ML20053A291
| ML20053A291 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 05/21/1982 |
| From: | Withers B PORTLAND GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20053A285 | List: |
| References | |
| IEIN-82-27, TAC-48402, NUDOCS 8205250177 | |
| Download: ML20053A291 (10) | |
Text
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PORTLAND GENERAL ELECTRIC COMPANY l
EUGENE WATER & ELECTRIC BOARD AND PACIFIC POWER & LIGHT COMPANY TROJAN NUCLEAR PLANT Operating License NPF-1 Docket 50-344 License Change Application 88 This License Change Application requests a waiver of Technical Specifi-cation 5.3.1 of Appendix A to Operating License NPF-1 for the Trojan Nuclear Plant for the purpose of using fuel assemblies modified with stainless steel rods and partial grids.
PORTLAND GENERAL ELECTRIC COMPANY
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B. D. Withers Vice President Nuclear Subscribed and sworn to before me this 21st day of May 1982.
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Notary Public of Orehon My Commission Expires:
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820S250177 820521 PDR ADOCK 05000344 P
Trojan Nuclear Plant Robert A. Clark Docket 50-344 May 21, 1982 License NPF-1 LCA 88 Page 1 of 7 LICENSE CHANGE APPLICATION This License Change Application proposes to replace the existing waiver of Technical Specification 5.3.1 contained in License Condition 2.C.(ll) with the following:
a.
"The requirement of Technical Specification 5.3.1 that each fuel assembly contain 264 fuel rods is waived for 20 fuel assemblies during Cycle 5 and up to 12 additional fuel assemblies during each fuel cycle after Cycle 5.
The modi-fied fuel assemblies may each be reused during later fuel cycles. This requirement is also waived for one cycle subsequent to Cycle 4 for the two fuel assemblies which were previously modified with stainless steel rods and were used in core locations B-12 and M-2 during Fuel Cycle 3.
The waiver for these two assemblies was previously approved by the NRC in Amendment 60.
b.
"The requirement of Technical Specification 5.3.1 that reload fuel shall be similar in physical design to the initial core loading is waived beginning with the Cycle 5 core for fuel assemblies with partial grids.
c.
"The Licensee shall provide a report containing an evalu-ation of the effects of the stainless steel rods similar to that contained in its February 5, 1981 letter prior to the startup of Cycle 5.
The Licensee shall perform a visual examination of the modified fuel assemblies at the end of Cycle 5 to provide assurance that further unanticipated baffle-jetting wear has not occurred.
Finally, the Licensee shall also provide a startup physics testind report for Cycle 5."
REASON FOR CHANGE During a planned fuel inspection at the end of Cycle 4 operation, fuel assembly dacage was detected in 17 fuel assemblies, 10 of which were located adjacent to baffle joints during Cycle 4 operation.
The 10 failures have been attributed to water-jet induced vibration resulting from gaps between the baffle plates adjacent to the fuel assemblies as described in Licensee Event Report (LER) 82-06.
The remaining 7 failures (1 of which was previously located adjacent to a baffle joint) had sipping indications only and were not visually damaged. The gaps in the corner-injection baffle joints were apparently opened up during the peening of the center-3 injection baffle joints at the end of Cycle 3 (see Figure 1).
Peening did not completely correct the problem with the center-injection assemblies, as damage was evident in three fuel assemblies of this type.
In order to preclude future occurrences, fuel assemblies which may be subject to this problem will be nodified.
Stainless steel rods will be utilized to replace selected fuel rods at all center-injection baffle joint locations.
In addition, partial grids will be used to provide midspan support of the
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Trojan Nuclear Plant Robert A. Clark Docket 50-344 May 21, 1982 License NPF-1 LCA 88 Page 2 of 7 fuel rods adjacent to corner-injection baffle joints together with stainless steel rods. Changes to the Plant Technical Specifications are necessary to allow implementation of this interim solution since Technical Specification 5.3.1 requires that each fuel assembly contain 264 fuel rods and that reload fuel be similar in physical design to the initial core loading. Pe rmanent solutions to the problem are currently being evaluated.
SAFETY / ENVIRONMENTAL EVALUATION 1.
Summary of Change a.
