IR 05000338/1986001

Insp Repts 50-338/86-01 & 50-339/86-01 on 860106-10.No Violations or Deviations Noted.Major Areas Inspected: post-refueling Startup Tests & Moderator Coefficient Measurements at Power

ML20214D456
Person / Time
Site:	North Anna
Issue date:	02/18/1986
From:	Burnett P, Jape F NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:
Shared Package
ML20214D449	List: IR 05000338/1986001 ML20214D447
References
50-338-86-01, 50-338-86-1, 50-339-86-01, 50-339-86-1, NUDOCS 8603050188
Download: ML20214D456 (5)

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UNITED STATES

[p Katogb o NUCLEAR REGULATORY COMMISSION

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I [ n REGION li g j 101 MARIETTA STREET, t

• g ATLANTA, GEORGI A 30323

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I Report Nos.: 50-338/86-01'and 50-339/86-01 '

i Licensee: Virginia Electric and Power Company 1 Richmond, VA 23261 i l Docket Nos.: 50-338 and 50-339 License Nos.: NPF-4 and NPF-7 l

l Facility Name: North Anna 1 and 2

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i Inspection Conducted: January 6 -10, 1986 Inspecto : 4C&&

P T Burnett V Date Signed

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Approved by: //

F. Jape, SectTon Chief ic#- -

N/ Nb Date Signed

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Engineering Branch-i Division of Reactor Safety l SUMMARY j

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Scope: This routine, unannounced inspection entailed 32 inspector-hours on site j in the areas of post-refueling startup tests and moderator coefficient measure-l ments at power.

Results: No violations or deviations were identifie ,

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REPORT DETAILS Persons Contacted

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Licensee Employees K. L. Basehore, Supervisor, Nuclear Engineering C. B. LaRoe, Senior Engineer, Nuclear Engineering

• E.W. Harrell, Station Manager

• J. Lebenstein, Licensing Coordinator

• D. L. Reid, Reactor Engineer

• E. P. Smith, Assistant Manager (NS&L)

N. Smith, Engineer, Nuclear Engineering C. T. Snow, Supervisor, Nuclear Fuel Operations

• J. A. Stall, Superintendent of Technical Services Other licensee employees contacted included engineers and office personne NRC Resident Inspectors M.W. Branch, Senior Resident Inspector L. King, Resident Inspector

• Attended exit interview Exit Interview The inspection scope and findings were summarized on January 10,1986, with those persons indicated in paragraph 1 above. The inspector described the areas inspected and discussed in detail the inspection findings. No dis-senting comments were received from the licensee. Proprietary material was reviewed by the inspector during this inspection, but is not included in this repor . Licensee Action on Previous Enforcement Matters This subject was not addressed in the inspectio . Unresolved Items No unresolved items were identifie . Post-Refueling Startup Tests (72700, 61708, 61710)

Post-refueling startup tests for Unit I were performed at the beginning of Cycle 6 for Unit I using periodic test procedure 1-PT-94 (Revision 3),

Refuelig duclear Design Check. After establishing the zero-power testing range, sh ch determined the upper limit for reactivity computer measurements without dappler feedback effects, the licensee established the reliability range of the reactivity computer as -38 pcm to +54 pc ~

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The all-rods-out (AR0) critical boron concentration was then measured to be 1824 ppmB. The predicted concentration was 1856 ppmB. Using the analyti-cally predicted boron worth of 7.26 pcm/ ppm, the reactivity difference was 232 pcm less reactive than predicte The ARO isothermal temperature (ITC) was measured to be -1.64 pcm/F, the average of two measurements. At the conditions of measurement, the ed ITC was -1.49 pcm/F. The moderator temperature coefficient (MTC) predict-at AR0 was determined to be +.1 pcm/F, after subtracting the analytically-derived fuel doppler temperature coefficient (DTC) of -1.74 pcm/F. At power levels less than 70% rated thermal power (RTP), a MTC as large as 6 pcm/F is permitted by Technical Specification 3.1. The reactivity worth of control rod bank B was was measured during boron dilution using the reactivity computer. The measured worth of 1292 pcm was within 10% of the design worth of 1429 pcm. The corresponding changes in endpoint baron concentrations were 1635 ppmB measured and 1646 ppm 8 calcu-lated. Thus the average boron reactivity worth from ARO to B bank-in was 6.8 pcm/ppmB, which is within 10% of the predicted worth of 7.45 pcm/ppm The reactivity worths of each of the remaining control and safety rod banks were determined by rod swap with bank B. In all cases, the measured worths were less than the preiicted values, but in no case was the difference greater than 10% of the predicted valu The licensee was asked if any changes would be made in the Unit 1, Cycle 6 plant curve book presentations of control rod and boron worths in view of the consistently low measured values. The response was negative because the curve book values reflect a 10% reduction in calculated values to accommo-date such uncertainties. Data from the plant curve book are use to calcu-late shutdown margin and estimated critical conditio At the time of the inspection, Unit 1 had attained 30% RTP, but had not achieved the flux stability necessary to perform a flux-power map at that power.

