ML17229A902

LER 98-008-00:on 981008,inadequate Reactor Protection Sys Trip Bypass TS Was Noted.Caused by Poorly Worded Ts. Submitted LAR to Clarify Power Requirements for High Rate of Power Trips.With 981104 Ltr

ML17229A902
Person / Time
Site:	Saint Lucie
Issue date:	11/04/1998
From:	Frehafer K, Stall J FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-98-280, LER-98-008, LER-98-8, NUDOCS 9811130285
Download: ML17229A902 (8)

Text

CATEGORY 1 REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9811130285 DOC.DATE: 98/11/04 NOTARIZED: NO DOCKET FACZL:50-335 St. Lucie Plant, Unit 1, Florida Power 6 Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION FREK<FER,K.W. Florida Power & Light Co.

STALL,J.A. Florida Power 6 Light Co.

RECZP.NAME . RECIPIENT AFFILIATION

SUBJECT:

LER 98-008-'00:on 981008,inadequate reactor protection sys trip bypass TS was noted. Caused by poorly worded TS.

Submitted LAR to clarify power requirements for high rate of power trips. With 981104 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), ncident Rpt, etc. E NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ZD CODE/NAME LTTR ENCL PD2-3 PD 1 1 GLEAVES,W 1 1 R INTERNAL: ACRS 1 1 AEOD/SPD/RAB 2 2 AEOD/S PD/RRAB 1 1 C 1 1 NRR/DE/ECGB 1 1 DE EELB 1 1 NRR/DE/EMEB 1 1 NRR/DRCH/HZCB 1 1 NRR/DRCH/HOHB 1 1 NRR/DRCH/HQMB 1 1 NRR/DRPM/PECB 1 1 NRR/DSSA/SPLB 1 1 RES/DET/EIB 1 1 RGN2 FILE 01 1 1 D

EXTERNAL: L ST LOBBY WARD 1 1 LZTCO BRYCE,J H 1 '

NOAC POORE,W. 1 1 NOAC QUEENER,DS 1 1 0 NRC PDR 1 1 NUDOCS FULL TXT 1 1 M

I' NOTE TO ALE "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE. TO HAVE YOUR NAME OR ORGANIZATION REMOVED FROM DISTRIBUTION LISTS OR REDUCE THE NUMBER OF COPIES RECEIVED BY YOU OR YOUR ORGANIZATION, CONTACT THE DOCUMENT CONTROL DESK (DCD) ON EXTENSION 415-2083 FULL TEXT CONVERSION REQUIRED TOTAL, NUMBER OF COPIES REQUIRED: LTTR 23 ENCL 23

Florida Power & Light Company,6351 S. Ocean Drive, Jensen Beach. FL 34957 November 4, 1998 APL L-98-280 10 CFR g 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re: St. Lucie Units 1 and 2 Docket Nos. 50-335/389 Reportable Event: 1998-008-00 Date of Event: October 8, 1998 Inadequate Reactor Protection em Tri B Techni 1 ification h

.,';",f~.~".;":".+eattached Lic'ensee Eve nt Report 1998-008 is being submitted pursu ant to the requirements of

.'.,;j~>v> .".p~l0,CFR$ 50,73 to provide notification of the subject event.

i a, - P ~

Very truly yours, J. A. Stall Vice President St. Lucie Nuclear Plant JAS/EJW/KWF Attachment cc: Regional Administrator, USNRC Region II Senior Resident Inspector, USNRC, St. Lucie Nuclear Plant 98ii130285 98ii04 PDR AMCK 05000:335 S PDR an FPL Group company

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150.0104 EXPIRES 06I30l2001 IS-1999)

Estimated burden per response to comply with this mandalory btfcrmagon collecbon requesl: 50 hrs. Reported lessons learned are incorporated into Ihe licensing process and fed back to Indusby. Fonvard comments regarding LICENSEE EVENT REPORT (LER) burden estimate lo the Records Management Branch (TW F33), US. Nudear

{See reverse for required number of Redudion Proiect (31500104 ]

Regulatory Commission. Washington. DC 205554001 ~ and lo Ihe Papenvrsk Olrce of Management and Budget, Washington. OC 20503. If an information cogecgon does nol display a currently valid OMB control number, the NRC may not conduct or sponsor, digits/characters for each block) snd a person is nol required to respond lo, the hformation collection.

