ML14192A726
| ML14192A726 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 12/23/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14192A725 | List: |
| References | |
| NUDOCS 8512260244 | |
| Download: ML14192A726 (5) | |
Text
SAFETY EVALUATION REVISED LOCA/ECCS ANALYSIS FOR H. B. ROBINSON UNIT 2 INTRODUCTION In reference 1, the Exxon Nuclear Company, Incorporated (Exxon) notified Region 5, pursuant to the requirements of 10 CFR 21.21(b), of an error in the LOCA analyses performed for D. C. Cook 1 and H. B. Robinson Unit 2. The error was an input error to the TOODEE2 code which resulted in an underprediction of the peak cladding temperature for a LOCA.
The TOODEE2 code is utilized as part of the Exxon ECCS Evaluation Model.
This code calculates the fuel rod heatup, following the end of the blowdown period, and the peak cladding temperature for the LOCA. In the affected analyses, the fuel pellets were modeled with eight radial rings. However, within the outer ring of the fuel pellet, the relative decay heat power density was set to zero. As a result, the total decay heat of the fuel rod was not modeled and the resulting peak cladding temperature was too low.
In reference 2, the licensee, the Carolina Power and Light (CP&L) Company, submitted the results of revised LOCA/ECCS analyses for H. B. Robinson Unit 2 with corrected input to the TOODEE2 code. This SER evaluates the licensee's submittal.
EVALUATION H. B. Robinson, Unit 2 is currently operating in its Cycle 10 reload.
LOCA/ECCS analyses were submitted, in references 3 through 5, to support the Cycle 10 reload. These analyses were reviewed by the staff, in reference 6, 8512260244 651223 PDR ADOCK 05000261 P
2 and were found to meet the acceptance criteria of 10 CFR 50.46.
In reference 2, the licensee informed the staff that the analyses in references 3 through 5 contained an error in the input to the TOODEE2 code.
Also within reference 2, the licensee presented the results of revised LOCA/ECCS analyses performed with the input error corrected in the TOODEE2 code. Specifically, the licensee repeated the burnup sensitivity studies and the analyses for the top peaked axial power shapes, used to establish the K(z) curve, of references 3 through 5. The reanalysis results in peak cladding temperatures in excess of the 2200OF criterion of 10 CFR 50.46 for the top peaked power shapes and the BOL cosine axial power shape. For the cosine power shape reanalyses at burnups of 9 MWD/kg and EOL, peak cladding temperatures of 1923 0F and 18880 F, respectively, were obtained. Thus, the revised analysis results indicated that, for burnups less than 9 MWD/kg, the Technical Specification total peaking factor (Fq) of 2.32 did not ensure compliance with 10 CFR 50.46. In addition, the Technical Specification K(z) curve was not supported by the revised analysis.
The licensee performed further reanalyses for the cases that violated the 22000 F criterion of 10 CFR 50.46. These analyses were performed by reducing the Fq in the TOODEE2 analysis until the 2200OF criteria was met. Using an Fq of 2.13, the BOL cosine power shape case resulted in a peak cladding temperature of 2064oF. The top peaked axial power shape resulted in peak cladding temperatures of 21950 F and 21870 F for the BOL and 9 MWD/kg cases, respectively.
3 As a result of the reanalysis, the licensee initially, in reference 2, administratively reduced power by 8 percent, reduced the allowable Fq to 2.13, and reduced the high flux trips by 8 percent. Subsequently, in reference 7, the licensee revised its corrective action by resetting the high flux setpoint to the value allowed by the current Technical Specifications and administratively limiting the allowed Fq and K(z) values to those values which were demonstrated acceptable by the revised analysis.
We have reviewed the licensee's analysis and corrective actions. The analyses were performed using the previously approved evaluation model with the TOODEE2 input corrected. Thus, an approved evaluation model was utilized. In addition, by only reducing the Fq in the TOODEE2 code, the effect of the reduced Fq values on the blowdown portion of the transient was conservatively neglected. Thus, we find that the revised Fq values and K(z) curve assure conformance with 10 CFR 50.46.
With respect to the licensee's corrective actions, we find the licensee's approach in reference 7 to be acceptable. Since the administrative values for Fq and the K(z) curve have been determined by appropriate analysis, there is no need to impose an additional power penalty as was initially utilized by the licensee. Furthermore, no reduction in the high flux trip setpoints are required as these are not determined by the LOCA analysis.
CONCLUSION With the revised Fq values and K(z) curve of reference 7, we find that H. B.
Robinson Unit 2 satisfies the requirements of 10 CFR 50.46.
REFERENCES
- 1.
Letter, C. Malody (Exxon) to J. B. Martin (NRC/Region V),
Subject:
Notification of Error in LOCA Analyses, September 30, 1985.
- 2.
Letter, A. B. Cutter (CP&L) to S. A. Varga (NRC),
Subject:
Recent Error in Exxon Fuel Calculation, October 8, 1985.
- 3. H, B. Robinson Unit 2 Large Break LOCA-ECCS Analysis With Increased Enthalpy Rise Factor, "XN-NF-84-72," July, 1984.
- 4. H. B. Robinson Unit 2 Large Break LOCA-ECCS Analysis With Increased Enthalpy Rise Factor:
Break Spectrum, "XN-NF-84-72," Supplement 1, August, 1984.
- 5. H. B. Robinson Unit 2 Large Break LOCA-ECCS Analysis With Increased Enthalpy Rise Factor:
K(z) Curve, "XN-NF-84-72, Supplement 2, August, 1984.
- 6. Memorandum, R. Wayne Houston to Gus C. Lainas, "SER Input for H. B.
Robinson, Unit 2, Cycle 10 Reload," October 5, 1984.
- 7. Letter, A. B. Cutter (CP&L) to S. A. Varga (NRC),
Subject:
Operating Plans Under Revised LOCA Analysis, October 15, 1985.
Mr. E. E. Utley Carolina Power & Light Company H. B. Robinson 2 cc:
G. F. Trowbridge, Esquire Mr. Dayne H. Brown, Chief Shaw, Pittman, Potts and Trowbridge Radiation Protection Branch 1800 M Street, N.W.
Division of Facility Services Washington, DC 20036 Department of Human Resources P.O. Box 12200 Raliegh, North Carolina 27605 Mr. McCuen Morrell, Chairman Darlington County Board of Supervisors County Courthouse Darlington, South Carolina 29535 State Clearinghouse Division of Policy Development 116 West Jones Street Raleigh, North Carolina 27603 Attorney General Department of Justice Justice Building Raleigh, North Carolina 27602 U.S. Nuclear Regulatory Commission Resident Inspector's Office H. B. Robinson Steam Electric Plant Route 5, Box 413 Hartsville, South Carolina 29550 Regional Administrator, Region II U.S. Nuclear Regulatory Commission Suite 2900 101 Marietta Street Atlanta, Georgia 30303 Mr. R. Morgan General Manager H. B. Robinson Steam Electric Plant Post Office Box 790 Hartsville, South Carolina 29550