ML20199C855
| ML20199C855 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 01/08/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2003, NUDOCS 9901190161 | |
| Download: ML20199C855 (8) | |
Text
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d USEC
. A Global Energy Company January 8,1999 GDP 99-2003 i
i United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 98-17 Pursuant to 10CFR76.120 (c)(4), Enclosure 1 provides the required 30 day Event Report for an event that resulted from a fire which caused damage to Cascade equipment containing radioactive material at the X-326 Building Side Purge Area at the Portsmouth Gaseous Diffusion Plant.
Investigation activities are continuing to determine the root cause and corrective actions for this event.' This report will be revised following completion of these activities. The revised event report is scheduled for February 18,1999. There are no new commitments contained in this report.
Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.
Sincerely, hJW
. Morris Brown General Manager Portsmouth Gascous Diffusion Plant i
Enclosures:
As Stated i
cc:
NRC Region III Office hD' i NRC Resident Inspector-PORTS 9901190161 99010g
.[DR ADOCK 07007002 j PDR _
P.O. Box 800, Portsmouth. OH 45661 Telephone 614-897-2255 Fax 614-897-2644 http://www.usec.com Offices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC
i GDP 99-2003 Page 1 of 7 Event Report 98-17 Description of Event On December 9,1998, at 0610 hours0.00706 days <br />0.169 hours <br />0.00101 weeks <br />2.32105e-4 months <br />, Fire Services personnel responded to a fire which occurred in Cell 25-7-2 in the Side Purge Area of the X-326 Process Building. The fire, which breached process j
equipment in several places, was contained by the building sprinkler system and was extinguished by plant Fire Services personnel. The fire damage was primarily limited to the Cell 25-7-2 equipment, housing, and three stages of the adjacent cell,25-7-4. Since the fire damaged proces equipment and piping which contained radioactive material, this event is reportable in accordance with 10CFR76.120 (c)(4). A description of the event is provided below.
Operations were normal on the morning of December 9,1998. Cell 25-7-2 was the bottom onstream cell of the Side Purge cascade. The purpose of the Side Purge is to vent most of the light gases, such as oxygen and nitrogen, from the cascade. Heavier intermediate weight gases, such as R-114 (coolant), continue up the cascade until they are vented by the Top Purge equipn ent. Low speed cell 25-7-2 is used to create a stripping section. The B-Stream exiting cell 25-7-2 typically contains less than 10% of the low molecular weight " light" gases which enter the Side Purge. The Side Purge configuration was normal with the exception that Cell 25-7-4 was ofTstream and out of::ervice.
A-Stream process gas flow was into Stage 4 A-suction of Cell 25-7-2, from Stage 12 of Cell 27-1-2, through a manual block valve. B-Stream process gas return flow was from Stage 1 of Ce1125-7-2, j
to the Stage 1 A-Stream of Cell 27-2-1. A coolant (R-114) " bubble" had moved up the cascade at about 0330 hours0.00382 days <br />0.0917 hours <br />5.456349e-4 weeks <br />1.25565e-4 months <br />. The Unit Operator making rounds of the cell floor at about 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> stated that Cell 25-7-2 equipment was running quietly with no unusual mdiations.
I At about 0605 hours0.007 days <br />0.168 hours <br />0.001 weeks <br />2.302025e-4 months <br />, the ACR-6 (Area Control Room 6) operator was taking hourly readings when the operator noticed the cell 25-7-2, Stage 2, Amp meter briefly deflect to about 70% full scale and then return to normal position of about 30% scale. The operator told the First Line Manager in Training (FLMIT), who was leaving the ACR, that it appeared there was another coolant " bubble" entering the Side Purge cascade. The FLMIT said he would tell the Section Manager when he reported to ACR-5. Meanwhile, the operator throttled the Side Purge vent remote control valve (CV-1261) to back the suspected coolant bubble out of the Side Purge cells.
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At about 0606 hours0.00701 days <br />0.168 hours <br />0.001 weeks <br />2.30583e-4 months <br />, the Amp meter in ACR-6 again deflected, which indicated that Cell 25-7-2, l
Stage 2, compressor surged and then retumed to normal load. Cascade Control personnel in X-300 l
Plant Control Facility (PCF) observed that the Cell 25-7-2 Amp meter, which indicates the total cell Amps from all six motors, was slowly climbing and called ACR-6 to determine the cause. During the phone call, at 0607 hours0.00703 days <br />0.169 hours <br />0.001 weeks <br />2.309635e-4 months <br />, Cell 25-7-2 immediately loaded up and tripped on motor overload before the operator could trip the cell motors. Adjacent Side Purge Cells 25-7-6,25-7-8, and 25 10 also loaded, with seal exhaust alarms activating. The operator depressed the cell oft full split 4
GDP 99-2003 Page 2 of 7 Event Report 98-17 button to close the three open block valves. The expected response of a green light, indicating the valves had completely closed, did not occur and the panel had a red and a green light indicating one or more of the valves was not fully closed. The cell had not been completely isolated because the internal A-Line, Stage 4, block valve used to create a stripping section remained open.
i The X-326 Building CC-Shift FLM was in route to the ACR-6, when the FLM heard the cell compressors and motors wind down. The FLM then proceeded to ACR-6 and found Cell 25-7-2 shut down. Isolation valve ESP-7 had closed automatically, isolating the Side Purge vent stream from atmosphere.
