ML20050C530

Nonproprietary Version of Cpc/Ceac Software Mod for Waterford 3.

ML20050C530
Person / Time
Site:	Waterford
Issue date:	03/31/1982
From:	ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML19268D129	List: ML20050B160 ML20050B172 ML20050C530 ML20050C531
References
CEN-197(C)-NP, NUDOCS 8204090008
Download: ML20050C530 (25)

Text

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l CEN-197(C)-NP l

CPC/CEAC '

SOFTWARE MODIFICATION FOR WATERFORD 3 i WATERFORD STEAM ELECTRIC STATION UNIT NO. 3 MARCH,1982

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LEGAL NOTICE THIS REPORT WAS PREPARED AS AN ACCOUNT OF WORK SPONSORED BY COM8USTION ENGINEERING, INC. NEITHER COMSUSTION ENGIN6ERING NOR ANY PERSON ACTING ON ITS BEHALF:

l A. MAKES ANY WARRANTY OR REPRESENTATION, EXPRESS OR IMPLIED INCLUDING THE WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY, WITH RESPECT TO THE ACCURACY, COMPLETENESS, OR USEFULNESS OF THE INFORMATION CONTAINED IN THIS REPORT, OR THAT THE USE OF ANY INFORMATION, APPARATUS, METHOO, OR PROCESS DISCLOSED IN THIS REPORT MAY NOT INFRINGE PRIVATELY OWNED RIGHTS;OR

8. ASSUMES ANY LIABILITIES WITH RESPECT TO THE USE OF, OR FOR DAMAGES RESULTING FROM THE USE OF, ANY INFORMATION, APPARATUS, METHOD OR PROCESS DISCLOSED IN THIS REPORT.

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I TABLE OF CONTENTS Section Title Page No.

1.0 INTRODUCTION

1.1 Report Scope 1-1 1.2 Report Summary 1-1 1.3 Reference for Section 1.0 1-3 2.0 SOFTWARE MODIFICATION .

2.1 Control Element Assembly Calculator (CEAC) Algorithm 2-1 Changes 2.2 Core Protection Calculator (CPC) Algorithm Changes 2 - 10 2.3 CPC Addressable Constant Changes 2 - 15 2.4 Data Base Constants for the RPC Algorithm 2 - 18 2.5 References for Section 2.0 2 - 19 l

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1.0 INTRODUCTION

1.1 REPORT SCOPE The Core Protection Calculator (CPC) System developed by Combustion Engineering is a digital mini-computer system which calculates the

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minimum Departure from Nucleate Boiling Ratio (DNBR) and the peak local power density (LPD) on-line and generates a reactor trip if either the minimum DNBR or the peakLPD approaches the Specified Acceptable Fuel Design Limit. The CPC System has been reviewed by NRC and approved for operation in Arkansas Nuclear One (ANO) Unit 2 and San Onofre Nuclear Generating Station (SONGS) Unit 2. The CPC software for the Louisiana Power and Light (LP&L) Unit 3 contains additional functional design changes because of incorporation of the Reactor Power Cutback (RPC) feature into the plant. This report presents the changes to the latest NRC approved CPC sof tware (ANO-2 Cycle 2). These changes were made to the CDC ,ystem in accordance with the NRC-approved CPC sof tware chany .m adure (References 1 and 2).

1.2 REPORT

SUMMARY

The basis for modifications made to the CPC/CEAC sof tware is to upgrade the CPC capabilities to be compatible with the Reactor Power Cutback System (RPCS).- The RPCS is designed to rapidly reduce the reactor power by dropping pre-selected Control Element Assemblies (CEAs) in response to either a large load rejection or loss of one feedwater pump without tripping the plant. The CPC/CEAC modifications consist of an algorithm to detect the actuation of RPC event, and a more accurate calculation of power during the down-power transient -

associated with a RPC. One sof tware change not related to the RPC is shifting the range limit of the addressable constants for the DNBR and LPD penalty f actor multipliers. This change provides a flexibility for eliminating inadvertent reactor trip due to single rod drops.

