ML19296C618

Describes Core Protection Computer/Control Element Assembly Cluster Software Mods to Improve Unit Availability & Enhance Overall Operation of Sys.Mods Will Reduce Probability of Spurious Trips & Provide Addl Diagnostic Info

ML19296C618
Person / Time
Site:	Arkansas Nuclear
Issue date:	01/31/1980
From:	Trimble D ARKANSAS POWER & LIGHT CO.
To:	Reid R Office of Nuclear Reactor Regulation
References
2-010-25, 2-10-25, NUDOCS 8002260718
Download: ML19296C618 (13)

Text

ARKANSAS POWER & LIGHT COMPANY POST OFFICE BOX 551 LITTLE ROCK, ARKANSAS 72203 (501) 371-4000 January 31, 1980 2-010-25 Director of Nuclear Reactor Regulation ATTN: Mr. R. W. Reid, Chief Operating Reactor Branch #4 U.S. Nuclear Pegulatory Commission Washington, D.C. 20555

Subject:

Arkansas Nuclear One-Unit 2 Docket (40. 50-368 License No. NPF-6 CPC/CEAC Software Modifications (File: 2-1510)

Gentlemen:

The operating history of ANO-2 has indicated the need for a number of CPC/CEAC software modifications to (1) improse the unit availability and (2) enhance

- the overall operation of the CPC/CEAC system. We are presently reviewing a sof tware revision to the CPC/CEAC sof tware that will accomplish the above objectives by (1) recucing the probability of spurious trips and (2) providing additional diagnostic information to the plant staff. The purpose of this letter is to provide a description of the software modifications subsumed by this revision for your review.

The software modifications are delineated below and are fully described in the attached 'Descripticn of Mod 2B/3 CPC/CEAC Sof tware Modifications'.

1. Modification of the CPC DNBR update logic to include cold leg temperature difference biE; algorithm for asymmetric steam generator transients to enhance CPC response to HSSS Transients.

2. Modification of 16-bit penality factor word to include the DNBR and LPD penalty factors and related operating flags which will improve the trans-fer of information between the CEACs and CPCs.

3. Addition of a pre-set LPD panalty factor to be used in the calculation of the LPD total CEA deviation penalty factor in the event both CEACs are flagged inoperable.

4. Calculation of an average of the hot channel power distribution for use in computing the integrated one pin radial peak which will improve com-puter efficiency.

5. Application of the CEAC deviation penalty factor to the core average heat flux rather than to the one pin radial peak to reduce the proba-bility of spurious channel trips and increase reactor availability.

O MEMBER M:OOLE SOUTH UTILITIES SYSTEM 8002260 9' 1 TI I

Mr. R. W. Reid January 31, 1980 Calculation of the integrated one pin peak, hot pin heat flux dis-6.

tribution, hot pin axial shape index, and integrated hot pin heat flux during the STATIC DNBR program in order to improve computer efficiency and to ensure the most up-to-date values are used in the calculation of the STATIC DNBR.

7. Addition of a deadband at the low end of the excore detector signal range to reduce the sensitivity of the low end out-of-range alarm to signal noise.

8. Modification c' the shape annealing correction logic to include checks and corrections to top and bottom detector responses.

9. Addition of CPC and CEAC sensors out-of-range status arrays and ac-cessibility of this information via the operator's module and a tele-type to increase the diagnostic capabilities.

10. Provision for a " snapshot" of CPC variables at the time of a CPC channel trip to increase the diagnostic information available to the operator and plant engineer to increase their ability to determine the cause of the trip.

11. Modification of logic to indicate which CEAC has failed to increase the availability of the operable CEAC to continue to provide computed deviation penalty factors and CEA positions.

12. Modification of the core average heat flux filter algorithm to reduce the sensitivity of the heat flux calculation to noise.

13. Modification of CEAC logic to compute both a DNBR and a LPD penalty factor to enhance the capabilities of the CPCs, to make the penalty factors sub-group-dependent, and to add flags to the 16-bit penalty factor word for CEAC failure and for multiple CEA deviations within a subgroup and large penalty factors.

14. Provisions for a " snapshot" of CEAC variables at the time of a CEAC penalty factor greater than one or when the larger PF flag is set.

15. Modification to CPCs to include a DNBR correction factor for rod de-viation events.

Note that Item 12 above is the software change designated MOD 3, while the re-maining items are part of the software change that ha'd been designated MOD 28.

