2CAN118608, Forwards Response to Requests for Info in Generic Ltr 86-06 Re plant-specific Concerns Not Covered in Previous Submittals.Parameters Used to Determine Need for Reactor Coolant Trip Include Subcooling Margin & RCS Pressure
| ML20214K989 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 11/24/1986 |
| From: | Enos J ARKANSAS POWER & LIGHT CO. |
| To: | Miraglia F Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.K.3.05, TASK-TM 2CAN118608, GL-86-06, GL-86-6, NUDOCS 8612020535 | |
| Download: ML20214K989 (4) | |
Text
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ARKANSAS POWER & LIGHT COMPANY POST OFFICE BOX 551 LITTLE ROCK ARKANSAS 72203 (501) 371-4000 November 24, 1986 2CAN118608 Mr. Frank J. Miraglia, Jr., Director Division of PWR Licensing - P U. S. Nuclear Regulatory Commission Washington, DC 20555
SUBJECT:
Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Implementation of TMI Action Item II.K.3.5
" Automatic Trip of Reactor Coolant Pumps" Response to Generic Letter 86-06
Dear Mr. Miraglia:
The attached information is provided in response to the requests for information in Generic Letter No. 86-06 (0CNA058625) regarding plant specific information not covered by the CE Ovners Group submittal or previous AP&L submittals.
By transmittal of the attached information AP&L considers NUREG-0737 Item II.K.3.5 satisfactorily addressed.
Very truly yours,
[J Ted Enos, Manager uclear Engineering anc Lir, sing l
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RESPONSE TO PLANT SPECIFIC CONCERNS ANO-2 1.
" Identify the instrumentation to be used to determine the RCP trip setpoints, including the degree of redundancy of each parameter signal needed for the criteria chosen."
Response
The parameters used to determine the need for RCP trip are subcooling margin, RCS pressure, and secondary side activity.
Secondary system activity can be determined from a condenser offgas I
radiation monitor (high alarm), two steam generator sample cooler radiation monitors (high alarm), two main steam line radiation monitors (increase), or two secondary radiation recorders (high alarm).
In addition steam generator sample activities are available on a more delayed basis.
Subcooled margin is available from the safety parameter display system (SPDS), the plant computer and from RCS pressure and temperature indicators (in conjunction with steam tables).
The primary indication of subcooled margin is, however, two subcooled margin monitors.
RCS wide range pressure is available from 4 loops of instrumentation plus SPDS.
2.
" Identify the instrumentation uncertainties for both normal and adverse containment conditions.
Describe the basis for the selection of the adverse containment parameters.
Address, as appropriate, local conditions such as fluid jets or pipe whip which might influence the instrumentation reliability."
Response
The RCP trip criteria are implemented to accommodate a very specific set of SBLOCA sizes, specifically 0.1 ft2 to 0.02 ft2 For breaks outside of this range, the analyses demonstrate that either tripping or not tripping the RCP's is acceptable.
For these breaks the criteria of low RCS pressure and loss of subcooling margin are both reached in a maximum of 94 seconds which corresponds to the smallest size break (0.02 ft2) in the relevant spectrum (larger breaks would of course reach the setpoints much faster).
These smaller breaks create adverse containment conditions very slowly compared to the largest breaks in the relevant spectrum.
The emergency operating procedure provides that one of the first steps taken following a reactor trip is checking the RCP trip criteria.
Therefore, not only will the trip criteria be reached in a short period of time, but it will be noticed by the control room operator in this short period of time as well.
In this
short period of time and for these small size breaks containment environmental conditions would be, at worst, only slightly more adverse than normal.
In addition, it is apparent that thermal lag of the instrumentation would prevent even these slightly more adverse than normal conditions from being experienced by the instrumentation before its use for RCP trip criteria is completed.
Therefore, the normal containment environmental conditions are considered relevant for uncertainty considerations for the specific RCP trip criteria.
Analysis done by Combustion Engineering in 1980 determined that "An inaccuracy of iSG psi was...a conservative value for all plants" (C-E plants - Arkansas and earlier).
Subcooling margin uncertainties vary with RCS pressure and temperature due to the slope of the saturation curve and its effect on the sensitivity of the signal processing to input variations.
CEN-268 indicates that, for relevant size breaks, the criteria of low pressure and low subcooling margin will be reached nearly simultaneously.
At 1300 psia the uncertainty in subcooling margin is 18 F.
This is based on data submitted to you in our January 18, 1980 letter (2CAN018518).
Secondary activity uncertainties are not relevant since steam generator tube ruptures, of a size large enough to cause the RCP trip criteria of low pressure and low subcooling margin to be reached, would also cause marked increases in the normally extremely low secondary activity.
Pressure transmitters of interest are not in an area subject to local conditions such as fluid jets or pipe whip.
They are mounted on the outside of the secondary shield wall in containment. The additional RTD inputs to the subcooling margin monitors provide 2 channels of input from each of 2 hot legs.
Each display receives input from each hot leg but uses only the highest of the two temperatures.
If local conditions cause the temperature input to go low, the good temperature input (on the other hot leg) is used.
If local conditions cause the temperature input to go high the bad temperature input will be used but it will be conservative.
The hot legs are sufficiently separated such that local conditions cannot affect RTDs on both hot legs simultaneously.
If the signal fails off scale either high or low, the signal is disregarded by the subcooling margin calculator and the
" good" signal is used.
3.
"In addressing the selection of the criterion, consideration of uncertainties associated with the CEOG supplied analyses values must be provided.
These uncertainties include both uncertainties in the computer program results and uncertainties resulting from plant specific features not representative of the CEOG generic data group."
Response
Section 3 of CEN-268 provides a description of the models and assumptions used as well the applicability to the spectrum of Combustion Engineering plants.
Additional modeling detail information is provided in CEN-268 Suppl. 1.
1
4.
" Identify all plant procedures (except for those concerning normal operations such as normal cooldown) which require RCP trip guidelines.
Reference to the CE0G EPGs is acceptable if endorsed by the licensee.
Include training and procedures which provide direction for use of individual steam generators with and without operating RCPs."
Response
The emergency operating procedure, 2202.01, requires the use of RCP trip guidelines.
This procedure is based on the current revision of the ANO-2 Emergency Operating Procedure Technical Guidelines which was submitted as part of our Procedures Generation Package in response to NUREG-0737, item I.C.1.
The training is also described in the Procedures Generation Package.
Since all 4 RCPs are not tripped for transients that cause use of individual steam generators, e.g. MSLB, SGTR and the first two tripped are always in opposite loops, use of individual steam generators has no relationship to RCP trip criteria.
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