IR 05000338/1981003
| ML19350C034 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 03/09/1981 |
| From: | Burnett P, Murphy C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML19350C032 | List: |
| References | |
| 50-338-81-03, 50-338-81-3, 50-339-81-02, 50-339-81-2, NUDOCS 8103240733 | |
| Download: ML19350C034 (8) | |
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UNITED STATES
~g EI NUCLEAR REGULATORY COMMISSION
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101 MARIETTA ST N.W.. SulTE 3100 ATLANTA.oEoRGIA 30303
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Report Nos. 50-338/81-03 and 50-339/81-02 Licensee: Virginia Electric and Power Company P. O. Box 26666 Richmond, VA 23261 Facility Name: North Anna Occket Nos. 50-338 and 50-339 License Nosc NPF-4. and NPF-7.. -
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Inspection at North Anna site near Mineral, Virginia Inspector:,
N mnM 9ksu fM P.T. BurnetT, Acting Chief, Test Program Section Date Signec Engineering Inspection Branch Approved by: 4/
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C. E. Murprty',J.'ia,,Jngineering Inspection Date Signec Branch, Division of Engineering and Technical Inpsection Dates of Inspection:. February 3-6, 1981 SUMMARY
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Areas Inspected This ' routine,' una'nnoun'ced inspection involved 22 inspector-hours ~onsite. The areas addressed included core performance and power distribution monitoring of both units and core performance-related startup tests of Unit 2.
Results.
No violations or deviations were identified.
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REPORT DETAILS 1.
Persons Contacted Licensee Employees
- W. R. Cartwright, Station Manager
- 0. L. 8enson, Superintendent - Technical Services
- J. P. Smith, Engineering Supervisor - Performance Tests
- M. A. Harrison, Resident CC Engineer Other licensee employees included two engineers and four office personnel.
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NRC Resident Inspectors
- E. H. Webster
'A. P. Tattersall
- Attended exit interview 2.
Exit Interview The inspection scope and findings were summarized on February 6, 1931 with those persons indicated in paragraph 1 above.
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Licensee Action on Previous Inspection Findings Not inspected.
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Unresolved Items Unresolved items were not identified during this inspection.
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Power Cistribution Monitoring a.
Documents Reviewed (References)
- (1) LER 50-338/79-001, January 15, 1979 (2) Letter, Baum (VEPCO) to O'Reilly (NRC),, Serial No. 024,
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January 11, 1979
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'(3)'. North Anna Power Stationi, Technical Specificatfort, Unit 1
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(4) ' Nor'tiUArina~~ Power ~ Station','Tectinical'Speciffcation;' Unit 2
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.(5). Letter, Browrt (VEPCO). to',0'. Reil.ly.(NRC), Serial N.o. 0248,
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February' 16, 1979
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'Xz-(6)'.: ;Lette, Brown ' (VEPCO)F to -O' Reilly ; (NRC)', -Sertal No- 024C,
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February 27, 1979 (7) K(Z)-Related Correspondence:
-(a) JLER 50-338/78-98-
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(b) Letter, Brown (VEPCO) to O'Reilly (NRC), Serial No. 5758,
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(c) Letter, Brown (VEPCD) to O'Reilly (NRC), Serial No. 575C, February 27, 1979 b.
Axial Power Distribution Monitoring System (APCMS)
The licensee has earlier reported (references 1 and 2) the failure of the APCMS, as built, to correct for movable detector (MD) background and leakage currents when monitoring the axial power distribution in accordance with specification 4.2.6.1 (references 3 and 4). ' This failure could have resulted in nonconservatively low measured peaking factors. The corrective action proposed or implemented by the licensee was described in references 5 and 6.
The corrective action taken was to reduce alarm setpoints to accomodate backgrounds as high as two
- percent of. the' signal. -This-was thought"to be a conservative - adjust--
ment since background currents were not expected to total more than one percent. of the. signal.