The separate designations arose from differences in time of origin, bases of origin, and other aspects. However, both MOD 2B and MOD 3 areFor being combined this reason, into one revision level of CPC/CEAC discs and documentation.

any reference to these modifications in this correspondence will be as MOD 2B/3, which better denotes the single revision level.

Mr. R. W. Reid January 31, U 30 All the software modifications of MOD 28/3 will be made in accordance with CEN-39(A), Rev. 2 and CEN-39(A), Supplement 1, Rev. 1. All modifications will be designed such that the CPC/CEAC system will automatically initiate shutdown of the reactor to assure that specified acceptable fuel design limits are not exceeded as a result of anticipated operational occurrences and to assist the Engineered Safety Features in limiting the consequences of cer-tain postulated accidents. The comprehensive software modifications testing program will assure that the modified CPC/CEAC system has been implemented in accordance with the specified functional design.

Our internal review of the MOD 2B/3 is incomplete at this time, but we expect that the software modifications will be found not to constitute an unreviewed safety question. Nonetheless, owing to the extent of the modifications, we are submitting this information for your review.

Sincerely yours, oDW (. Yb David C. Trimble Manager, Licensing DCT:WBM:nak Attachment D

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DESCRIPTI0fi 0F MOD 2B/3 CPC/CEAC SOFTWARE MODIFICATI0fiS

1. Change: Modify CPC DIiBR update logic to include cold leg temperature difference bias algorithm for asymmetric steam generator tran-sients.

Reason: This modification provides a CPC OfiBR penalty based on the cold leg temperature difference caused by an asymmetric steam generator transient. The design basis event is the instantaneous closure of one MSIV. This modification ensures a reactor trip will occur when the DNBR margin is projected to a 1.3.

Description:

CPC protection is prvvided by determining a penalty factor based on the difference between the two cold leg temperatures and then applying this factor to the calculation of the updated CPC-calculated DiiBR. The computed temperature difference is compensated by a digital filter. The component temperature difference is used to determine a temperature-related PF component, and the core average power is used to determine a power-related PF component. These PF components are com-bined to yield the asymmetric SG transient penalty factor (PFASGT). Calculation of the updated Dt4BR is modified to include the PFASGT.

2a. Change: Modify 16-bit penalty factor word and associated logic to be con-sistent with the CEAC modifications.

Reason: Since modifications to the CEAC will nos include calculation of a LPD penalty factor (separate from the DNBR penalty factor) and

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the setting of a flag indicating multiple CEA deviations in a sub-group, the 16-bit penalty factor word will have to be modified to transmit this information.

Description:

The 16-bit penalty factor word will transmit to the CPCs the following information in bits location 0-15, respectively:

1. CEAC fail bit (1 bit)

2. Dr4BR PF minus 1.0 (7 bits)

3. Multiple CEA deviations in subgroup flag (1 bit)

4. LPD PF minus 1.0 (6 bits)

5. Scale flag (1 bit)

Logic will be added to the CEACs and CPCs to pack and un-pack this information in the 16-bit penalty factor word.

2b. Change: Add scale type to processing of penalty factors and include scale flag in 16-bit penalty factor word.

Reason: For packing and unpacking the penalty factors in the 16-bit PF word, the highest resolution is obtained if the PF word processed falls within the range of 0 to 1. Therefore, where the adjusted PF (i .e., PFadj. = PF - 1.0) is greater than one, a pre-defined scalir.g factor is used to convert the adjusted PF to within the 0 to 1 range.

Description:

In the CEACs, the adjusted PF, during processing, is compared with small-scale and large-scale limits. The small-scale limit designates the upper bound of the acceptable small-scale PF region. The large-scale limit designates the upper bound of the acceptable large-scale PF region. If the adjusted PF is less than the small-scale limit, it is adjusted by the small-scale scaling factor to fit the 0.0 to 1.0 range. If the adjusted PF lies between the small-scale and large-scale limits, the adjusted PF is scaled down by the large-scale scaling factor to fit the 0 to l range. The scaled PF is then processed for packing into the penalty factor word. If the adjusted PF is equal to or greater than the large-scale limit, the large PF flag is set; and a bit pattern indicating a large PF is set in the penalty factor word.

