ML19340A926
| ML19340A926 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/18/1963 |
| From: | Bryan R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19340A925 | List: |
| References | |
| NUDOCS 8009080624 | |
| Download: ML19340A926 (5) | |
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HAZARDS ANALYSIS BY THE PESC/EH AND PO*.iER REACTOR SAFETY BRANCH DIVISION OF LICENSING AND REGULATION IN TRE MATTER OF COMMONWEALTH EDISON COMPAh'l PROPOSED CHANGE NO. 4 - TYPE III FUEL RELOAD Introduction Ccemonwealth Edison Company has requested, by application dated August 5, 1963, suthorization to load up to 200 Type III fuel assemblies in the Dr'esden reactor at the forthcoming refueling period. This change, which was considered by the staff pursuant to the provisions of Section 50.59 of 10 CFR 50, has been designated Proposed Change No. 4.
Backcround On January 27, 1961, Commonwealth Edison Company requested revision of its license authorizing reactor operation with "Dresden Core
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to provide for the loading of 100 Type 11 fuel elements and 12 experimental ruel elements into "Dresden Core II."
Subsequently, this request was modified in scope to request a reconstitution of "Dresden Core 1" to permit. the use of only two Type II fuel ele =ents and one.each of the 12 experimental elements, with the balance of the i
fuel to be Type I elements ("Dresden Core I, Modified"). The modified request was approved on June 9, 1961.
On August 6,1962, on the basis of its application dated January 5,1962, j
Edison was authorized to load up to 108 of the Type 11 stainless steel clad i
fuel assemblies into the Dresden reactor at the 1962 refueling period. Addi-i tional background material regarding this refueling may be found in the i'
Division of Licensing and Regulation hazards analysis also dated August 6,1962.
In the fuel reload now proposed, up to 200 Type'III fuel elements would be i
used in the Dres' den Core, up to 107 Type II elements, PF elements 8 through 12, and the remainder of Type I elements for a maximum loading of 488 elements.
Discession The proposed Type III fuel is quite similar to the original Type I fuel. The table on the following page presents a comparison of the characteristics of these two types of elements. The basic differences between the Type III fuel and the Type I fuel is that the Type III fuel rods are non-segmented, each contains 1500 ppm of Er2 3 burnable poison, and five rods in each fuel 0
8009080 Qp
assembly have thickened clad and reduced diameter fuel pellets to reduce i
locci power peaking due-to control blade ef fects.
The fuel loading proposed is a scattered configuration similar to that used in loading the Type II fuel elements. Sketches of possible loading configurations are included in the application. Calculations by the appli-cant indicate that, with the maximum Type III loading proposed, the result-ing core reactivity is expected to be' less than that of the initial Dresden core. Further, the difference in reactivity is calculated to be greater than the reduction in control rod worth from that of the initial core. Thus, conditions arising from additions of reactivity to the core are expected to be less severe than those previously analyzed and found to be acceptable.
The temperature and void coefficients of reactivity of the Type III core have been calculated to be negative at operating temperatures (5460F), as was the case with previous cores. The void coefficient is expected to be negative for all temperatures and the temperature coefficient, which is positive at room temperature, is expected to become negative at about 3150F - 3780F. This is permissible under current license requirements. Additionally, the cold shutdown margin is expected to increase with core life since the erbium oxide burnable poison is calculated to deplete at a rate slower than that of the fuel with respect to reactivity worth.
Erbium oxide, which was not used in the initial Type I fuel, has been used in several of the experimental fuel bundles (FF-1, PF-2, and PF-10), previously irradiated at Dresden. Cladding failures of the PF-1 and PF-2 fuel rods have not been attributed to the presence of the burnable poison, and there has been no evidence to indicate that the use of Er2 3 as a burnable poison would be 0
detrimental to safe operation.
Commonwealth Edison anticipates using a scattered fuel loading. Calcu-lations of two possible scattered loadings under conditions of umximum primary and secondary steam flow rates at 125% power indicate that for all cases the burnout ratio will be greater than 2.0.
The specific power of the Type I fuci
.. elements, at a maximum steady state heat flux of 320,000 Btu /(hr)(ft ), was Z
limited to 14 Kv/ft The Type III fuel, with a higher heat flux of y
330,000 Btu /(hr)(ft ), but with a smaller fuel pin diameter, will also generate the same specific power of 14 Kw/ft. Based upon a review of these calculations, the staff has concluded that thermal conditions expected for these loadings are not significantly different from previous loadings and are acceptable from a safety standpoint.
