ML19197A042
| ML19197A042 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Columbia |
| Issue date: | 07/12/2019 |
| From: | Robertson J Univ of Missouri - Columbia |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2019-04-00 | |
| Download: ML19197A042 (8) | |
Text
University of Missouri Research Reactor Center 1513 Research Park Drive Columbia, MO 65211 PHONE 573-882-4211 WEB murr.missouri.edu July 12, 2019 ATIN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
REFERENCE:
Docket No. 50-186 University of Missouri-Columbia Research Reactor Renewed Facility Operating License No. R-103
SUBJECT:
Written communication as required by University of Missouri Research Reactor Technical Specification 6.6.c(3) regarding a deviation from Technical Specification 3.4 The attached document provides the University of Missouri-Columbia Research Reactor (MURR)
Licensee Event Report (LER) for an event that occurred on July 1, 2019, that resulted in a deviation from MURR Technical Specification 3.4.
If you have any questions regarding this report, please contact Bruce A. Meffert, the facility Reactor Manager, at (573) 882-5118.
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fo:vid Robertson, PhD Reactor Facility Director JDR/jlm Enclosure xc: Reactor Advisory Committee Reactor Safety Subcommittee Dr. Mark Mcfutosh, Vice Chancellor for Research, Graduate Studies and Economic t:_EZ L Development _:.--
Mr. Geoffrey Wertz, U.S. Nuclear Regulatory Commission Mr. William Schuster, U.S. Nuclear Regulatory Commission
Enclosure U.S. Nuclear Regulatory Commission July 12, 2019 Licensee Event Report No. 19 July 1, 2019 University of Missouri Research Reactor Introduction On July 1, 2019, with the reactor shutdown for scheduled, routine maintenance, a deviation from Technical Specification (TS) 3.4 occurred during performance of scheduled maintenance on two (2) shim control rod drive mechanisms (CRDMs) and unscheduled electrical preventative maintenance on two (2) breakers. For approximately ten (10) minutes, the reactor containment building ventilation system's automatically-closing doors referred to as Doors 504 and 505 in Section 6.2.3.4 of the MURR Safety Analysis Report (SAR), which are required by TS 3.4.a(3) for reactor containment integrity to exist, were inoperable at the same time that maintenance was being performed on the CRDMs causing the condition of the reactor to be shutdown per TS 1.27 but not reactor secured per TS 1.26.
- With the reactor not secured at the same time that the automatically closing doors were inoperable, because of the unscheduled electrical preventative maintenance (the breakers for the doors were open), is a deviation from TS 3.4.b which states, "Reactor containment integrity shall be maintained at all times except when: (J) The reactor is secured, AND ... "
Background - Technical Specification Relationships A. Technical Specification Excerpts 1.26 Reactor Secured - The reactor shall be considered secured when:
- a. There is insufficient fuel in the reactor core to attain criticality with optimum available conditions of moderation and reflection with all four (4) shim blades (rods) removed, OR
- b. Whenever all of the following cond~tions are met:
(1) All four shim blades (rods) are fully inserted; (2) One of the two following conditions exists:
- 1. The Master Control Switch is in the "OFF" position with the key locked in the key box or in custody of a licensed operator, OR ii. The dummy load test connectors are installed on the shim rod drive mechanisms and a licensed operator is present in the reactor control room; (3) No work is in progress involving the transfer of fuel in or out of the reactor core; (4) No work is in progress involving the shim blades (rods) or shim rod drive mechanisms with the exception of installing or removing the
?dummy load test connectors; and Page 1 of 7
Enclosure U.S. Nuclear Regulatory Commission July 12, 2019 (5) The reactor pressure vessel cover is secured in position and no work is in progress on the reactor core assembly support structure.
1.27 Reactor Shutdown - The reactor is shutdown when:
- a. It is subcritical by at least 0.0074 i!klk in the reference core condition with the reactivity worth of all installed experiments included, AND
- b. All four (4) of the shim blades (rods) are fully inserted and power is unavailable to the shim rod drive mechanism electromagnets.