3. Change: Provide pre-set LPD penalty factor for CEAC inoperable mode.

Reason: At present, if both CEACs are inoperable, a pre-set maximum penalty factor is used to calculate the total CEA deviation penalty tactor. By modifying the CEAC-CPC logic to include a LPD penalty factor, a pre-set maximum LPD penalty factor must be added to ensure the logic for the LPD deviation pen-alty factor is consistent with that for the DNBR deviation penalty factor when both CEACs are inoperable.

Description:

This modification to the CPCs adds logic to compare and select the larger of the two LPD penalty factors received from the CEACs in order to complete the LPD total CEA de-viation renalty factor. If one CEAC is failed or in-test, this modification includes logic to compare and select the larger of the penalty factors between (1) the operable CEAC and (2) the previously stored penalty factor from the failed CEAC. It also provides a pre-determined maximum penalty factor to be used in the event both CEACs are inoperable due to being in-test or failed.

4. Change: Calculate an average of the hot channel power distribution and use this variable in calculating the integrated one pin radial peak.

Reason: At present, the pseude hot in axial power distribution is cal-culated during the power Ji .tribution up-date, and this 20-mode power distribution is transferred to the " POWER" program out-put buffer. It is then used in the calculation of the hot pin heat flux distribution and the integra' edt one pid radial peak.

A nodal summation is performed for each calculation of the one pin peak. Since the pseudo hot pin axial power distribution does not change with each calculation of the one pin peak and updated CPC-calculated ONBR, elimination of this additional summation will improve- computer efficiency.

Description:

As part of the calculation of the pseudo hot pin axial power distribution, the average of the hot channel power distribution will also be determined. This factor will be transferred to the output buffer for use in the cal-culation of the integrated one pin radial peak.

Sa. Change: Apply the CEAC deviation penalty factor to the core average heat flux rather than to the one pin radial peak.

Reason: CEA deviations currently cause everly conservative DNBR cal-culations because the penalty factor is applied to the one '

pin radial peak. This modification applies the deviation penalty factor to the heat flux as an overpower margin cor-rection rather than to the one pin peak.

Description:

The CEA deviation penalty factor is deleted form the cal-culation of the hot pin heat flux distribution and the in-tegrated one pin radial peak in the UPDATE program and is added to the calculation of the adjusted compensated core average power (core average heat flux) in the STATIC pro-gram. In addition, the calculation of the integrated one pin radial peak is modified to replace the nodal sommation of the pseudo hot pin axial power distribution with the average of the hot channel power distribution.

Sb. Change: Modify CEA deviation penalty factor in the calculation of the local power dcasity.

- Reason: Present operating limits yield a much greater local power density (LPD) margin than DNBR margin. At pr'sent, the same CEA deviation penalty factor is applied to both the 'NBR and LPD margin calcula-tions. As a result, a Df4BR-initiated reactor trip will always occur before a LPD-initiated trip. To conserve the same relation-ship between DNBR and LPD, a separate LPD penalty factor is cal-culated and applied to the calculation of the uncompensated local power density in te UPDATE program.

Description:

In the UPDATE program, the equation for the uncompensated local power density is modified by substituting the CEA deviation LPD penalty factor for the CEA deviation DNB penalty factor.

6. Change: Perform calculation for integrated one pin peak, hot pin heat flux distribution, hot pin axial shape index, and integrated hot pin heat flux in the STATIC program.

Reason: The calculation of the STATIC DNBR is initiated immediately' af ter the power distribution calculation. However, the heat flux data used in the STATIC DNBR calculation are obtained from the UPDATE program, which uses power distribution data from the last execution of the POWER program. This could re-sult in these data being as much as 1.0 seconds old, and, therefore, inappropriate for use in the STATIC DNBR calcula-tion. This modification ensures the most up-to-date power distribution data are used in the calculation of the STATIC DNBR.

Description:

This modification calculates the integrated one pin peak,

- hot pin heat flux distribution, hot pin axial shape index, and integrated hot pin heat flux in the STATIC program prior to the calculation of the revised STATIC DNBR. Out-put buffer storage space is conserved by not transferring these values to the output buffer of the UPDATE program.

7. Change: Add deadband at low end of excore neutror, flux detector signal rbnge.

Reason: The low end of the excore detector signal range is equivalent to a hot standby operating condition. If the raw excore detector signal is less than the raw excore detector signal lower limit, the detector signal is set equal to the scaled detector signal lower limit and a sensor failure alann is initiated. This for-mat is sensitive to signal noise and results in unnecessary spurious sensor failure alarms at zero power. This modifi-cation adds a deadband to the low end of the excore detector signal range, which reduces the probability of spurious alarms.

