05000245/LER-1996-063, :on 961126,discovered Downscale Trip Fuctions for Steam Tunnel Vent Radiation Monitors Did Not Trip as Required by Design.Caused by Procedural Deficiency.Procedure for Steam Tunnel Vent Monitors Changed

:on 961126,discovered Downscale Trip Fuctions for Steam Tunnel Vent Radiation Monitors Did Not Trip as Required by Design.Caused by Procedural Deficiency.Procedure for Steam Tunnel Vent Monitors Changed

ML20137S872
Person / Time
Site:	Millstone
Issue date:	04/09/1997
From:	Robert Walpole NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20137S844	List: 05000245/LER-1996-063, :on 961126,discovered Downscale Trip Fuctions for Steam Tunnel Vent Radiation Monitors Did Not Trip as Required by Design.Caused by Procedural Deficiency.Procedure for Steam Tunnel Vent Monitors Changed 05000245/LER-1996-063-01, Forwards LER 96-063-01,documenting Event Occurred at Unit 1 on 961126.Commitments Made within Ltr Listed as Submitted
References
LER-96-063, LER-96-63, NUDOCS 9704150269
Download: ML20137S872 (4)

LER-1996-063, on 961126,discovered Downscale Trip Fuctions for Steam Tunnel Vent Radiation Monitors Did Not Trip as Required by Design.Caused by Procedural Deficiency.Procedure for Steam Tunnel Vent Monitors Changed

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)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
2451996063R00 - NRC Website

text

- _ ~. -. ---.

e NRC 70RM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB No. 3150-0104 (4-95)

EXPIRES 04;30!98 j

fN O A'T O RE0uE'ST COL ECT ON

$0 o R$

E ORTED I

t'tC??o^"A&&"t "^?amoi'os!= JMa$ *N!

a o

l LICENSEE EVENT REPORT (LER) jNguy 'gucgyjRygug^yj'(g4s" "go'gsygg j

OUICE OF MANAGEMENT AND BUDGET. W ASHINGTON. DC 20503 (See reverse for required number of digits / characters for each block)

FACluTV NAME (1)

DOCKET NUMBER (2)

PAGE (3) l Millstone Nuclear Power Station Unit 1 05000245 1 of 4 TrrLE 14)

Steam Tunnel Vent, Reactor Building Vent and Refuel Floor Vent Radiation Monitors Downscale Trip Function inoperable l

EVENT DATE (6)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR FACtWTY NAME DOCKET NUMBER NUMBER l

11 26 96 96 063 01 04 09 97 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIR IMENTS OF 10 CFR 5: (Check one or more) (11) l ODE m N

20.2201(b) 20.2203(a)(2)(v) 50.73(a)(2)(i) 50.73(a)(2)(viii)

POWER 20.2203(a)(1)

LEVEL (10) 000 20.2203(a)(3)(i) 50.73(a)(2)(ii) 50.73(a)(2)(x) 20.2203(a)(2)(i) 20.2203(a)(3)(ii) 50.73(a)(2Hiii) 73.71 20.2203(a)(2)(ii) 20.2203(a)(4) 50.73(a)(2)(iv)

OTHER g,

20.2203(a)(2)(iii) 50.36(c)(1) 50.73(a)(2)(v) specify in Abstract below or in NRC Form 366A 20.2203(a)(2)(iv) 50.36(c)(2)

X 50.73(a)(2)(vii)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER linckxle A,ea Codel Robert W. Walpole, MP1 Nuclear Licensing Manager (860)440-2191 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE To NPROS To NPRDS t

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MoNTil DAY YEAR SUBMISSION g

YES NO

~'-

(If yes, complete EXPECTED SUBMISSION DATE).