At about 0610 hours0.00706 days <br />0.169 hours <br />0.00101 weeks <br />2.32105e-4 months <br />, sprinkler system 462, which is located in proximity to Cell 25-7-2, alarmed in the Fire Station and the PCF. Operators in the nearby X-600 Steam Plant heard the external X-326 Building sprinkler system alarm bell, observed white smoke, smelled an electrical type odor, and heard a muflied pop. A Protective Force Officer on the cell floor heard a roar followed by two pops.
4 At 0611 hours0.00707 days <br />0.17 hours <br />0.00101 weeks <br />2.324855e-4 months <br />, Cascade Control told the ACR-6 FLM that there were reports of smoke and flowmg sprinklers in the south end of X-326. The FLM reported a cell coolant alarm, indicating high coolant temperature or low coolant pressure, but did not report :moke. The Fire Services arrived on the scene at 0613 hours0.00709 days <br />0.17 hours <br />0.00101 weeks <br />2.332465e-4 months <br />. By 0615 hours0.00712 days <br />0.171 hours <br />0.00102 weeks <br />2.340075e-4 months <br />, smoke was entering ACR-6. The operator and the FLM did not immediately evacuate because their respirators were stored outside the ACR. Firemen entered X-326, Door 7, and reported heavy, light colored smoke.
At 0617 hours0.00714 days <br />0.171 hours <br />0.00102 weeks <br />2.347685e-4 months <br />, the S:cCon Manager and the FLMIT en route from ACR-5, were attempting to reach ACR-6 with four respirators, but encountered heavy smoke and called the PCF for information. The Cascade Controller reported the sprinkler 462 alarm, smoke coming out of the building and that the UF front had been pushed down the cascade into the X-330 Building. The Section Manager and 6
FLMIT continued to attempt to reach ACR-6 while avoiding the heavy smoke.
l The unit operator, wearing respiratory protection, entered the cell floor and proceeded toward Cell j
25-7-2. The operator saw there was smoke coming from the cell and valved off the lube oil supply located at the top of the exit stairway before he exited the building. Smoke was light but slowly becoming denser above the cell floor.
At 0619 hours0.00716 days <br />0.172 hours <br />0.00102 weeks <br />2.355295e-4 months <br />, ACR-6 personnel evacuated the control room without respiratory equipment by entering the ACR-6 Basement and going into the tunnel which provided egress from the area. At 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br />, Fire Services personnel checked ACR-6 and determined that it had been evacuated. At 0621 hours0.00719 days <br />0.173 hours <br />0.00103 weeks <br />2.362905e-4 months <br />, the Section Manager and the FLMIT entered ACR-6 by a rear door and began a search
Enclosure i GDP 99-2003 Page 3 of 7 Event Report 98-17 of the ACR to be certain the area was empty. The Section Manager pushed the cell off full split button and received a green light within seconds, indicating the valves were nearly fully closed by the ACR operator on the previous isolation attempt. The Section Manager closed motor operated valve 7 ESP-1, the first isolation valve beyond the Cell 25-7-2, Stage 4, manual valve, which isolated Cell 25-7-2 from the Side Purge supply line and the operating cascade.
At 0622 hours0.0072 days <br />0.173 hours <br />0.00103 weeks <br />2.36671e-4 months <br />, ACR-4 personnel manually activated the building recall horn. At 0623 hours0.00721 days <br />0.173 hours <br />0.00103 weeks <br />2.370515e-4 months <br />, the Section Manager pushed the automatic recall button located in ACR-6. The recall signal is to alert building personnel to report to designated assembly locations. At 0625 hours0.00723 days <br />0.174 hours <br />0.00103 weeks <br />2.378125e-4 months <br />, the Section Manager and FLMIT exited the building and proceeded to the Command Post.
At 0626 hours0.00725 days <br />0.174 hours <br />0.00104 weeks <br />2.38193e-4 months <br />, Fire Services personnel entered the cell floor and reported a fire in progress. Flames were reported around the cell housing and from motor openings. Ileavy black smoke was filling the area making visibility poor and the oil / water mixture on the cell floor created difficult footing for the firefighters. The Fire Services personnel returned to the Command Post and developed a plan to extinguish the fire.