1-1

The general format used in describing each software modification contained in this report is a statement of the change, the reason for the change, and a detailed description of the change including algorithm descriptions in symbolic algebra. This is the same format e used in CEN-143(A)-P which described software changes for Arkansas Nuclear One - Unit 2 relative to the implementation of an improved

. DNBR calculation.

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1.3 REFERENCES

FOR SECTION 1.0

1. CEN-39(A)-P, Revision 02. The CPC Protection Algorithm Software Change Procedure, December 21, 1978.

2. CEN-39( A)-P, Supplement 1-P, Revision 01, January 5,1979.

3. CEN-143(A)-P, Revision 1-P, CPC/CEAC Software Modifications for Arkansas Nuclear One - Unit 2, September,1981.

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2.0 SOFTWARE MODIFICATIONS 2.1 CONTROL ELEMENT ASSEMBLY CALCULATOR (CEAC) ALGORITHM CHANGES

1. Change:

An algorithm has been adde,d for detecting the actuation of a Reactor Power Cutback (RPC) event.

Reason:

The CPC/CEAC is part of the plant protection system and operates independently and physically separated from the RPC control system.

It is necessary for the CPC/CEAC System to have the capability of distinguishing between a RPC event and a CEA deviation event and to improve the DNBR calculation in order to prevent an inadvertent' reactor trip.

Description:

During the occurrence of a reactor power cutback event, certain pre-selected CEA group (s) will be dropped to reduce the reactor power rapidly. The rate-of-charge of the processed CEA positions are used to determine whether the CEAs are dropping. If and only if all of the CEAs in one or more of the pre-selected RPC groups are dropping, then the reactor power cutback flag will be set (IRPC=1) and remain set for a pre-determined time period. The flag will be reset automatically after a time interval equal to a preset value.

Insert the following algorithm after the raw CEA positions are .

converted to inches withdrawn and before the determination of deviations (between Sections 4.1.1 and 4.1.2 of Reference 2.5.3).

2-1

The variables used in this section of the program are:

CB1(J1 ),CB2(J )

2 CH3(J) = array of CEA number in cutback groups 1, 2 and 3.

3 (J=1.NCBG1;J=1;NCBG2.,J=1.NCBG3) i 2 3 CBSP = distance that determines if a CEA is dropping (in inches)

CEA tyg = total number of CEAs .

CONTAB = array of indices for defining subgroups and groups for each CEA .

CPOS(1.j) = CEA #1 position from j-1 CEAC execution cycles ago, (in inches withdrawn; 1 = 1. CEALIMI d " I' ICYCLE+1)

OROP(ii) = array of CEA number which are dropping into the corelii=1,CEALIM)

ICYCLE = number of CEA execution cycles used in determining CEA drop IRPC = RPC flag JR = a counter indicating the total number of CEAs dropping NCBG1.NCBG2

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NCBG3 = Number of CEAs in cutback groups 1, 2 and 3 NDi = a flag indicating CEA in cutback group i is dropping (i = 1,3) 2-2

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PBOT = bottom position for dropping CEA (in inches withdrawn)

. PPOS(1) = array of present CEA positions, inches withdrawn (i = 1. CEALIM)

TCBP = maximod time period that the RPC flag can remain set (in seconds)

TGROUP .

= delay time in comparing the CEA motions in the RPC group (in seconds) t RPC

= time elapsed since the RPC flag was first set (in seconds)

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2. Change:

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The multiple CEA deviation, Case = 2, is determined only when the RPC flag is not set.

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Reason:

During a RPC event, multiple CEA deviation may exist when all the CEAs in the RPC group (s) are dropping into the core. Therefore, the Case =

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2 which indicates abnormal multiple CEA deviations should not be used for RPC.

Description:

The CASE 2 deviation is determined only when the RPC flag is set and both the most withdrawn and the least withdrawn CEAs are outside the deadband.

If IRPC = 0, perform the CASE 2 deviation calculation, otherwise bypass the CASE 2 deviation calculation.

