ML20072K610
| ML20072K610 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 03/03/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20072K608 | List: |
| References | |
| NUDOCS 8303300658 | |
| Download: ML20072K610 (6) | |
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'k UNITED STATES NUCLEAR REGULATORY COMMISSION g
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WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR' REGULATION
,,,g SUPPORTING AMENDMENT NO. 79 TO FACILITY LICENSE NO. DPR-30 COMMONWEALTH EDISON COMPANY AND IOWA-ILLIN0IS GAS AND ELECTRIC COMPANY QUAD CITIES NUCLEAR POWER STATION, UNIT 2 DOCKET NO. 50-265
Background
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The planned demonstration irradiation of pellet / cladding interaction (PCI)-resistant BWR fuel involves a large-scale (144 bundles) irradiation in Unit 2 of the Quad Cities Nuclear Power Station, starting with Cycle 6.
It is proposed that about half (64) of the bundles would be power ramped, in groups of 16, i.e., one group of 16 would be ramped at the end of each of four successive reactor cycles.
The term " barrier fuel" stems from the use of a 0.003-inch : hick, high purity zirconium liner, i.e., barrier, which is metallurgically bonded to the Zircaloy-2 structural part of the fuel rod cladding. The di-mensions of the fuel rods and the mechanical design of the fuel bundle are the same as the current General Electric (GE) prepressurized 8x8 retrofit bundle (P8X8R). A general description of the barrier fuel program, including information on the program scope, fuel loading and operation, fuel mechanical design, and safety analyses, was presented in a General Electric topical report, NED0-24259, (Ref.1) which was reviewed and approved by NRC in October 1980 (Ref. 2). Approval for the Quad Cities 2 (QC-2)
Cycle 6 Barrier Fuel demonstration was granted (Ref. 3) in December 1981, l
following (1) the receipt and review of some additional information on the proposed ramp and (2) the commitment (Refs. 4 and 5) of the licensee, Commonwealth Edison Company (Ceco) to provide more detailed information at a later date and to perform certain on-line monitoring and post-irradiation i
examinations. A letter satisfying the requirement for further information
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was submitted in November 1982 (Ref. 6).
Introduction In a recent letter (Ref. 7), requested that the QC-2 license be amended th allow l
a 10 percent increase in the allowable Linear Heat Generation Rate (LHGR) limit for the barrier fuel assemblies that will be power ramped (these demonstration barrier fuel assemblies are termed "special" assemblies). The current LHGR limit, specified in Technical Specification 3.5.J Local LHGR, is 13.4 kW/ft for all 8X8 fuel types. The new limit, specified in the attachment to the January 27, 1983 CECO letter (Ref. 7), would apply only to the Barrier Ramp 8303300658 830303 PDR ADOCK 05000265 p
2-Cell Fuel, and would be 14.7 kW/ft.
According to CECO, the requested increase in the LHGR limit is necessary to allow for the effects of Traversing Incore Probe (TIP) measurement asymmetries and other uncertainties on tha QC-2 process computer program P-1 that typically result in calculated peak LHGRs that are greater than the GE 3-D simulator results. Using GE's 3-D Core Simulator, a maximum LHGR of 13.02 kW/ft had been obtained.
Thus, the LHGRs calculated by P-1 for the special barrier fuel assemblies during the power ramps could be higher than the current Technical Specification limit of 13.4 kW/ft, thereby forcing corrective action, including control rod reinsertion, in accordance with the requirements of Technical Specification 3.5.J.
The license amendment proposed by CECO to accommodate the high LHGRs expected during the QC-2 Cycle 6 ramp adds a footnote to Technical Specification 3.5.J to read as follows:
For the purpose of the end-of-cycle 6 Barrier Fuel Ramp Test, the steady-state LHGR for the Barrier Ramp Cell fuel may exceed the maximum allowable LHGR identified in Technical Specification 3.5.J by no more than 10 percent (14.7. KW/ft), effective from initiation of the test;_
until end of Cycle 6 shutdown.