FACIUTY NAME (1) DOCKET NUMBER {2) PAGE (3)

St. Lucie Unit 1 05000335 Page 1 of 4 TITLE (4)

Inadequate Reactor Protection System Trip Bypass Technical Specification EVENT DATE (5 LER NUMBER 6 REPORT DATE 7) OTHER FACILITIES INVOLVED 6 SEQUENTIAL REVISION FACIUTV NAME DOCK ET NUMatn MONTH DAY NUMBER NUMBER MONTH OAY St. Lucie Unit 2 05000389 FACIUTV NAME DOCKET NUMSER 10 08 1998 1998 008 00 04 1998 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQ UIREMENTS OF 10 CFR 9: (Check one or moro) {11)

MODE (9) 20.2201 (b) 20.2203(e) {2)(v) 50.73(a) (2) (i) 50.73(a) (2) (viii)

POWER 20.2203(a) { I ) 20.2203 (a) (3) (i) 50.73(a) (2) (ii) 50.73(a) (2) (x)

LEVEL {10) 100 20.2203(a)(2) (i) 20.2203(e)(3) (Ii) 50.73(a)(2)(iii) 73.71

20. 2203(e) (2) (ii) 20.2203(a) {4) 50.73 (a) (2) (iv) OTHER 20.2203(a)(2) (iii) 50.36(c)(1) 50.73(a) (2)(v) Specify In Abstract below or 20.2203(a)(2) (iv) 50.36(c)(2) 50.73{a) (2) (vii) In NRC Form 3SSA UCENSEE CONTACT FOR THIS LER 12 NAME TELEPHONE NUMBER Snclude Ares Cocci ~

K. W. Frehafer, Licensing Engineer (561) 467 - 7748 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13 REPORTABLE REPORTABLE CAUSE SYSTEM COMPONENT MANUFACTURER CAUSE SYSTEM COMPONENT MANUFACTURER TO EPIX TO EPIX JC n/a N/A NO 6 PP TAL R ORT XPECTED (14) EXPECTED YES SUBMISSION (If Yoe, complete EXPECTED SUBMISSION DATE). NO DATE (15)

ABSTRACT [Limit to 1 400 spaces, i e., approximately 1 5 singlespeced typewritten lines/ {16)

On October 8, 1998, St. Lucie Units 1 and 2 were in MODE 1 at 100 percent reactor power. FPL determined that the Technical Specification governing the trip bypass setpoints for the high rate of change of power reactor protection system trip was in error. The explicit term THERMAL POWER used in the affected Technical Specification table notation relative to the high rate of change of power trip bypass function can not be satisfied prior to ent'ry into MODE 2 from a MODE 3 condition due to the normal level of heat transfer to the reactor coolant as a result of reactor core decay heat.

The terms of the specification can not be achieved since decay heat is not a directly measurable parameter and the. operative parameter for removal of the bypass is excore neutron flux that is measured by the wide range logarithmic neutron flux monitors.

During past reactor startups, literal compliance with the Technical Specifications for the high rate of change of power trip was not met.

The cause of this event was a poorly worded Technical Specification that did not explicitly exclude decay heat from the power level at which the high rate of change of power trip bypass is required to be removed. As a corrective action, St. Lucie has developed and submitted an amendment to the license to clarify the power requirements for the high rate of change of power trip. The revision ensures that the meaning of

'explicit terms used in the affected Technical Specifications are consistent with the intent of the stated requirements based on each St. Lucie Plant design.

NAC FORM 3SS IS.1999)

NRC FORM 366A I8- I 888)

I U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FAGIUTY NAME I1) DocKET NUMBER 2 LER NUMBER (6) PAGE I3)

SEQUENTIAL REVISION NUMBER NUMBER St. Lucie Unit 1 05000335 Page 2 of 4 1998 - 008 - 00 TEXT (ffmore speceis required, use eddi tionel copies of NRC Form 366A/ I 17)

Description of Event On October 8, 1998, St. Lucie Units 1 and 2 were in MODE 1 at 100 percent reactor power. FPL determined that the Technical Specification governing the trip and bypass setpoints for the high rate of change of power (HRCP) reactor protection system (RPS)

[BZISIJC] trip bypass was in error. Specifically, the Technical Specification incorrectly defines the HRCP trip bypass as a function of THERMAL POWER, instead of indicated wide range logrithmic power.