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No violations or deviations were identified in the review of the completed

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portion of the startup test progra . Moderator Temperature Coefficient Measurement at Power (51708) Unit 2 l

To measure the MTC at power, once boron concentration has dropped to 300 i ppmB, as required by Technical Specification 4.1.1.4.b. the licensee uses

! periodic test procedure 2-PT-13 (Revision 3). The method of measurement avoids the use of a reactivity computer at power, because the licensee has estimated that the error in such measurements, due to doppler feedback effects, is at least 30% of the reactivity measurement. Instead, a method based on the careful determination of the controlled change in boron con-q centration and boron worth, which is constantly monitored during the fueT

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cycle, is used. In the measurement, the reactor is subjected to two small transients. In the first, turbine power is held constant, although thermal power may change slightly, while boron concentration is changed. In the second, power is changed without changing boron concentration. Symbolically the two transients may be described as follows:

RHO = (CB 4 - CB f)x RH08 = ITC(TAVG4 - TAVGf )B + DPC(Pj - Pf)B and 0 = ITC(TAVG; - W 7G )p + D N(Py-P)p f After some algebra, the combined equations may be written as:

ITC = RHOB(CB4 - CB f )B (TAVGj - TAVG f ) - (P9 - Pf)p x (TAVG9 - TAVGf )

(P9 - Pf)p and finally MTC = ITC - DTC where: RH0 = reactivity in pcm CB = boron concentration in ppm 8 RH0B = boron worth in pcm/ppmB ITC = isothermal temperature coefficient in pcm/F TAVG = average reactor coolant temperature in F DPC = doppler power coefficient in pcm/% power, and reflects the effect of changing power independent of moderator effect P = percent rated thermal power MTC = moderator temperature coefficient in pcm/F, and reflects the effect of changing moderator temperature onl DTC = doppler temperature coefficient in pcm/F,and reflects the effect on fuel temperature when moderator temperature is change and the subscripts are: i = initial conditions f = final conditions B = during boron change P = during power change When the licensee performed the test on October 29, 1985, at a boron concen-tration slightly less than 300 ppmB the result, an average of two measure-nents, was -32.3 pcm/F, Since the limiting value of -31 pcm/F was exceeded, the Technical Specifications require that the measurement be repeated every 14 effective full power days (EFPD) to assure that the coefficient does not become more negative than - 40 pcm/ Six sets of measurements had been completed by the time of this inspectio . -. - . . - . -. . . . . _ _ _ - _ _

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! 2-PT-13 permits deleting the power change part of the measurement when the

change in power during the boron change is less than 0.3% RTP. This intro-duces a small, but non-conservative, error in the calculation of MTC. For i that reason, the inspector chose to reanalyse only the four complete sets of measurements, since the licensee had used the procedure option in two cases, j The inspector's results were in good agreement with those obtained by the I

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The last measurement was performed at an average concentration of 55 ppmB,

and the licensee was anticipating difficulty in performing further measure-

ments during power coastdown to the refueling shutdown two months hence.

The licensee performed a least-squares fit to the six sets of data and

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projected a MTC at zero baron of -38 pcm/F. The inspector performed a i least-squares fit to the four complete data sets and obtained a zero-boron i value of -39 pcm/F. Since changing boron concentration is the mechanism by which the MTC changes, there is good assurance that the limit will not be l

exceeded during the remainder of the cycle. No measurement uncertainty was '

added to the extrapolated values, because that was taken into account in setting the limi The DTC is the only calculated value not supported by meacurement. However, 1, it represents a correction to the ITC of only about 7%. Hence, errors in I

the calculation would have a very small effect on the result. The licensee i has demonstrated that replicative samples of boron concentration reproduce i to +1- 2 ppm, which is less than 10% of the boron change used in the ITC

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measurement. Throughout the cycle the reactivity balance required by Technical Specification was performed about every three EFPD. Without the

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initial normalization of prediction to observation permitted at 60 EFPD, the

] points consistently fell on the predicted curve. That consistency gives

credibility to the value of boron worth used in calculating MTC.

j Subsequent to the inspection, the licensee used the analyses described

above to support an emergency change to the Technical Specifications to j allow suspension of MTC determinations during the balance of the cycle.

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) No violations or deviations were identified during this inspection. Howev-l er, the issue identified in UNR 339/85-33-01 was not addressed in this ,

i inspectio I

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