ML18066A263
| ML18066A263 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 07/31/1998 |
| From: | Robert Schaaf NRC (Affiliation Not Assigned) |
| To: | Haskell N CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| References | |
| TAC-M95134, NUDOCS 9808100134 | |
| Download: ML18066A263 (4) | |
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Mr. Nathan L. Haskell Director, Licensing Palisades Plant 27780 Blue Star Memorial Highway Covert, MI 49043 July 31, 199-
SUBJECT:
PALISADES PLANT-REQUEST FOR ADDITIONAL INFORMATION RELATED TO CONSUMERS ENERGY COMPANY'S REACTOR VESSEL FLUENCE CALCULATION (TAC NO. M95134)
Dear Mr. Haskell:
By letter dated April 4, 1996, Consumers Energy Company submitted a revised reactor vessel fluence calculation for the Palisades Plant. By letters dated June 12, June 21, August 28, September 9, September 19, and October 1, 1996, Consumers Energy replied to staff requests for additional information dated May 31 and August 14, 1996.. Additionally, meetings have been held on May 15, 1996, and January 15, February 23, and May 28, 1998, to facilitate technical dialog between Consumers Energy and NRC staff and their contractors regarding the proposed reactor vessel fluence calculation.
While the staff believes that it has communicated its concerns clearly in previous correspondence and meetings, Consumers Energy requested at the May 28, 1998, meeting that the staff prepare_questions stating the information needed to complete our assessment of the calculated 17% reduction in the Palisades reactor vessel fluence. The enclosed request lists the specific issues that the staff believes have not been addressed in the previous submittals or meetings regarding the Palisades reactor vessel fluence calculation. Without this information, the staff believes that Consumers Energy has not provided an adequate basis to approve the proposed reduction in the Palisades reactor vessel fluence. The enclosed list of questions is narrowly focused on issues that have not been addressed in terms of a consistent physical explanation of the methodology and measurements. We believe that by narrowly tailoring the questions, Consumers Energy will be able to address the issues in a precise and rigorous fashion, and will support its arguments with information that has a sound basis in the physics of fluence phenomena.
Please provide a response to the enclosed request for additional information within 60 days from the date of this letter. Should you have any questions regarding this request, please contact me at (301) 415-1312.
Sincerely, Original signed by CACarpenter for:
(~--~9808100134980731 PDR ADOCK 05000255 Robert G. Schaaf, Project Manager Project Directorate 111:..1 Division of Reactor Projects - Ill/IV Office of Nuclear Reactor Regulation p
PDR Docket No. 50-255
Enclosure:
Request for Additional Information cc w/encl: See next page DISTRIBUTION:
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NAME DATE
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Mr. Nathan L. Haskell Consumers Energy Company cc:
Mr. Thomas J. Palmisano Site Vice President Palisades Plant 27780 Blue Star Memorial Highway Covert, Michigan 49043 Mr. Robert A Fenech, Sr Vice Pres Nuclear, Fossil, and Hydro Operations Consumers Energy Company.
212 West Michigan Avenue Jackson, Michigan 49201 M. I. Miller, Esquire Sidley & Austin 54th Floor One First National Plaza Chicago, Illinois 60603 Mr. Thomas A McNish Vice President & Secretary Consumers Energy Company 212 West Michigan Avenue Jackson, Michigan 49201 Judd L. Bacon, Esquire Consumers Energy Company 212 West Michigan Avenue Jackson, Michigan 49201 Regional Administrator, Region Ill U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, Illinois 60532-4351 Jerry Sarno, Supervisor Covert Township P. 0. Box 35.
Covert, Michigan 49043 Palisades Plant Office of the Governor P. 0. Box 30013 Lansing, Michigan 48909 U.S. Nuclear Regulatory Commission Resident Inspector's Office Palisades Plant 27782 Blue Star Memorial Highway Covert, Michigan 49043 Drinking Water and Radiological Protection Division Michigan Department of Environmental Quality 3423 N. Martin Luther King Jr Blvd P. 0. Box 30630 CPH Mailroom Lansing, Michigan 48909-8130 Gerald Charnoff, Esquire Shaw, Pittman, Potts and Trowbridge 2300 N Street, N. W.
Washington DC 20037 Michigan Department of Attorney General Special Litigation Division 630 Law Building P.O. Box 30212 Lansing, Michigan 48909 July 1998
REQUEST FOR ADDITIONAL INFORMATION RELATED TO CONSUMERS ENERGY COMPANY'S REACTOR VESSEL FLU ENCE CALCULATION PALISADES PLANT DOCKET NO. 50-255
- 1.