The rate of change of reactor power is measured by four wide range logarithmic channels. Each channel independently monitors the neutron flux by processing signals from fission chambers located external to the reactor core and covers a ten decade range from approximately 10 percent to over 100 percent of full power. The excore neutron flux in the vicinity of the fission chambers is proportional to the incore nuclear fission rate and is not significantly influenced by heat transfer from the core to the coolant from the long-term decay of radioactive fission products.

The logarithmic power level signal is differentiated to provide rate of change of power information. from approximately -1 to +7 decades per minute (DPM) The rate signal is processed and input to a bistable that actuates the HRCP trip when the rate

~

of change of reactor power exceeds 2.49 decades per minute. A reactor trip is initiated when reactor power exceeds the setpoint as measured by any two wide range channels. Each wide range logarithmic neutron flux monitor also operates a bistable to disable this trip below 10 percent power and, conversely, ensure that this bypass is automatically removed at greater than or equal to 10 percent power. The trip feature may also be bypassed above 15 percent power, but setting removing this bypass is accomplished by the power range channels (linear, narrowandrange neutron flux monitors) which also monitor the excore neutron flux.

The Technical Specifications define THERMAL POWER as the total reactor core heat transfer rate to the reactor coolant. In addition to the heat generated the incore fission rate, this definition of THERMAL POWBR includes decay heat bywhich is produced from the radioactive decay of core fission products. For a previously operated reactor, decay heat continues to exist during reactor shutdown and would take several years to decay to a level where the core heat transfer rate corresponds to 10 percent, or less, of RATED THERMAL POWER. Decay'heat is not a directly measureable parameter, does not reflect the reactivity condition of the reactor, and is not a variable normally associated with the rate of change of reactor power.

Therefore, decay heat is not suitable for use as an operative parameter for automatic protective actions and there is no evidence to indicate that decay heat was considered in the design of the HRCP trip function.

Cause of the Event The cause of this event was a poorly worded Technical Specification that did not explicitly exclude decay heat from the power level at which the HRCP trip bypass is required to be removed.

Analysis of the Event, This event is reportable under 10 CFR 50.73(a)(2)(i)(B) as "any operation or condition prohibited by the plant's Technical Specifications." The following NRC FORM 388A (8.1888)

NRC FDRM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LlCENSEE EVENT REPORT (LER)

TEXT CONTINUATION DOCKET LER NUMBER (8) PAGE (3)

FACILITY NAME (1) NUMBER (2)

SEQUENTIAL REVISION

'UMBER NUMBER St. Lucie Unit 1 05000335 Page 3 of 4 1998 - 008 - 00 TEXT (if more spece is required, use edditionel copies of iIfRC Form 366AI (17)

F Technical Specification table notations apply to the wide range logarithmic neutron flux monitor functional unit:

For both Units:

TS 1.25: RATED THERMAL POWER shall be a total reactor core heat transfer rate to the reactor coolant of 2700 MWt.

TS 1.33: THERMAL POWER shall be the total reactor core heat transfer rate to the reactor coolant.

TS 1.20, OPERATZOMAL MODE: An OPBRATZOHAL MODE (i.e., MODE) shall correspond to any one inclusive combination of core reactivity condition, power level, and average reactor coolant temperature specified in TS Table 1 '.

RATED THERMAL POWER is modified with a footnote that states,

• Excluding decay heat.

Zn TABLE 1.2, the term 0 Unit 1:

TABLE 2.2-1, NOTE (4): Trip may be bypassed below 10  % and above 15% of RATED THERMAL POWER TABLE 3.3-1, Note (d): Trip may be bypassed below 10 0 and above 15% of RATED THERMAL POWER) bypass shall be automatically removed when THERMAL power is above 10 0 or below 15% of RATED THBRKQ POWBR.

Unit 2:

TABLE 2.2-2, NOTE (4) and TABLE 3.3-7, NOTE (e): Trip may be bypassed below 10 and above 15%. of RATED THERMAL POWBR; bypass shall be automatically removed when THERMAL power is above 10  % or below 15% of RATBD THERMAL POWER.