Description:

A raw excore neutron flux signal low limit alarm setpoint value has been added to the sensor failure logic in the CPCs. The alarm setpoint is less than the signal lower limit. If the raw signal lies between the signal lower limit and the low limit alarm setpoint, the signal is set equal to th2 lower limit. If the raw signal is equal to or less thar the lcw limit alarm setpoint, the signal is set equal to the lower limit and a sensor failure alarm is initiated.

8. Change: Modify shape annealing correction logic to include checks and corrections to top and bottom detector responses.

At present, the logic indicates that if the detector segment Reason:

response for the upper third of the core is less than 3%, then the peak is in the bottom of the core; and the detector seg-ment response '.' the lower third of the core is not checked.

This modificatien ensures that both the upper and lower detector responses are c.:ecked. ,

Description:

The shape annealing correction logic has been adjusted to ensure that both the apper and lower detector responses are checked.

9. Change: Add CFC and CEAC sensors out-of-range status arravs and make accessible for display via the operator's module and a tele-type.

Reason: Sensor status information is provided so the operator is aware of which sensor has failed and to aid the plant engineer in compiling a history of sensor out-of-range failures.

Description:

Both a s oC and a CEAC failed sensor stack will be im-plementec Each stack will contain a maximum of six failed sen. s, the failed sensor ID, a sensor status and failure type indicator, and a time associated with the failure. New failed sensors will be added at the top of the stacks, and excess failed sensors (in excess of six) will be deleted from the bottom of the stacks.

The sensor failure stacks will be accessible for display through the operator's module and a teletype. -

10. Change: Provide a " snapshot" of CPC variables at the time of a CPC channel trip.

Reason: There is currently no CPC/CEAC information retained to deter.nine the inputs and calculated variables at the time of trip. As a result, determining the cause of trip is sometimes difficult, particularly if caused by spurious, momentary causes external to the CPC/CEAC system. Providing a list of variables at the time of channel trip will increase the ability of the operator and plant engineer to determine the precise cause of the trip.

Description:

When a trip signal is generated in a CPC channel, a " snap-shot" of specified variables will be transferred to a buffer that is accessible by teletype. These specified variables will include the following:

1. All CPC inputs (Pump Speeds in Fraction, not counts)

2. From Trip Sequence Program:

MINDNB - Minimum DNBR with uncertainty factor.

3. From Flow MC - calibrated CPC mass flow rate MCS - past value of calibrated CPC mass flow rate XI - flow projected DNBR

4. From UPDATE BDT - CPC Static Thermal Power BDTD - Total Th' mal Pcwer

- PHICAL - Neutron Fiux Power PF - DNBR Per.alty Factor PFLPD - Local Power Density Penalty Factor LPDDC - Compensated Local Power Density FCALC - Core Average Heat Flux P1 - One Pin Radial Peak D - Maximum Value of FR 4FZ QASI - Hot Pin Axial Shape Index DXMIN - Updated Minimum Quality X2 - Updated DNBR X3 - Pressure-Projected DNBR TCMAX - Maximum Cold Leg Temperature O

6. From POWER ASI - Axial Shape Index

6. From STATIC DST - Static Maximum of FR 4FZ MCST - Static Mass Flow Rate PRST - Static Pressure TCMST - Static Cold Leg Temperature FCALCST - Static Heat Flux (Compensated Core Average Power)

HMAX - Maximum Core Exit Enthalpy HF - Enthalpy of Saturated Fluid PFST - Static DNBR Penalty Factor

7. The addressable constants

8. The time of the trip.

An addressable constant will be provided to reset (clear) the buffer. The " snapshot" will be of the first channel trip after the buffer is cleared. In addition, an auto-restart will not clear the buffer, but a software reload will.

11. Change: Modify logic to indicate which CEAC has failed.

Reason: At present when operating in the CEA Ih0P code, if one CEAC is indicated inoperable, then both CEACs are considered in-operable. This modification expands the CEAC IN0P status in

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the CPCs to indicate which CEAC is inoperable and to specify the DNBR and LPD penalty factors to be used. In this manner, if one CEAC is inoperable, the penalty factors from the oper-able CEAC will continue to be used.

Description:

The addressable constant CEANOP, which indicates to the CPC which CEAC has failed, will have four allowable values: CEAN0P = 0,1, 2, 3. The following listing summarizes the steps the CPC will take for each value of CEAN0P.

