ML19274E466
| ML19274E466 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 03/19/1979 |
| From: | Vandenburgh D Maine Yankee |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| WMY-79-20, NUDOCS 7903260219 | |
| Download: ML19274E466 (4) | |
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- TURNPIKE ROAD (RT. 9) s ENGINEERING OFFICE WESTBORO, MASSACHUSETTS 01531 y
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<t'f 617-366-9011 7;12O WMY 79-20 March 19, 1979 United States Nuclear Regulatory Cocmission Washington, D. C.
20555 Attention: Office of Nuclear Reactor Regulation
Reference:
- 1) License No. DPR-36 (Docket No. 50-309) 2)
A. Husain et.al., " Application of Yankee-WREM Based Generic PWR ECCS Evaluation Model to Maine Yankee," YAEC-1160, July 1978.
- 3) Letter, R. H. Groce to Office of Nuclear Reactor Regulation, January 16, 1979, WMY 79-4.
- 4) " Status Report by the Directorate of Licensing in the Matter Combustion Engineering, Inc. ECCS Evaluation Model Conformance to 10 CFR50, Appendix K", October 15, 1974.
Dear Sir:
Subjec t: NODALIZATION CHANGES TO ELOWDOWN AND HOT CHANNEL MODELS OF YAEC'S WREM-BASED GENERIC PFR ECCS EVALUATION MODEL Nodalization changes have been made to the Maine Yankee Blowdown and Hot Channel Models (Figures 2.1 and 2.22 of Reference 2) in order to avoid calculational instabilities occurring during the ECC injec tion phase and to more accurately represent core behavior when analyzing cores with top peaked axial power shapes. The revised blowdown and hot channel model are shown in Figures 1 and 2 (attached).
Modification to the Intact Looo Cold Leg Nodalization In the Maine Yankee Blowdown Model presented in Figure 2.1 of Reference 2, the intac t loop cold legs were modeled utilizing two RELAP4 control volumes.
In the proposed model, the intact cold legs will be modeled as one control volume as shown in Figure 1.
This modification of enlarging receiver volumes for ECC injection in order to eliminate excessive computer running time caused by high condensation rates is in line with suggestions made by EGSG, Idaho, Inc. at the INEL Code Users Workshop held in August 1978.
A study was performed to determine the sensitivity of this model change on peak clad temperature.
To be consistent with the calculations reported in Reference 2, the 1.0 DECLG Sample Problem Case (1.406 Top Peak, 14.5 kw/ft 7 90326 0 Ali
w, United States Nuclear Regulatory Commission March 19, 1979 WMY 79-20 Page 2 Peak LHCR) was reanalyzed using a single intact loop cold leg volume in the blowdown model. The peak clad temperature was calculated to be 2060 F, an 80F reduction in PCT from the previously reported value of 20680F for this case (Reference 3).
Thus, modeling the intact cold legs as one volume does not appear to have a significant impact on predicted peak clad temperatures.
Modification of the Core Nodalization In the three loop sample problem blowdown (Reference 2), the core was divided into six volumes, i.e. two sets of three axially stacked volumes--one set for :'ie hot assembly and one set for the rest of the core. A top peaked axial power shape was shown in Section 3.2 of Reference 2, to be uore limiting than a cosine power shape for a given peak linear heat generation rate. YAEC stated in Section 3.2 that the top peaked axial power shape will be used in licensing evaluations for Maine Yankee. A ten volume model of the core which allows for a better representation of a top peaked axial power shape than a six volume core representation is being proposed.
Figures 1 and 2 show the modified model.
Work performed by the Regulatory Staff in its review of Combustion Engineering, Inc.'s ECCS Evaluation Model (Reference 4) justifies the use of a ten volume core representation, i.e. two sets of axially stacked volumes representing the core and hot assembly re gi ons.
In its review, the Staff states "Five axial nodes were selected for the evaluation model because:
(1) models with two or three axial nodes are not able to properly represent different axial power shapes and do not provide a converged flow rate solution; and (2) among core models having four or more axial nodes, considering all power shapes, the five axial node model produced the highest clad temperature."
Thus, YAEC will use the ten volume core representation in all future licensing applications for Maine Yankee and other cores with top peaked axial power shapes.
We trust that the above information is satis f ac tory.
Please note that the Maiue Yankee Cycle 5 LOCA/ Break Spectrum analysis is scheduled to begin forthwith and if any questions or problems should arise concerning our use of these revised models, please feel f ree to call Mr. W. J.
Szymczak as soon as possible at our Engineering office, 20 Turnpike Road, Westboro, Massachuseets, (617) 366-9011, extension 215.
Very truly yours, MAINE YANKEE ATOMIC POUER COMPANY D. E. Vandenburgh Vice President WJS/ nam Attachments
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ACCUMUL A TOR ACCUMULATOR Figure 1 Maine Yankee Blowdown Model REV 1 3-19-79
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