ML20116C587

Responds to NRC 960613 RAI Ltr Re Proposed Amend LS-94-013 to License NPF-62

ML20116C587
Person / Time
Site:	Clinton
Issue date:	08/01/1996
From:	Lyon M ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20116C590	List: ML20116C587 U-602613, Calcs for Functional Requirements for First & Second Level Undervoltage Relays at 4kV 1A1,1B1 & 1C1
References
L47-96(07-24)LP, L47-96(7-24)LP, U-602613, NUDOCS 9608010006
Download: ML20116C587 (12)

Text

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n ilhnois Power Company l Chnton Power Station  !

P.o. Box 678 i Chnton, IL 61727 Tel 217 935-8881 ILLIN915 u-6026t3 P6MR u7.%( 07. 24 )Lp i 8E.100a L

l- . Docket No. 50-461 10CFR50.90 l l Document Control Desk l Nuclear Regulatory Commission l Washington, D.C. 20555 l

Subject:

Clinton Power Station Response to Request for AdditionalInformation Related to Proposed Amendment i

, of Facility Operating License No. NPF-62 (LS-94-013) I

Dear Sir:

I By letter dated February 22,1996 (letter number U-602554), Illinois Power (IP)

' Company proposed an amendment to the Clinton Power Station (CPS) Operating License  ;

(License No. NPF-62) to revise the setpoint for the degraded voltage protection I l instrumentation and modify or delete other Loss of Power Instrumentation Technical l Specification (TS) requirements. Additionally, changes were proposed to the minimum l~

required diesel generator voltage specified for certain diesel generator surveillances.

i To support review ofIP's application for amendment, the NRC has requested (via NRC letter dated June 13,1996)IP to provide additionalinformation. Attachment I to

'this letter provides IP's response to each of the questions contained in the NRC's request.

Also please find Attachment 2, IP Calculation 19-AN-19.

l -It should be noted that proposed modifications associated with this request cannot be implemented until NRC approval of the proposed TS changes. Because these modifications will enhance the safety of CPS with regard to the degraded voltage protection, IP is requesting that the February 22,1996 application for amendment, as supported by this letter, continue to be reviewed on a schedule sufficient to support implementation of these modifications beginning during the sixth refueling outage, currently scheduled to begin October 13,1996.

l Sincerely yours, l

9608010006 960001 l PDR ADOCK 05000461 M b. EkX.

P PDR

! Michael .L on /

Director-Licensing dCD/ '/ I

.- AJP/csm

.. -. . - . . . - . . . . . . _ . . . . . ~ . _ . . . . - _ . . . _ . . - . ~ . _ , .

U-602613 Page 2

- Attachments cc: NRC Clinton Licensing Project Manager NRC Resident Office, V-690 Regional Administrator, Region III, USNRC Illinois Department ofNuclear Safety i

4.

l 1

I Attachment 1 to U-602613 LS-94-013 i Page1 of9 l l

By letter dated June 3,1996, the NRC staff requested additional information related to Illinois Power's (IP's) February 22,1996 request to amend the Operating License for Clinton Power Station (CPS). IP's request involved proposed changes to the Technical

. Specification (TS) requirements related to the degraded voltage protection system at CPS.

IP's response to each of the NRC's questions is provided below.

1. "With regard to the proposed deletion of the channel check requirement every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, are there alarms in the control room or elsewhere that would prevent a single undervoltage relay, which has failed to the tripped state, from going undetected for a significant length of time (as much as the 31 day frequency between channel functional tests)? If there are no such alarms, please discuss the significance of a single relay being in an undetected tripped state for up to 31 days."

Response: There is no indication of Loss of Power (LOP) degraded voltage relay trip status in the Main Control Room (MCR) for the individual relays.

However, if both relays for a division trip and the timer times out, the automatic actuation sequence is initiated which will result in a diesel generator (DG) start and breaker actuation. These actions would generate '

an alarm in the MCR. There is however, local indication of trip status (i.e.,

a flag) for each individual degraded voltage relay at the electrical panel where the relay is installed. There is no TS surveillance requirement for ,

checking these trip flags. However, these flags are routinely checked by operators each shift during operator rounds as currently required by plant procedures.

