05000423/LER-1997-033, :on 970527,P-6 Bistable Reset Function Was Set non-conservatively Resulting in TS Violation.Cause Is Indeterminate.Intermediate Range Neutron Flux Will Be Brought Into Compliance W/Ts

:on 970527,P-6 Bistable Reset Function Was Set non-conservatively Resulting in TS Violation.Cause Is Indeterminate.Intermediate Range Neutron Flux Will Be Brought Into Compliance W/Ts

ML20148T209
Person / Time
Site:	Millstone
Issue date:	06/26/1997
From:	Danni Smith NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20148T202	List: 05000423/LER-1997-033, :on 970527,P-6 Bistable Reset Function Was Set non-conservatively Resulting in TS Violation.Cause Is Indeterminate.Intermediate Range Neutron Flux Will Be Brought Into Compliance W/Ts
References
LER-97-033, LER-97-33, NUDOCS 9707080427
Download: ML20148T209 (4)

LER-1997-033, on 970527,P-6 Bistable Reset Function Was Set non-conservatively Resulting in TS Violation.Cause Is Indeterminate.Intermediate Range Neutron Flux Will Be Brought Into Compliance W/Ts

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4231997033R00 - NRC Website

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I NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OM8 NO. 3160-0104 l-g_ gej EXPIRES 04/30/98 T1oN R QU S O ATO COLL O

S E RT D L n^c"."'?o^"Ao'5?."! "*! Sat '04'a" olo"ffs'S ^Sta o

LICENSEE EVENT REPORT (LER) 1*W3*n '! ',tglf a"A'g/1g "'gg,gagao'a%=" gc o

s Mnh'ea!"1'l=!#1'fs%?r"o;"?!!!a?" *-

(See reverse for required number Of digita/ characters for each block)

FACILITY NAME (1)

DOCKET NUMBER (2)

PAGE (3)

Millstone Nuclear Power Station Unit 3 05000423 1 of 4 Tr,'tt (4) l P-6 Bistable Reset Function Set Non-Conservatively Resulting in Technical Specification Violation J

EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENTIAL REVislON MONTH DAY YEAR FACluTY NAME DOCKET NUMBER NUMBER NUMBER 1

05

.27 97 97 033 00 06 26 97 OPERATING 5

THIS REPORT is SUBMITTED PURSUANT To THE REQUIREMENTS oF 10 CFR 5: (Check one or morel (11)

MODE (9) 20.2201(b) 20.2203(a)(2)(v)

X 50.73(a)(2)(i) 50.73(a)(2)(viii)

POWER 000 20.2203(a)(1) 2o.2203(a)(3)(i) 50.73(a)(2)(ii) 50.73(a)(2)(x)

LEVEL (10) 20.2203(a)(2)(i) 20.2203(a)(3)(ii) 50.73(a)(2)(iii) 73.71 20.2203(a)(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 m Abstract below 20.2203(a)(2)(sv) 50.36(C)(2) 50.73(a)(2)(vii).

LICENSEE CONTACT FoR THis LER (12)

)

ImME TELEPHONE NUMtlER (include Area Code)

David A Smith, MP3 Nuclear Licensing Manager (860)437-5840 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE l

TO NPROS TO NPRDS l

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTH DAY YEAR YES X No sUBMissloN DATE (15)

(if yes, Complete EXPECTED Submission DATE).

1 ABSTRACT (Limit to 1400 spaces,l.e., approximately 15 single-spacedtypewrittenhnes) (16)

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i On May 27,1997, with the Unit in Mode 5, a system engineering review of Technical Specification (TS) interlocks concluded that the intermediate Range Neutron Flux, P-6 interlock was calibrated in a manner that did not comply with TS, Table 2.2-1, " Reactor Trip System Instrumentation Setpoints," Functional Unit 18(a). The P-6 interlock reset value of 5.0 E-11 amps, where the interlock function is automatically reinstated on decreasing power, is set per approved procedures lower, and therefore, less conservative than the Allowable Value specified in TS Table 2.2-1 of greater l

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than or equal to 6.0 E-11 amps. This would result in instances between 5.0 and 6.0 E-11 amps where the Intermediate Range Neutron Flux, P-6 interlock would be bypassed and the Source Range Neutron Flux monitoring instrumentation not re-energized and OPERABLE as required. This condition is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B), as a condition or operation prohibited by the plant's Technical Specifications.

