2CAN058305, Provides Results of Technical Evaluation of Need to Upgrade Core Protection Calculator Local Power Density Penalty Factor Software & Proposed Implementation Schedule,Per 830414 Commitment
| ML20071N433 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 05/31/1983 |
| From: | John Marshall ARKANSAS POWER & LIGHT CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| 2CAN058305, 2CAN58305, NUDOCS 8306070054 | |
| Download: ML20071N433 (2) | |
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ARKANSAS POWER & LIGHT COMPANY POST OFFICE BOX 551 LITTLE ROCK. ARKANSAS 72203 (501)371-4000 May 31, 1983 2CAN058305 Director of Nuclear Reactor Regulation ATTN: Mr. Robert A. Clark, Chief Operating Reactors Branch #3 Division of Licensing U. S. Nuclear Regulatory Commission Washington, DC 20555
SUBJECT:
Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 CPC Software Discrepancy Gentlemen:
In our letter dated April 14,1983,(2CAN048307), we agreed to provice additional information regarding the Local Power Density (LPD) penalty factor (PF) software.
The information below provides the results cf our technical evaluation of the need for this upgrade and the proposed implementation schedule.
We would like to rest;.te our position regarding the impact on safety of operation with the present Core Protection Calculator (CPC) software configuration. The proposed software modification concerns application of the LPD PF by the CPC's when both Control Element Assembly Calculators (CEAC) are in the " failed" or "in-test" mode without having been declared inoperable by the plant operator (the CEAC inoperable flag is not set to 3*).
Under these conditions, the CPC Functional Design S that a large Departure from Nucleate Boiling Ratio (DNBR)pecification states PF and a large LPD PF should be applied.
These large penalty factors would compensate for the lack of CEA Deviation PFs that would normally be provided by the CEAC if a CEA deviation occurred.
In the current ANO-2 CPC software, only the DNBR PF is applied under these conditions. However, this error does not represent a safety concern because the DNBR PF is sufficiently large to cause an immediate reactor trip under all operating conditions.
- CEAC inoperable flag can be set to one of four values: 0 = both CEAC's are operable; 1 = CEAC1 is considered inoperable; 2 = CEAC2 is considered inoperable; 3 = both CEAC's are considered inoperable.
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Mr. Robert A. Clark
> May 31, 1983 g.-
The reasons for this are:
1.
The hinimum pcwer; used by the CPC's in the DNBR and LPD calculatiens is 20% of rated power; 2.
The value of the DNBR PF as applied by the CPC's is 13.44; 3.
The DNBR PF is multiplicatively' applied to the CPC calculated power to yield an equivalent power level of 268.8% at 20% power or below and up to'1344.0% at 100% power.
This equivalent power
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-level is then used as the power input to the DNBR algorithms.
,This equivalent power level is well above the power level needed
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. 4.. ;to generate a DNBR trip in all four CPC channels.
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To subst;intiate the preceding conclusion, a worst case calculation was 3
perfo'rmed foriANO-2 by Combustion Engineering using the COLSS/CPC Simulator.
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After!ths introduction of the DNBR PF (13.44), the maximum possible value for CNBR'for any postulated plant operating condition is 0.3 which is well below the-DNB.R trip setpoint of 1.24.
Therefore, the application of such a large DNBR PF to each channel will result in an immediate reactor trip an DNBR. Application of a large LPD PF, causing immediate CPC LPD channel trips, is ? thus not necessary.
As noted'in our letter o'f April 14, ev'en a minor software change must go through a lengthy and co'stly development, verification, implementation and testing ' program.
Specifically, we have estimated that a minimum of approximately 1000 manhours at an estimated cost of $57,000 would be required over a two month period to iinplement the software change.
Since the implementatiois of the propo' sed LPD PF software modification does not constitute
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-a safety concern, the expense and effort associated with an immediate implementation is not warranted. ' Therefore, we propose to combine this modification with other changes which are being considered. Accomplishment of all software changes together, by the en'd of the fourth refueling outage, g
-will sign'ificantly: decrease the overall' verification and review efforts on
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s the partfof the vendor, the Commission and ourselves.
Very truly yours, Lff lohn R. Marshall Manager, Licensing JRM: WAR:sl 4
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