3.4 Reactor Containment Building Specification:
- a. For reactor containment integrity to exist, the following conditions must be satisfied:
(1) The truck entry door is closed and sealed; (2) The utility entry seal trench is filled with water to a depth required to maintain a minimum water seal of 4.25 feet; (3) All of the reactor containment building ventilation system's automatically-closing doors and automatically-closing valves are operable or placed in the closed position; (4) The reactor mechanical equipment room ventilation exhaust system, including the particulate and halogen filters, is operating; (5) The personnel airlock is operable (one door shut and sealed);
(6) The reactor containment building is at a negative pressure of at least 0.25 inches of water with respect to the surrounding areas; and (7) The most recent reactor containment building leakage rate test was satisfactory.
- b. Reactor containment integrity shall be maintained at all times except when:
(1) The reactor is secured, AND (2) No movement of irradiated fuel with a decay time of less than sixty (60) days or experiments with the potential for a significant release of airborne radioactivity outside of containers, systems, or storage areas, AND (3) No movement of experiments that could cause a change of total worth of greater than 0.0074 i!klk.
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Enclosure U.S. Nuclear Regulatory Commission July 12, 2019 B. Conditions During the Event with Respect to Technical Specifications
- 1. The reactor was shut down per TS 1.27 because both conditions 1.27.a. and 1.27.b were met.
2: The reactor was not secu~ed per TS 1.26 because conditions 1.26.a and 1.26.b(4) were not met; the reactor was fueled for criticality with all eight (8) elements in the core, and work was in progress on the shim rod drive mechanisms.
- 3. Reactor containment integrity did not exist according to TS 3.4.a because an automatically-closing door of the reactor containment building ventilation system was inoperable due to the electrical supply breaker to the closing motor for the door being in the 'Open/Off position.
The above statements 2 and 3 combined caused a deviation from TS 3.4.b which states, "Reactor containment integrity shall be maintained at all times except when: (1) The reactor is secured, AND ... "
Description of the Containment Actuation System As described in Section 7.8.2, Containment Actuation (Reactor Isolation) System, of the MURR SAR, the Containment Actuation System (CAS) is designed to completely isolate the reactor containment building, thereby preventing or mitigating any uncontrolled release of radioactive materials to the environment during an accident. Isolation of the reactor containment building can be automatically initiated by radiation detectors located at the reactor pool upper bridge and in the containment building exhaust plenum. Isolation can be manually actuated by switches in the reactor control room or the facility lobby.
Manual or automatic actuation of the CAS causes the following actions to occur:
- 1. Reactor will scram;
- 2. All normally-open reactor containment building penetrations with automatic sealable closures will close;
- 3. An audible alarm will sound throughout the containment building; and
- 4. A flashing light at the entrance to the containment building personnel airlock will illuminate.
The reactor containment building ventilation system's automatically-closing doors mentioned in TS 3.4.a(3) are part of the reactor containment building penetrations that are automatically closed by the CAS as described in SAR Section 6.2.3.4, Supply and Exhaust Air Ducts.
The supply and exhaust air ducts contain two (2) electric-motor-driven horizontal sliding doors located in the ventilation plenums on the fifth level of the reactor containment building. When these doors are in the open position, a path is created for containment air to be circulated through Page 3 of7
Encfosure U.S. Nuclear Regulatory Commission July 12, 2019 the east tower and then back into the containment building. The openings in the containment building wall for each plenum are approximately 4 feet by 4 feet (1.2 m x 1.2 m). The motorized isolation door for the supply plenum is designated as Door 504, and the motorized isolation door for the exhaust plenum is designated as Door 505.
The doors are constructed of :4-inch (0.64-cm) thick metal plate welded to a steel frame. Each door is suspended from a 12Yi-foot (3.8-m) long, 6-inch (15.2-cm) I-beam by two adjustable Yi-ton (453-Kg) trolleys. To insure proper alignment, the doors travel in a guided slot mounted along the bottom of the door opening. A 3-phase, 440-volt, 1-HP motor connected through a gear reducer to a chain drive assembly drives the door open and closed. When a door is in the fully-closed position, a rotary limit switch energizes a solenoid-operated three-way valve, inflating a gasket mounted in the door facing, thus sealing the door.