• The significance of a single relay being in an undetected tripped state is that i the "two-out-of-two" trip logic will become a "one-out-of-one" trip logic. )

The LOP degraded voltage relays have been chosen for high reliability. As l

a result, the probability of relay failure in a 31-day period is small. The l probability of two relays failing would equal the square of the probability for one relay failure. Because the failure rate for one relay is low, the probability of the second relay in the same trip system failing during this time period is very low. In addition, the failure of a single relay will neither cause an inadvertent trip to occur nor prevent a valid trip from occurring.

As a result, IP has concluded that elimination of the 31-day channel check requirement is acceptable.

2. "The submittal indicates that the setpoint proposed to be specified for the degraded voltage function was determined using a setpoint methodology which has been approved by the NRC. Identify the staffs evaluation which .

approved this methodology. Also, provide the setpoint calculations used to determine the analytical limits, trip setpoints, and allowable values."

I

4 a

Attachment 1 i to U-602613 LS-94-013

Page 2 0f 9 j Response

The setpoints were calculated and are shown in IP calculation 19-AN-19 contained in Attachment 2 to this letter. The calculation methodology

, utilized by CPS for calculation 19-AN-19 is delineated in Nuclear Station i Engineering Department Standard CI-01.00, " Instrumentation Setpoint

! Calculation Methodology." This standard is based on ISA S67.04, j "Setpoints for Nuclear Safety-Related Instrumentation," and NEDC-31336, j " General Electric Improved Setpoint Methodology," October 1986. The j methodology employed within these documents was reviewed by the NRC

] as documented in Regulatory Guide 1.105 and NRC letter from Bruce A.

, Boger, Director Division of Reactor Controls and Human Factors to

, Robert A. Pinelli of the Boiling Water Reactor Owner's Group dated November 6,1995, respectively.

j 3. "The proposed technical specifications indicate an allowable degraded i voltage value for Divisions 1 & 2 (3876V) that is identical to Division 3.

l Because the Division 3 distribution system is rubstantially different from i Divisions 1 & 2, please verify that this value is correct."

i I Response: While the Division III distribution system is different from Division I and

=

II, the present and the proposeo setpoint were both determined by a j calculation that is based on the worst case with all divisions considered.

! The current setpoint for the Division III degraded voltage trip function is

different solely due to a different type of relay for the Division III degraded l voltage trip function from the relays that are currently used for the Division f I and Division II degraded voltage trip function.

The proposed TS change will support planned modifications to the degraded voltage instrumentation. After installation of the planned plant modifications, the relay types for the degraded voltage trip function will be identical for all three divisions. Since the Division III channel will no longer be different from Division I and Division II, all three divisions have the same proposed allowable value.

4. "The submittai indicates that the degraded voltage relay reset value is the appropriate value to specify in the Technical Specifications. The submittal further states that the drop-out voltage that is associated with these relays are more appropriately specified in the Operational Requirements Manual (ORM) and controlled under 10CFR50.59. It is the staffs view that the allowable value ofhgih. the relay reset point and dropout point should be specified in the Technical Specifications. A correct reset point is necessary to ensure the safety buses will not separate from the offsite system during sequencing of safety loads when the offsite voltages are sufficient to support the loads. A correct dropout point is necessary to ensure the safety buses will

Attachment 1 to U-602613 LS-94-013 Page 3 of 9 l separate from the offsite system when the voltages are insufficient to support l the safety loads. Therefore, please change the technical specification l submittal to include both a lower bound (allowable value for the dropout point) and upper bound (allowable value for the reset point)."

Response

The approved configuration for the CPS offsite power source is described l

within Section 8 of the CPS Safety Evaluation Report (NUREG-0853) and Supplement 7 (SSER 7). These documents and Chapter 8 of the Updated Safety Analysis Report (USAR) contain the CPS commitments regarding offsite power and degraded voltage protection. The current requirements l for the degraded voltage trip function and the associated setpoints were established based on NRC requirements stated in Standard Review Plan (NUREG-0800) Section 8.2. Those requirements ensure proper operation of equipment in response to postulated accidents (i.e., LOCA). CPS TS 3.3.8.1 currently specifies the allowable values for the degraded voltage trip functions. The CPS-specific configuration has been reviewed and accepted by the NRC (reference SSER 7 Section 8) as meeting the requirements in effect at the time of receiving an Operating License for CPS.

