ML19199A418
| ML19199A418 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/31/1976 |
| From: | Babcock & Wilcox Power Generation Group, Metropolitan Edison Co |
| To: | |
| Shared Package | |
| ML19199A414 | List: |
| References | |
| ZAR-761231, NUDOCS 7905020068 | |
| Download: ML19199A418 (10) | |
Text
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DECE'4TLER 1976 Irradiatien of Sixteen Gadolinia-Uranium Dioxide Demonstration Fuel Rods in T:fI-2, Cycle 1 Babcock & Wilcox Power Generation Group Nuclear Power Generation Division P.O.
Box 1260 Lynchburg, Virginia 24505 1
(,
4#
790502006f
TABLE OF CONTENTS Pace 1.
Introduction.
1 2.
Nuclear Design............
2 3.
Mechanical Design 3
3.1 Performance Models 3
3.2 Materials Ccapacibility.
4 5
4.
Thermal Hydraulic....
References.
6 Figure 1.
Location of Four Demonstration 7
Rods Figure 2.
Fuel Loading Pattern for TMI-2, 8
Cycle 2 t
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1 INTRODUCTION Four fuel assemblies, each containing four gadolinia (Gd 0~)
2 a bearing fuel rods will be irradiated in TMI-2, cycle 1.
The demonstration rods will contain 3 w/o Gd 0 and 97 w/o UO nd 23 2,
are to be placed in four batch 1 (1.98 w/o 235-U) assemblies which will be discharged at the end of the first cycle.
An evaluation of the nuclear, mechanical, thermal hydraulic, and safety related aspects of this deaonstration design indicates that the sixteen Gd 0 bearing fuel rods will not adversely affect the safety and 23 operation of TMI-2, cycle 1.
%)
- s 2.
NUCLEAR DESIGN Compliance with the nuclear design criteria (principally power peaking) was verified using the same techniques and procedures as are used in standard fuel cycle design.
The gadolinia bearing rods are located in the fuel pin positions shown in Figure 1.
To com-Pellet thermal conductivity pensate for a decreas in Gd 0 -UO2 23 (relative to pura UC ),
the enrichment in the gadolinia bearing 2
rods was reduced from 1.98 w/o to 1.80 w/o U-235.
With this lower enrichment, the maximum gadolinia pin power remains less than 81*'.
of the peak pin power in the core at all times during the cycle.
Locations H-12, N-8 and their symmetric counterparts (Figure 2) were chosen for the demonstration assemblies because these locations minimize the impact upon the peak pin in the core.
The maxfr.um increase in the core peak pin power because of the presence of the gadolinium pins is 1.2%.
This peaking change decreases as the gadolinium depletes so that by about 200 EF?D the core peaking behavior is the same as the behavior of a comparable fuel cycle with no demonstration pins.
The sixteen gadolinia bearing fuel pins will have no discernable effect on the shutdown margin of the core.
The Doppler, power, and moderator coefficients will be unaffected.
None of the other critical nuclear safety performance characteristics recuired as input to TMI-2 cycle 1 safety analysis will be affected.
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CdV 3.
MECHANIC.\\L DESTCN An evaluation of the nechanical behavior of the Gd 0, bearing 2a demonstration fuel rods was performed.
The mechanical design requirements were that the Gd 0. containing rods and assemblies 2a must be mechanically equivalent to the othec batch 1 Mk-34 fuel assemblies for the duration of their one cycle lifetime in TMI-2, cycle 1.
The Gd,0 -UO, fuel pellet dimensions, total column length, s tack
.O u
height, cladding material and dimensions, grids, and end fittings are identical to those in the non-gadolinia fuel bearing Mk-34 fuel assemblies.
The percent of theoretical density of the Gd 0 -UO 23 2
pellets and the UO2 pellets are identical, thus there is only a slight difference in stack weight.
The change in stack weight results frca the difference between the theoretical density of a solid solution of 3 w/o Gd 0
- 97 w/o UO and the ths.retical 23 2
density of pure UO.