It was later determined that seven sprinkler heads had activated. Three at the rooflevel, two under the bypass housing, and one in the aisle way that most likely activated when hot gas jets burned through the cell housing at Stages 1,3 and 4. One under the coolant platform activated most likely when the cell housing door panel adjacent to Stage 6 became warped and opened. The high pressure fire water sprinkler discharge was successful in containing the fire.
At 0630 hours0.00729 days <br />0.175 hours <br />0.00104 weeks <br />2.39715e-4 months <br />, Fire Services personnel proceeded to lay hoses on the east side of the building and applied water to the outside of the Cc!! 25-7-2 housing. Other firefighters gained access to the south door of the building and proceeded to lay hose.
At about 0730 hours0.00845 days <br />0.203 hours <br />0.00121 weeks <br />2.77765e-4 months <br />, the soutn door of the cell housing was opened and the firefighters proceeded to spray water inside the cell housing. The fire was extinguished and upon examination for hot spots, an open process pipe was observed from the West Side of the cell. Fire fighting activities were curtailed and the firefighters returned to the Command Post. After consultation with the Incident Commander on Nuclear Criticality Safbty (NCS) concerns, the firefighters went back to the cell housing and performed cool down operations while avoiding the open pipe. At 0749 hours0.00867 days <br />0.208 hours <br />0.00124 weeks <br />2.849945e-4 months <br />, the sprinkler system was valved off. Total sprinkler discharge was approximately 35,000 gallons. At 0815 hours0.00943 days <br />0.226 hours <br />0.00135 weeks <br />3.101075e-4 months <br />, Emergency Squai personnel valved off the Cell 25-7-2 hydraulic oil supply. The fire was declared out by Fire Services at 0817 hours0.00946 days <br />0.227 hours <br />0.00135 weeks <br />3.108685e-4 months <br />.
s GDP 99-2003 Page 4 of 7 Event Report 98-17 Fire damage was limited primarily to Cell 25-7-2 and consisted of severe damage to the components in the compressors, the converters, and the R-114 coolers. A stage control valve disk was melted.
Holes were burned in process piping elbows in three stages, several process pipe expansion joints were ruptured, and holes were melted in three stage converters. Minor damage also occurred in three stages of the adjacent cell,25-7-4.
1 The material that outgassed was enriched UF at less than 7.0% U-235. The quantity of material 6
released during the event was estimated as approximately 5 Kg of uranium.
Cause of Event On December 9,1998, immediately following the event, an investigation team was established to determine the root and contributing causes for the event. Outside technical experts were added to the team to assist in the cause determination. The extensive fire damage experienced by Cell 25-7-2 equipment has made it difficult to determine the root cause. Much of the equipment has been damaged to the extent that evidence needed to determine the root cause was destroyed. As a result, investigation activities are continuing and this event report will be revised when the investigation is complete. The investigation team's current understanding of the most likely direct cause for the l
exothermic chemical reaction is provided below.
The investigation team reviewed plant operating conditions that existed prior to the event to determine if there were any abnormal conditions that could have initiated an exothermic reaction.
Cascade operating parameters for the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to the time surging was first detected by the operator, such as purge rates, UF front location, feed and withdrawal rates and surge drum bleed 6
back information were reviewed, but did not indicate any activity which could have initiated the event. Cascade monitors such as alarms, line recorders, space recorders, oxidant monitors and cascade laboratory sample analysis did not reveal any unusual activity. A review of cascade and feed plant valving orders and operational logs also did not reveal any unusual activities that would have initiated the event. Based on these findings, the investigation team concluded that the exothermic reaction was not caused by any abnormal concentration of gases or unusual operating l
conditions.
The investigation team has determined that the exothennic reaction was most likely caused by rubbing of internal compressor parts. Friction, resulting from rubbing of cempressor parts, is believed to have generated enough heat to reach the melting point of aluminum. The molten aluminum then chemically reacted with the UF. process gas generating additional heat. As the cell continued to operate onstream, additional UF was available to feed the reaction and spread it to 6
other stages. At least one gas cooler eventually ruptured releasing R-114 coolant into the cell. The
GDP 99-2003 Page 5 of 7 Event Report 98-17 release and expansion of the coolant into the cell increased the cell pressure and generated additional heat as aluminum chemically reacted with the coolant. The high temperatures and potentially elevated pressure led to the destruction of the converter tube bundles and breach of the cell
- boundary, j
During the investigation, issues potentially related to the prevention or mitigation of an exothermic reaction were identified by the investigation team. The team identified that the design and operational characteristics of Cell 25-7-2 may have contributed to the severity and extent of the exothermic reaction. These issues are discussed below and immediate actions taken to address these issues are described in the corrective action section.
