ML19320C177
| ML19320C177 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 06/27/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19320C171 | List: |
| References | |
| NUDOCS 8007160376 | |
| Download: ML19320C177 (7) | |
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b [ f aar: gk UNITED STATES NUCLEAR REGULATORY COMMISSION a
L rj WASHINGTON, D. C. 20666
\\*****/ SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 45 TO FACILITY OPERATING LICENSE NO. NPF-1 PORTLAND GENERAL ELECTRIC COMPANY THE CITY OF EUGENE, OREGON PACIFIC POWER AND LIGHT COMPANY TROJAN NUCLEAR PLANT DOCKET NO. 50-344
1.0 Background
By application dated May 12,1980 (Ref.1), Portland General Electric Company (the licensee) oroposed to amend Operating License NPF-1 to permit installation of two assemblies with a maximum of three rods per assembly with dummy (solid) stainless steel (SS) rods. Specific-ally, it was requested that the requirements of Technical Specification 5.3.1, that each fuel assembly in the core should contain 264 Zircaloy-4 clad fuel rods, be waived to permit replacement with the dumy SS rods in two locations which have been subject to cross flow (baffle jetting).
The rt.ason for the proposed change was that the fuel inspection performed during refueling after cycle 2 operation revealed that significant degrad-ation of one fuel rod in two separate fuel assemblies had occurred.
One fuel assembly was located on the outside of the core adjacent to a baffle corner during the second cycle of operation.
The other fuel assembly j
had been located on the outside of the core adjacent to a Saffle corner during the first cycle and had then been moved to an inside position dur-ing the second cycle. Tiie method of failure was identified as fuel rod j
vibration caused by impingement of cross flow through the, baffle joint at the corner. A description of the incident is provided in Licensee L
Evpnt Report (LER) 80-06 (Ref. 2).
800 716 03N
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2.0 Evaluation A review was conducted based on (a) fuels (materials) and (b) physics (neutronic) considerations.
Materials considerations included the likelihood of further damage to modified peripheral assemblies, and potential effects on fuel assembly structural integrity.
Physics concerns mainly involved the potential effects on power distribution, and surveil lance requirements.
2.1 Materials Considerations With regard to the likelihood of further damage to the modified peripheral assemblies, PGE cited (Ref.1) Westinghouse analyses that indicated that potential damage is restricted to the three fuel pins adjacent to the gap between baffle plates. The W analytical models are substantia'ai by the fact that no instances have been observed to date damage to fuel rods other than those adjacent'to the gap, for a baffle af the Trojan configura-tion.
Thus, replacing the most susceptible fuel rod (the one most nearly aligned with the baffle plate gap) with a dummy rod should reduce the likelinood of further baffle-jetting-induced damage at that rod location during cycle 3, while replacement of the two adjacent rods would provide additional assurance that the central rod will not impinge on fuel rods during any jetting-induced vibratory motion.
Moreover, the increased stiffness of the stainless steel dummy rods compared with normal fuel rods
. should tend to reduce the amplitude of the baffle jetting-induced vibration, thereby reducing the likelihood of propagation of dam-age to adjacent rods. The above factors thus provide support for the licensee's belief that the stainless steel rods will provide a satisfactory temporary corrective solution to the baffle i
jetting problem.
With regard to the effect of the stainless steel dummy rods on fuel assembly structural response, it was noted by the licensee that the structural response is dominated by the skeleton design of the assembly, that is, the axial loads are taken up primarily by the guide thimbles rather than the fuel rods. Therefore, there is substantial reason to believe that the overall effect of re-placing three of the 264 fuel rods with dummy stainles; steel rods on the capability of the assembly to withstand normal operating i
seismic or refueling loads should be negligible.
Notwithstanding the apparent reasonableness of the above arguments oncerning the material performance aspects of the dummy stainless steel rods, we balieve that further surveillance is required, both to confirm the adequacy of the ' temporary fix as well as to assure
'that further baffle jetting failures have not occurred at the other ten "inside corr.er" baffle locations.
Potential strupillance re-quirements were discussed with PGE representatives (Ref. 3). At that time the PGE representatives asserted that the reactor coolant l
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radiochemistry could be used to ascertain the status of the core (with regard to number and general location of fuel failures) and that further surveillance was, therefore, unnecessary.
Further information concerning the radiochemistry aspects of baffle jetting was subsequently submitted by Westinghouse (Ref. 4). While we believe that radiochemistry monitoring and analysis holds con-siderable promise as an alternative or an adjunct to physical sur-veillance of the fuel, that approach is sufficiently novel to re-quire more extensive review than could be carried out on a schedule consistent with the cycle 3 reload.
Therefore, we will require the licensee to perform a visual examination of the 12 fuel assem-blies located near "inside" baffle corners (10 standard assemblies plus 2 modified a> emblies) to assure that further unanticipated baffle jetting wear has not occurred. As a general rule, however, we would be receptive to the use of radiochemistry approaches to j
fuel performance monitoring, and we would be willing to review fu-ture submittals in 'this area (e.g., cycle 4 reload).
2.2 Physics - Neutronics Considerations As acknowledged by the licensee Ira f.1 ),
2 placing an active fuel roo with a dummy red has the +ffect I cau *ng a small local flux increase with a redistribution of p at.
'o the adjacent fuel pins.
Because only two assemblies will be modified, the change is asym-metric and will introduce a flux tilt into the core. -However.
3 aince the assemblies are on the periphery of the core and are in low power regions, the effects of the asymmetry on power distribu-tion are expected to be very small; viz., about 0.2% quadrant tilt throughout the cycle. Moreover, since measured power distri-butions will be compared with predicted power distributions every 3
month, these comparisons will be a good indicator of whether the core is operating as desired.
The licensee is required to submit a report of the phfsics startup tests to the NRC within 90 days of completion of the tests.
The report will include measured vs. predicted power distributions at low power and at full power, as well as temperature coefficient, rod worth, and boron endpoint comparisons.
3.0 Sumary In summation, based on our review of the predicted effects of the proposed changa, the physics startup test report commitment, and the required fuel surveillance, we find the change acceptable for cycle 3 operation. The I
' acceptance is limited to the placement of the modified assemblies in the two peripheral core locations B12 and M2.
?f the licensee desires either to relocate these two assemblies or to 4r:rease the number of modified assemblies in future reloads, further application and review will be re-quired.
- 4.0 Environmental Conclusion We have determined that the proposed license amendment does not authorize a change in effluent types or total amounts nor an increase in power
'evel and will not result in any significant environmental impact.
Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environ-mental impact and, pursuant to 10 CFR 551.5(d)(4), that an environmental impact statement, or negative declaration and environmental impact apprais-al need not be prepared in connection with the issuance of this amendment.
5.0 Conclusion We have concluded, based on the considerations discussed above, that: (1) because the proposed license amendment does not involve a significant increase in the probability or consequences of accidents previously con-sidered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the propesed manner, and (3) such activities will be conducted in compliance with the Commission's regula.
tions and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
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' References 1.
C. Goodwin, Jr. (PGE), Letter to Robert A. Clark (NRC) Transmitting License Change Application 61, May 12, 1980.
2.
License Event Report 80-006/0lT-0, April 25,1980.
3.
P'. Tokar and C. Trammell (NRC), Telecommunication with G. Baer (PGE),
hay 30, 1980.
4 4.
George Rymer (W), Telecon-BR-DF05 to M. Tokar (NRC), June 10, 1980.
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