ML20076L271
| ML20076L271 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 07/12/1983 |
| From: | ARKANSAS POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML20076L265 | List: |
| References | |
| NUDOCS 8307190101 | |
| Download: ML20076L271 (6) | |
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ll INSTRUMENTATION ll ll INCORF DETECTORS ll-ll
.llLIMITINGCONDITIONFOROPERATION ll ll 3.3.3.2 The incore detection system shall be OPERABLE with:
ll l
ll a.
At least 75% of all incore detectors with at least one l
ll incore detector in each quadrant at each level, and l
ll l
ll b.
At least 75% of all incore detector locations, and l
ll 1
ll c.
Sufficient operable incore detectors to perform at l
ll least six tilt estimates with at least one tilt l
ll estimate at each of three levels.
l ll l
ll An OPERABLE incore detector location shall consist of a fuel ll assembly containing either a fixed detector string with a minimum l
ll of three OPERABLE rhodium detectors or an OPERABLE movt.ble incore l
ll detector capable of mapping the location.
l ll ll A tilt estimate can be made from two sets of symmetric pairs of l
ll incore detectors. Two sets of symmetric pairs of incore detectors l
ll are formed by two pairs of diagonally opposite symmetric incore l
ll detectors, one incore detector per quadrant.
ll ll APPLICABILITY: When the incore detection system is used for ll monitoring the AZIMUTHAL POWER TILT, radial peaking factors, local
-ll power density or DNB margin.
ll ll ACTION:
ll ll With the incore detection system inoperable, do not use the system ll for the above applicable monitoring or calibration functions. The ll provisions of Specifications 3.0.3 and 3.0.4 are not applicable.
ll llSURVEILLANCEREQUIREMENTS
-ll ll 4.3.3.2 The incore detection system shall be demonstrated OPERABLE:
ll ll a.
By performance of a CHANNEL CHECK within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior ll to its use and at least once per 7 days thereafter when ll required for monitoring the AZIMUTHAL POWER TILT, radial-ll peaking factors, local power density or DNB margin.
llll b.
At least once per 18 months by performance of a' CHANNEL ll CALIBRATION operation which exempts the neutron detectors ll but includes all electronic components. The neutron de-ll tectors shall be calibrated prior to installation.in the ll reactor core.
ll ll ARKANSAS - UNIT 2-3/4 3-28 F307190101 830712 PDR ADOCK 05000368 P-PDR t
1 PROPOSED REVISION OF ANO-2 TECHNICAL SPECIFICATION 3.3.3.2 BASIS FOR CHANGE AND EVALUATION OF EFFECT ON PLANT OPERATION Technical Specification 3.3.3.2 defines the criteria by which the ANO-2 fixed incore detector system may be determined to be operable.
Under the provisions of the specification, incore system operability requires:
a.
At least 75% (33) of all incore detector locations be operable, and; b.
A minimum of two quadrant symmetric incore detector locations per core quadrant be operable.
An operable incore detector location consists of a fuel assembly containing either a fixed detector string with at least four operable detectors or an operable movable incore detector capable of mapping the location.
The purposes of the incore instrumentation system are to evaluate core power distributions, perform calibrations of the out-of-core flux measurement system, and provide inputs to the Core Operating Limit Supervisory System (COLSS).
The incore instrumentation system consists of 44 fixed detector strings, each positioned in the center guide tube of selected fuel assemblies.
Each string contains five self powered rhodium detectors located at different vertical positions and a thermocouple at the coolant exit from the fuel assembly.
Twelve of the strings also contain a background detector.
The plant computer system corrects the incore detector signals for background and changes in sensitivity with burnup.
The incore detector signals are used by the off-line computer code CECOR to calculate the spatial power distribution in the core including the tilt and power peaking factors.
The information is used to calibrate the out-of-core detectors at cycle startup and also to confirm the power distribution required by the Technical Specifications. The Core Protection Calculators (CPC's) use the out-of-core signals and the calibration information with other plant parameters to calculate the departure from nucleate boiling ratio (DNBR) and the linear heat rate (LHR) values.
A reactor trip signal is generated when necessary to assure that the specified acceptable fuel design limits on either DNBR or LHR will not be exceeded.
The incore detector signals with other plant parameters are used by the COLSS monitoring program to assist the operator in maintaining DNBR, peak linear heat rate, tilt, axial shape index, and core power within their specified operating limits during normal operation.
The proposed revision to Technical Specification 3.3.3.2 would place additional requirements on the spatial distribution of operable detectors while redefining an operable detector location. A second modification would alter the requirement of two quadrant symmetrical locations per core quadrant for incore system operability.