The licensee also revised and modified a computer program for the' unit computers, FQSURVEY, which, on operator demand, performs the same surveillance as the APCMS. FQSURVEY modifi-cations included corrections for background current and for computer roundoff error in the APCMS reported earlier (reference 7) for K(Z),
normalized FQ(Z).
a More recently the NRC senior resident inspector reviewed the results of an incere flux map and observed that two movable MD's were analyzed as having' background currents in excess of three percent of the signal.
Although corrective maintenance actions were taken, the licensee did not report the event or otherwise address it in terms of the corrective action implemented for the APCMS. (The issues of reportability of that event and adherence to related commitments will be addressed in inspec-tion report 50-338/81-05 and 50-339/81-03.) At the time the high
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background was observed, power distribution monitoring was being performed under FQSURVEY. Hence, there was no concern that a hotspot ha.d gone undetected..
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i Nevertheless, the inspectors did express concern fer future monitoring being performed under APCMS 'with background being analyzed only once every 31 effective full power days (EFPD) in the course of the full-core flux map. This concern was intensified by.two other considera-
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tions:
(1) an earlier practice, never formalized, of observing MD backgrounds on the associated strip-chart recorders had fallen into disuse on, Unit 1 and had.never been instituted on Unit 2.
(2) Although
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...,.ea'chl.of..the '.two. APCMSi channen on.. eachl unit' hadi the capability ' to
' 1 alter'niitely ' address 'two MD's','each traversing Yifferent' fuel" bundles;
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.the practice.had been to dedicate.each APCMS channel. to one. MD and fuel
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The licensee had speculated that the.v0 background did not in fact exist and that the indications were a result of electrical or elec-
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tponic interface ' problems ~ between the MD sigrral conditioriing system and the. computer. Such prcblems would not-have affected the APCMS. In the
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exit interview the licensee made a commitment to investigate the suspect ci rcuitry and simulate, if possible, the high background indicated earlier. The licensee reported by telephone the following week that no interface problems were detectable, and that no combina-tion of switching errors gave the high backgrounc indications.
The licensee then agreed to the rollowing commitments for which tech-nical feasibility had been established:
(1) All APCMS would be operated in the alternate mode, and placards would be placed on the chassis immediately to that effect.
Further, whenever it was not possible to alternate detectors, FQSURVEY would be run at least weekly (Inspector Followup Items 50-338/81-03-01 and 50-339/81-02-01)..
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(2) The appropriate periodic test procedures and operating procedures would be revised to formalize the actions in (1) above. Reviewed and approved procedures would be in place by March 17, 1981.
(Inspector Followup Items 50-338/81-03-02 and 50-339/81-02-02).
(3) Plant and corporate offices personnel would cc,ecinately estan11sh mechanisms for tracking and trending MD performance and for not.ifying the plant staff when high MD backgrounds were observed from analysis of core flux maps.
(Inspector Followup Items 50-338/81-03-03 and 50-339/81-02-03)
The inspector reviewed internal memoranda addressed to the modification of FQSURVEY to eliminate round-off errors and account for MO background and a manual prepared for the operation of the modified program.
It was concluded that the program had been modified acceptably and tested adequately.,
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6.
Temperature Coefficient (61708)
a.
Documents Reviewed (References)
(1) North Anna Power Station, Units 1 and 2, FSAR Table 4.3-2 (2) North Anna Power Station, Units 1 and 2, FSAR Table 14.1-2
~ (3) North Anna Unit 1, Technical Specification 3/4.1.1.4.b
(4) North Anna Unit 2, Technical Specification 3/4.1.1.4.a l
(5),1-PT-13, Moderate Temperature Coefficient Measurement at Power
~ (.6)"' 2'-S0918', Nuclear Design Check Test
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7(7) LER '50-339/80-28" ' " ^ ' M " '
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.(8) VEP-FRD-39, NorthLAnna. Unit 2, Cycle.1 Startup Physics Test Report (9)' North Anna' Power Station, Unit 1 Startup Report
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Unit 1-Pursuant to' the. requirements offreference 3~,
the-moderator temperature
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coefficient. (MTC) at power with less. than 300 ppm 3 in the reactor coolant system (RCS) was measured by timely implementation of referer.ce
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5 on August 14, 1980. The test method used recuired precisely estab-lished and controlled equilibrium conditions for baron, xenon, power temcerature and pressure. Then RCS boron concentration was increased at constant power forcing a concomitant decrease in PCS temperature (T-avg). After establishing and measuring new equilibria, the boron concentration was reduced at constant power until T-avg was returned to the normal steady-state value. Baron concentration ranged feom 283 ppm to 300 ppm to 283 ppm during the test. Temperature swings were aoout -
and +4*F.
