ML20199D349

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Topical Rept Evaluation of BAW-1875, B&W Owners Group Cavity Dosimetry Program. Rept Acceptable for Referencing in License Applications
ML20199D349
Person / Time
Issue date: 03/18/1986
From:
NRC
To:
Shared Package
ML20199D338 List:
References
TAC-59826, NUDOCS 8606200219
Download: ML20199D349 (4)


Text

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,. ENCLOSURE BAR 18 m EVALUATION OF THE B&W OWNERS GROUP CAVITY DOSIMETRY PROGRAM REPORT BAW-1875 (TAC NO 59826)

INTRODUCTION The B&W Owners Group by letter dated September 16, 1985 (Reference 1) requested evaluation of a reactor cavity dosimetry program which is under development for use in B&W plants. Additional information was submitted on January 16,1986 (Reference 2) and a staff applicant meeting was held in Rethesda on January 29, 1986 to discuss the report.

The purpose of the fast neutron surveillance program is to ascertain at any

  • point in plant life the accumulated fast neutron fluence and, hence, the p . material toughness through a fluence vs toughness relationship. The .

regulatory requirements,for fracture toughness and beltline material e

surveillance are specifdd in 10 CFR 50, Appendix G and Appendix H respectively.

For the B&W plants the currently approved integrated surveillance program will provide all of the required empirical information for the fluence-toughness relationship by the early 1990's when most or all of the surveillance capsul,es will have been removed. The cavity dosimetry program will continue to provide pressure vessel irradiation data beyond the end of the capsule surveillance, in an accurate and convenient manner. Cavity dosimetry has been the subject of research and development programs in several organizations i for several years. It is now possible to accurately measure and calculate the I

fast neutron flux in the reactor cavity due to advances in dosimetry technology and computational techniques.

THE BAW CAVITY DOSIMETRY PROGRAM The B&W program consists of a benchmarking phase to be carried out in the Davis Besse plant and a plant specific phase, where the results of the benchmarking will be adapted for plant specific applications.

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A variety of dosimeters has been selected to assure accurate and wide energy

]' range measurements with the potential of self consistency checks. Axial and azimuthal measurements will be performed. The experiment provides the means for accurate identification of the detector location with respect to the core to minimize a known potential source of measurement error. Proven analytical techniques will be used to determine the cavity neutron streaming and to evaluate its effects on the dosimeters and cavity flux distribution.

The exposed monitors will be counted and calculated by four different institutions with acknowledged expertise. The benchmarking will allow B&W to

accurately measure the fast flux in the cavity and to correlate it with the measured and estimated value of the flux in the inside surface of the pressure vessel. In this manner a semiempirical method will be developed to correlate cavity fast flux measurements with pressure vessel fast flux.
  • This program proposes to introduce dosimeters for recording integrated vessel fluence over the lifetime of the vessel. Such dosimeters (not required by the regulations) will be ab,le to provide actual measured fluence vs time for long irradiation times. Therefore, the cavity dosimetry program has the potential i to provide the means for short and long term pressure vessel flux measurements
to be performed accurately and conveniently.

l CONCLOSION The B&W Owners Group has submitted a report outlining a program for the development of a cavity dosimetry method which will be able to correlate rea.ctor cavity fast flux measurements with the pressure vessel\fast neutron flux. The outlined method discusses all of the known critical problems for such measurements, for example, cavity streaming, detector location, detector orientation, etc. The method has the potential to provide the means for an extension of the current surveillance programs in the B&W plants and continuous long term measurements of the vessel fluence. Such a program is highly desirable.

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,, REFERENCES

1. Letter,~J. H. Taylor, B&WOG to C. O. Thomas, NRC dated September 16, 1986
2. Letter, J. H. Taylor, B&WOG to H. N. Berkow, NRC dated January 16, 1986 l

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