UNIVERSITY of MISSOURIRESEARCH REACTOR CENTER

January 29, 2016

U.S. Nuclear Regulatory CommissionATTN: Document Control DeskMail Station P 1-37Washington, DC 20555-0001

REFERENCE:

SUBJECT:

Docket No. 50-186university of Missouri-Columbia Research Reactor

Amended Facility License No. R- 103

Written communication as required by University of Missouri Research ReactorTechnical Specification 6.1 .h(2) regarding a deviation from Technical Specification3.2.a

The attached document provides the University of Missouri-Columbia Research Reactor (MURR)Licensee Event Report (LER) for an event that occurred on January 5, 2016, that resulted in a deviationfrom MURR Technical Specification 3.2.a.

If you have any questions regarding this report, please contact John L. Fruits, the facility ReactorManager, at (573) 882-5319.

Sincerely,

Ralph A. Butler, P.E.Director

RAB:jlb

Enclosure

1513 Research Park Drive Columbia, MO 65211 Phn:573-882-4211 Fa:538266 e:www.murr.missouri.edu

Fighting Cancer with Tomorrow's Technology

Licensee Event ReportU.S. Nuclear Regulatory CommissionJanuary 29, 2016

Licensee Event Report No. 16-01 - January 5, 2016University of Missouri Research Reactor

Introduction

On January 5, 2016, with the reactor operating at 10 MW in the automatic control mode, the Lead Senior

Reactor Operator (LSRO) observed a noticeable internal snap of the three-position ("In-Normal-Out")

shim switch (1S$4) while attempting to perform a routine control blade shimming evolution. Operation of

switch 15$4 failed to cause movement of control blade 'D' in either the inward or outward direction and

the switch would also not automatically spring return to the "Normal" mid-position. A manual scram was

immediately initiated by the LSRO due to the inability to operate the control blade shim switch. The

LSRO completed all Immediate and Subsequent Actions of reactor emergency procedure REP-2,

"Reactor Scram," and verified all control blades were fully inserted. Failure of the shim switch to operate

control blade 'D' resulted in a deviation from Technical Specification (TS) 3.2.a, which states, "All

control blades, including the regulating blade, shall be operable during reactor operation."

Description of the Rod Control System

The reactivity of the reactor is controlled by five neutron absorbing control blades. Each control blade is

attached to a Control Rod Drive Mechanism (CRDM) by means of a support and guide extension (offsetmechanism). Four of the control blades, referred to as the shim blades, are used for coarse adjustments to

the neutron density of the reactor core. The fifth control blade is a regulating blade. The low reactivity

worth of this blade allows for very fine adjustments in the neutron density in order to maintain the reactor

at the desired power level. The nominal speed of the shim blades is one inch per minute in the outward

direction and two inches per minute in the inward direction. Nominal speed of the regulating blade is 40

inches per minute in both the inward and outward directions. The speed of the control blades cannot beadjusted without physically altering the system. The four shim blades are actuated by electro mechanical

CRDMs that position, hold, and scram each shim blade. Each CRDM consists of a 0.02-LIP, 115-volt,

one-amp, single-phase, 60-cycle motor connected to a lead screw assembly through a reduction gearboxand overload clutch. The reactivity worth and speed of travel for the control blades are sufficient to allow

complete control of the reactor system from a shutdown condition to full power operation. The insertionrate of the shim control blades is adequate to ensure prompt shutdown of the reactor in the event a scram

signal is received.

Control blade movements, interlocks and bypasses, and control modes are managed by the Rod Control

System. The Rod Control System is a relay and switch logic system used to prohibit accidental orincorrect operation which could result in an unsafe condition. During normal operation, Master Control

Switch 1Si1 allows the shim blades to be withdrawn or inserted manually by a three-position ("In-Normal-

Out") shim switch (1S4) located on the reactor control console. The switch is spring return to the mid-

position ("Normal") when released. A five-position ("A-B-C-D-Gang") selector switch (1S$3) enables thereactor operator to select the shim blades individually or as a group. 115 VAC power is supplied to the

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Licensee Event ReportU.S. Nuclear Regulatory CommissionJanuary 29, 2016

CRDM motor windings through motor relays; KI for shim control blade insertion and K2 for shimcontrol blade withdrawal (see Attachment 1).