0 - Both CEACs ope'rable. Use DNBR and LPD penalty factors determined by the CEAC's.

1 - CEACl inoperable. Use last good DNBR and LPD pena'.ty factors from CEACl. Auctioneer with penalty factors from CEAC2. Record failure in failed st'enr stack.

2 - CEAC2 inoperable. Use last good DNBR and LPD penalty factors from CEAC2. Auctioneer with penalty factors from CEAC1. Record failure in failed sensor stack.

3 - Both CEAC's inoperable. Use predetermined DNBR and LPD penalty factors.

12. Change: Modify core average heat flux filter algorithm Reason: In the calculation of the core average heat flux, the adjust-ment of the static component of thermal power by the dynamic component can result in increases in the total thermal power that are highly sensitive to noise. This modification reduces the step increases and decreases due to the biases and, there-fore, reduces the sensitivity to noise. It includes the addi-tion of a second digital filter to optimize for increasing power.

Description:

Up until now the static thermal power has been biased with the dynamic component to yield the total thermal power.

The larger of the thermal power and the calibrated neutron flux power is returned as the core average power, which is con,ansated by two digital filters to yield the core average heat flux. Because of the wide swings in power due to the dynamic bias and the filter compensation, this method has been sensitive to noise.

This modification to the CPCs separates the application of uncertainty terms and filter compensation to the calibrated neutron flux power and thermal power. The calibrated neutron flux power is biased for uncertainties and compensated by a digital filter to optimize for increasing power. The static component of thermal power is increased by the dynamic component. The resulting total thermal power is biased for uncertainties and compensated by two digital filters to optimize for increasing and decreasing power. The larger of the optimized thermal power values and the optimized calibrated neutron flux power is returned as the core average heat flux. This modification also includes changes to the data base constants to account for the additional digital filter and for the functional change in the application of the original two digital filters.

This modification provides for:

a) reduced workload requirement for the dynamic component, b) compensation of the calibrated neutron flux power with the uncertainty bias and digital filter to optimize for increasing power, c) computation of a value of core average neat flux with a reduced value of the dynamic compensation, d) compensation of the total thermal power with an un-certainty bias and two digital filters to optimize for increasing and decreasing power, e) selection from the optimized calibrated neutron flux power and optimized total thermal power the maximum value as the core average heat flux.

13a. Change: Modify CEAC logic to compute both a DNBR and a LPD deviation

". penalty factor.

Reason: At present, the same CEA deviation penalty factor is applied to both the DNBR and the LPD margin calculations. As a result, the limiting value of two penalty factors must be used by the CEAC in its data base for calculating a penalty factor to be passed to the CPC. Since the limiting value is the LPD penalty factor,'which is significantly higher than the DNBR penalty factor, an excessively conservative penalty factor is applied to DNBR calculations. This modification adds a separate LPD penalty factor, which is processed for output to the CEAC-CPC data link.

Description:

In computing the DNBR and LPD penalty factors, the CEAC de-termines the lowest and highest CEA position in each sub-group and then computes the de.iation ;aagnitude between these two positions. If the deviation magnitude is less than a deviation deadband, then no penalty factor is re-quired for that subgroup. Otherwise, the penalty factors are determined based on the amount of the deviation magni-tude. With this method, the penalty factors are group-dependent.

13b. Change: Modify CEAC logic to compute a dynamic Xenon PF component and apply component to the calculation of the DNBR and LPD subgroup penalty factors.

- Reason: Any excessive CEA deviation will result in Xenon redistribution within the core. The impact and magnitude of the Xenon redistri-bution is directly dependent on the length of time of the devia-tion. For a case where a CEA is withdrawn from the core, the power in the region of the withdrawn CEA is increased which burns off the Xenon in that region. With less Xenon in that region than in the remainder of the core, the radial peak will increase. For a case where a CEA in inserted into the core, the power in the region of the inserted CEA is decreased which causes a buildup of Xenon in that region. As a result, the core will have rel-atively less Xenon than the region of the inserted CEA and the core average radial peak will increase. The impact of Xenon re-distribution occurs over a period of hours. To account for this phenomenon, a dynamic component is determined and applied to the calculation of the DNBR and LPD subgroup penalty factors.