The first change to the current specification additionally requires that 75%
(165) of all detectors (220) be operable. At least one detector at each of five levels in each quadrant would be necessary for system operability, and
the definition of an operable detector location would necessitate operability of at least three detectors in the string.
The change in the definition of an operable location from four working detectors to three working detectors is consistent with the definition of an operable string on other plants which have only four detectors per string.
However, to constrain the total number of detector failures allowed, the requirement that 75% of the detectors be operable has been added.
To further ensure that all parts of the core are instrumented, at least one detector is required in every quadrant at every level.
Currently, 37 incore detectors out of 220 total are considered failed.
Since 183 of the detectors are operable, an additional 19 detectors would have to fail before the provisions of the revised specification could not be met.
Such a large number of detector failures occurring prior to scheduled replacement is considered improbable.
l The present axial distribution of operable detectors is shown in Table I.
Failure of as few as three detectors could now cause the system to be declared inoperable. Under the revised specification, at least five more detectors would have to fail at level 3, quadrant 1, before the system would be inoperable. A gain in operable locations would also be obtained under the proposed revision. Ten locations are now considered inoperable, but five of these have only two failed detectors; and these would be considered operable under the revision.
In order to make an estimate of azimuthal flux tilt for one of the five axial detector levels, either a set of four quadrant symmetric detectors, or two sets of symmetric pairs of detectors must be operable on the desired level.
Failure of as few as four more detectors could result in exceeding the part b. limit of the present specification which requires a minimum of two quadrant symmetric incore detector locations per core quadrant.
Since the two symmetric locations could each contain a failed detector at different levels, the current specification in effect requires six tilt estimates.
The proposed specification states this requirement explicitly, and further requires at least one tilt estimate be available at three levels to ensure redundancy and a representative core average.
Under the revised operable location definiation, greater than 10 tilt estimates at each level would become available.
A substantial margin would thus exist with the revised specification.
The proposed amendment request does not involve a Significant Hazards Consideration because:
a.
Operation of AN0-2 in accordance with this change would not involve a significant reduction in a ma. gin of safety, nor involve a significant increase in the probability or consequences of an accident previously evaluted, nor introduce the possiblity of a previously analyzed accident; and b.
The proposed amendment is an exact match of the following example (Ref: DLOP 228, Federal Register, Vol. 48, p.14870):
(vi) A change which either may result in some increase to the probability or consequences of a previously-analyzed accident or may reduce in some way a safety margin, but where the results of
.. =
s"s the change are clearly within all acceptable criteria with respect to the system or. component specified in The. Standard Review Plan.
For example,.a change resulting from the application of a small refinement of a previously used calculational model or design method.
4 Basis.
The proposed Technical Specification allows greater variance in_ failed detector patterns but still is consistent with the' data base included in the approved.CECOR Topical, CENPD-153-P, Rev. 1-P-A,~May 1980. -The three reactor cycles in the Topical with the most detector failures have been examined.
In particular, the total number of instrument failures, the number of strings rendered inoperable (i.e., having fewer.than three working.
detectors), and the number of strings with three or less operating detectors have been summarized in Table II, which records the i
instrument failure data.
J
' Table II supports operation with up'to 25% instrument failures and 25% of string failures.
It also shows that the data base was in fact evaluated with up to 61% of the strings with three or less detectors operating.
Using the proposed specification with 25%
instrument failures, the-least possible number of strings with three operating detectors would be 61% for ANO-2. :Thus, the Topical data base supports the proposed operability requirements.
Simulation test cases with instrument failures extrapolated.to the limits in the revised Technical Specifications have been performed.
The results show no deterioration in the uncertainties beyond the currently approved values.
All values are well below those in the approved topical.
Therefore, the revised Technical Specifications are consistent with the approved CECOR Topical uncertainties.
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TABLE I ANO-2 CYCLE 3-TOTAL NUMBER OF OPERABLE DETECTORS PER. QUADRANT I
I LEVEL l
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2
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5 l
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l Quadrant (Total #)
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'l (9) 7 7
5 8
6 l
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-l 12 (13) 12 12 13' 13 13 l
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l 3 (9) 7 l
7 7
7 7
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4 (13) l 12 l '12 l
8 l
11 l
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TABLE II INSTRUMENT FAILURE DATA FROM
-CENPD-153-P, REV. 1-P-A DATA BASE Per Cent Per Cent Per Cent Strings Instrument Inoperable.
With Three or Less
- Case No.
Failures Strings Operating Detectors l'
21 16 36 2
20 20 36 3
' 24 -
25 61 1
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