The supply and exhaust air doors are normally kept open. Actuation of the reactor isolation or facility evacuation switches located in the reactor control room, or the facility evacuation switch located in the facility lobby, will close Door 504 and Door 505. A radiation level greater than the set point of either of the reactor bridge radiation monitors, or either of the exhaust plenum radiation monitors, will also close both doors automatically. A closure signal from any of the above causes two (2) parallel relays to de-energize, closing a contact associated with each relay, and completing the circuit to the closing coil of each motor. The motors will drive the isolation doors to the closed position, actuating their rotary limit switches and energizing the solenoid-operated three-way valves, thus sealing the doors. It takes approximately seven (7) seconds from the initiation of the isolation signal until the isolation doors are closed and sealed.
Description of the Shim Control Blade Operation As described in SAR Section 4.2.2., Control Blades, the reactivity of the reactor is controlled by five neutron-absorbing control blades, which are all located external to the pressure vessels. Each control blade is coupled to a 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 within the reactor core.
The shim blades are positioned by four (4) CRDMs mounted on the upper bridge over the reactor pool surface. Each CRDM consists of a 0.02-HP, 115-volt, one-amp, single-phase, 60-cycle motor connected to a lead screw assembly through a reduction gear box. The lead screw assembly converts the rotating motion of the drive motor to the linear motion of the control blades. A ball nut coupled directly to a drive tube is driven inward and outward by the lead screw. Connected to the bottom end of the drive tube is an electromagnet which engages a cadmium-plated carbon ~teel anvil attached above the water level to the end of a lift-rod assembly. The lift-rod assembly allows the positioning of a shim blade through a support and guiding mechanism ( offset mechanism) mounted on a pedestal attached to the reflector tank.
Limit switches mounted on each CRDM stop the drive motor at the top and bottom of travel.
These limit switches also provide indication on the reactor control console that the CRDM is either in the full-in or full-out position.
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Enclosure U.S. Nuclear Regulatory Commission July 12, 2019 The shim blade can be withdrawn when the electromagnet is energized. When the reactor is scrammed, the electromagnet is de-energized, releasing the anvil, and allowing the shim blade and lift-rod assembly to drop. Loss of electrical power to the control blade system results in a reactor scram and safe shut down of the reactor.
Detailed Event Description Work on the CRDMs was in progress, which consisted of removal and transfer to the Instrumentation Support Shop for maintenance, from approximately 07:30 to 12:30 on July 1, 2019. This CRDM work placed the reactor in only the TS 1.27 'reactor shutdown' condition, but not the TS 1.26 'reactor secured' condition because no work in progress on CRDMs is a specific TS 1.26 requirement for the reactor to be considered secured when the reactor core is fueled for criticality. TS 1.26 states, "The reactor shall be considered secured when:
- a. There is insufficient fuel in the reactor core to attain criticality with optimum available conditions of moderation and reflection with all/our (4) shim blades (rods) removed, OR
- b. Whenever all of the following conditions are met: ...
(4) No work is in progress involving the shim blades (rods) or shim rod drive mechanisms with the exception of installing or removing the dummy load test connectors; and ...
At approximately 11 :00, an Electronics Technician (ET) requested permission from the Lead Senior Reactor Operator (LSRO) to _perform preventative maintenance on the electrical breakers in Motor Control Center 4 (MCC4) in accordance with electronics preventative maintenance procedure EMP-14, "Motor Control Centers." The LSRO understood that opening breakers on MCC4 had no effect on ot1:er maintenance day activities nor would it have an effect on required TS-required systems, Therefore, permission was granted to conduct the MCC4 electrical breaker maintenance.