Description:

A Xenon PF component is applied by maintaining an elapsed time counter for each subgroup. The counter is started when excess deviation in the subgroup is first detected, is frozen at a maximum elapsed time, and is reset to zero wnen the excess deviation is removed. The Xenon PF com-ponent is computed as a function of elapsed time.

13c. Change: Add a flag to indicate CEA failure to the 16-bit penalty factor word.

Reason: An excessive number of deviations in a core quadrant or an ex-

! cessive number of failed CEA sensors throughout the core could be indications of power supply problems. If the number of de-viated CEAs per core quadrant or the number of failed CEA sen-sors exceed pre-set values, the CEAC failure flag is set.

Description:

Up until now, the left-most bit in the 16-bit penalty fac-tor word has been used to indicate a CEAC in-test mode of operation. This modification to the CEAC program expands -

the use of this bit to indicate CEAC failure. This indi-cator or flag may be set as a result of failure summations in two sections of the CEAC program. When the raw CEA po-sitions are interrogated, if the CEA position exceeds the out-of-range or rate-of-change checks, the sensor failed flag is set for that CEA and the failure is added to a running sum. In the next section of the program, the de-viation magnitude and deviation type are determined. Dur-ing this process, the number of subgroups containing exces-sive deviations is summed per core quadrant. During the cal-culation of the penalty factors, the total number of sensor failures and the total number of deviated CEAs per core quad-rant are checked. If either of these sums exceed pre-set val-ues, the CEAC failure flag is set.

13d. Change: Add a flag to the penalty factor word to indicate 2 or more de-viated CEAs within a subgroup.

Reason: Two or more deviations within a subgroup could indicate excessive RSPT failures or power supply problems Therefore, if this con-dition exists, the 16-bit penalty factor word should be set to a multiple deviation indicator and the operator alerted to the con-dition.

Description:

The processed CEA positions are manipulated on the subgroup level to determine the deviation magnitude, deviation type (CEA withdrawal or CEA insertion), and overall group con-figuration. These quantities are found by first sorting the CEAs in the subgroup by relative position. The deviation magnitude is calculated from the most and least withdrawn CEAs. The definitions for the deviation types are the following:

0 - subgroup lies totally within the upper or 'ower core deadband (i.e., no CEA deviation).

il - single CEA withdrawal (+1) or insertion (-1).

ill - 5 CEA subgroup to distinguish deviations of center CEA.

2 - multiple CEA deviation within a subgroup.

During determination of the deviation types, if multiple CEA deviations are detected in a subgroup, the deviation type is set to 2. As a result, the large PF flag is set

and processed for output to the CEAC-CPC data link as one bit of the 16-bit penalty factor word; and the deviation alarm is initiated. The large PF flag is also set if the adjusted DNBR and LPD penalty factors equal or exceed the large-scale PF region limits.

14. Change: Provide a "snapshr t" of CEAC variables at the time of a CEAC penalty factor greater than one or when the large PF flag is determined.

Reason: There is currently no CPC/CEAC information retained to determine the CEA position inputs and calculated penalty factors at the time a large penalty factor is calculated or the large PF flag is set.

As a result, determining the cause of failure is sometimes difficult, particularly if caused by spurious, momentary causes external to the CPC/CEAC system. Providing a list of variables at the time of either of the aforementioned occurrences will increase the ability of the operator and plant engineer to determine the precise cause of the trip.

Description:

A " snapshot" of CEA positions, penalty factors, and time of deviation occurrence shall be stored when initiated by a CEAC penalty factor greater than one or by the large PF flag. This " snapshot" shall be accessible by teletype. In addition, the CRT display will exhibit an indicator over each subgroup with a deviation to indicate whether the de-viation initiated an alarm or a penalty factor.

15. Change: Add DNBR correction factor algorithm to CPC UPDATE program.

Reason: In the past, a red insertion event would-in all likelihood-cause a reactor trip because the penalty factors generated as a result of the rod deviation would be conservative. This process did not fully take into consideration available over-power margin. These changes, which incorporate a DNBR correc-tion factor into the CPCs, take credit for dvailable overpower ma rgi n .

Description:

The DNBR penalty factor is saved in a PF array for 35 executions of the UPDATE program. After updating for DNBR and quality changes, the power margin loss is com-puted using the most recent and the oldest DNBR penalty factors from the PF array. If the power margin loss violates minimum acceptable conditions, a DNBR correction factor is selected and applied to the calculation of the updated CPC calculated DNBR (X2).

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