Thus for mechanical design analyses, the 2
Gd 0 -UO r ds and assemblies were considered to be identical with 23 2
the TMI-2, batch 1 Mark-B4, 15x15 fuel assembly design.
Since the irradiation will only be for one cycle at relatively low power levels,
it was concluded that the gadolinia containing rod and assembly mechanical design would not adversely affect TMI-2, cycle 1 core per-formance or safety.
3.1 Performance Models The fabrication of 3 w/o Gd 0.
- 97 w/o UO3 pellets forms a 2a solid solution of these constituents.1 The mechanical and thermal hydraulic evaluations required descriptions of the thermal conducti-vity, melting point and swelling behavior.
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\\C The intenral of the thermal conductivity oF the solid solution frca room temperature to ac1t is about 20t less than the integral
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for UO,.-
Part of this decrease i s the result of the melting temperature reduction to 4530 F nd part of it results from a decrease in the lower temperature thermal conduc tivity due to phonon dispersion.
This decrease in thermal conductivity results in increased fuel temperatures-therefore, the mechanical behavior of the fuel pellet is affected by the introduction of Gd 0-into a 2a UO matrix.
However, as the power levels are low and the 2
assemblies will have only one cycle of exposure, the effect on mechanical perf ormance is insignificant.
Similarly, it was determined tha t there was no discernible difference between the UO, and Gd,0 -UO densification, swelling, and thermal 3
2 s
expansion.
Also due to only one cycle exposure at relatively low power levels, the demonstration fuel assemblies are expected to be less limiting with regard to fission gas release than the three cycle UO, fuel assemblies.
3.2 Materials Comcatibility The compatibility of Gd 0 - 02 pell ts with other fuel assembly 23 and reactor coolant system components was investigated and fcund to be acceptable.
Important verification of the compatibility is that Gd 0 -UO pell ts clad in :ircaloy-2 (very similar to circo loy-4) 23 2
are used in BWR's without any operating or safety problems.
g 4.O Tf 8FR'O T. liYDRMfL T C DFSIGN The reduction in the Gd,0 -UO solutien's thermal conductivity a
3 integral results in the Gd 0 bearing rods being inherently more 2a thermally limiting than UO rods.
To insure that under normal and 2
transient accident conditions the red design would not result in fuel melting, a ccmparison of the peaking in the demonstration rods to the UO r ds peaks in the core was made.
The comparison showed 2
that because of the enrichment difference and the location of the demonstration fuel rods, the UO r ds were more limiting than the 2
Gd 0;-UO2 r ds.
2 A DNB analysis was made using the BAW-2 correlation.
The analysis for the Gd 0 -UO uel r ds resulted in a DNBR significantly above 23 2
the MDNBR in UO bearing fuel rods.
The already available design 3
margins for the peak UO rods were more than adequate to absorb the 2
1.2's peak pin power increase resulting frca the gadolinia insertion.
Thus, it is concluded that there was no additional thermal-hydraulic limitation associated with placing the gadolinia containing assemblies in TMI-2, cycle 1.
}
g References 1.
- Deals, R. J.
and Handwerk, J.
H.,
" Solid Solutions in the Systems Urania-Rare-Earth Oxides-I, fl0,-Gdo Journal o# An c ric an
- 5 Ce ramic Scc ie ty iS, 5 (1965) 271:74, 2.
Docket 50-237, Dresden Nuclear Power Station Unit 2, Tonical Report DPR-19.
Modification 71-1, Fefueling (January 15, 1971 and January 25, 1971).
3.
- Beals, R. J. Handwerk, J.
H.,
and Wrona, B.J.,
" Behavior of Urania-Rare-Earth Oxides at Hich Temperatures," Journal of American Ceramic Societv 51, 11 (1969) 578-S1.
4.
Docket 50-254, Quad-Cities Station Units 1 and 2 Amendnent 9, Contained Burnable Neutron Absorber as Supplementary Centrol.
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