The Safety Analysis Report (S/ d), Section 3.1.2.2.2, Isolation of Failures, states that,"If the Amp loading in a single stage begins increasing, the problem may have been initiated by compressor parts j
rubbing, deposits in the compressor, bearing failure, or some other failure associated with the motor itself, which requires immediate shutdown". The Side Purge cascade operating procedure did not contain guidance to help the operator differentiate between load changes due to controllable factors j
such as compressor surging and load changes due to equipment failure, and it did not contain j
guidance as to the type of Amp increases which would require a cell shutdown.
The investigation team also determined that Cell 25-7-2, Stage 2 and 4 compressors, had been replaced approximately three weeks before this event due to high vibrations. The compressors that l
were removed from the cell because of the high vibrations were examined. The Stage 4 compressor l
was found to have extensive first stage impeller damage. Implications of this finding are being further evaluated as it relates to this event.
l Corrective Actions l
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Immediate Actions Taken The following actions have been initiated and/or completed to address issues identified during the investigation. A complete list of corrective actions will be provided in a revised event report after i
the root and contributing causes have been determined.
1.
On December 23,1998, a briefing was initiated for X-326 Facility Operations personnel.
The briefings included a description of what happened, how the incident was handled and what to look for as indicators that such an event is happening. The briefing emphasized the steps necessary for tripping and isolating a cell. Actions to be taken if the cell block valves do not fully close were also addressed.
l GDP 99-2003 Page 6 of 7 Event Report 98-17 2.
On December 15, 1998, the development of a training module was initiated to address recognition of cell surging, cell loading and cell shutdown requirements. This training j
moduleis currently being piloted.
1 3.
On January 6,1999, a lessons learned was developed and issued to Cascade personnel to i
communicate operating conditions that may increase the possibility of a similar exothermic reaction.
4.
On December 9,1998, administrative controls were established to prevent retuming the Side Purge cells to service.
5.
On December 10, 1998, a vibration survey was conducted on running motors and compressors in the Top Purge Cascade. Engineering initiated weekly vibration surveys on operating purge cascade equipment.
6.
The X-326 Daily Operating Instructions for January 4,1999, emphasized the procedure administrative controls that state "upon cell startup, any cell indicating abnormal vibration shall be followed up with a full set of vibration readings unless the vibration is excessive upon which the cell shall be shut down".
7.
The December 21,1998 Daily Operating Instructions for cascade process areas contained the administrative control that, "Any centrifugal compressor that is shut down due to high L
vibration will not be re-started in the presence of UF ".
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8.
On December 11,1998, as a result of the damage observed on Cell 25-7-2, an ultrasonic inspection was performed on B-line elbows in the other Side Purge cells. No evidence of thinning was observed.
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L Corrective Actions Planned Corrective actions will be provided with the revised event report Extent of Exposure ofIndividua?s to Radiation or Radioactive Materials Personnel in the facility at the time of the fire, and all responders to the fire, were monitored for potential intake of radionuclides. Fifty-two personnel involved with the event submitted urine samples. Of these, nineteen personnel working in the building at the onset of the emergency were placed on precautionary restriction until their samples were evaluated. Each sample was analyzed
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s GDP 99-2003 Page 7 of 7 Event Report 98-17 i
for uranium and technetium and all results were less than 5 ug/l uranium and 6,000 pCi/l for technetium. Since all samples were less than the SAR Action levels, no further actions were i
required. All precautionary restrictions were removed for the 19 individuals.
Area radiation readings during and following the event noted no increase over normal background j
readings for that area. Area posting requirements remained the same (Contamination Area). With the exception of some precautionary expansions of boundaries within already posted " Restricted Areas", only minimal boundary changes were necessary. Personnel access to the area was not restricted for radiological protection reasons nor were radiological dose reduction measures required during or following the emergency response. Air sampling results within the facility indicated slight increases in the airborne radioactivity levels during the fire, while monitors outside of the facilit" indicated no readings above the minimal detectable activity for the equipment. Prior to tht.
termination of the event, airborne radioactivity levels within the facility had returned to normal.
Although the fire created several contamination control concerns, worker, environmental and public exposures were not significantly affected. SAR, Section 5.3 requirements were maintained and normal procedural controls were effective in maintaining contamination control and returning the area back to pre-fire conditions from a radiological control standpoint.
Recovery activities have been successful in removing the oil and water from the affected area.
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Decontamination efforts have restored the operating floor to pre-fire entry requirements for i
Personnel Protective Equipment. Approximately eighty percent of area boundaries have been returned to their pre-fire positions and decontamination efforts are continuing to restore the remaining boundaries.
Lessons Learned Lessons Learned will be provided with the revised event report.
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