The final result was dependent on the measured differentials in baron concentrations and temperature, which could be determined more accurately than the end point values, analytically determined values of baron reactivity worth (units of pcm/ ppm), and a small correction for fuel doppler effects.
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The licensee concluded that the MTC at ocwer was -22.9 4.58 pcm/ F.
The analytically predicted value was 24.8 pcm/*F.
The limiting most negative value from reference 3 is -31 pcm/*F.
It follows that tne reported value is acceptable.
An alternate method of measuring the MTC at power using control-rod motion and the reactivity computer was attempted. The licensee judged the method to be unacceptable because it was difficult to evaluate the reactivity computer response during power transients.
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Unit 2 1sothermal temperature and moderator coefficients were measured during the startup program, reference 2, for the all-rods-out (1332 ppm B) and D-bank-in (1193 ppm B) conditions. Both refererice 6, the controlling test procedure, and reference 9 were reviewed to determine the accept-ability a.nd test results.
The test method was straightforward. At zero power, constant baron concentration and ' control-rod positions, and constant RCS' pressure, T-AVG was varied and the resulting reactivity measured in pcm, from the calibrated reactivity computer. Typically, the RCS was cooled 4*F, heated 8'F, and finally cooled back to the initial conditions to provide three measurements of the isothermal temperature coefficient.
~ The analytically derived value of the zero power doppler coefficient was then algebraically subtracted from the isothermal coefficient to obtain the MTC.
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' ~ Fir the fffstlieasErim'eni(d32ippmTB)Ttfie MTC' wfs positive, a' condi-
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tiort; contrary.to. technical,specificationspeference 4).,
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A timely report of'the' observation"was made to-t.ie NRC by'the licensee
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(reference 7).
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The second measurement at 1193 ppm B yielded a negative MTC.
The licensee used t$e method described in reference 8 to interpolate between the two measurements and to construct a set of roc-inser-tion-limit curves to ensue that under operating conditions the MTC was in the range reported in the FSAR (reference 1) anc required by the technical specifications (reference 4).
The isothermal temperature coefficients measured for Unit 2 were compared with those for Unit I under nearly identical conditions (reference 9). For 0-bank in the agreement between the two tests was within two percent of the mean.
For all-rods-cut the magnitude measured for Unit 2 was only two-thirds that of Unit 1.
In performing the Unit 2 measurement the scaling factor for reactivity was 10 pcm/
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inch.t 'In, performing.ather. measurements the licensee used either 5 pcm/ inch or 1 pcm/ inch, either of which gives better resolution of the reactivity change than the scale used. In this case the error, if any, was in the conservative' direction; hence the issue of proper scaling was not pursued.
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Control Rod Calibration (61710) Boron Reactivity Worth and Reactivity Monitoring a.
