ML16033A405
| ML16033A405 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Columbia |
| Issue date: | 01/29/2016 |
| From: | Rhonda Butler Univ of Missouri - Columbia |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML16033A405 (7) | |
Text
UNIVERSITY of MISSOURI RESEARCH REACTOR CENTER January 29, 2016 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P 1-37 Washington, DC 20555-0001
REFERENCE:
Docket No. 50-186 university of Missouri-Columbia Research Reactor Amended Facility License No. R- 103
SUBJECT:
Written communication as required by University of Missouri Research Reactor Technical Specification 6.1 .h(2) regarding a deviation from Technical Specification 3.2.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 deviation from MURR Technical Specification 3.2.a.
If you have any questions regarding this report, please contact John L. Fruits, the facility Reactor Manager, 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 Report U.S. Nuclear Regulatory Commission January 29, 2016 Licensee Event Report No. 16-01 - January 5, 2016 University 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 (offset mechanism). 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 be adjusted 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 gearbox and 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 insertion rate 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 or incorrect 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 the reactor operator to select the shim blades individually or as a group. 115 VAC power is supplied to the I of 3
Licensee Event Report U.S. Nuclear Regulatory Commission January 29, 2016 CRDM motor windings through motor relays; KI for shim control blade insertion and K2 for shim control 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, the LSRO 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 switch 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 manually operate the shim control blades. 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 shim switch 1S4 resulted in a deviation from TS 3 .2.a, which states,. "All control blades, including the regulating blade, shall be operable 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 reactor operation. 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 LSRO had just successfully completed the shimming evolution for control blades 'A,' 'B' and 'C' and was beginning the process of withdrawing control blade 'D' to bank the rods as required by procedure when the failure of the switch occurred. While the ability to manually withdraw or insert the control blade may have been unavailable for a very short period of time (-5-10 seconds) between the observed failure and initiation of the reactor scram, at no time was the ability to scram the reactor, either through automatic initiation or manually by the control room operator, affected by this failure. The shim switch is not a part of the Reactor Safety System. This failure would also not have prevented the Rod Run-In System from functioning normally.
Corrective Actions When the LSRO discovered that the shim switch was inoperable, he immediately initiated a reactor scram and completed all actions of reactor emergency procedure REP-2, "Reactor Scram," to ensure the reactor was 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 associated contacts from engaging (see Attachments 2 and 3). An exact replacement Type SBM Switch B3A02N 1S2N 1 was installed and tested satisfactory.
2 of 3
Licensee Event Report U.S. Nuclear Regulatory Commission January 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. I declare under penalty of perjury that the foregoing is true and correct.
ENDORSEMENT:
Reviewed and Approved, Sincerely, John L. Fruits Ralph A. Butler, P.E.
Reactor Manager Director xc: Reactor Advisory Committee Reactor Safety Subcommittee Dr. Garnett S. Stokes, Provost Dr. Mark McIntosh, Vice Chancellor for Research, Graduate Studies and Economic Development Mr. Geoffrey Wertz., U.S. NRC Mr. 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
Com*missioned ror lltoward County My Commission Exlpiles: Maih 26, 2019 Jaoql~l*i Bhnm, Nota PubI::. .., .- !
3 of 3
z ATTACHMENT 3 GEH- 2038 Torsion Spring TYPE Slim CONTROL SWITCHES GEK7-41*?A
- N 72 17A
- 19 12 I?,
1A Handle 22 Front Bearing 5 Mouri ting Scrfew 23 Front Support 8 Target Escutcheon 24 Barrter Cover 12 Front Plate 25 Cam Follower and Moving Contact Assembly 13 Stops 26 Cans for Contacts 15 Rocker Arm 27 Upper Stationary Contact 16 Sleeve 28 Lower Stationary Contact 17A Positioning Wheel 29 Terminal Screw 18 Positioning Spring 30 Barrier 31 Barrier Assembly ATorsion Srn 32 Rear Bearing T3 Sping Actuator 33 Bearing Retainer 34 Tie Bolt Figure 1 - 018485484) Exploded View of Type SBM Switch 7
UNIVERSITY of MISSOURI RESEARCH REACTOR CENTER January 29, 2016 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P 1-37 Washington, DC 20555-0001
REFERENCE:
Docket No. 50-186 university of Missouri-Columbia Research Reactor Amended Facility License No. R- 103
SUBJECT:
Written communication as required by University of Missouri Research Reactor Technical Specification 6.1 .h(2) regarding a deviation from Technical Specification 3.2.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 deviation from MURR Technical Specification 3.2.a.
