ML13331B227
| ML13331B227 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/03/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13331B226 | List: |
| References | |
| NUDOCS 8911130236 | |
| Download: ML13331B227 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION 9
WASHINGTON, D. C. 20555 ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO INTERIM-ACCEPTANCE-CRITERIA-FOR THE THERMAL SHIELD MONITORING PROGRAM SOUTHERN CALIFORNIA EDISON SAN ONOFRE NUCLEAR GENERATING STATION DOCKET NO. 50-206
1.0 INTRODUCTION
By letter dated September 6, 1989, the Southern California Edison Company, the licensee for the San Onofre Unit 1 nuclear power plant, submitted the interim acceptance criteria for the reactor vessel thermal shield monitoring program, (Ref. 1).
These interim criteria are required by License Condition 3.M, Amendment 127, issued May 15, 1989. License Condition 3.M was required in response to thermal shield support damage which was discovered in the last refueling outage. These interim criteria are in,effect until the licensee operates the plant for at least 45 calendar days at power levels above 85% and is able to establish final acceptance criteria.
2.0 EVALUATION Thermal shield monitoring is accomplished using both neutron noise analysis from the ex-core detector signals and acoustic noise analysis from the loose parts monitoring signals.
2.1 Neutron Noise In this method, at least three neutron noise inputs are recorded at least once a week. These recordings are then analyzed for power spectral density (PSD),
cross power spectral density, coherence and in-phase and out-of-phase PSDs.
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A number of baseline PSD curves were obtained from 80% to 90% power and interim acceptance levels were defined (1) at 80% above the baseline PSD where systematic data analyses will commence and (2) the level at which NRC notification is required. The last level is lower than the analytically estimated level when the last flexure is assumed failed. These levels will be adjusted for burnup and boron concentration changes throughout the cycle.
The above levels satisfy the requirements of License Condition 3.M and are acceptable.
However, the staff recommends the following improvements for the permanent surveillance criteria:
- 1. There should be a stated quantitative definition of the second level in the PSD baseline curves,
- 2. Although it is known from analytical work that the likely PSD changes from anticipated deterioration will be higher values in the 2-8 Hz frequency range, it is prudent to define lower PSD surveillance criteria, and
- 3. The bases for the projected adjustments as a function of burnup and boron concentration should be defined and quantified.
2.2 Acoustical Noise, Loose Parts Monitorin Acoustical noise monitoring is accomplished with the analyses of the signals of four accelerometers mounted on the reactor vessel upper flange. Audio recordings at power levels of 15, 30, 70 and 85% have been collected to establish a baseline. An accelerometer impact sensitivity test was performed which satisfies the requirements of Regulatory Guide 1.133. Acoustical noise spectral characteristics have been recorded at 85% power level.
Acoustical level (RMS values) is recorded at least five minutes twice a day. The recordings are examined once a week by a cognizant member of the licensee's staff. The acoustical recordings satisfy the requirements of License Condition 3.M and are acceptable.
3 However, the staff recommends the following improvements for the permanent surveillance criteria:
- 1. The results of the sensitivity tests should be given in terms of RMS vs time, rather than in terms of the raw signal.
- 2. While it is stated that measurements at power have been made, Figure 2L does not indicate any Mode 1 operation with the corresponding RMS volts.
- 3. The quantitative bases for the chardacterization of an "abnormal" acoustical signal in terms of signal RMS or signal signature should be developed and incorporated in the final acceptance criteria.
3.0 CONCLUSION
S The NRC staff has reviewed the "Interim Acceptance Criteria for the Thermal Shield Monitoring Program" of the San Onofre nuclear power plant. We find the acceptance criteria acceptable on the basis that they satisfy the requirements of License Condition 3.M and Regulatory Guide 1.133. However, the staff identified several improvements for the permanent acceptance criteria to be issued in the near future.
4.0 REFERENCE
- 1. Letter from F.R. Nandy, Southern California Edison Company to U.S.N.R.C.,
"Interim Acceptance Criteria for the Thermal Shield Monitoring Program, San Onofre Nuclear Generating Station Unit 1," September 6, 1989.
Principal Contributor: L. Lois