Documents Reviewed (references)
(1) North Anna Power Station, Units 1 and 2, FSAR, Table 14.1-2, Item
(2) North Anna Power Station, Technical Specifications Unit 1 (3) North Anna Power Station, Technical Specifications Unit 2 (4) 2-50-20, Red and Boron Worth Measurements During Boron Additions (5) 2-5U-17, Initial Criticality (6) VEP-FRD-39, North Anna Cycle 1 Startup Phys.ics Report (7) North Anna Power Station, Unit 1 Startup Test (8), 1-PT-11, Core Reactivity Balance
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Unit 2 Rod Calibration Calibration of the Control banks A, B, C, and 0 was accomplishad under
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The completed copy of that procedure was reviewed in its entirety. The reactimeter traces which were a part of the test record were spot checked for correct interpretation of reacti-vity incr y.ents and no discrepancies were found. Records of the inter-
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pretati.on of' each' reactivity ' increment in sequence 'as wel.1 ~ as the
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co'rrespondini df ffdentf al reactivity add' integral"refeti'vity "as a
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function; of, average bank position, were contained..in_ data sheets,
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'. enclosu'res ts 'tha procedure.' Review of ~ those records showed that two independent' asse'sment'of reictivity increments and control bank ' worths '
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s had been performed by the licensee staff. Acceptable agreement ::etween assessments was obtained in all cases.
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Prior to making reactivity measurements the reactivity computer was calibrated for both positive and negative reactivity insertions (refer-ence 5). Test records (reference 4) indicate that the calibration was repeated on two occasions, each with acceptable results, in the course of the control rod calibrations.
In both the tests reviewed and in other control rod. calibrations reported in reference 6 the agreement between measured and predicted control-bank and safety-bank reactivity worths satisfied the numerical acceptance criteria specified by the licensee, c.
Boron Reactivity Worth (Unit 2)
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In the-course of performing; the rod.-bank calibrations the RCS baron.
concentration was measured with care at five different red configura-tions at five different reactivity states, integrations of reactivity computer output.
The five point plot of reactivity over-the-range of 0 to 5978 pcm against boren concentration over-the-range 1332 to 784 ppm yielded a straight line, the slope of wnich was -10.87 pcm/ ppm B (reference 6).
The corresponding value for Unit I during startup tests was -11.08 pcm/ ppm (reference 7) to which tae licensee had added a range of 0.55 pcm/ ppm to define the numerical acceptance criterion.
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Unit 2 Shutdown Margin (61707)
Based upon the measurements <iiscussed above the licensee calculated the shutdown margin to 'oe 3485 pcm or 1715 pcm greater than the minimum required by specification 3.1.1.1 of reference 3.
' Reactivity Anomaly (Unit.1) '
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Speciffcat' ion 4.1.liof'refere'nce 2 requires a monthly comparison of
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observed and expected reactivity balance as a function of fuel burnup.
This requirement is implemented by a' periodic test (reference 8). The test, actually an analysis, was performed ten ti.'res in the course of cycle 2, which was terminated in December 1980.
The results and
~ frequency of all observations were within the limits of the speciff-cations.
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.J. ncore/Ex~ core Detector} Cal.fbrationsf(61705)
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'~'(1) JNorth-Anna Power Station;'FSAR '
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(2) ' North Anna Unit 1, Technical Specifications (3) North Anna Unit 2, Technical Specifications
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1-PT-20.2, Axial Flux-Dif ference Every-31-Effective Full Power'
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1-PT-22.1, Incore vs Excore Axial Offset Evaluation (6)
1-pT-22.2, Incore vs Excore Axial Off set (7) 2-SU-30, At power Nuclear Instrument Calibration b.
Unit 1 Monitoring the relationship between the axial flux offset incere, determined by periodic use of the movable detector syster., and the continuously monitored excore, power range nuclear was accomplished by performance of either of two periodic tests (references 5 and 6).
Review of the tests completed during cycle 2. showed that the tests were completed with acceptable results and frequency. The requirements of specification 4.2.1.3 (reference 2) were satisfied.
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Unit 2 The initial determination of the relationship between excore uoper and lower chamcer currents for the power range nuclear instruments in comparisen with measured incore axial flux differences was performed in the startup program (reference 7), prior to exceeding 75% power.
Review of the completed test, the data obtained in the test, and the analysis of of the data showed the results to be satisfactory. This test also satisfied the calibration requiremants of specification 4.3.1.1.1 (reference 3).
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Inspector Followup Items (Closed) 50-338/80-05-05. This item related to the method of determining the boron reactivity coefficient is closed based upon the observation reported in paragraph 7.c of this report and paragraph 7.c of report 50-338/80-12.
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