ML19340A904
| ML19340A904 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 08/06/1962 |
| From: | Case E US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19340A903 | List: |
| References | |
| NUDOCS 8009080570 | |
| Download: ML19340A904 (3) | |
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tj HAZARDS ANALYSIS BY THE RESEARCH AND POWER REACTOR SAFETY BRANCH DIVISION OF LICENSING AND REGULATION IN THE MATTER OF C_0.$NONWEALTH EDISON COMPANY TYPE II FUEL RELOAD Introduction The Commonwealth Edison Company is proposing to increase the power output of the Dresden reactor.
Applications have been submitted to change the mode of plant operation in several discrete stages, These stages can be categori:cd as follows:
1.
Increase in primary and secondary steam flow limits 2.
Use of a new burnout correlation 3,
Authorization to load up to 10S " Type II" fuel elements 4
Increase in maximum heat flux limits 5,
Increase in maximum reactor power to 700 Me (thermal)
This hazards analysis is concerned only with Item No. 3.
Items 1 and 2 have been previously authorized by the Director, Division of Licensing and Regulation.
Items 4 and 5 will be consioered at a forthcoming public hearing scheduled for August 8, 1962.
Background
On Jar.uary 27, 1961, Commonwealth Edison Company requested revision of its license authorizing reactor operation with "Dresden Core I" te provide for the loading of 100 Type II fuel elements and 12 experimental fuel elements into "Dresden Core II".
Subsequently, this request was modified in scope to request a reconstitution of "Dresden Core l' to permit the use of only two Type Il fuel elements and one each of the 12 experimental elements, with the balance of the fuel to be Type I elements
("Dresden Core I, '!odified"),
The modified request was approved on June 9, 1961.
In the fuel reload now propused, up to 108 Type II clements would be used and the number of experimental elements previously authori:ed would remain unchanged.
The total number of fuel elements in the Dresden core would still be limited to 4SS elements.
Commonwealth Edison proposes also to amend the Technical succifications to reficct these changes and climinate reference to ini >-
startup and pre-operational testing, and to designations of "Dresdct.
re I" and "vresden Core I, 'lodi fied".
Discussion The basic Dresden Tyrc I fuel clerent conc Jts cf c 6 x 6 array of 80 09 0 EF0 ;5757 cc)
. t
' ircaloy. clad cylindrical fuel rods.
The Type II element consists of a 7 x 7 array of 304 SS clad non-segmented cylindrical fuel rods enriched 4
to 2.5's UO2 (compared to 1.5% for the Type I rod!).
Nine special 'corne r rods" in each Type II clement are loaded with thoria pellets.
The Type II fuel has improved heat transfer characteristics o/er the i
Type I fuel due to the increased number of rods per assembly, increased heat transfer area, reduction of corner rod peaking factor, and increased coolant flow through the assemblies, There have been two Type Il fuel elements in the Dresden reactor since authorization of their use on June 9, 1961.
No Type II fuel rod failures have been reported, in addition, no failures of experimental elements PF1.PF12 have occurred.
Two core configurations have been analyzed by the anplicant for the fuel loading now proposed. The n ast severe thermal conditions for Type II fuel are expected to occur when the Type II elements are concentrated in the central region of the core and surrounded by Type I clements.
The d
extreme thermal conditions for Type I fuel are expected when both types of elements are distributed throughout the core, Commonwealth anticipates using such a scattered loading.
Calculations of both central and i
distributed loadings under conditions of the recently author 2 zed maximum primary and secondary steam flow rates at 125% power indicate that for all cases the burnout ratio is greater than 2.0.
Based upon a review of these calculc+. ions, the staff has concluded that thermal conditions expected for these loadings are acceptable from a safety standpoint.
In order to meet the minimum shutdown margin requirements specified in the Dresden-Technical Specifications, certain limitations on core l
loading must be observed. A Type II central loading configuratien, using all Zircaloy fuel channels would exceed the minimum shutdown m egin.
)
However, arrangement of about 50% 2r channels and 50% SS channeis in a uniform array will meet the shutdown margin requirements for any central loading arrangement, For a distributed configuration, calculations 1
indicate that the shutdown margin requirements are met in the controlled e :.
region of the core, and can be met on the periphery of the controlled region for a 464 assembly core configuration.
The staff has concluded I
that adequate control of the modified core will be maintained so long as j
the miniuum shutdown margins are met.
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, fuel assembly location error, and the maximum credible accident.
With regard to reactivity additions, control rod worths are less with Type II than with Type I fuel, This results in less severe reactivity accidents than those previously analy:cd.
The loss of coolant accident analysis indicates that the minimum burnout i
ratios reached are larger than those previously analyzed for all Type 1 loadings.
The previous fuel cladding failure analysis considered the failure of 4000 fuel element segments.
The Type II rods are not segmented so that th: postulated Icalage would occur with failure of onh 1000 Wpe Il mds.
However, the staff belicies that the factor of four decrease in
..c nua ::
of welds-should adequately compensate for the increase of consecuen:es ci failure by decreasing the probability of such failures l
3-If a Type I fuel assembly were inadvertently inserted into the center 4
of a Type II central loading configuration, the Type I rods could overheat i
and rupture. However, this accident would be less severe than that postu.
lated for the fuel cladding failure analysis, t
The use of a Type 11 fuel loading will not change the energy release 1
in the event of the maximum credible accident, although some stainless steel cladding would be expected to reach melting temperature slightly faster, and some Zr cladding of the Type I elements vould reach melting temperatures slightly slower than would have occurred in the previous core.
We believe this effect would not have a significant effect on nuclear i
s afety.
Based upon the Commonwealth Edison /GE safety analysis and our evaluation, we have concluded that the Dresden reactor can be operated with the Type II loading proposed without undue risk to the public health and safety.
Technical Specif_ications In connection with the request for the proposed fuel reload, Common-wealth Edison.has proposed eleven changes to +.he Technical Specifications.
The specific purposes of these changes are the following:
Proposed change 2, 3, 6, and 11 request authori:ation for the loading of 108 Type II elements and climinate the " Core I" and " Core I - Modified" designations in the Specifications; proposed change 1, 4, S, 7, S, 9, and 10 request elimination of the sections involving initial. loading, critical testing, and power test program.
Items applicable to power operation in these sections are transferred to the " Power Operation" section of the Speci-fications.
Items applicable to refueling and maintenance in these sections are transferred to the " Refueling and Maintenance" section of the Specifications.
I Discussions between the licensee and the AEC staff regard'ing the i
i need for an adequate " refueling instrumentation" specifications have resulted in a submittal from Commonwealth dated July 16, 1962, outlining-a proposed refueling instrumentation specification.
We believe this
,l specification is adequate for its intended purpose, and accordingly believe it should be included in the Technical Specifications, as amended.
, Conclusions We believe that the loading of up to 108 Type II fuel bundles in the tresden core does not involve significant ha:ards considerations not described or implicit in the license application as amended, and have concluded that there is reasonable assurance that the reactor can be eperated under the proposed modified Technieni Specifications without undue risk to the health and safety of the public, c4,e ! W N L c.cne Edson G. Case, Assistant Director Facilities Licensing
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Division of Licensing and Regulation 1.
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