3. Change:

The RPC flag is included in the 16 bits CPC/CEAC data communication link.

Reason:

The algorithm described in 2.1.1 can detect a RPC event. The result is transmitted to the CPC over the 16 bit data communication link.

One of the 16 bits is designated for the RPC flag.

Description:

The 16 bits are assigned in the following manner: .

0 1 7 8 9 10 14 15

• DLINK LLINK 2-8

where:

• IFAIL - A failure flag which is set (bit 0 = "1") when the CEAC unit contains an excessive number of failed sensors.

DLINK -

The transmitted scaled maximum DNBR penalty factor, which is equal to the calculated maximum DNBR penalty factor minus one. The range of DLINK is from 0 to 127 which represents a floating point range of 0.0 to 1.0 scaled over seven bits (least significant bit value is 0.0078125)

• • ICASE2 - A flag which is set (bit 8 = "0") when there are multiple CEA deviations in a subgroup. -

• ** I RP C - A flag V t set (bit 9 = "1") when a reactor power t a event is determined.

LLINK -

The transmitted scaled maximum LPD penalty factor, which is equal to the calculated maximum LPD penalty factor minus one. The range of LLINK is from 0 to 31 which represents a floating point range of 0.0 to 1.0 scaled over five bits (least significant bit value is 0.03125)

• • • • ISCALE - A flag which is set (bit 15 = "0") when the maximum DNBR and LPD penalty factor are both less than the small scale limits. This flag indicates the method to be used in scaling the penalty _

factors for packing into the 16-bit output buffer. (The CPCs include options in the unpacking elements which will adjust the transmitted penalty factors by the appropriate scaling factor indicated by this flag.)

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2.2 CORE PROTECTION CALCULATOR (CPC) ALGORITHM CHANGES

1. Change:

. Determine from the 16-bit penalty factor word output from the CEAC whether a Reactor Power Cutback (RPC) event is detected by the

. CEAC.

Reason:

During a RPC event, CPC may use a more accurate logic in the calculation of power and avcid inadvertent trips.

Description:

In the CPC UPDATE program the CPC extracts from each penalty factor word output from each CEACj (i = 1 or 2) the following information:

ICAS21 (i = 1 or 2) =

the case 2 deviation flag from CEACj where,.

after unpacking, O indicates no case 2 deviation and 1 indicates a case 2 deviation.

PFj =

the DNBR penalty factor from CEACj PF tj =

the LPD penalty factor from CEACj I PFCBi =

the reactor power cutback bit from CEACj e

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2. Change:

During the period that the CPC RPC flag is set, IRPC = 1, the following factors are used in the DNBR and LPD calculations a) the off-line calculated CEA deviation penalty factors are used in lieu of the penalty faators transmitted by the CEAC.

b) the out-of-sequence penalty factor PFog = 1.0 is used.

c) the last calculated subgroup deviation penalty factor is used.

d) the last calculated radial peaking factors and rod shadowing _

factor are used.

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Reason:

When one or more of the RPC group CEAs are dropped into the core, the differences in CEA dropping speed may cause multiple CEA deviation and subgroup deviation. In previous design, large penalty factors which would trip the plant were used for these cases because they were not part of the design basis. .Nevertheless, when the RPC group CEAs are dropped, the actual DNBR increases because of rapid core heat flux decrease. This software change allows the CPC calculation to more closely model core conditions (Reference 2.5.1) and prevents an inadvertent trip in the event of, a RPC.

Description:

a) In the CPC UPDATE program, if the reactor power cutback flag is set, IRPC = 1, use the off-line calculated RPC penalty factors.

