ML20005E227

LER 89-009-01:on 890511,reactor Trip Occurred Due to Power Range Neutron Flux High Negative Rate Signal.Caused by Procedural Inadequacy.Procedures Changed to Require Rods to Be Unlatched Before Rod Drop Time connection.W/891229 Ltr

ML20005E227
Person / Time
Site:	Millstone
Issue date:	12/29/1989
From:	Conway R, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-009, LER-89-9, MP-13905, NUDOCS 9001040124
Download: ML20005E227 (4)

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December 29, 1989 MP-13905 Re: 10CFR50,73(a)(2)(iv) .  ;

L U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Reference:

Facility Operating License No. NPF-49 Docket No. 50-423 Licensee Event Report 89-009-01 Gentlemen:

This letter forwards updated Licensee Event Report 89-009-01, which is being sub-  :

mitted to correct the corrective action completion date. Licensee Event Report-89-009-00 was submitted pursuant to 10 CFR 50.73(a)(2)(iv), any event or condition that resulted in automatic actuation of the Reactor Protection System. i Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY i

FOR: Stephen E. Scace >

Station Superintendent hiillstone Nuclear Power Station

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BY: arl H Station Services Superintendent Millstone Nuclear Power Station SES/RDC:tjp

Attachment:

LER 89-009-01 cc: W. T. Russell, Recion 1 Administrator D. H. Jaffe, NRC' Project Manager, Millstone Unit No. 3 W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos.1, 2 and 3 00 kOb$k f h

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LICENSEE EVENT REPORT (LER) f ACl6t T 4 NAME(1) U M 4iNJMidhise '

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At 1514 on May 11,1959 while operating in Mode 1,100ci reactor power, 557 deprees and 2:50 psia, a reactor inp occurred due to a power range neutron flux high negative rate signal. Lpon deenergizing a rod drop time recording system connected to the Control Rod Dnve System, the control rods unlatched. The recording system had been connected in preparation for tests dunng the second refuehng outape, scheduled to start May 12, 1989. Root cause of the reactor tnp was procedural inadequacy in that the procedure did not specify that control rods must be unlatched prior to connecting the rod drop time recording system.

Spurious rod drop signals were generated by the rod drop time recordmg system while being deenergized.

This condiuon does not occur every time the system is deenergized. To present recurrence plant procedures were changed to require rods to be unlatched before connectmg the rod drop time recordmp system.

Smce this event occurred withm 45 hours5.208333e-4 days <br />0.0125 hours <br />7.440476e-5 weeks <br />1.71225e-5 months <br /> of the scheduled start of the second refueling outage, the refuehng outage commenced immediately after the trip.

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1. Descetinn of Event 1

At 1514 on May ll,1989 while operating in Mode 1, at 100cc reactor power,557 degrees and 2250 psia, a reactor trip occurred on power range neutron flux high negathe rate, when a rod drop time recording system connected to the Control Rod Drne System was deenergized, causmg control rods to unlatch.

A reactor shutdown was scheduled for Niay 12,1989 to commence the second refuehng outape.

The measuring of control rod drop times was scheduled to follow reactor shutdown. On May 11, 1989 preparations for the outage were in progress, meludmp connection of the Automatic Rod Drop Test Can to the Digital Rod Position Indication Sptem and the Control Rod Drne System in accordance with approved plant procedures. The Automatic Rod Drop Test Cart is a microprocessor-based system which is used to unlatch a preselected group of rods and measure the rod drop times. Following satisfactory completion of installation tens the cart was deenergized.

Upon shutdown of the cart, spurious signals were sent to the Control Rod Dnve power cabmets, which interrupted power to the rod drive mechanisms, causing rods to unlatch. A negative neutron flux rate reactor trip resulted.

At the time of the trip, operators serif ed that the reactor inp breakers were open, that all control iod were fully inserted and that neutron flux was decreasing. A Feedwater Isolation was recched due to low average reactor coolant system temperature following the trip. An Auxiliary Feedwater actuation occurred as a result of a steam generator low-low level signal. These are normal plam responses following a trip. Other automatic and manual-itutiated Engineered Safeguards Features actuations were not required. Main Steam isolation valves were shut, and Mam Feedwater Pumps were stopped to control the plant cooldown.

The turbine-driven Auxiliary Feedwater Pump was out of service for surveillance testing. The motor-drhen Auxihary Feedwater Pump started in response to the Auxihary Feedwater Actuation.

Operators controlled plant cooldown by adjusting auxihary feedwater flow to the steam generators.

The hand controller for auxiliary feedwater flow from the motor-dnven Auxihary Feedwater Pump to the *D" steam generator failed "as-is", preventing flow adjustment. Operators reset the feedwater isolation signal and fed the *D" steam generator from the main feedwater system.

Following reset of the feedwater isolation signal, an isolation valve malfunction prevented feeding the A steam generator from the main feedwater system. Operators continued to feed the

• A" steam generator from the auxiliary feedwater system. A normal cooldown rate was mamtained throughout the shutdown.

Approximately 15 minutes after the reactor trip, with reactor coolant system pressure increasing toward the normal operating pressure, it was obser ed that a pressurirer spray control valve was panially open, and the pressure control system was directing 20c'c spray. Operators took rnanual control of pressurizer spray to control reactor coolant system pressure.

The plant was stable in Mode 3 (Hot Standby), 557 degrees, and 2250 psia, at 1540 based on average reactor coolant system temperature returning to a stable value.

11. - Cnute of Event The root cause of the event was procedural inadequacy. The procedure governing operation of the Automatic Rod Drop Test Cart did not specify that control rods must be unlatched prior to connecting to the Control Rod Drive System. The procedure was developed from the vendor's technical and operating manual, which does not explicitly specify that rods must be unlatched prior to connecting the system. In discussion with the sendor, it was learned that the vendor assumed rods would always be unlatched prior to connecting the system. While being deenergued the l Automatic Rod Drop Test Cart generated a drop signal.

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. LICENSEE EVENT REPORT (LER) TEXT CONTINUATION

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After consulting with the vendor for the Automatic Rod Drop Tcst Cart, it was learned that one or more signals to the power cabinets may undergo transition to a low voltage state, unlatchmp the i

affected rods as the can is deenergized. This occurrence is not always repeatable. On at least one occasion during rod drop time tests conducted in the first refueling outage, the cart was deenergired without unlatching control rods that had been withdrawn in preparation for drop tests m accordance with approved plant procedures.

The failure in the *D" steam generator auxiliary feedwater hand controller was caused by a broken internal strmg. The hand controller was replaced. The malfunction in the A steam generator main feedwater isolation valve was due to a slight misalignment of a position switch. The sultch was aligned. The pressurizer spray controller malfunction is being imestigated in accordance with approved plant administrative and work control procedures. Redundant systems, the inherent flexibility and safety of designed systems, operator training and plant procedures prevented any of the above equipment malfunctions from posms a danger to the health and safety of the public, or the potential for adverse safety implications.

IV. Correcthe Action The procedure for conducting rod drop tests was revised on November 17, 1969, to require that' control rod drive mechanisms be unlatched prior to cannecting and disconnecting the Automatic Rod Drop Cart to the Control Rod Drhe System.

V, Addninnni inintmntion There are no previous Licensee Event Reports with the same root cause and sequence of events.

The Automatic Rod Drop Test Can is manufactured by Westinghouse Electric Corporation (W351).

SYSTF N19 Control Rod Drive System - AA CON 1PONENT9 Special Recorder (Automatic Rod Drop Test Cart) - XR Hand Controller - HC Position Su1tch - 33 l

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