If you have any questions regarding this report, please contact John L. Fruits, the facility Reactor Manager, 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 Report U.S. Nuclear Regulatory Commission January 29, 2016 Licensee Event Report No. 16-01 - January 5, 2016 University 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 (offset mechanism). 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 be adjusted 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 gearbox and 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 insertion rate 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 or incorrect 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 the reactor operator to select the shim blades individually or as a group. 115 VAC power is supplied to the I of 3
Licensee Event Report U.S. Nuclear Regulatory Commission January 29, 2016 CRDM motor windings through motor relays; KI for shim control blade insertion and K2 for shim control 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, the LSRO 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 switch 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 manually operate the shim control blades. 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 shim switch 1S4 resulted in a deviation from TS 3 .2.a, which states,. "All control blades, including the regulating blade, shall be operable 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 reactor operation. 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 LSRO had just successfully completed the shimming evolution for control blades 'A,' 'B' and 'C' and was beginning the process of withdrawing control blade 'D' to bank the rods as required by procedure when the failure of the switch occurred. While the ability to manually withdraw or insert the control blade may have been unavailable for a very short period of time (-5-10 seconds) between the observed failure and initiation of the reactor scram, at no time was the ability to scram the reactor, either through automatic initiation or manually by the control room operator, affected by this failure. The shim switch is not a part of the Reactor Safety System. This failure would also not have prevented the Rod Run-In System from functioning normally.
Corrective Actions When the LSRO discovered that the shim switch was inoperable, he immediately initiated a reactor scram and completed all actions of reactor emergency procedure REP-2, "Reactor Scram," to ensure the reactor was 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 associated contacts from engaging (see Attachments 2 and 3). An exact replacement Type SBM Switch B3A02N 1S2N 1 was installed and tested satisfactory.
2 of 3
Licensee Event Report U.S. Nuclear Regulatory Commission January 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. I declare under penalty of perjury that the foregoing is true and correct.
ENDORSEMENT:
Reviewed and Approved, Sincerely, John L. Fruits Ralph A. Butler, P.E.
Reactor Manager Director xc: Reactor Advisory Committee Reactor Safety Subcommittee Dr. Garnett S. Stokes, Provost Dr. Mark McIntosh, Vice Chancellor for Research, Graduate Studies and Economic Development Mr. Geoffrey Wertz., U.S. NRC Mr. 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
Com*missioned ror lltoward County My Commission Exlpiles: Maih 26, 2019 Jaoql~l*i Bhnm, Nota PubI::. .., .- !
3 of 3
z ATTACHMENT 3 GEH- 2038 Torsion Spring TYPE Slim CONTROL SWITCHES GEK7-41*?A
- N 72 17A
- 19 12 I?,
1A Handle 22 Front Bearing 5 Mouri ting Scrfew 23 Front Support 8 Target Escutcheon 24 Barrter Cover 12 Front Plate 25 Cam Follower and Moving Contact Assembly 13 Stops 26 Cans for Contacts 15 Rocker Arm 27 Upper Stationary Contact 16 Sleeve 28 Lower Stationary Contact 17A Positioning Wheel 29 Terminal Screw 18 Positioning Spring 30 Barrier 31 Barrier Assembly ATorsion Srn 32 Rear Bearing T3 Sping Actuator 33 Bearing Retainer 34 Tie Bolt Figure 1 - 018485484) Exploded View of Type SBM Switch 7