ML051020012
| ML051020012 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Columbia |
| Issue date: | 04/01/2005 |
| From: | Rhonda Butler Univ of Missouri - Columbia |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 05-01 | |
| Download: ML051020012 (5) | |
Text
Research Park Research Reactor Center Columbia, MO 65211 9 University of Missouri-Columbia PHON'E (573) 882-4211 FAX (573) 882-6360 April 1, 2005 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555
REFERENCE:
Docket Number 50-186 University of Missouri - Columbia Research Reactor Amended Facility License R-103
SUBJECT:
Licensee Event Report The attached document provides the Missouri University Research Reactor (MURR) Licensee Event Report (LER) for an airlock door malfunction that occurred on March 10, 2005, which resulted in a deviation from MURR Technical Specification 3.5.a. This report is submitted in accordance with Technical Specification 6.1.h (2).
Please contact Les Foyto, Reactor Manager, at 573-882-5276 if you have questions regarding this report.
Sincerely, Ralph A. Butler, P.E.
Director RAB/djr Enclosure cc: Mr. Alexander Adams, Jr., U.S. NRC Mr. Craig Bassett, U.S. NRC Region II Dr. James S. Coleman, Vice Provost of Research, University of Missouri-Columbia Reactor Advisory Committee Reactor Safety Subcommittee 1a*4IYHZe Th.$u 's CHRISTINE M.ERRANTE Notary Public - State of Missouri County of Boone I My Commission Expires Apr. 14, 2007
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AN EQUAL OPPORTLNTry/ADA LNS1rTnYION
Attachment U.S. Nuclear Regulatory Commission April 1,2005 Licensee Event Report No. 05 March 10, 2005 University of Missouri Research Reactor Introduction On March 10, 2005, with the reactor operating at 10 MW, a failure of the reactor containment building inner airlock door air supply control valve resulted in a loss of air pressure to its sealing gasket. This condition was reported to the console operator who placed the rod control Master Control Switch in the "Off' position. This action immediately scrammed the reactor and placed the reactor in a secured condition. Failure of the personnel airlock door to provide an adequate seal resulted in a deviation from Technical Specification 3.5.a; one of two Limiting Conditions for Operation regarding containment integrity.
Technical Specification 3.5.a requires that containment integrity be maintained at all times except when the reactor is secured, and irradiated fuel with a decay time less than sixty days is not being handled. One of the six conditions for reactor containment integrity to exist is "The personnel airlock door operable."
This implies that one of the two personnel airlock doors must be fully closed with its gasket inflated, thus providing a satisfactory seal.
Description of Personnel Airlock Door System The physical description of the reactor containment building personnel airlock doors is considered sensitive information from a security perspective. This information is kept onsite and is available to the U.S. Nuclear Regulatory Commission for inspection and review. The following information describes the airlock door interlock circuitry.
The airlock door control circuit is designed and interlocked to ensure that one door is always closed and sealed. The interlock consists of a relay logic circuit, which detects both door open and closed positions from a rotary limit switch assembly, as well as seal inflation pressure for each door. A three-way, dual solenoid-pilot valve controls the air supply pressure to the door-sealing gasket. The solenoids are normally de-energized and only momentarily energize to either inflate or deflate the door-sealing gasket.
A latching mechanism keeps the three-way valve in either the pressurized or vent position after the solenoid de-energizes. The logic circuit enables one door to open only if the other door indicates closed and sealed.
When a door is in the fully closed position, the rotary limit switch energizes the closing solenoid, which aligns the three-way valve to inflate a gasket mounted in the door facing, thus sealing the door. The three-way valve then remains in the "latched" position, as depicted on page 4, after the solenoid de-energizes. When a door is in the fully open position, the rotary limit switch energizes the opening solenoid, which aligns the three-way valve to vent the sealing gasket to atmosphere. The three-way valve then remains in the "unlatched" position after the solenoid de-energizes. The purpose of using a dual solenoid is to prevent the three-way valve from getting out of phase. The position of the three-way valve will not change if the same solenoid is energized twice in succession (the opposite solenoid must be energized to reverse the valve).
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Attachment U.S. Nuclear Regulatory Commission April 1,2005 Additionally, the reactor containment building is maintained at a slightly negative pressure with respect to the surrounding laboratory building. This ensures that the direction of airflow is into the containment building should a leak develop in the building structure.
Event Description On Thursday, March 10, 2005, at 14:13, a control room operator was exiting the reactor containment building through the personnel airlock. The operator noted that the inner airlock door sealing gasket pressure gauge was reading 0 psig with the door shut. With the assistance of another operator, it was determined that the inner airlock door gasket inflated as intended when the door reached the "closed" position, but then immediately deflated after the cycle was complete (the door remained closed).
