to 80% of their maximum values and, as indicated in N D '
item 3.9, the hign neutron flux scram setting will be no higher than an indicated 120% of the rated reactor power.
However, in no case will the high neutron flux setting me allowed to exceed as iadicated reactor thermal power of 782 Mw (125% of the planned operational power of the fully loaded core).
"The reactor will be operated within the above limits such that a minimum ournout ratio of at least 2.0 will be maic-tained in each type of fuwl closest to burnout in the hottest channel in the core based on a uniform steam quality over the cross section of the channel."
In accordance with paragraph 3.a(b) of LPR-2, a Joacription and Hazards Evaluation Report of the rsquested amendment is attached hereto.
Submitted and sworn to oefore me this C r day of March, 1962 COMMONW3ALTH 3DISON COMPAN'?
by said I. L.
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801027059 0 Y/
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Notary Puolic Administrative Engineer t_
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a SUPP MfIEG IEFtmekTI S AED EAf.AED ETALUATI M O-I RESPECTI M TER APPLICATION F W
.T IECERASE IE ERAT FLUE LDETB
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February 26, 1962 CUQ.
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IETRODUCTIN:
The current limit of heat flux as specified in License DPR-2 for the Dresden ' type I fuel is 350,000 stu/hr-sq ft.
'!his linitation was of necessity established at this ecnservative level because of the pre 14=i=7 nature of the internation available at the time operation of Dresden ccamenced. The additienal intcmaticn from a number of scurces which is ncy available shows that an increase in heat Cux can be ac-ccameodated with no decrease in reactor safety. Due to turn-up of fuel, the criginal heat flux limitatica vill eventually have the effect cf m rhdv restrictin6 the pcver output of the Dresden reacter to less than the authorized $30 E T.
AcccrdinIly, applicant requests that the r.nenam heat flux levels to incWased to permit ccatinued cperati:n of Dresdan at 630 WT and eventual pcver increases abcva this icvel.
This repcrt is submitted in suppcrt of applicant's ccuelusion that the requested increases in heat flux levels say be per=itted without decreasing :nar31ss of safety criginally considered apprcpriate.
l DISCUBSICE:
f
% sts -f Gelecti n of U-~= den "'rv* I M 1 ?'F9 met m The criginal limiting heat flux for Dresden was based en experimental data which indicated void formatica occurred in the center of a fuel pellet in a Type I segment which was operated at best timres greater than 350,000 Btu /(hr)(sq ft). It was assumed that this central void formatica vse due to melting of U02 which occurs at abcut 4950 F.
Althcugh it had never been descastrated experimentally that central void or molting was detrimental to fuel perfermance, applicent propcsed in the interest of acaservatism that operatica with the Type I fuel should be limited to avoid this condition. Therefore, the technical specifications preposed by applicant and inscrporated in Appendix A to license DPR-2, issued November 16,/(hr)f sq ft).
1959 provided that the peak heat flux in the Type I thel be limited to 350,000 Bta On a sindinely conservative basi the effective thermal conductivity of UO was 2
determinedtobe1.15 Btu /hrft The central temperature of the fuel element is calculated as fciloess Equatica 30. 1 T,
. Tg + A 1
D (D
D 1
D
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+
o o
o o
f cl di}
D h
g 8
2, where T,
= Fuel ca ter te.perature cr Bulk water temperature UF 7,
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February 26, 1962 Face 2 g/A e Best flam - Bta/hr-eg-ft D,
s Ftasi rod outside At===ter - ft Di n Final rod inside dieuwter - ft h
e Bacleate boiling heat transfer coefficient at elad g
o.Jt.-sta/hk-se-ft"F h
. Esat transfer coefficient betvoen fuel pellet and g
siming-Sta/hr-eg-ft1
- Thermalconductivityoffusipellet-Btu /hr-ft.F
- hems 1 Ocnductivity of :ladding =aterial - Mu/hr-ft C7 k
n el In the Type I fttel, the fell =ving values vere than used to esiculate pellet :entral temperature T,
5M.6 F D
,o.567 in.
o Di s 0 5o3 in.
h
.13,000 Btu /hr-sqftOF f
l h
= -,20 Stu/hr-sq.5 7 7
e1.15stu/hr-ft7 E
=8.2Stu/hr-ftF el Substituting these values in Equation No. 1, a central temperatum of 4717 D is obtained in Type I ftaal for a peak homo flux of 350,000 stu/hr-sqft. The following is a br==hd=n of the temperatures To : Water temperature + film aT + clad a T + gap A T + pellet.i T
= 547 + 35 + 121 + 419 + 3595
= 4717*F.
Using information, similar to that given above, the temperature profiles shown in Figum 1 were cb*minad.
