ML20054H763
| ML20054H763 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 06/18/1982 |
| From: | Withers B PORTLAND GENERAL ELECTRIC CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| IEIN-82-27, TAC-48402, NUDOCS 8206240406 | |
| Download: ML20054H763 (6) | |
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Evt o em ite Puomt June 18, 1982 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Regulation ATTN:
Mr. Robert A. Clark, Chief Operating Reactors Branch No. 3 Division of Licensing U. S. Nuclear Regulatory Coranission Washington, DC 20555
Dear Sir:
Modified Fuel Assemblies Attached is the Westinghouse evaluation of the effects of the stainless steel rods in the Cycle 5 core at the Trojan Nuclear Plant. This report includes the stainless steel rods used in the previously modified fuel assemblies (which were used in Cycle 3 and Cycle 4 cores) as well as the stainless rods which will be used in the modified Region 7 fuel assemblies as described in License Change Application 88.
Submittal of this report satisfies both the current and proposed change to License Condition 2.C.(ll) of Facility Operating License NPF-1.
As expected, the evaluation showed that the stainless steel rods will not have a significant impact on the Cycle 5 core. Therefore, prompt approval of LCA 88 is requested so the startup of the Plant will not be delayed.
Sincerely, Bart D. Withers Vice President Nuclear Attachment J
c:
Mr. Lynn Frank, Director State of Oregon Department of Energy 8206240406 820618 PDR ADOCK 05000344 P
PDR 121 S.w Salmon Street. Portland, Oregon 97204
Trojan Nuclear Plant Robert A. Clark Docket 50-3'44 June 18, 1982 License NPF-1 Attachment Page 1 of 2 4
EVALUATION OF THE USE OF FUEL ASSEMBLIES CONTAINING STAINLESS STEEL FUEL R0D REPLACEMENTS I.
INTRODUCTION The Trojan Cycle 5 core loading contains 22 assemblies bearing stainless steel fuel rod replacements (SS Rods). Table 1 summarizes the number of stainless steel rods by assembly and by core location.
Figure 1 shows the core loading pattern for Cycle 5.
The following discussion evaluates the impact of SS rods on core physics and nuclear core design. A similar evaluation was done for Cycle 4 and was supplied in Reference 1.
II.
LOADING PATTERN AND NUCLEAR MODELING The Cycle 5 core loading contains 48 Region G feed assemblies, 45 Region F once-burnt assemblies, 60 Region E twice-burnt assemblies, 25 Region D thrice-burnt assemblies, 1 Region D once-burnt assembly from Cycle 2, and 14 Region A assemblies from Cycle 1 (see Figure 1).
In the 22 modified assemblies these stainless steel replacement rods are explicitly modelled in Westinghouse's two-dimensional, two-group i
diffusion theory code TURTLE. These explicit models are used to obtain radial peaking factors for the entire Cycle 5 design. As in previous cycles with SS rods modelled, nuclear design is done with the normal reload design methodology and procedures.
III. EFFECTS OF STAINLESS STEEL RODS
Background
In both Cycle 3 and Cycle 4, two Region E assemblies (E05 and E15) contained three SS rods each. Previous evaluations of these six SS rods showed in both Cycle 3 and Cycle 4:
(1) that the impact of power peaking was small and local, (2) that the assembly average power was reduced (causing <50 MWD /MTU burnup reduction), (3) that the core loading pattern search was not more difficult, (4) that design models are capable of accounting for the SS rod effects, and (5) that normal fuel management schemes are definitely possible.
Baffle jetting damage in Cycle 4 has resulted in the requirement for an additional 76 SS rods in Cycle 5.
Evaluation Method To examine effects of SS rods on power distribution in general the Trojan Cycle 4 design was considered to be an equilibrium cycle.
Trojan Nuclear Blant Robert A. Clark Docket 50-344 June 18, 1982 Lic:nse NPF-1 Attachment Page 2 of 2 Twelve feed assemblies (F's) with five SS rods each were modelled and placed in the center injection baffle locations.
The resultant power peaking and assembly powers for this perturbed Cycle 4 design were then compared to those of the as-designed Cycle 4 loading. Next, twelve once-burnt center injection assemblies (E's) were modelled with five SS rods each and included into the perturbed Cycle 4 model. The subsequent effects were studied.
Last, twelve twice-burnt center injection assemblies (O's) were similarly modelled, incorporated, and studied.
The SS rod locations are indicated on the Cycle 4 loading pattern shown in Figure 2.
These three cases represent the effects of feeding 60 SS rods each cycle for three cycles (for a total of 180 SS rods) in a normal out-in type loading pattern.
These cases indicated an increase in FaH of less than 1 percent.
Therefore, SS rods can be loaded on the edge of the core and these assemblies can subsequently be moved inboard without severely affecting the nuclear design.
Cycle 5 Design The 76 additional Cycle 5 SS rod: are positioned symmetrically in the four core quadrants with each quadrant receiving the same number of rods. The only overall effect of such a loading is to lower very slightly the power on the core periphery with no increase in quadrant tilt.
Note that the additional 2x8 grids in the 8 corner injection baffle assemblies add little extra parasitic neutron absorption, are posi-tioned in areas of low neutron importance, low rod powers, and high neutron leakage. The incremental local power distribution perturba-tion of these mini-grids is estimated to be very small.
IV. CONCLUSIONS The use of SS rods has been accommodated in the nuclear design with appropriate modeling. Generally, the effect of SS rods is to produce small changes in radial peaking factors. Mini-grids at the 8 corner injection locations have a negligible effect. For Cycle 5, SS rods are considered in the design which otherwise is performed l
with standard reload methodology.
V.
REFERENCE
- 1) PGE to NRC (Withers to Clark) letter dated February 5,1981 (LCA 70).
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LSP/4dg10.3A26 l
TABLE 1 STAlf4LESS STEEL ROD LOCATION SUMt1ARY
- of Assembly Cycle 5 Number of SS Rods assemblies Identification Core Location per Ass'e'mbly Comment 8
G03, G36, G10, G41, L-1, E-1, R-5, A-5, 5 with 2x8 partial Cornerinjectis l
G37, G23, G35, G12 R-11, A-11, L-15, E-15 mini-orids baf fle. joints
- j-12 G02, G45, G30, G01, N-2,
_M-2, 0-2, B-3, 3
Center injectit i
G33, GIS, G40, G42, P-4, B-4, P-12, B-12, baffle joint G47, G06, G21, Gil P-13, M-14, 0-14, C-14 2
EIS, E05 M-8, D-8 3
Center injectit ba f fle.ioin ts' used in Cycles
- and 4 O
e 4
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TROJAfi CYCLE 5 CORE LOADIf1G R
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L K
J H
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C B
A 1
2 3
4 5
6 7
8 9
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5x 5x I'
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G 3x 3x
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D A
F D
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E D
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G G
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G F
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G 3x
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G D
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5x 5x A - Region 1 2.1 w/o F - Region 6 3.2 w/o From Cycle 1 0 - Region 4 3.1 w/o G - Region 7 3.2 w/o
- From Cycle 2 E - Region 5 3.1 w/o zz Region y
number / position of SS rods s
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FIGURE 2 POR CYCLE 4 REACTIVITY ARRANGEMENT IN QUARTER CORE SYMMETRY
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- region number 10 - Region 1
- asgembly location /
1 - Region 3 Q
orientation of the 62 - Region 4 - twice burnt 5 stainless steel rods 64 - Region 5 - once burnt 56 - Region 6 - feed
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