Stainless Steel Rods The proposed change will allow the replacement of five fuel rods with stainless steel dummy rods in fuel assemblies located adja-cent to eight corner-injection baffle joints (Core Positions:
A-5, A-11, E-1, E-15, L-1, L-15, R-5 and R-11) as shown in Figure 1 during Cycle 5.
In addition, three fuel rods will be replaced by three stainless steel dummy rods in fuel assemblies located adjacent to the 12 center-injection baffle-joint locations (Core Positions:
B-3, B-4, B-12, C-14, D-2, D-14, M-2, M-14, N-2, P-4, P-12 and P-13) during Cycle 5.
The stainless steel dummy rods will be of the same diameter and approximately the same length as the fuel rods they replace. The proposed change will also allow the reuse of the eight corner-injection and 12 center-injection fuel assemblies in core cycles after Cycle 5.
Since 12 of the 20 modified fuel assemblies (ie, the center-injection fuel assemblies) may be relocated in the core during future core cycles, 12 additional modified fuel assemblies may be needed as replacements on center-injection locations during the fuel cycles which follow Cycle 5.
The waiver of Technical Specifica-tion 5.3.1 has been written to accommodate the above.
Modified fuel assemblies with stainless steel rods has been licensed and utilized previously. Two fuel assemblies were modi-fled for Cycle 3 operation at Trojan as a result of the baffle-jet problem described in Licensee Event Report (LER) 80-06.
Ihree fuel rods in each of two assemblies were replaced with solid stainless steel rods of the same diameter and approximately the sate length as the fuel rods. The modified fuel assemblies were located in Core Locations B-12 and M-2 on the outside of the Cycle 3 core, adjacent to the baffle corners where water-jet induced fuel damage had occurred.
In Amendment 45 to the Facility Operating License NPF-1, the NRC approved a waiver from Technical Specification 5.3.1 for Trojan which allowed placement of the tuo modified assemblies in Core Locations B-12 and M-2 for Cycle 3 operation.
This waiver was extended in Amendment 60 to allow use of the modified assemblies in interior core locations for Cycle 4 and for one subsequent fuel cycle. No damage was observed in the previously modified assemblies at the end of Cycle 3 or at the end of Cycle 4.
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Trojan Nuclear Plant Robert A. Clark Docket 50-344 May 21, 1982 License NPF-1 LCA 88 Page 3 of 7 The proposed change will allow the continued use of stainless steel-rodded assemblies as an interim solution to the baffle gap /
water-jet problem and allow reuse and replacement of the modified fuel assemblies during future fuel cycles.
b.
Partial Grids In order to provide additional margin against water-jet induced failures, partial grids will be used on fuel assemblies adjacent to corner-injection joints (the partial grids will encompass a 2 x 8 array of rods). The partial grids increase the frequencies and decrease the amplitudes of the fundamental modes of vibration for the rods in the 2 x 8 partial grids. This significantly raises the threshold for susceptibility to water-jet induced vibration and subsequent failure. Partial grids will be included in eight modified assemblies located adjacent to corner-injection baffle joints. For each fuel assembly, a total of seven partial grids will be inserted midspan between the full grid assemblies as shown in Figure 2.
The partial grids will provide additional support for the five stainless steel rods and three adjacent fuel rods in Row 1 of the modified fuel assemblies plus the eight fuel rods in Row 2 behind the stainless steel rods.
The materials and design of the partial grids are similar to that for the standard grid assemblies. Stainless steel sleeves will be welded on two stainless steel rods above and below the partial grids as shown in Figure 2 to ensure that the partial grids are properly located. The fuel rods and stainless steel dummy rods are supported by grid springs and dimples in the same manner as the standard grid assemblies. No changes will be made to the standard grid assemblies. Fuel asseaolies modified in this manner will be located on the periphery of the core during subs;.quent fuel cycles.
2.
Discussion of the Likelihood of Further Damage, Effect on Structural Integrity and Effect on Core Performance a.