Detailed Event Description

On January 5, 2016, at 00:39 with the reactor operating at 10 MW in the automatic control mode, theLSRO observed a noticeable internal snap of the three-position ("Tn-Normal-Out") shim switch (1S4)while attempting to perform a routine control blade shimming evolution. Operation of the shim switchfailed to cause movement of control blade 'D' in either the inward or outward direction and the switchwould also not automatically spring return to the "Normal" mid-position. A manual scram wasimmediately initiated by the LSRO due to the inability to manually operate the shim control blades. TheLSRO completed all Immediate and Subsequent Actions of reactor emergency procedure REP-2,"Reactor Scram," and verified all control blades were fully inserted. Failure of shim switch 1 S4 resultedin a deviation from TS 3 .2.a, which states,. "All control blades, including the regulating blade, shall beoperable during reactor operation. "

Safety Analysis

The basis for TS 3.2.a. is to ensure that the normal method of reactivity control is used during reactoroperation. When operating the reactor at 10 MW in the automatic control mode, the control blades are,routinely shimmed in the outward direction as a result of poison buildup and fuel depletion. The LSROhad just successfully completed the shimming evolution for control blades 'A,' 'B' and 'C' and wasbeginning the process of withdrawing control blade 'D' to bank the rods as required by procedure whenthe failure of the switch occurred. While the ability to manually withdraw or insert the control blade mayhave been unavailable for a very short period of time (-5-10 seconds) between the observed failure andinitiation of the reactor scram, at no time was the ability to scram the reactor, either through automaticinitiation or manually by the control room operator, affected by this failure. The shim switch is not a partof the Reactor Safety System. This failure would also not have prevented the Rod Run-In System fromfunctioning normally.

Corrective Actions

When the LSRO discovered that the shim switch was inoperable, he immediately initiated a reactor scramand completed all actions of reactor emergency procedure REP-2, "Reactor Scram," to ensure the reactorwas in a safe shutdown condition. All four shim control blades were verified to be fully inserted.

Troubleshooting efforts identified the fracture• of the torsion spring on the three-position ("In-Normal-Out") shim switch (1S4) which prevented the complete travel of the switch; causing the associatedcontacts from engaging (see Attachments 2 and 3). An exact replacement Type SBM SwitchB3A02N 1 S2N 1 was installed and tested satisfactory.

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Licensee Event ReportU.S. Nuclear Regulatory CommissionJanuary 29, 2016

Additionally, this event was captured in the MURR Corrective Action Program as CAP entry No. 16-0001 and any additional information or corrective actions will be considered and documented.

If there are any questions regarding this Licensee Event Report, please contact me at (573) 882-5319. Ideclare under penalty of perjury that the foregoing is true and correct.

Sincerely,

John L. FruitsReactor Manager

ENDORSEMENT:Reviewed and Approved,

Ralph A. Butler, P.E.

Director

xc: Reactor Advisory CommitteeReactor Safety Subcommittee

Dr. Garnett S. Stokes, Provost

Dr. Mark McIntosh, Vice Chancellor for Research, Graduate Studies and Economic Development

Mr. Geoffrey Wertz., U.S. NRCMr. Johnny Eads, U.S. NRC

Attachments:1. MURRR Drawing Number 42, Sheet 2 of 2, Reactor Control System

2. GE Type SMB Switch broken torsion spring picture

3. Exploded View of GE Type SBM Switches

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ATTACHMENT 3

GEH- 2038

Torsion Spring

TYPE SlimCONTROL SWITCHES

- N

GEK7-41*?A

7217A

*1912

I?,

1A Handle5 Mouri ting Scrfew8 Target Escutcheon

12 Front Plate13 Stops15 Rocker Arm16 Sleeve17A Positioning Wheel18 Positioning Spring

ATorsion SrnT3 Sping Actuator

22232425262728293031323334

Front BearingFront SupportBarrter CoverCam Follower and Moving Contact AssemblyCans for ContactsUpper Stationary ContactLower Stationary ContactTerminal ScrewBarrierBarrier AssemblyRear BearingBearing RetainerTie Bolt

Figure 1 - 018485484) Exploded View of Type SBM Switch

7