In support of the above requirements, analyses have been performed which demonstrate that all safety-related equipment receives adequate voltage at i the second-level undervoltage relay reset point to start under accident I conditions (i.e., under LOCA block-start conditions). These analyses also demonstrate that all safety-related equipment receives adequate voltage at the second-level undervoltage relay trip point to continue to operate following an accident. These requirements fulfill the current Licensing Bases for CPS. Further, analyses have been performed which demonstrate that all safety-related equipment will start and continue to operate at the minimum expected offsite voltage level under accident conditions.

As explained on page 4 of Attachment 2 ofIP's February 22,1996 submittal (letter U-602554), the current setting for the relay reset is based on a LOCA block start scenario. The original design is such that the drop-out and the reset values are not independently adjustable and thus, only one setpoint value was specified in the TS. The TS Table 3.3.8.1-1 item 1.c and 2.c allowable value is currently specified as 2 3762 V and s 3832 V.

These two values represent the high and low limit for the allowable value for the relay drop-out (i.e., trip) point only. Since the difference between

the relay drop-out and the relay reset are constant, the reset setpoint was specified by specifying only the setpoint for the drop-out in the TS.

l

f r . .

, Attachment 1 to U-602613 l LS-94-013 I Page 4 of 9 l After implementation of planned modifications to replace the degraded l

! voltage relays, IP will have the capability to adjust the degraded voltage l l drop-out voltage independent of the reset voltage. The characteristics of I' l the voltage decrease during starting oflarge AC motors following a postulated accident is such that the setpoint of the relay drop-out is not critical for ensuring the timer for the degraded voltage trip is initiated.

)

l What is critical is the voltage to which the bus recovers following the block-start voltage transient. This voltage must be high enough to ensure safety loads will start and continue to run post-LOCA. Thus, the proposed TS change requires the degraded voltage relay reset allowable value to be 2 3876 volts.

As stated in your question, a correct relay drop-out setting is necessary to ensure the safety buses will separate from the offsite power system when ,

the voltages are insufficient to support the safety loads. . As stated above, I the characteristics of the voltage decrease during starting oflarge AC l motors following a postulated accident is such that the setpoint of the relay drop-out is not critical for ensuring the timer for the degraded voltage trip l is initiated (i.e., a drop-out setpoint which is adequate for equipment safety will be sufficient to ensure initiation of the timing sequence during a LOCA block start scenario) . Thus, the minimum drop-out voltage has been 1 chosen to ensure continued operation of safety loads. Because, as discussed above, recovery of adequate bus voltage is ensured by the l degraded voltage relay reset setpoint, the minimum relay drop-out voltage l j is not part of the current Licensing Basis for CPS.

, - It should also be noted that, in accordance with the General Design Criteria l of 10CFR50, Appendix A, accidents are postulated to occur "with or without offsite power available." Thus, demonstrating proper equipment operation with offsite power available is met by demonstrating proper equipment operation with offsite power at the minimum expected offsite i

voltage. Accidents are not required to be postulated to occur with offsite l

voltage below the minimum expected offsite voltage. Thus, inclusion of protection requirements to mitigate the consequences of accidents with

, offsite voltage below the minimum expected offsite voltage does not meet j the criteria of 10CFR50.36(c)(2)(ii) for inclusion in TS [i.e., the function is not (1) installed instrumentation that is used to detect, and indicate in the control room, a significant abnormal degradation of the reactor coolant

[ pressure boundary; (2) a process variable, design feature, or operating

. restriction that is an initial condition of a design basis accident or transient I analysis that either assumes the failure of or presents a challenge to the j integrity of a fission product barrier; (3) a structure, system, or component I

i i

f i 1 . .