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)

On November 26,1996, with the reactor "OLD SHUTDOWN and no fuel in the reactor vessel, surveillance tzsting discovered that the downscale trip

.ons for both steam tunnel vent radiation monitors did not trip as required by design. The downscale trip points, were adjusted and tested satisfactorily. Concurrent failure of both steam tunnel vent downscale trips to function could have resulted in undetected failures of both monitors. This condition was reported pursuant to 10 CFR 50.72(b)(2)(iii)(C) as a condition that alone could have prevented the j

fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. On March 11,1997, witt % reactor in COLD SHUTDOWN and no fuel in the vessel, a review of other Millstone Unit No.1 radiation mot ws concluded that similar deficiencies exist which could prevent the reactor building vent and refuel floor radiation monitors to trip as required by design. This condition is reportable as a common mode failure which caused independent trains or channels to become inoperable in a system designed ts g

control the release of radioactive material. There were no safety consequences as a result of this event since the upscale trip functions for these radiation monitors were operable and therefore would have performed as required if an actual radiction condition existed. The cause of this event has been attributed to a procedural deficiency which requires adhsting the monitor's downscale trip points to a value with little margin to the signal failure point in the event of set point drift. Corrective actions will correct the procedural deficiency and change the downscale trip point to a value that is sufficiently above the s:gnal failure point to allow adequate margin.

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

9704150269 970409 PDR ADOCK 05000245 S

PDR

.U.S. NUCLEAR REGULATORY COMMISSloN

(&95)'

i LICENSEE EVENT REPORT (LER) i TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL REVISION Millstone Nuclear Power Station Unit 1 05000245 NUMBER NUMBER 2 of 4 96 063 01 TEXT (11more space is required, use additional copies of NRC Form 3GSA) (17) 1.

Description of Event

On November 20,1996, with the reactor in COLD SHUTDOWN and no fuel in the reactor vessel, during parformance of SP 406W " Steam Tunnel Ventilation Radiation Monitor Functional Test and Calibration," it was i

discovered that the downscale trip functions for both steam tunnel vent radiation monitors did not trip as required by design. The downscale trip function actuates when the detector signal falls below the low level trip point and provides a fail-safe action for failures such as loss of detector high voltage or signal. Technical Specifications (TS) do not require a downscale trip nor specify a setpoint for the downscale tnp.

j l

On November 27,1996, it was determined that the steam tunnel vent radiation monitors were inoperable and would not fully perform their intended safety function to isolate steam tunnel and reactor building ventilation i

when both monitors fail downscale and direct releases to the Standby Gas Treatment System (SGTS) to maintain instantaneous releases to the environment below 10 CFR Part 20 limits, l

This condition was reported on November 27,1996, pursuant to 10 CFR 50.72(b)(2)(iii)(C) as a condition that l

alone could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. After further review it was determined to be a common mode failure reportable pursuant to 10 CFR 50.73(a)(2)(vii)(c) and not reportable under 50.72 since both monitors would have functioned on a high radiation condition. The 10 CFR 50.72 report was amended on December 26,1996.

On March 11,1997, with the reactor in COLD SHUTDOWN and no fuel in the vessel, a review of other Millstone Unit No. 1 radiation monitors concluded that similar deficiencies exist which could prevent the monitors' downscale trip functions to trip as required by design. The review concluded that the reactor building vent and re, fuel floor vent radiation monitors downscale trip points have little margin for drift between the trip points and ths signal failure point. The downscale trip function actuate when the detector signal falls below the low level trip point and provides a fail-safe action for failures such as loss of detector high voltage or signal. TS do not require a downscale trip nor specify a setpoint for the downscale trip.

It was determined that the reactor building vent and refuel floor radiation monitors were inoperable and would not fully perform their intended safety function to isolate steam tunnel and reactor building ventilation when any two monitors fait downscale and direct releases to the SGTS to maintain instantaneous releases to the environment b: low 10 CFR Part 20 limits. This condition is being reported pursuant to 10 CFR 50.73(a)(2)(vii)(c) as a common mode failure which causes independent trains or channels to become inoperable in a system designed to control tha release of radioactiva material.

The upscale trip functions for the steam tunnel vent, reactor building vent and refuel floor vent radiation monitors were operable and would have performed their intended function if an actual radiation condition existed.

Therefore, there ere no safety consequences as a result of this event.

II. Cause of Event

The cause of this event has been attributed to a procedural deficiency which requires adjusting the monitors downscale trip points with little margin for drift between the trip points and the signal failure point.

