ML19340A894
| ML19340A894 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/13/1964 |
| From: | Boyd R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19340A891 | List: |
| References | |
| NUDOCS 8009050621 | |
| Download: ML19340A894 (5) | |
Text
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O HA"lRIS A:*lLYSIS EY T E RESEARCH AND FO'4ER FIACTOR SAFETY BPlNCH DI7ISION OF PIAC70R LICENSING IN THE FATTER.0F COMM0lTr.'EALTH EDISON COMPA1H Po.0DCSED CHAIGE O. 8 - IUCREASED HEAT FLUX LIMITS Introduction Com-onwealth Edison Company, by letter dated September 17, 1963, has requested authorization to (1) increase the maximum allowable steady state heat flux limits of the various types of fuel in the Dresden reactor, and (2) decrease the minimu~. burnout ratio for each type of fuel.
Iten (2) was authorized by Change No. 6 dated March 13, 19 S.
This change, designated Froposed C"= ge No. 8, relates only to Item No. (1). Additionally, by letter cated March 25, 19614, Co= mom ealth revised its request for an increase in maxir:u: heat flux to include only Type I and Type III fuel. This change was censidered by the staff pursuant to the provisions of Section 50.59 of 10 CFR 50.
Sur'.ary In accorusnee with the present Technical Specifications the maxinum steady suate heat flux of Type I and Type III fuel eierents is 320,000 2
2 Stu/(hr)(ft ) and 330,C00 Btu /(hr)(ft ), respectively. Authorization of Fr:p: sed Change Uc. 6 would increase the maxinun permissible heat 2
flux for the Type I fuel to 350,000 Btu /(hr)(ft ) and to 360,000 2
Etu/(hr)(ft ) for the Type III fuel. The heat flux limits for the Type II fuel, the ??-S thru FF-12 fuel, and the special SA-1 fuel bundle would remain the sane.
800005,0[
t q
~
H 1
.i
_2-Evaluation Fuel in damage can occur as a result of burnout and/or center melting.
Burnout is expected whenever the naximum local heat flux equals or exceeds the burnout heat flux.
The burnout heat flux varies 2
l with steam quality, mass flow rate, reactor pressure, hydraulic diameter of the flow channel, and the ratio of pin heated periphery to total flow f
i y
periphery. The Dresden Technical Specifications require that the burnout ratio, referenced to overpower conditions (125% of rated power) never be less than 1 5 at the point in the core closest to burnout. Thus, the sat flux limits quoted abo ve and referenced to overpower conditions may never be reached in sone cases due to this burnout ratio limitation.
1 i
i Accordingly, the proposed increase in heat flux will not affect safety.
l-4 I
f The consequences of center melting in ceramic UO2 fuel pir.s are not well known.
Presently, we believe it prudent to limit heat flux such that i
i center melting will not occur. This requires that temperatures in the fuel not exceed 5000 F.
To consider whether, under a given set of circumstances, center melting would occur, one must know the maximun heat flux, fuel pin diameter, fuel-clad interface clearance (gap), heat transfer ccefficient, clad and surface film tenperature drop, and the thermal conductivity of UO.
Thernal conductivity is a function of tenperature, irradiation, 2
original grain sice, and the 0:U ratio. All the effects of the above variables, except thermal conductivity, can be conbined in the conservative
'c manner to obtain a paraneter defined as k dt in units cf watts /cm, where D
t
+
yr y
yw w
. r k = therral conductivity, watts /(cm)( C)
T = center fuel tenperature, OC dt = differential of temperature, OC In some instances, the evaluation of center melting has been performed using a similar parameter, specific power, which is de-Tc fined as k dt, exuressed in Kw/ft. Tnis,-however, may not
.T 3 present an equitable basis for consideration since T, the surface s
temperature of the fuel (00), is dependent upon gap hect transfer coefficient, fuel-clad interface clearance, film and cladding ten-perature drop, and temperature of the coolant.
For example, if l
two fuel pins had equivalent Kw/ft ratings, but different surface temperatures, the fuel pin with the higher surface temperature would I
have the higher center fuel temperature.
Thus, it is possible, for
}
l a given Kw/ft rating, to have center Zuel melting in one of the fuel pins (with the higher surface temperature) and not in the other.
The above specified integral, k dt uses a cc:rnon base, 0
s 0 C, to provide an equitable basis for a specific UO2 density for
-Tn comparison to k dt, where T is the melting temperature of m
- o 0
UO2 (2800 0), to establish if center fuel melting would be expected to occur. Recently determined values of this integral range from 85 to 95 watts /cm, for irradiated UO -
2 Evaluation of-the Types I, II, and III fuel is presented in Table I, Tc below.
It can be seen, that at the 125% overpower concition, the k dt r T_
0 s
is vnproximately 10's below the conservative value of k dt = c5 watts /cm.
-L-Table I Maximum Steady k dt, watts /cm Type State heat flux, 0-
- T"k dt, watt;/en 2
fuel Stu/(hr)(ft )
loog. power 125% power
-0 I
350,000 6h 78 85 II h10,000 6h 76 85 III 360,000 6h 78 85 In addition, information from in-pile testing and come ost-irradiation examinations at VBWR exists for fuel similar to that of Ty;es 1 :.nd III at
-Tc values of k dt in excess of 78 watts /cm and expocures up to 10,000
.I O T"k dt in the range Mwd /T.
These data tend to substantiate the value of
- 0 of 85 to 96 watts /cm.
Therefore, in our opinion, the proposed increase in heat flux limits in Types I and III fuel are acceptable and will have no substantial effect on the probability or consecuences of accidents previously analyzed for this facility.
1 Technical dpecifications We believe that the tabulation in Section D.3, page 12 of the Technical Specifications, should be changed to read as follows:
Fuel Type I 350,000 Fuel Type II 410,000 Fuel Typc III 360,000 Fuel Type PF-8 and PF-9 470,000 Fuel Type PF-10 thru PF-12 510,000 Fuel Type SA-1 425,000 Conclusion Based upon our review of the information subnitted we have con-cluded that proposed Change No. 8 does not involve significant hazards considerations not described or implicit in the hazards sum =ary report and that there is reasonable assurance that the health and safety of the public wiil not be endangered.
Original signed by:
Roget S. Boyd Roger S. Boyd, Chief Research & Power Reactor Safety Branch Division of Reactor Licensing M AY i 31964
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