Uncertainty Values. In the methodology utilized for fluence determination, the calculated fluence value and the contribution of high energy dosimeters is effectively ignored. The staff suspects that this effect probably arose from the assignment of large uncertainties to the calculated values in the methodology. Please provide a complete list of all the uncertainties, including the covariances (and associated gamma values),
for all the quantities involved in the FERRET calculation and justify application of these values to the Palisades plant fluence determination. The justification should be based on analytical as well as physical reasoning. Any values and/or assumptions based on educated guesses or that are not quantified or justified with data should be clearly identified.
- 2.
Dosimeter Discrepancies. The staff noted that the high and low energy dosimeter readings imply a different calculational bias; the high energy dosimeters indicate an M/C of approximately 1.0 while the low energy dosimeters indicate an M/C of approximately 0.83. However, the staff cannot identify a physical reason for these differences. Please identify and discuss the physical basis for the difference between the bias inferred from the high and low energy dosimeters.
- 3.
Position Uncertainty. The Consumers Energy/Westinghouse Palisades "best-estimate" fluence is based entirely on the dosimeter measurements. Because of the extremely strong fluence attenuation, the fluence measurement is sensitive to the position of the dosimeters relative to the few peripheral fuel assemblies that dominate the dosimeter response.
The current Palisades dosimetry measurements (before adjustments) have been corrected twice for geometrical causes. In view of these corrections and the position sensitivity of the measurements, the proposed relatively small(< 5%) dosimetry position uncertainty does not appear credible. In order to support the use of these measurement uncertainty values, provide a detailed justification for the following measurements:
(1) accelerated capsule, (2) in-vessel capsules, and (3) cavity measurements. To the extent possible, this justification should be based on Palisades-specific as-built geometry data and should account for the effect of radial, axial, and azimuthal displacements.
ENCLOSURE
2
- 4.
Cavity Dosimetry. In view of the difference between the cavity and in-vessel neutron spectrum, identify and discuss the physical mechanism that justifies the use pf the cavity measurement to calculation (M/C) comparisons to reduce the 1.0 MeV < E < 3.0 MeV in-vessel spectrum. Specifically, the number of in-vessel 1.0 MeV < E < 3.0 MeV neutrons is determined by the complex slowing down process that takes place at the steel/water interface at the inner wall of the vessel while the neutrons detected by the cavity dosimetry (especially the Cu-63, Ti-46, Fe-54, and Ni-58 dosimeters) are independent of this process. In fact the cavity neutrons undergo the entirely different slowing down process resulting from the attenuation through the 8.25-inch thick steel vessel. Therefore, justify the use of the cavity M/Cs to adjust the 1.0 < E < 3.0 MeV in-vessel fluence.
- 5.
Guide E944-96. "Standard Guide for Application of Neutron Spectrum Adjustment Methods in Reactor Surveillance," E-944 states that "Adjustment methods provide a means for combining the results of neutron transport calculations with neutron dosimetry measurements in order to obtain optimal estimates of neutron damage exposure parameters with assigned uncertainties. The inclusion of measurements reduces the uncertainties for these parameter values and provides a test for the consistency between measurements and calculations and between different measurements. This does not however imply that the standards for measurements and calculations of the input data can be lowered; the results of any adjustment procedure can be only as reliable as are the input data" (emphasis added).
In view of the energy spectrum dependent M/C results, how was the data reliability, compatibility, and statistical significance for the adjustment operation established?
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Fluence Methodology. The proposed Palisades adjustment of 17% in the vessel fluence has been called a calculational bias. This implies that fluence measurements in similar plant settings that have been analyzed with the same methodology should exhibit the same trend of substantial underprediction with respect to the calculation.
However, this is not the case with the Westinghouse/Palisades method. For the 21 plants analyzed by Westinghouse (and presented in previous meetings) identify the physical phenomena that cause them to exhibit different behavior than Palisades.
- 7.
Fluence Methodology. The proposed Westinghouse/Palisades vessel fluence is based on an assumed DORT calculated overprediction of the E < 3.0 MeV fluence of approximately 17% and an essentially correct DORT prediction of the E > 3.0 MeV fluence. Please identify the flaws in the Palisades fluence calculation by providing an explanation of this overprediction including: (1) the identification of the physical mechanism or approximation responsible for the overprediction (e.g., group structure, cross sections, fission spectrum, etc.), (2) a discussion of the responsible mechanism describing the phenomena and the source of error, and (3) a revised DORT calculation correcting the E < 3.0 MeV overprediction.