Stainless Steel Rods With regard to the center-injection assemblies, the most suscep-tible fuel rod (the one most nearly aligned with the baffle-plate gaps) and the two adjacent fuel rods in the first row will be replaced with dummy stainless steel rods to preclude the possi-bility of further baffle-jet induced failures. Previous failures at Trojan have been limited to the third rod for fuel assemblies located adjacent to center-injection baffle joints. The increased stiffness of the stainless steel dummy rods compared with normal fuel rods will tc.a to reduce the amplitude of vibration induced by baffle-jetting. Replacement of the adjacent rod on both sides ensures that damaging vibration will not be propagated to fuel rods.
l Trojan Nuclear Plant Robert A. Clark Docket 50-344 May 21, 1982 License NPF-1 LCA 88 Page 4 of 7 With regard to fuel assemblies located adjacent to the corner-injection baffic joints, the water-jet passes along the face of the fuel assembly, rather than impinging directly on the face of l
the fuel assembly. Excessive mass flow past the fuel rods can cause vibration which ultimately results in failure of the rods.
The first five fuel rods on the face of the eight fuel assemblies subject to this type of flow will be replaced with stainless steel rods.
Here age *-
the increased stiffness due to the stainless steel rods tc.ms to reduce the amplitude of the baffle-jetting induced vibration and the likelihood of propagation to adjacent rods. The fuel assemblies located next to the remaining eight corner-injection baffle joints will not be modified since they are not likely to be subject to baffle-gap / water-jet induced vibration. The baffle joints in these locations (Core Positions:
B-3, B-13, C-2, C-14, N-2, N-14, P-3 and P-13) are covered by baffle angles which wrap around and are bolted to the back of the baffle plate joints. No damage was observed in fuel assemblies located in these eight locations during the visual and sipping examinations at the end of Cycle 4.
The stainless steel dummy rods are expected to have a negligible effect on the fuel assembly structural response since the latter is dominated by the skeleton design of the fuel assembly and the axial loads are primarily taken up by the guide thimbles. Tne rods are held in place axially by spring friction at each grid.
Differences that may occur in the axial growth of the stainless steel rods compared with that of the normal fuel rods are accom-modated by axial slip at the grids. This assures that dummy rods will not tend to bow and thereby alter adjacent flow channel areas. Hence, coolant flow rates in the neighborhood of the dummy rods will be unaffected.
Operation with the current baffle gaps will not lead to excessive core bypass flow. The corner-injection baffle joint gaps were measured and determined to be smaller than the limits set by Westinghouse for excessive core bypass flow. The center-injection baffle joint gaps are expected to be smaller than the corner-injection joint gaps, since they were peened and measured at the end of Cycle 3.
Therefore, the core bypass flow assumptions used in previous accident analyses remain valid.
The stainless steel rods will not greatly impact nuclear design.
The effect of the stainless steel rods, both in the periphery of the core and in the interior locations, was evaluated prior to using the two previously modified assemblies in Cycle 3 and Cycle 4 (
References:
LCA 61 and the PGE-to-NRC letter dated February 5, 1981). These evaluations concluded that the stain-less steel rods will have an insignificant impact on nuclear and thermal limits and that the use of stainless steel-rodded assemblies can be accommodated in normal fuel management schemes.
Although a larger number of stainless steel rods will be used in
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Trojan Nuclear Plant Robert A. Clark Docket 50-344 May 21, 1982 License NPF-1 LCA 88 Page 5 of 7 Cycle 5 and in future cycles as a result of the proposed change, the impact on nuclear and thermal limits is again expected to be small. The effect of the stainless steel rods will be addressed prior to Cycle 5 startup as part of the Westinghouse and PGE Cycle 5 Reload Safety Evaluation. This evaluation will verify that existing Technical Specification limits will not be exceeded i
and that all applicable FSAR safety analyses remain valid. The evaluation of the effects of the stainless steel rods will be submitted to the NRC prior to startup of Cycle 5.
Similar evaluations will be performed for other fuel cycles which include the modified assemblies.
Comparisons between expected and measured values will be obtained during startup testing and a physics startup test report will be submitted to the NRC within 90 days of completion of the Cycle 5 startup tests. In addition, measured power distributions will be compared with predicted power distributions routinely in accor-dance with Technical Specification 4.2.2.3 to provide assurance that the core is operating as designed.
b.
Partial Grids The partial grids act to increase the frequencies and decrease the amplitudes of the funda.aental modes of vibration for the rods in the 2 x 8 partial grids, and thereby raise the threshold for rod vibration which leads to damage. Westinghouse analyses have shown that the midspan supports will significantly increase resistance to damaging vibration. The number of rods to be encompassed by the partial grids has been chosen to ensure that the section of fuel assemblies most susceptible to damage are sufficiently protected against failures so that the damage will not propagate to adjacent fuel rods.