Additionally, the sound of air flowing past the gasket seal could be heard. The operator immediately informed the control room of the condition and the reactor was shutdown and secured by 14:15.
Upon investigation, it was determined that the inner airlock door three-way, dual solenoid-pilot valve had not remained in the "latched" position following the door closing cycle. Once the closing solenoid de-energized, the three-way valve returned to the "unlatched" position, thereby venting air pressure from the sealing gasket resulting in a loss of containment integrity. The three-way valve bonnet and dual solenoid-pilot control assembly were replaced. The door was then cycled five times to verify proper adjustment and operability.
Safety Analysis The basis for Technical Specification 3.5.a is to ensure that the reactor containment building can be isolated at all times except when plant conditions are such that the probability of release of radioactivity is negligible. When the personnel airlock door system malfunctioned, resulting in a deviation from the Limiting Conditions for Operation, a reactor scram was immediately performed to make negligible the already low probability of release of radioactivity while operating the reactor.
Corrective Actions When the Limiting Condition for Operation regarding containment integrity was not satisfied with respect to the personnel airlock doors (Technical Specification 3.4.a), the reactor was immediately scrammed and placed in the secured condition. This is the fastest way to restore Technical Specification compliance.
The three-way valve bonnet and dual solenoid-pilot control assembly were replaced. The personnel airlock was placed back into service and tested before being determined operable. The reactor was refueled and returned to 10 MW operation with Reactor Manager's approval at 21:35, March 10, 2005.
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Attachment U.S. Nuclear Regulatory Commission April 1, 2005 This event has been entered into the MURR Corrective Action Program as CAP 05-0021 and any additional improvements or corrective actions will be considered. This type of airlock door failure had never previously occurred at MURR. The removed air control valve was disassembled and the exact cause of the valve failing to remain in the "latched" position could not be determined. Some of the possible causes include a loss in magnetic field strength of the control solenoid, undetectable wear of the latching mechanism or wear debris or dirt which prevented the valve from latching. Although sufficient spare valves and solenoids do exist for the foreseeable future, this particular vendor no longer supports this style valve. The facility's engineering staff is researching a possible future replacement for this valve.
If additional information is desired, please call me at 573-882-5276.
Les P. Foyto Reactor Manager University of Missouri Research Reactor Page 3 of 4
Attachment U.S. Nuclear Regulatory Commission April 1, 2005 Containment Airlock Door Three-WVay, Dual Solenoid-Pilot Valve IMPULSE VALVES WithIlCSolenolds THREE-WAY SOLENOID-PILOT Current ISrequired only momentarily to changs positions of the Impulse Valve.
SUBBASE MOUNTED Dual Solenoid: To prevent valve In automatic syteram, from getting out of phase the position oathe valve will not AIR 15 to 150 PSI be changed If the same solenoid Is energized twice In succession (the opposite solenold must be energized to reverse the valve) 2-1134J SERIES It circuit requires that current be applied continuously, the ambient temperature should not exceed 100F. FLOVWPATTERNS OF THREE-WAY VALVES (viewed from solenoid end)
INTERNAL PILOT SUPPLY The pressure supply to operate the pilot section Seal Deflated ratetd through Internal channels leading from the S7ea elate line pressure Inlet.
The plot valve exhausts Into the subbase Independent of ASAS'YM8OL the main valve exhaust. CAUTIONI NEVER PLUG ORRE.
STRICT PILOT EXHAUST VALVE CHARACTERISTICS AND ORDERING DATA:
IMPORTANT - When orderIng plase speclfr SIze, Ordering Number. Pressure Range, Voltage, and Frequency.
Approx.
Pipe Cv Ship.
Sin Press. Ordering Weight (N4PT Factor Range Number (Lbs.)
1/4' 1.80 15.150 2.1134J 5 3/tt 2.88 15-150 2.113432J 5 1/2_ 5.04 15-150 2.113452J 5Y/4 3/4' 8.08 15.150 2.113462J 6 SPECIAL IC IDIFICATIONS STANDARD VOLTAGES: 115,230 or 460 AC,60 cycles; Available whee qeantily warrants.
110, 220 AC.50 cycles; Consult factory fer price and delivery.
12,24.28 and 115 DC Subbae with bottom A side VA*ut.
For other voltages end/or frequencies, consult Factory. A.N.D. partil.
peed control Yre, Instilled In esrsit ports.
Explosion proeof senoid enclenure Ss sthlethanstandardBins H.
ClassH oile.
POWER CONSUMPTION (At 20*C)
'Mach-2' Three-Way Pilot Valve
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