'i i

This is an historical event and the cause is indeterminate. The potentialimpact of the P-6 interlock bistable reset j

value'on TS compliance was only recognized recently during the reviews of design and licensing basis documentation.

The Source Range Neutron Flux trip is not credited within the safety analyses but provides a tertiary backup to j

the Power Range Neutron Flux - Low Setpoint trip if an uncontrolled rod withdrawal error event from a subcntical or i

' low power condition occj red. Consequently, even though a violation of the TS occurred there were no adverse safety consequences as a result of this event. The Intermediate Range Neutron Flux, P-6 interlock bistable calibration will be brought into compliance with the TS.

9707090427 970626 PDR ADOCK 05000423 S

PDR

gR FORM 366A U.s. NUCLEAR REGULATORY Commission LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL REVISION Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 2 of 4 97 033 00 TEXT Uf more space is required, vse additionalcopies of NRC form 366A) (17) 1.

Descrintion of Event On May 27,199~7, wnh the Unit in Mode 5, a system engineering review of Technical Specification (TS) interlocks concluded that the Intermediate Range Neutron Flux, P-6 interlock was calibrated in a manner that did not comply with TS, Table 2.2-1, " Reactor Trip System [RTS] Instrumentation Setpoints," Functional Unit 18(a). The P-6 interlock reset vslue of 5.0 E-11 amps, where the interlock function is automatically reinstated on decreasing power, is set per cpproved procedures !ower, and therefore, less conservative than the Allowable Value (AV) specified in TS Table 2.2-1 of greater than or equal to 6.0 E-11 amps. TS Limiting Condition for Operation (LCO) 2.2.1, Action b states;"With the Rractor Trip System Instrumentation or Interlock Setpoint less conservative than the value shown in the Allowable Values column of Table 2.2-1,.. (which leads to Action b.2 which states] Declare the channelinoperable and apply the rpplicable ACTION statement of Specification 3.3.1 until the channel is restored to OPERABLE status with its Setpoint adjusted consistent with the Trip Setpoint value." TS Table 3.3-1," Reactor Trip System Instrumentation," Functional Unit 17(a) specifies that the P-6 interlock is required to be OPERABLE in Mode 2##. The double asterisk notation signifies that the interlock is to be OPERABLE *Below the P-6 (Intermediate Range Neutron Flux Interlock) Setpoint."

The P-6 bistable reset setpoint, as currently set, would allow the Source Range Neutron Flux neutron monitoring instrumentation (NIS) to remain bypassed on decreasing reactor power down to the P-6 interlock bistable reset setpoint of 5.0 E-11 amps, which is less than the AV of 6.0 E-11 amps specified in the TS. This could result in instances between 5.0 and 6.0 E-11 amps where the Intermediate Range Neutron Flux, P-6 interlock would be bypassed and the Source Range Neutron Flux monitoring instrumentation not re-energized and OPERABLE as required. This condition is r: portable pursuant to 10 CFR 50.73(a)(2)(i)(B), as a condition or operation prohibited by the plant's Technical Specifications.

j A descriptionof the licensing bases for the Intermediate Range Neutron Flux, P-6 interlock is provided in the Bases to the Millstone Unit 3 TS and the Nuclear Regulatory Commission (NRC) Safety Evaluation Report (SER) for Millstone Unit 3.