Evaluation Our technical evaluation of the proposed license amendment focused primarily on the question of whether fuel damage limits and licensing safety limits would be compromised by a 10 percent increase in LHGR.
In its January 27, 1983, submittal, CECO made the following key technical points in support of the proposed license amendment:
1.
"The basis for setting' the LHGR operating limit is that the peak LHGR during the normal or abnormal transient be less than or equal to the LHGR at which one percent plastic strain is calculated to occur.
For P8X8R fuel (U02 rods) this corresponds to an LHGR value of 22.7 kW/ft for exposures up to 25,000 mwd /t (Table 2-3 of NEDE-240ll).
2.
"Since only the sixteen bundles in the four ramp cells are expected to reach LHGR values near 13.4 kW/ft (actually only the 16 wide-wide corner pins in these bundles) the relaxation need only apply to these bundles.
3.
... the duration of operation above 13.4 kW/ft is expected to be
'less than 2 months due to local and core-wide fuel depletion as the coast-down progresses.
4.
"The Minimum Critical Power Ratio (MCPR) and Maximum Average Planar Heat Generation Rate (MAPLHGR) values are calculated to remain well below the operating limits during the demonstration and, therefore, no waiver of these limits is necessary."
E.
. We conclude that Items 2, 3, and 4 above are straightforward and provide unequivocal support for the proposed increase in LHGR limit.
Thus, the fact that (a) only relatively small fraction of the total number of rods in the core will be affected, (b) the duration of operation above the current 13.4 kW/ft limit will be limited, and (c) MCPR and MAPLHGR limits are not threatened provides substantial assurance that the fuel will perform satisfactorily.
From our review of Reference 7 for example, we have found that the calculated MCPR for the affected bundles during the Barrier Fuel Ramp test is not less than the previously approved Technical Specification operating limits, and the decay ratio for the affected fuel bundles, which have a lower power peaking factor, 1.35 as compared to 1.4 used for the Cycle 6 thermal hydraulic stability analysis, is less than the previously approved value specified in Cycle 6 operation. We, therefore, conclude that the thermal hydraulic acceptance criteria, viz., that MCPR is greater than 1.07 and that the design of the core must not be susceptible to thermal hydraulic instability, will not be violated during the test and the Technical Specification MCPR limit for the Cycle 6 operation is acceptable for the test.
The key issue concerns the basis for the LHGR limit. With respect to the basis for the LHGR limit, Section 3.4.3.4.2 of the QC-2 FSAR contains the ' statement that the " operating limit LHGR is established to provide margin between operating and fuel damage heat generating rates." The fuel damage heat generating rate that CECO refers to is the LHGR for one percent cladding strain..There are three minor problems, however, with the CECO analysis.
The first problem is that the 22.7 kW/ft LHGR value that CECO cites as corresponding to the one percent cladding strain value for UO2 rods at 25,000 mwd /t burnup is not the value listed in the latest amendment to GE's generic fuel design report, GESTAR-II (Ref. 8). Table 2-3a, LHGR of Calculated 1 Percent Plastic Diametral Strain for P8X8R and BP8X8R.
Fuel, lists >23.1 kW/ft for U02 r ds and 20.4 kW/ft for Gd-poison rods at 25,000 MW7/mt burnup, while the 22.7 kW/ft cited for U02 is, in fact, the value listed in Table 2-3a for Gd rods at zero burnup. Because these apparent discrepancies are quite small relative to the overall margin to the one percent strain LHGR, we do not consider them significant with respect to the activities related to the proposed license amendment. We will, however, clarify this matter as part of our on-going generic review of the barrier fuel amendment to GESTAR-II.
The second problem with the LHGR values for one percent strain is that the cited table in NEDE-240ll-P-A-5 indicates the same LHGR limit for fuel rods with standard Zircaloy cladding as for barrier cladding.
