ML20106B499

Ro:On 920904,discovered Operating Anomaly on Console Which Would Drive Out of Core in Pulse Mode If Square Wave Button Pressed While Pressing Rod Drive Up Button.Caused by Failure to Remove Transient Rod.Second Switch Installed

ML20106B499
Person / Time
Site:	Armed Forces Radiobiology Research Institute
Issue date:	09/25/1992
From:	Bumgarner R, Maria Moore ARMED FORCES RADIOBIOLOGICAL RESEARCH INSTITUTE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9210020012
Download: ML20106B499 (4)

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Mcf! E r 5d-176 ic (FM Td 73 l - fii7pl . DEFENSE NUCLEAR AGENCY

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h. AHMt O FOhCl.5 H A DIOUiOLOGY Hi SE AHCH ll45111Ull' Di 1 HE SD A. M AR YL A t4D 208H9-5145 DIR 25 SEPTEMBER 1992 United States Nuclear Regulatory Commission Document Control Deck Washington, DC. 20555 Please tind encioned Licensee Event Report (LER) for a reported event that originally occurred 4 September 1992 which was investigated and verifiod on 9 September. Corrective action was completed on 25 September 1992. For information, the point of contact is the Reactor Facility Director, Mr. Mark Moore at 301-29S-1290.

Sincerely, 4 ;

p/; 44 / 4-ROBER ' L. I JMGARNER Captain, MC, USN Director

Enclosure:

Licensee Event Report 1or the AFRR1 TRIGA Reactor Faci 11ty Copy Furn:

United States Nuclear Regulatory Commincion Region 1 47S Allendale Road King cf Prussia, PA. 19406-1415 Attn: Mr Thomas Dragoun United States Nuclear Regulatory Commission Attn: Mr Marvin Mendonca, Mail Stop 11H10 Washington DC. 20S55 9

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9210o20o12 92o92 PDR ADOCK 050001 0 S PD

r Licensee Event Report for the AFRR1 TRIG 4 Reactor Facility Prepared By:

Mr. Mark L. Moort.

Mr. Robert George Mr. Stephen Miller Approved:

.W Mr. M. L. Mog[e Reactor Facility Director Approved for Release:

72< > for d e /

ROBERf L. T5DMCARNER Captain, MC, USH

/ Director Abstract A reactor operating anomaly was discovered in the AFRRI Triga reactor. The. anomaly discovered allows the reactor to automatically pull.a control rod out of the core in pulse mode.

Accidental reoccurrence of this anomaly was prevented by an-administrative order _and the installation of a temporary additional switch 'into the pulse and square wave mode _ circuit. The switch was replaced by a permanent change c' the software. interlock system designed and programmed by the cyw ole manufacturer.

Narrative Description of Event On 4 September 1992 during the daily startup checklist a reactor trainee discovered an operating anomaly on the console in which a '

rod would. drive out of the core in pulse mode. With a shutdown core the trainee was asked to repeat the steps he had performed to cause the event to occur. The trainee then pressed the PULSE mode.

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r . %g button while pressing a roi drive UP b: '1 3r. to shop that the event

]6- gan repeatable. The Senior Reactor G :erator on console notified the Deactor L'7111ty Director and demon strated the situation to the

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RFD The RFD directed the operator is call the supnliar of the mole for f urther inf ormatirn o: the problern and to determine the

, ieters of the problem through cauticus experimentation with the N 3m.

y n M iq further testing it was discovered that rods would drie out tne core if th^ Square wave button was pressed whil; pressing a H drive UP button. Also discovered was that the event does not r if the AUTO button is pressed while pressing a rod drive UP i b on.

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y, The Reactor Facility Direr, tor notified the NRC on 9 September 1992.

The NRC Region One wa.; notified telephonically as per NRC regulations and a ca was received from the NRC Non-Power Reactor (NPR) staf f at NRC H uarters sportlv thereafter. The telephon'  %

call was followed by visit by from tw i endquarters Non-Powe. @d Reactor Decomienioning and Environmental Pro j ect Directorate where the anomaly was demonstrated as well ca tR Uaction of a temporary additional key switch to prevent accident 1 ac":currence .

Assessment of Safety Consequences i ..e event was discovered during a chechout mode. Each time the event was tested it occurred with a fully scrammed shutdowr reactor. The shutdown margin with the most reactive control rod (Transient Rod) fully removed is $ 2.65. The transient rod was never removed during these tests. With the most reactive standard control rod removed by the ancmaly the reactor would be safely shutdown by $ 4.03. The reactor is considered shutdown if it is subcritical by at least $ .50. The reactor power did not increase f rom source level during these tests and at no time did it approach critical.

This event would not normally occur when the reactor is preparing for a pulse. When the reactor is critical and an operator is preparing for a petse, the operator would not be raising a control rod while entering pulce mode. Doing so would change the computed insertion above critical.

Description of Corrective Actions Until the permanent software fix by General Atomics, the cor3cle manufacturer, was installed, an administrative directive not to press a rod up button and either the pulse or squarc wave button at the samu time was implemented. A second switci. Was installed in series with both the pulse and square wave buttor: , The new switch causes the operator to be required to use two h n# for entering pulse nr square wave mode. With both hands beine J to enter the nr. -

a: tor mode the operator can not press a r. GP button at the a.,am, _ mm-.. - - - - ' - - - - - - - -

k. .

same time as he presses a mode button. A permanent corrective action which required e. software correction was implemented on 23 Sept. Testing verified the corrective software fixed the anomaly.

Upon successful testing of the permanent sof tware fix the temporary preventive actions were removed. In addition a complete checkoat of all identifiable interlock combinations will be performed in October 1992 during the annual maintenance shutdown.

Reference to any previous similar events j l

During an earlier console checkout a similar occurrence resulted i-  ;

an unsolved single occurrence during prestarts. The anomaly may s c_  ;

may not have been caused by this sequence of events. Extensive '

testing at that time failed to cause a reoccurrence.

Point of Contact for any~ Questions j Points of contact for further information are Mr. Mark L. Moore, Reactor Pacility Director, or Mr Robert George, Senior Reactor operator. Telephone 301-295-1290 4'

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