MCC4 is located on the fifth level of the reactor containment building. Though not a part of MCC4, the breakers for the emergency air compressor, Door 504, and Door 505 are located on a wall all within eight (8) feet of MCC4. The ET proceeded not only to conduct maintenance on MCC4 breakers, but also conducted the same maintenance to the breakers for the emergency air compressor, Door 504, and Door 505, as well. Each breaker was placed in the 'Open/Off' position for approximately five (5) minutes to perform the maintenance.
Therefore, sometime between 11:00 and 12:00 on July 1, 2019, with the reactor shutdown and during scheduled CRDM work, the ET opened the two (2) electrical motor breakers to the reactor containment building ventilation system's two (2) automatically-closing doors (Doors 504 and 505) one at a time for approximately 5 minutes each to conduct preventative breaker maintenance. This prevented the ability of Doors 504 and 505 to automatically close and seal in the case of a reactor isolation event. Therefore, Doors 504 and 505 were inoperable preventing TS condition 3.4.a(3) from being met, and thus reactor containment integrity did not exist.
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Enclosure U.S. Nuclear Regulatory Commission July 12, 2019 TS 3.4.a(3) states, "For reactor containment integrity to exist, the following conditions must be satisfied: ... (3) All of the reactor containment building ventilation system's automatically-closing doors and automatically-closing valves are operable or placed in the closed position; ... "
The combination of the reactor not being secured and reactor containment integrity not existing is a deviation from TS 3.4.b which states, "Reactor containment integrity shall be maintained at all times except when: (1) The reactor is secured, AND ... "
Though this event happened on July .1, rio NRC-licensed operator knew that the automatically-closing door motor breakers had been opened until July 3. Once the abnormal occurrence was realized, the Reactor Facility Director was briefed on the situation on the afternoon of July 3, and he gave permission to continue reactor operation in accordance with TS 6.6.c(4).
Safety Analysis As described in Section 6.2.1, Introduction, of the SAR, the containment system is designed to completely isolate the reactor containment building, thereby preventing or mitigating any uncontrolled release of radioactive materials to the environment during an accident. The potential for release of radioactive materials to the reactor containment building is increased when the reactor is not secured or movement of the following are occurring: irradiated fuel with a decay time of less than ~ixty (60) days, experiments with the potential for a significant release of airborne radio~ctivity, or experiments that could cause a change of total worth greater than 0.0074 Lik/k.
These are the bases of TS 3.4.a and 3.4.b.
During the approximately ten (10) minutes that reactor containment integrity did not exist, no movements of irradiated fuel, experiments with airborne potential, or experiments that could cause a change of total reactivity worth of greater than 0.0074 Lik/k occmTed. The only deviation to TS 3.4.b was that the reactor was not secured because two (2) CRDMs were not installed during the event.
Corrective Actions The cause of this event was the ET' s performing work without proper authorization, performing work outside the scope of the approved procedure, and lack of understanding of the effect of his actions on TS-required systems. When questioned after the event was realized, the ET commented. that he was verbally instructed by a senior ET (who has since retired from MURR) that he should always conduct maintenance on all breakers on the fifth level when conducting preventative maintenance procedure EMP-14 on MCC4. The ET who performed this maintenance now fully realizes the effect of his actions.
To prevent reoccurrence of this type of event, enhanced MURR ET training will be developed and implemented to emphasize proper authorization required to work on reactor-related systems, procedural compliance, and identifying equipment related to TS-required systems. All ET personnel will receive this training upon initial employment and as refresher training biennially.
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Enclosure U.S. Nuclear Regulatory Commission July 12, 2019 Additionally, this event has been entered into the MURR Corrective Action Program as CAP Number 19-0097. Any additional improvements or corrective actions will be considered and documented in that CAP entry. ' , ,
If there are any questions regarding this LER, please contact me at (573) 882-5118. I declare under penalty of perjury that the foregoing is true and correct.
I ENDORSEMENT:
Sincerely, iewed and Approved,
~~y-Reactor Manager
~~~
avid Robertson, PhD Reactor Facility Director JAoCQUl!lJNE L*1YAS .
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