The TS Bases states,"On increasing power P-6 allows manual block of the Source Range trip (i.e., prevents premature block of Source Range trip) and deenergizes the high voltage to the detectors. On decreasing power, Source Range 1: vel trips are automatically reactivated and high voltage restored." The NRC SER for Unit 3 states: "The source range trip provides protection during reactor startup and shutdown when the neutron flux channel is below the P-6 interlock setpoint (6 E-11 amp)[ Allowable Value for the Intermediate Range Neutron Flux, P-6 interlock). This trip can be minually blocked above the P-6 interlock setpoint and automatically reinstated when power is reduced below the P-6 int rlock setpoint."

The intermediate Range Neutron Flux, P-6 interlock bistables were first calibrated during preoperational testing of the i

RTS instrumentation using calibration information supplied by the Nuclear Steam Supply System (NSSS) vendor in tccordance with approved plant procedures. This condition has existed since prior to startup At the time of discovery, th;re was no immediate impact on equipment operability and immediate corrective actions were not required as the intermediate Range Neutron Flux, P-6 interlock is required to be OPERABLE in Mode 2 and the plant is currently in Mode 5 in an extended shutdown.

11.

Cause of Event

This is an historical event and the cause is indeterminate. The potential impact of the P-6 interlock bistable reset value on TS compliance was only recognized recently during the reviews of design and licensing basis documentation.

NAC F0FIM 366A (4-95)

- ~,,.

NRC FDRM 366A U.s. NUCLEAR REGULATORY Commission (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (0)

PAGE (3)

YEAR SEQUENTIAL REVISloN Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 3 of 4 97 033 00 TEXT (If more space is required, use additionalcopies of NRC Form 366A) (17) ill. Analysis of Event

_ Th3 Source Range Neutron Flux trip is not credited within the safety analyses but provides a tertiary backup to the Power Range Neutron Flux - Low Setpoint trip if an uncontrolled rod withdrawal error event from a suberitical or low power condition occurreo. Consequently, even though a violation of the TS occurred there were no adverse safety consequences as a result of this event.

As described in FSAR Section 15.4.1, "an uncontrolled rod cluster control assembly (RCCA) withdrawal from a subcritical or low power condition is defined as an uncontrolled addition of reactivity to the reactor core caused by withdrawal of RCCA banks resulting in a power excursion. While the occurrence of this type of transient is highly unlikely, such a transient could be caused by a malfunction of the reactor control or control rod drive systems. This could occur with the reactor either subentical, at hot zero power, or at power. Should a continuous RCCA withdrawal accident occur the transient is terminated by [one of) the following automatic features of the reactor protection system."

These features include the Source, intermediate, Power (Iow or high settings) Range High Neutron Flux trips or the High Neutron Flux Rate Trip. FSAR Section 15.4.1.2 indicates that the Power Range Neutron Flux (Iow setting) is credited in the safety analysis for providing the reactor trip to terminate the transient (at an analysis assumed value of 35 percent power). FSAR Section 15.4.1.3 concludes that"the core and [ Reactor Coolant System] RCS are not

~ dversely affected since the combination of thermal power and coolant temperature result in a [ Departure from a

Nucleate Boiling Ratio] DNBR greater than the limit value." The reactor power at the P-6 interlock level is extremely low (l;ss than 1 percent), consequently the impact of an accident at that power level compared to the FSAR 15.4.1 analysis r:sults is negligible.

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IV. Corrective Action

No immediate corrective actions were required as the intermediate Range Neutron Flux, P-6 interlock is only required to be OPERABLE in Mode 2 (as described previously) and the plant is currently in an extended shutdown.

The following corrective actions will be taken, prior to entry into Mode 4:

2 I

1.

The Intermediate Range Neutron Flux, P-6 interlock bistable calibration will be brought into compliance with the Technical Specifications.

V.

Additional Information

None

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YEAR SEQUENTIAL REVISION NUMBER NUMBER 4.of 4 Millstone Nuclear Power Station Unit 3 05000423 97 033 00 TEXT (If more space is required, use additionalcopies of NRC Form 366A) (17)

Manuf acturer Data Ells System Code Plant Protection System..

..JC i

Ells Component Code l

l Control Device, Permissive.

.69 l

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