The partial grids will not encompass the guide thimbles which serve to take up the axial load on the fuel assembly. Since the pertial grids are being added to the normal fuel assembly and are not replacing any section of the fuel assembly skeleton, they are not expected to affect the capability of the fuel assemblies to withstand normal operating, seismic or refueling loads. Axial growth of the stainless steel rods and the fuel rods can be accommodated by axial slip through the partial grids. Sufficient clearance has been allowed between the stainless steel sleeves and the grid-strap dimples to accommodate this growth. Therefore the structural integrity of the modified fuel assemblies will be essentially the same as the standard fuel assemblies.
t Trojan Nuclear Plant Robert A. Clark Docket 50-344 May 21, 1982 License NPF-1 LCA 88 l
Page 6 of 7 With regard to core physics considerations, the addition of the partial grids is expected to have a negligible effect due to the small amount of material involved. The partial grids will be made of Inconel 718, which is not a strong adsorber of neutrons.
In addition, their location on the periphery of the core will minimiza the impact on neutron flux in the l
core. A visual examination of all the fuel assemblies con-taining partial grids will be performed at the end of Cycle 5 to assure that the partial grids are performing as expected and to verify that further baffle-jetting damage has not occurred.
3.
Effect on Technical Specifications Including Design Bases A waiver of Technical Specification 5.3.1 is necessary to allow modification of fuel assemblies with stainless steel rods and partial grids. Since the effects of stainless steel rods and partial grids are expected to be small, no change to existing power distribution limits in the Technical Specifications are expected to be necessary due to the proposed modifications alone. However, changes to the F
and FAH Technical Specifications may be necessary as a result xy of the need to replace the damaged fuel assemblies. These changes have been requested in LCA 87, which was submitted to the NRC on May 10, 1982. Being descriptive in nature, the design specifications have no specific bases, and thus, no changes to the bases for the Technical Specifications are necessary.
4.
Effect on FSAR Mechanical design of the fuel is described in FSAR Section 4.2, Nuclear Design in Section 4.3, and Thermal Hydraulic Design in Section 4.4.
The effects of the stainless steel dummy rods and partial grids are expected to be minimal and within the tolerances and allowances accounted for in the Safety Analysis Report. The areas of performance and analysis most likely to be affected have been addressed above. The effects on nuclear and thermal hydraulic design will be accounted for in the fuel management program and reload safety analysis. As a result of the negligible effects of this LCA on mechanical design, nuclear design and thermal hydraulic design, this change is not considered to involve an unreviewed safety question, and will not increase the probability or conse-quence of accidents previously considered, nor will it create any new accidents.
5.
Environmental Effects The proposed change will not change effluent types or increase amounts.
The Trojan Nuclear Plant operated within the reactor coolant activity Technical Specification limitations, even though fuel failures had occurred during Cycle 4.
Since the proposed modifications will act to reduce the potential for future fuel failures, activity levels are I
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Trojan Nuclear Plant Robert A. Clark Docket 50-344 May 21, 1982 License NPF-1 LCA 88 Page 7 of 7 expected to decrease (compared with Cycle 4) as a result of this change. No unreviewed environmental matter exists, and there will be no significant detrimental impact on the environment from this change.
6.
Effect on Other Licensing Documents, Commitments or Criteria The proposed change adds a commitment to provide information on the effect of the stainless steel rods prior to the atartup of Cycle 5.
In addition, commitments were added to inspect th. modified fuel assemblies at the end of Cycle 5 and to submit a Cycle 5 startup physics testing report to the NRC.
SCHEDULE CONSIDERATIONS Prompt review and approval of this LCA is requested in order to finalize the Cycle 5 core loading pattern and the corresponding reload safety analyses without impacting the refueling / maintenance outage schedule or the resumption of power operation scheduled for the first week of July, 1982.
BASIS FOR DETERMINATION OF AMENDMENT CLASS This LCA has been determined to result in a Class III amendment in accor-dance with criteria of 10 CFR 170.22. This LCA involves a single issue and does not involve a significant hazards consideration. A Class III amendment requires a fee of $4,000.
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