. Attachment 1 j to U-602613 l

LS-94-013 '

Page 5 of 9 that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier; nor (4) a structure, system, or component which operating experience or probabilistic risk assessment has shown to be significant to public health and safety.] Therefore, to allow for changes to the relay drop-out setpoint as required by changes in equipment load characteristics and when required because of changes in the minimum expected offsite voltage conditions, the  ;

l minimum relay drop-out voltage will be specified within the ORM and j controlled under 10CFR50.59.

l

5. "The submittal states that the allowable value is specified to provide j adequate safety margin from the analyticallimit. Provide the amount of

( safety margin between the lower bound analytical limit (generally based on >

l the most limiting steady-state or transient equipment terminal voltage) and j the allowable value. Provide the amount of safety margin between the upper l l

bound analyticallimit (generally based on the minimum expected switchyard i operating voltage) and the allowable value. Identify what the analytical

limits are based upon and where they are used in the setpoint calculations

! provided in response to question 2 above."

r Resoonse: The lowe- Sound analytical limit at the 4 kV level is 3.870 kV and is high l l enough to ensure proper starting of safety loads folicwing a postulated l accident. This is the lower bound analytical limit used for calculating the i relay reset setpoint. The proposed Allowable Value is 3.876 kV and the l safety margin is the difference which is 6 volts. l The upper bound analytical limit at the 4 kV level is 3.938 kV and is based l on the minimum expected offsite voltage levels following a postulated l l accident. This is the upper bound analytical limit used for calculating the l relay reset setpoint. Since the degraded voltage trip timer is started based l

on the relay drop-out setting which is well below the minimum expected offsite voltage, there is not a Technical Specification Allowable Value specified for the degraded voltage relay drop-out point. The maximum reset calibration limit is chosen to povide a 95 percent confidence level that there will not be a spurious transfer due to offsite voltage being at or above the minimum expected offsite voltage following a postulated accident. The maximum reset calibration limit is 3.890 kV. The safety margin is the difference between'the upper bound analytical limit, 3.938 kV, and the maximum pick-up calibration limit, 3.890 kV, which is 48 volts. For further discussion, please see Calculation 19-AN-19 contained in Attachment 2 to this letter, beginning at " Evaluation" on page 13.

l

. Attachment 1 to U-602613 LS-94-013 Page 6 of 9

6. "The submittal also states that the calibration setpoints are determined considering calibration errors and anticipated drift. Besides calibration errors and drift, were other uncertainties considered; such as PT accuracy, repeatability, temperature effect, power supply variation, and test equipment accuracy?"

Response: Nuclear Station Engineering Department Engineering Standard CI-01.00,

" Instrument Setpoint Calculation Methodology," requires that the various conditions under which an instrument may operate be taken into consideration and evaluated when establishing instrument setpoints.

Calculation 19-AN-19, Rev. 2, Volume C considered the following as potential contributing errors when establishing the degraded voltage relay setpoints:-

e Relay repeatability e Relay repeatability with respect to temperature e Relay repeatability with respect to the control voltage e Relay drift with time e Radiation effects

• Seismic effects e RFI effects e Calibration instrument and calibration loop accuracies e Potential transformer accuracy, including the impacts of change in PT burden See Section I, " Inputs," of Calculation 19-AN-19 contained in Attachment 2 to this letter for more information.

7. "Because the degraded voltage setpoints themselves are not specified in the Technical Specifications, discuss how the trip setpoints and changes to the setpoints are controlled by plant procedures."

Response: In the same manner as all TS-required instruments with allowable values specified in the TS, the degraded voltage relay nominal trip setpoints will be specified in the CPS Operational Requirements Manual (ORM).

Contrei f these degraded voltage setpoints will be in accordance with the design control procedures. Presently, the method for controlling setpoints '

included in the ORM requires changes to be submitted, approved and processed in accordance with the ORM revision procedurr, CPS No.

1038.03, " Revising the USAR and ORM." All changes a c required to be evaluated in accordance with 10CFR50.59. The setpoints recorded in the I

.A

I

., Attachment 1 I to U-602613 j l LS-94-013 Page 7 of 9 ORM must also agree with the appropriate design documents, including the l trip setpoint calculations. As stated above, design documents are  !

controlled in accordance with design control procedures and calculations 1 are prepared, reviewed, and approved in accordance with design control l procedures

8. "The Technical Specifications require a montbly channel functional test to be performed on the Loss of Power Instrumentation to verify operability. If the results of a monthly channel functional test should indicate that a degraded voltage relay's actual setpoint is within the allowable value but very near to it; what action,if any, would be taken on that specific relay? Would the relay's actual setpoint be adjusted back to its specified nominal setpoint?"

