ML20138B970
| ML20138B970 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 11/27/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20138B968 | List: |
| References | |
| TAC-56794, NUDOCS 8512120419 | |
| Download: ML20138B970 (5) | |
Text
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>= assg'o, UNITED STATES NUCLEAR REGULATORY COMMISSION g
.a WASHINGTON, D. C. 20655
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 91TO FACILITY OPERATING LICENSE NO. NPF-3 TOLEDO EDISON COMPANY AND THE CLEVELAND ELECTRIC ILLLMINATING COMPANY DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET NO. 50-346
1.0 INTRODUCTION AND BACKGROUND
By letter dated February 13, 1985 (Ref. 1) Toledo Edison Company, the licensee for Davis-Besse Unit 1 made application for amendment to Facility Operating License No. NPF-3. Changes were proposed to the Davis-Besse Unit 1 Technical Specifications, Appendix A, which involve Figures 2.1-2, 2.2-1 Table 3.2-1 and the Bases. The proposed changes are revisions to the minimum Reactor Coolant System (RCS) fl s requirement to take credit for a decrease in core bypass flow as a result af using 64 new Lumped Burnable Poison Rod Assemblies (LBPRAs) in Cycle 5.
The licensee presented information to show that with the proposed changes adequate cooling of the reactor core is maintained such that the minimum required Departure From Nucleate Boiling Ratio (DNBR) is maintained.
2.0 EVALUATION The major bypass flow paths that exist in the Davis-Besse reactor vessel include: (1) empty guide tubes in fuel assemblies, (2) baffle plates, and (3) gaps around the hot leg nozzle in the upper core internals. In Cycle 5 64 new LBPRAs were inserted which reduced the bypass flow by filling empty guide tubes. The licensee provided the results of a hydraulic analysis which takes into account the decreased bypass flow area because of the insertion of the 64 LBPRAs. This resulted in a decrease of bypass flow from the 10.7% as used in the Cycle 5 Reload Report (no credit was taken for flow area reduction in Cycle 5 from that in Cycle 4) to a value of 8.1%.
The decrease in bypass flow results in a net increase in core flow even though there is a slight decrease in system flow from the added resistance of the 64 LBPRAs.
In discussions with the licensee, we requested information on the methods used in arriving at the old and new bypass flow values of 10.7% and 8.1%,
respectively. A sununary of the core bypass flow methodology, including a flow path model and various combinations of resistances and flow areas, was provided (Ref. 2) for clarification.
The licensee has proposed new values for the minimum RCS flow for both four reactor coolant pump and three reactor coolant pump operation as shown in 8512120419 851127 PDR ADOCK 05000346 P
PDR l
. Table 1 of this Safety Evaluation. These values take into account the increased core coolant flow because of the reduction of bypass flow from 10.7% to 8.1%.
New minimum RCS flow values were presented for use in Table 3.2-1 (page 3/4 2-14 of Technical Specification Section 3.2.5).
For four pump operation, the minimum RCS flow value was reduced from 396,880 gpm (110% of design flow plus 2.5% uncertainty) to 389,664 gpm (108% of design flow plus 2.5% uncertainty). For three pump operation, the minimun RCS flow value was correspondingly reduced from 297,340 gpm to 291,080 gpm. The minimum DNBR requirement remains unchanged from the Cycle 5 Reload Report.
This is because the new value of minimum RCS flow and the core coolant flow associated with it and the 8.1% bypass flow is greater than or equal to the present minimum flow associated with the 10.7% bypass flow.
The licer.see stated (Ref. 2) that the measured RCS flow from a heat balance was found to be 406,533 gpm. With a reduction of 2.5% for measurement error, this is 112.6% of the design flow (352,000 gpm) and 104.3% of the proposed Technical Specification minimum RCS flow (380,160 gpm). We have found the 2%
reduction (110% to 108% of design flow) in the minimum RCS flow acceptable because of the corresponding increase in core flow from the reduction in bypass flow. In addition, the measured RCS flow indicates that there is additional flow margin available. This evaluation is based on 64 LBPRAs. A decrease in the number of LBPRAs increases the core bypass flow and therefore reduces the active core flow. Therefore, the statement "These flows are based on having a minimum of 64 Lumped Burnable Poison Rod Assemblies in the core.", has been added to footnote (3) of Table 3.2-1 DNB Margin (page 3/4 2-14) of the Technical Specifications.
3.0 EVALUATION OF TECHNICAL SPECIFICATION MODIFICATIONS The minimum acceptable reactor coolant flow in gpm has been revi;ed as a result of reducing the percent of design flow rate from 110% to.08%.
This was possible because of the increase in core flow resulting from a decrease in core bypass flow as discussed in Section 2.0.
Table 1 lists the current and proposed Technical Specification flow rates for four and three pump operation as provided in Reference 1.
The pertinent Technical Specification pages shown below have been modified accordingly to include the proposed changes presented in Table 1 of this Safety Evaluation.
Page 2-3 (Required System Flow)
(Figure 2.1-2)
Page 2-7 (Required System Flow, 3-pump) - also contains (Figure 2.2-1) an editeHal change to clarify three pump operatt represents an " approximate" 25% flow reduction.
Page B 2-1 (Required System Flow, 4-pump; percent of Design Flow)
Page B 2-8 (Required System Flow) - also a typo error was (Bases Fig.2.1) corrected to change 89.3% for three pump 1
operation to 89.1%.
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- Page 3/4 2-14 (Required System Flow plus measurement error) -
(Table 3.2-1) also modified footnote (3) to include minimum number of lumped burnable poison rod assemblies at 64.
4.0
SUMMARY
We have reviewed the changes in flow rate shown on these pages in the Technical Specifications as proposed in Reference 1 and have found them acceptable for the reasons explained in Section 2.0.
5.0 ENVIRONMENTAL CONSIDERATION
This amendment involves changes in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes in surveillance requirements. We have determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase-in individual or cumulative occupational radiation exposure. The Comnission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment' on such finding. Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)f 9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.
6.0 CONCLUSION
We have concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not' be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations 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.
Dated:
November 27, 1985 The following NRC personnel contributed to this Safety Evaluation:
H.-Balukjian i
4.
)
TABLE -1 MINIMUM ACCEPTABLE REACTOR COOLANT FLOW (GPM) 4-Pump Operation 3-Pump Operation Current TS Proposed TS Current TS Proposed TS Required System Flow 387.200 380,160 290,100 283,980 Required System Flow 396,880 389,664 297,340 291,080 Plus 2.5% Measurement Error Percent of Design 110%
108%
110%
108%
Flow Rate
.i 6
l
- 4 References i
1.
Letter from R. P. Crouse, Toledo Edison Company, to John Stc1z, NRC, dated February 13, 1985.
4 2.
Letter from R. P. Crouse, Toledo Edison Company, to John Stolz, NRC, dated May 29, 1985. (Proprietary submittal.)
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