This informatica (1) was sabeitted to the AEC in early 1958.
(1) GEAP-3009, " Amendment No.1 to Preliminary Basards Summary Report for the l
Dresdam Raclear Fever Station, May 1,1958.
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Febmary 26, 1962 Page 3 Investigations cf Centml Void ph=== man Subsequent irradiation of Dresden type sesmaats operated with central v:id at the GE-YAL facilities ind_ testes that central void fomation is not contributcry to ftaal alament failure. Fuel rois which have been cperated at best fluzes which prcduce central void show changes in UO, graia sise==those near the center developing an elongated er eclusznar abspe, thUse near the cuter periphery. :
9 M na "a + =ced.
Cncks were evident, ocas ciretanterential, but pr=&=inantly M=11y oriented.
Cire m feren+dal cracks which appeared were "_---117 1ccated midway between the pellet center and cuter pe n et periphery.
A recrystallization regicneen+= Ming 00 grain sizes greater than those initially 3
present su.h the central void if tF.e v:ia is present, but occupies tha central regi:n of the fuel pellet when the void is absent. Recrystallized regi:ns centain ccall veids within Jrain er 6: sin ::cundarica *.hich are irregular in shape.listant, frem the 7211et center but 'Aich are cylindrical er ellipsoidal near the entral z:ne.
High temperature laboratcry experiments have hantrated(2) that UC,, begins to create a central void (subline) at temperatures as icv as 3000 7.
Erecver, it has been found that the fermatics of void was time dependent thrcugh the slow sigratien of mall chevren-shaped v-ids ot: served near the vicinity of the central void, sad
- 2e still 21:ver nigrati:n f cyliMrical er ellipscidal voids fr m the cuter regicas of the rec:/stanized UO2 regicus. These experi=cnts ccnfirmed that the f::=ati:n ;f vcids in 002 does =ct imply that the fuel has reached h950'7, the melting point Of UC 3 0
In fact, the fcmatica cf central voids at tausperatures o* abcut 3000 F is ccasistent-with the calculated tecrperatures given here cf sbcut 3300' at 350,000 Btu /hr-sq-ft in Oc ';/pe I fuel.
Investigaticas of Thermal Cenductivity of UOg Since the Type I fuel was designed, a considerable number of investigations have been nade and results published (3) ':n the thermal conductivity of U0. A particularly 2
significant investigation is that performed by J. Iambert Estes of Hanford Atcaic Cparation(4). Sates postulates that the radiant energy tranafar, eWm11y throuGh ther observed columnar 002 grains, should =mh, contributions to the thermal condn=tivity 0
above about 2000 F.
Bates derives a temperature dependent relationship for the themal ccaductivity of UO2 which is as follows 2 55 x 10-12 23 Iquation No. 2 k 30 x-M T
vbere k
Theremi conductivity watts / cme 0
T s
Absolute temperature CK
'(2) Reake, W. and Bates, J.I,., Trans, A8ME, Yol. IY, Cbtems Meeting, 3cvember 1959 (3) see for a= ple, J. Belle, "Ursaiumi Dioxide, Prm3 w and Nucles:? Applications,"
U.S. Goverment Printing Office,19613 and !!och A. b the Dependence of the Thermal Conductivity of UO2 on Density, Mid a oc~ w, Stoichicastry, and themal Eeutron Irradiatice,' CIF 8817, Alk'<
uj h 1960.
(4)
J. Iambert Bates, "Themm1 Condnetivity of Urt Improves at 31gh Temperatures,"
Dielsonies. Vol. 19, Bo. 6, June 1961.
m February 26, 1962 Page 4
(*. Speciment density C
Theoretical crystallographic density The thermal cenductivity of 9% dense UO2 is graphically illustrated in Figure 2.
It is noted that the general fom of this equation ist CT3 Zquation No. 2.1 1-A
+
3+T The thermal ccaductivity as repcrted by varicus Other investigaters is 0 :parel to 3ates's correlatica in Figure 3 It is seen that, at temperatures tet.een 100 F 0
an.1220 F, Lates's ccrrelation la 711te sin 11ar to the majority of other investigatcra.
It is noted that, in this te:rpersture ra:ge, the equatica fcr ther:21 c:sinctivity takes the fcrz:
Equatica Jo. 3 k-B+?
Equatics No. 3 is the fem used fer the first term of sates's ccrrelatica, as well as the fem used by cumercus other investigaters. Data repcrted by :ncat of the investigaters reiste to temperatures belev 3000'F. Reisvig(5) reporte data up te abcut 3800*F. Sates c rrelates ocatirrsdistica enm5ati:n data up to ecut 50007 fr:n.2 direct fecervati:ns cf irrsdiated UO2 grain atructure, whien he alac dupli-cated in vell centrciled labcrstcry experiments.