Rgsponse The following response is provided with the understanding that "a degraded voltage relay's actual setpoint" refers to the "as-found" data obtained during instrument calibration. In accordance with the standard TS requirements for Channel Functional Tests, the monthly Channel Functional Test for the degraded voltage instmmentation does not determine the as-found setting. The as-found setting is required to be determined only

, during Channel Calibrations which are at 18-month intervals. The as-found setting for the degraded voltage instrumentation must fall within the calibration limit as defined within the applicable surveillance procedure.

If an as-found setting is found outside the calibration limit, then the instrument setting must be adjusted in accordance with the applicable procedure so as to be within the calibration limit. However, if the as-found setting is within calibration limits, then no adjustment is required. The  !

calibration limit takes into account appropriate drift characteristics and i other possible sources of error so that equipment drift will not result in exceeding the allowable value in the interval between calibrations.

9. " Discuss the coordination of downstream breakers, thermal overload devices, and fuses during degraded voltage conditions prior to the offsite source  !

breakers being opened by the degraded voltage relays. Also discuss the coordination between downstream overcurrent devices and the degraded voltage relays during fault conditions to ensure faults are not transferred to other sources."

Response: Regarding the coordination of downstream breakers, thermal overload devices, and fuses during degraded voltage conditions prior to the offsite source breakers being opened by the degraded voltage relays, CPS has j specifically evaluated the relaying associated with the 4.160 kV Emergency Safety Feature (ESP) motors during the LOCA block-start scenario.

i Assuming the worst case is a transient where the block-start voltage i

Attachm:nt I to U-602613 LS-94-013 Page 8 of 9 recovers to a valuejust below the relay reset point and the buses subsequently transfer to the on-site sources, IP has verified that the overcurrent relaying will not trip the 4.160 kV ESF motors during the transient nor will the motors be damaged by this transient.

The control fuses for the 120 volt control circuits in five Motor Control Centers have been analyzed in a similar fashion at the contactor minimum pickup voltage. The conclusion of this analysis is that the control fuses will not open as a result of the degraded voltage during the block start transient. The coordination of other breakers and relays have been evaluated using standard coordination curve analyses. No specific transient analyses are required nor could they be economically performed due to the large number of possible permutations.

The coordination between downstream overcurrent devices and the upgraded voltage relays during fault conditions has been evaluated to ensure faults are not transferretto other sources. Faults of the magnitude that would drop the voltage on the 4.160 kV bus low enough to initiate the degraded voltage relaying scheme would require high currents. Faults of this magnitude would rapidly be sensed by the overcurrent devices and the appropriate breakers would open prior to the 15-second degraded voltage time delay relay timing out. This time delay allows time for both faults to clear as well as large motors to start. The time delay will prevent spurious transfer to the onsite power source unless a true degraded voltage condition exists. 1 I

10. "The submittalindicates that, as a result of the calculations performed for the degraded voltage setpoints, CPS determined that the required minimum steady state voltage specified for certain diesel generator surveillances should be increased to 3870 volts. Provide the calculations that were used to determine this diesel generator minimum voltage."

Response: A new Diesel Generator (DG) calculation was not performed. The voltage  ;

ranges currently specified for the DG surveillances are equal to 4.160kV 1 10 percent in accordance with the recommendations ofRegulatory Guide '

1.19. Despite the broad range of allowable voltages specified in the DG surveillance requirements, CPS surveillance procedures and good operating practices ensure that the DGs are always run with a voltage as close to the nominal required voltage of 4.160kV as practical. However, ongoing work on the revised degraded voltage relay setpoint calculations led to the observation that the lower voltage limit for operation of the DGs as specified in several DG surveillance requirements was below the lower bound analytical limit for the degraded voltage reset setpoint. In order to

%->. , .. x - ..

. Attachment I to U-602613 4 l LS-94-013 Page 9 of 9 l 4

establish a more appropriate lower limit voltage for the DGs, IP is I proposing to increase the required minimum steady-state voltage specified l in these DG surveillance requirements to be consistent with the lower bound analytical limh for the degraded voltage relays. (The basis for the l lower bound analytical limit was previously presented in response to Question five.) j l

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