Hazards Evaluation The safety evaluation submitted by the applicant considers situations with the new core involving additions of reactivity, loss of coolant, system stability, fuel cladding failure, and the maximum credible accident. With regard
3 GBLE 1.
CCMPARISON OP THE CHARACTERISTICS OF DRESDEN TYPE I AND TYPE III FUEL ASSEMBLIES Type I Type III
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Cladding Material Zr-2 Zr-2 O.D., inches 0.567 0.555 Wall Thickness, inches 0.030 0.035*
Configuration 6x6 6x6 Regular Rods Nt=ber Required 36 31
- 7. Fuel Composition 1007. UO2 99.857. UO2 0.15% Er2 3 0
- 7. UO2 Enrichment 1.5 1.83 Pellet Diameter, inches 0.498 0.478 Special Corner Rods Number Required 5
- 7. Fuel Composition 99.857. UO2 0.157. Er 0 23
- 7. UO Enrichment 2
1.83 0.438 Pellet Diaceter, inches
- Wall thickness for the corner rods is 0.055 inches
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R l
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- c recctivity additions, control rod worths are less eith Type III than
,with Type I fuel. This results in less severe reactivity accidents attributebic to rod motion than those previously analyzed. The loss of ec61snt eccident analysis indicates that-the minimum burnout ratios reached are larger than those previously calculated for all Type I loadings. The previous fuel cladding failure analysis for Type I fuel considered the potential conse-quences of failure of 4000 fuel element segments. The Type II and Type III rods are not segmented, so that the same' consequences would result from f ailure of only 1000 of these typte of rods. However, we believe that the factor of four decrease in the number of welds in Type 11 and Type-III rods chould adequately compensate for the increase of consequences of failure of single rods by decreasing the probability of such f ailure,s.
Expericental evidence obtained through special testing and regular operation of the Dresden reactor indicates a large mr.rgin exists from conditions of instability.
Operation with Type III fuel is not expected to contribute to any stability problems.
Due to the similarity between Type I and Type III fuel assemblies, it is expected that the use of Type III fuel will have a negligible effect on the safety or performance of the Dresden reactor. We have concluded that the use of Type III fuel will have no substantial ef f ect on the probability or consequences of the maximum credible accident previously analyzed for this facility.
Technical Specifications l
To provide authorization of Proposed Change No. 4, the technical j
specifications of License No. DPR-2 should be amended as follows:
j-1.
Section B.2, page 1, in its entirety, as follows:
j
.i.
Nuclear Core Maximum Core Diameter (circumscribed circle) 129 in.
Maximum active fuel length - cold 112 in.
Maximum number of fuel assemblies by types:
Type I 352 Type II 107 Type III 200 Type PF-8 through PF-12 (one cach) 5 Maximum total number of fuel assemblies 488
. The various fuel assemblies may be located in any position of the reactor, provideo overall core sppmetry is preserved and provided that fuel cssemblies Type rF-8 through 12 are each separated from any other
.such assembly by at least four Type I, Type II, or Type II fuel assenblies.
The reactor may be operated at'any power up to and including rated power with any nucher of the various types of fuel assemblies installed, provided the e ximum nus er and location are within the limits specified e.bove.
- 2. Section B.3, page 2, second paragraph, as follows:
The minimum fuel pellat density averaged over a feel segment is 94% of thccretical for all fuel asse=blies except PF-8 and PF-9 which hcvc fuel der.sities 90% of theoretical.
- 3. Tc? tabulation in Secton D.3, page 12, is amended to read as follows:
Fuel Type I 320,000 Fucl Type II 410,000 Fuel Type III 330,000 Fuel Type PF8 and PF-9 510,000 470,000 feel Type PF-10 through PF-12 6 Table II (revised December 31, 1961) is replaced by Table II (revised June 15,1963) set forth in Commonwealth Edison's application dated August 5,1963.
Conclusion Ecsed upon our review of the information submitted, we have concluded that operation of the reactor in accordance with the proposed change does not icvelve significant hazards considerations not described or implicit in the Ers:ards eur: mary report and that there is reasonable assurance that the health 2:s safety of the public' will not be endangered.
Accordingly, we believe that the technical specifications of License No.
'Jr 42 shculd be revised as indicated above.
c:
v Robert H. Bryan, Chief Research & Power Reactor Safety Branch Division of Licensing & Regulation
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