The HRCP trip was provided with the St. Lucie Unit 1 and Unit 2 analog RPS as" backup protection against power excursion events initiated from subcritical conditions. The trip is required to be operable i.n Modes 1 and 2, but may be bypassed below 10 percent and above 15 percent of reactor power. As such, the trip is based on both the OPBRATZONAL MODB of the reactor and on how fast the measured parameter representing reactor power changes in a given time period. The setpoint is specified in units of reactor startup rate, i.e., in decades per minute (DPM).

The startup rate is obtained from the wide range logarithmic neutron flux monitors which monitor the excore neutron flux. The excore neutron flux is proportional to the incore fission rate, and therefore, is proportional to the reactor power produced from the incore fission rate. During startup of a commercial nuclear reactor from subcritical conditions, heat transfer to the reactor coolant as a result of only the fission rate is typically insufficient to significantly affect the reactor coolant temperature when less than approximately 0.1 percent of full power and the rate of change of neutron flux is essentially the only measureable parameter that provides rate of change of power information.

Table 1.2 of the facility Technical Specifications defines the OPBRATZOHAL MODBS of plant operation in terms of reactivity, thermal power, and average coolant temperature. The term percent RATED THERMAL POWER is clearly annotated and footnoted with an asterisk to clarify that the numerical values used in the table exclude decay heat. This exclusion applies to the power level that, in part, defines MODE 2 wherein the HRCP trip is required to be operable during reactor startup.

NAG FOAM 386A (6-1998)

NRC FORM 366A U.S. NUCUAR REGULATORY COMMlSSlON 18-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACIUTY NAME t1) 0OCKET t.ER NUMBER (6) PAGE (3)

NUMBER 2l SEQUENTIAL REVISION NUMBER NUMBER St. Lucie Unit 1 05000335 Page 4 of 4 1998 - 008 00 TEXT llfmore specs is reguired, use edditionel copies of NRC Ferm 36&i/ I17)

The use of excore neutron flux as the measured parameter to implement the HRCP trip function is appropriate, and the RPS nuclear instrumentation channels designed to cover the startup ranges of the St. Lucie reactors are the wide range logarithmic neutron flux monitors. Similar to design features of the trip, the power level at which the trip function bypass must be removed during a reactor startup is associated with the OPERATIONAL MODB of the reactor and must be in a range of reactor power that will assure success of the protective action. The onset of operability for the HRCP trip in MODE 2 during startup is at an excore neutron flux that corresponds to approximately 10 percent of the incore full-power fission rate. However, the thermal power produced from this fission rate is typically below the THEMQ POWER defined by TS 1.33 which, absent an explicit modifier to indicate otherwise, includes decay heat. In the St. Lucie reactors following shutdown from extended power operations to below MODE 2, the thermal power produced from decay heat is typically higher than the thermal power produced only by the fi.ssion rate.

Although the exclusion of decay heat from the HRCp trip is implied by the definition of OPERATIONAL MODE, literal compliance with the Technical Specification requirements for defining the HRCP trip bypass setpoint as a function of THERMAL POWER was not met.

Analysis of Safety Significance The Technical Specification inadequacy does not apply during shutdown reactor operations or MODB 1 reactor operation above 15 percent power. Currently, both St.

Lucie units are operating in MIODE 1 above 15 percent power, so no current Technical Specification compliance issue exists.

During past reactor startups, literal compliance with the Technical Specifications for the HRCP trip was not met. However, the design of the HRCP trip function and its automatic bypass removal feature are associated with the reactor power generated only by the fission process and excludes consideration of decay heat. Decay heat is not a directly measureable parameter, does not reflect the reactivity condition of the reactor, and is not a variable normally associated with the rate of change of reactor power. Therefore, the health and safety of the public were not affected by this event.

Corrective Actions

1. St. Lucie has developed and submitted an amendment to the licenses to clarify the power requirements for the 'HRCP trip. The Techni.cal Specification changes will need to be approved by the NRC prior to any subsequent unit start up.

2. FPL reviewed the Technical Specifications governing the automatic removal of, and permissives for, other RPS trip bypasses for the incorrect use of THERMAL POWER and decay heat. The license amendments submitted in action (1) above also replaces the term THERMAL POWER with the power measured by the appropriate neutron flux monitor for the trip bypasses associated with the RPS zero power mode bypass, local power density trip bypass, and turbine trip bypass.

Additional Information None NRC FORM 3BBA 18-1998)