If IRPC

" I then PF = PF DRPC and PF LPD = PF LPRC where:

PF = total CEA DNBR deviation penalty factor PF LPD

= total CEA LPD deviation penalty factor PF -

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. PF LRPC

= corresponding DNBR and LPD penalty factors for the reactor power cutback event 2 - 14

b) In the CPC POWER program, if the reactor power cutback flag is set, IRPC = 1, set the out-of-sequence penalty factor PF05 = 1.0, otherwise calculate the out-of-sequence penalty factor as described in the previous CPC functional specification (reference 2.5.2).

c) In the CPC Power program, if the addressable "CEAC/RSPT Inoperable" l l

flag, CINOP, is less than thrra, then determine PF3g as follows:

If I RPC "

I' then PF 3g = PF 3gp where:

PF 3g = subgroup deviation penalty factor for this POWER execution cycle Pf 3gp = subgroup deviation penalty factor calculated from last execution of the POWER program.

d) In the CPC POWER program if the reactor power cutback flag is set IRPC = 1, skip the planar radial peaking factors and CEA shadowing factors calculations. The planar radial peaking factors and CEA shadowing factors remain the same as those calculated in the last execution of the POWER program. If IRPC = 0, calculate the planar radial peaking factors and the CEA shadowing factors as described in the previous CPC functional specification.

2.3 CPC ADDRESSABLE CONSTANT CHANGES

1. Change:

Shif t,_the positive range limit on the CEAC penalty factor multipliers from 1

- a 2 - 15 s i

i Reason: l l

l In the CPC design, the CEAC penalty factors are modified by the addressable constant multipliers PFMLTD and PF MLTL. Based on the

. ANO-2 operating experience, inadvertent CPC trip due to single rod drop may be prevented with PFMLTD and PFMLTL set within a range

• limit of The new sof tware provides the flexibility to set PFM .T to values that would eliminate inadvertent trips due to single rod drops, when, at some time in the future, analyses might be done to justify such an approach. This change in the range limits does not by itself change the actual ,PFMLT values set into the CPC.

Description:

The r;.. s for the DNBR penalty factor multipler PFMLTD are The ranges for the LPD penalty factor muiltiplier PFMLTL are

2. Change:

Addressable constants have been added to the CPC and CEAC to define the duration that the RPC flags can remain set.

Reason:

This change makes the CPC/CEAC functional design specification generic and applicable to the plants with or without the RPC feature. For those plants without the RPC system or if the RPC system is deemed .

inoperable, the RPC algorithm can be nullified by setting the RPC duration to 0.

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I 2.4 DATA BASE CONSTANTS FOR THE RPC ALGORITHM (typical for Waterford 3)

RPC FLAG TIMER SETPOINT 5 SECOND

- TCBSP { PCB EXECUTION TIME 5 SECOND

• DTB '(L J DELAY TIME Ih COMPARING BOTH CEACS

                       . _ OR RPCS                              5 SECOND PENALTIES FOR DNBR AND LPD DURING REACTOR    5 DIMENSIONLESS

_ _ POWER CUTBACK PFORPC,' PFLRPC' _ _ ARRAY OF CEA NUMBER IN RPC GROUP W DIMENSIONLESS C81(1-4) ' CB1(S-81 CR2(1-4) CO2(5-8) CB3(1-4) CB3(5-8) W DIMENSIONLESS NUM_BER OF CEAS IN RPC GROUP NCBG1 NCBG2 NCBG3 __ DISTANCE THAT DETERMINES CEA IS DROPPING W INCH BSP {_ ] NUMBER OF CEAC EXECUTION CYCLE USED IN  % DINENSIONLESS _QETERMINING CEA DROP ICYCLE B[0T,TOMPOSITIONFORDROPPINGROD 5 INCH PBOT

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• SECOND MAXIMUM TIM 2 THAT THE RPC FLAG CAN REMAIN ,

   ,      TCOP       [] SET DELAY TIME Ih COMPARING CEA MOTIONS

_ _IN TFE RPC GROUP V SECOND TGROUP { 2 - 18

2.5 REFERENCES

FOR SECTION 2.

1. CEN-200, P. Safety Evaluation of the Reactor Power Cutback

• System March, 1982.

2. CEN-147(S)-P,FunctionalDesignSpecificationforaCore Protection Calculator, January 1981.

3. CEN-148(S)-P, Functional Design Specification for a Control Element Assembly Calculator,, January 1981.

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COMBUSTION ENGINEERING, INC. ( s l 4-}}