Applicaticn of hates Fe== da t.o Fuel in the Dresden Reacter Using Bates's correlation for themal conductivity to esiculate the center tempera-ture of the fuel by Equation No.4, it is fcund that a heat flux of abcut 710,000 Btu /hr-ft'and 890,000 Btu /hr-ft' is requind to obtain a central temperature of 5000 F in the Type I fuel and Type II fuel, respectively. This result is presented graphically in Figo " 4.
Equation No. I does act consider self-shielding cf the neutren flux in the pellet. Considering the latter, a heat flux of 760,000 Btu /hr-ft2 vonld be required to ' btala a central temperature of 5000*F in the Type I fuel as c
shown in Figure k.
It is now proposed to limit the heat flux in DEF5 fuel to that imposed by the bemont limit and in no case exceed 500,000 stu/hr-ft in the Type I fuel.
Ecte that this spplies at the 0io.gwr cception so that, at rated pcver, the heat flux vill be limited to h00,000 Btu /hr-ft.
These heat flux limits shculd assure a satisfactory wargin to avoid melting in Type I fuel.
(5)'5eisvig, R.D.
"Themal Cenductivity of 00 t
0 2 to 2100 C," Journal of the American Ceramic Scciety, Vol. 44, No.1, h6, k9 (1961).
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February 26, 196e Pase.5 To establish limits fbr each of the other types of fuel, it is propcsed that the peak heat flux at overposer be restricted to that level imposed by p burncut limit and in no case vill it allev the center temperature to exceed h2507 as calculated by Equation )
No.1, using Bates's correlation for the themal ccednetivity of 00. Specifically, j
2 it is propened that the heat fluz levels for the fuel now in DEFS shall not exceed i
the following limits:
TABLE 1 IIAT FLUE IJMIfS FOR INPS FtEL FUEL PEAK '5AT FLUX 2
type I 500,000 Btu /hr-ft 2
Pfpe II 025,%0 Btu /hr-ft
?F 1 4 595,000 Btu /hr-ft-t 2
PF 5-9 f00,0003tu/hr-ft
?F 10-12 Sho,000 2tu/hr-ft2 Safety Evnlustien The prepceed changes in thermal limits have no significant effect cn the results Of hypcthesized accidents previously analyzed arei repcrted in Ocnnection with licensing cf Dresden Nuclear Power Station *.
yer an excursicn that la presumed to starc with tae fuel and :accerascr at essenn.C.1/
the same temperature, the thexuel conductivity of the fuel has no significant effect on the :nagnitude and duration cf a short-pericd power excursien. Since these transients are terminated by the Dcppler effect in a fractica of a seccad, the heat transferred from the UO2 during such a transient has an insignificanterfect on the excursica.
For pn excursion fra a rated power ccaditica, a lower peak fuel temperature vill result than that indicated by previous analysis for the same presissed excursion. This peak feel temperature is reduced becense the higher theriaal conductivity results in a lower rated peak ftsel temperature at the start cf a presumed excursica than that which was used in the previous analyses. Fct example, with a peak heat flux 260,000 Bta/hr-sq-ft (30% of 3&000 stu/hr-eg-ft) at rated power, the calculated peak fuel temperature is about 39007 by using the old thermal ccanductivity value. With the proposed thermal conductivity value med proposed peak heat flux of 400,000 Btu /hr-et-ft (80% of 500,000 Bta/hr-eg-ft) at rated power, the calculated ;eak fuel temperature is about 3500*F.
As exampled, this gives a lower starting temperstare, which with an essentially similar temperature rise results in a final temperature lower than that indicated by previcus analysis fcr the same presumed escursica.
l
- Easards Summary Repcrt for the Dresden Nuclear Pcwor Statien, GEAp-lokk and Amts.
N February 26, 1962 Pass 6 In sumary, all short-perice transients will result in equal or lower =awi-fuel temperatures than thcee calculated previcualy. The propcsed thermal condactivity initiates no other significant change in the results of analyses presented in the Essards Reports.
In our cpinica, incorporatica of the proposed changes in therumi limits imposes no hasards to the operatica of Dresden greater than those stated in the Hazards Sa mary Reports.
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FIGURE 1 TEMPERATURE DISTRIBUTION IN TYPICAL FUEL RODS tl5fHG A CONSTANT UO THERMAL CONDUCTIVITY OF 1.15 BTU /HR FT *F 2
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- F FIGURE 3 COMPARISCH OF SEVERAL PUBLl5HED YALUE5 OF THERMAL CONDUCTIVITY OF UNIRRADIATED ANDIRRADIATED U02
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