Inasmuch as 10 percent of the barrier fuel thickness is comprised of high purity zirconium, which is considerably more ductile than Zircaloy-2 (this is, in fact, believed to be the reason that the barrier cladding is more l
. resistant to pellet / cladding interaction (PCI) cracking than standard Zircaloy cladding), it follows that the LHGR for one percent strain for barrier fuel cladding should be siightly less than for standard Zircaloy-2 cladding. We would not expect the difference to be great, however, because the fraction of cladding wall thickness is small and the zirconium, itself, has some strength. We do not believe this issue is significant enough with respect to the activities related to the proposed license amendment. We will clarify this matter, however, as part of our on-going generic review of the barrier fuel amendment to GESTAR-II.
The third problem with the CECO analysis is that it focuses only on the margin to the one percent strain LHGR. Thus, analytical results are provided to show that there is substantial margin between the peak LHGR for overpower events (such as rod withdrawal error, fuel loading error, generator load rejection without bypass, and loss of feedwater heating) and the one percent strain LHGR.
From telephone discussions with the licensee and with GE to clarify the bases for the LHGR limit, it is clear-that the plastic strain criterion would be satisfied with a much higher limit than the 13.4 kW/ft now in place for Quad Cities - 2 (and all other BWR's of similar type).
It is clear also that the restraint on rod power resulting from the LHGR limit also serves to assure satisfactory fuel performance from the standpoint of a number of known potential fuel damage mechanisms, including hydriding, pellet-cladding interaction (PCI), and water-side corrosion. The conservation of plastic strain margin is, thus, a relatively insignificant factor in this case. The more important con-siderations that provide assurance that overall fuel performance will not be compromised are that the limit iincrease applies only to the special barrier fuel assemblies (i.e. a very limited number of rods) and for a limited duration (the last few months of the current operating cycle).
Evaluation Conclusions We conclude that there is reasonable assurance that a 10 percent increase in the allowable peak LHGR value for barrier fuel demonstration assemblies during the remainder of the current operating cycle (Cycle 6) will not compromise licensing safety limits on MCPR, MAPLHGR, or one percent cladding strain and that overall fuel performance will not be compromised by the LHGR limit increase.
Therefore, we conclude that the proposed license amendment is acceptable.
Environmental Consideration We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level 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 environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an environmental impact statement, or negative declaration and environ-mental impact appraisal need not be prepared in connection with the 1
issuance of this amendrent.
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. Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of an accident previously evaluated, does not create the possibility of an accident of a type different from any evaluated previously, and does not involve a significant reduction in a margin of safety, 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 proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimicab to the common defense and security or to the health and safety of the pubitc.
Dated:
March 3, 1983 Principal Contributor: Michael Tokar 1
1
References 1.
" Generic Information for Barrier Fuel Demonstration Bundle Licensing,"
NED0-24259, May 1980.
2.
L. S. Rubenstein (NRC) memorandum to R. L. Tedesco, "GE Barrier Fuel Topical Report Evaluation," October 17, 1980.
3.
L. S. Rubenstein (NRC) memorandum to R. L. Tedesco, " Quad Cities 2 Cycle 6 Barrier Fuel Demonstration," December 17, 1981.
4.
Thomas J. Rausch (CECO) letter to D. G. Eisenhut (NRC),
" Quad Cities Unit 2 Cycle 6 Barrier Fuel Demonstration Program," November 4,1981.
5.
L. DelGeorge (CECO) letter to D. G. Eisenhut (NRC), December 3,1981.
6.
T. J. Rausch (CECO) letter to D. G. Eisenhut, November 1,1982.
7.
T. J. Rausch (CECO) letter to H. R. Denton (NRC), " Quad Cities Station Unit 2 Proposed Amendment to Operating License DPR-30 Concerni.g the LHGR Limit During the Cycle 6 Barrier Fuel Ramp Test," January 27, 1983.
8.
"GE Standard Application for Reactor Fuel," NEDE-240ll-A-5, submitted by letter, J. S. Charnley (GE) to Frank J. Miraglia (NRC), November 19, 1982.
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