NRC f0RM 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 1 05000245 NUMBER NUMBER 3 of 4 i

96 063 01 TEXT lit more space is required, use additional copies of NRC Form 366Al (17) 111. Analysis of Event Par the Millstone Unit No.1 Updated Final Safety Analysis Report, Section 11.5.1, the safety related functional requirement of these TS radiation monitors is to monitor the steam tunnel ventilation exhaust plenum, the reactor j

building, and the room air at the refueling floor area to provide prompt indication of a gross release of radioactive j

material, if setpoints are exceeded or if two monitors in any one location fail downscale, signals will isolate the normal reactor building and steam tunnel ventilation systems and initiate operation of the SGTS. The only i

required trip value for these radiation monitors in TS are the high radiation trip setting of 50 mR/hr for the steam tunnel vent,11 mR/hr for the reactor building vent, and 100 mR/hr for the refueling floor as specified in 3.2.E.3.c.

i These radiation monitors' safety function is to limit instantaneous releases to within 10 CFR Part 20 limits. The l

)

high trip setting is based upon maintaining the total instantaneous activity released from the reactor and steam j.

tunnel ducts within the limits defined in the Offsite Dose Calculation Manual.

The downscale trip feature actuates when detector signal falls below the low setpoint and provides fail-safe action for such failures as loss of detector signal when not accompanied by a loss of power. With a complete loss j

of signal, the monitor indication fails to the lowest readable meter gradation. Normal background radiation levels during shutdown vary and may approach the downscale setpoint. Therefore, the set point is adjusted during i

a calibration to a value which is low enough to prevent spurious downscale trips during shutdown yet high enough to generate a trip on loss of signal. The downscale trip is functionally verified to operate. A minimal margin between the downscale setpoint, the signal failure, and background levels can result if the setpoint drifts, j

4 Direction for adjusting the downscale trip setpoints was provided in the surveillance procedure. The procedural l

4 guidance to adjust the out of specification setpoint was considered to be adequate corrective action, since the original failure was indicative of instrument drift and not significant monitor degradation.

A failure of the downscale trip function of radiation monitors would not, in itself, degrade the principal safety l

j j

barrier (secondary containment) of the plant provided the radiation monitors remain capable of responding to a valid high radiation condition. Since the monitors responded to a known radiation field and, the high rediation trip function performed satisfactorily as demonstrated during surveillance testing, any one monitor would have l

isolated reactor building and steam tunnel ventilation and started SGTS in the event of a gross release of 4

radioactivity. Also, in the event of a loss of power, the de-energization of the high level trip relays would have Initiated the protective function independent of the downscale trip function.

j A procedural inadequacy which provided guidance for adjustment of the downscale trip points is reportable i

pursuant to 10 CFR 50.73(a)(2)(vii)(c) as an event or condition where a single cause or condition caused l

independent channels to become inoperable in a system designed to control the release of radioactive material.

IV. Corrective Action

l The procedure for the steam tunnel vent radiation monitors has been changed and has been performed j

satisfactorily to adjust the downscale trip point to a value sufficiently above the meter zero so that sufficient i

mergin exists.

The procedure changes and the performance of the surveillance for the reactor building vent and refuel floor rediation monitors will be completed by May 15,1997.

NRC FORM 386A (4 95)

NRC F,ORM 366A U.S. NUCLEAR REGULATORY COMMISSION 14 95)

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 1 05000245 NUMBER NUMBER 4 of 4 96 063 01 TEXT (If more space is required. use additional copies of NRC Form 366A) (17)

A review of all Millstone Unit No.1 radiation monitors has been performed to identify if any similar procedural deficiencies exist which may set the downscale trip points with little or no drift margin to the signal failure point.

This review concluded that the isolation condenser radiation monitor and several radiation monitors not required by TS also have similar deficiencies. The procedures for the isolation condenser radiation monitor and other j

radiation monitors not required by TS will be completed by July 15,1997.

{

V.

Additional Information

1

Similar Events

1 There were no similar events involving any radiation monitors within the last two years.

Manufacturer Data None.

1 RRC FORM 366A (4-95)