ML20212C702

Forwards Event Rept 97-10,rev 2 for Event Involving UF6 Cylinder High Pressure Alarm Actuation at Portsmouth Gaseous Diffusion Plant,Per Section 6.9,Table 6.9-1,J(2). Revision of Event Rept Is Scheduled for 980216

ML20212C702
Person / Time
Site:	Portsmouth Gaseous Diffusion Plant
Issue date:	10/23/1997
From:	Allen D UNITED STATES ENRICHMENT CORP. (USEC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GDP-97-2024, NUDOCS 9710300116
Download: ML20212C702 (5)

Text

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United St:t;n

, (e Er'.'ichm:nt Corpor: tion 2 Democr*. cy C:nt:r 1

6903 nockledge Drive Da; esda.MD208tr Tel. (301)$64 3200 g -

Fax:(301)$64 3201 October 23,1997 ODP-97 2024

> United Stater Nychar Regulatory Commission Attentbn: Documer.t Control Desk Washington, D.C. 20555-0001 Portsmouth Gaseous Dihslon Plant (PORTS)- Docket No. 70 7002 - Event Report 9710, Revision 2 Pursuant to Safety Analysis Report (SAR), Section 6.9, Table 6.91, J (2), Enclosure 1 provides Event Report 97 10, Revision 2, for an event involving a UF. cylinder high pressure alann actuation

' at the Portsmouth Gaseous Diffusion Plant. The revised event report is being submitted to provioe additional information regarding this event. Changes from the previous report are marked with a vertically dashed line in the right margin. Investigation activities are continuing to determine the e

root cause and corrective actions for this event. This event report will be revised following completion of these activities. The revised report is scheduled for February 16,1998.

Should you require additional information regarding this event, please contact Scott Scholl at (614) 897 2373..

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Sincere'y, Dale Allen General Manager

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Portsmouth Gaseous Diffusion Plant DIA:SScholl:cw cc:

NRC Region 111

- D. Ilartland,-NRC Resident Inspector, PORTS llll1l!llIll!ll(l!Ilill[Illl.ij O

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C PDft Ofrices in L.tvermore. California Paducah. Kentucky Portsmouth. Ohio Washington, DC

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Docket No. 70 7002 Page1of4 Event Report 9710 Revision 2 Description of Event o

On May 23,1997, at 0125 hours0.00145 days <br />0.0347 hours <br />2.066799e-4 weeks <br />4.75625e-5 months <br />, X-343 Autoclave (AC) #5 was in Mode 11. heating 30 inch (2.5 ton) Russian Uranium llexafluoride (UF.) cylinder #LUO705 when the audible alann for the cylinder high pressure autoclave steam shutoff was received. Operators responding to the alarm s*.

, observed that the intemal cylinder pressure was 115 psia, which was also the alann setpoint. Steam supply valve F%513 was verified closed as designed. Five minutes later at 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br />, while in Mode VII and with the steam supply valve still closed, AC #5 alarmed a second time when the

cylinder pressum reached 130 psia. The actuation of the UF cylinder high pressure autoclave steam shbtoffis reportable in accordance with the Safety Analysis Report (SAR), Table 6.9-1, J (2).

At 0105 hours0.00122 days <br />0.0292 hours <br />1.736111e-4 weeks <br />3.99525e-5 months <br />, at the start of the cylinder heating process the cylinder cold pressure reading was 6.0

.' psia. At 0124 hours0.00144 days <br />0.0344 hours <br />2.050265e-4 weeks <br />4.7182e-5 months <br />, during the heating process the operator observed the cylinder pressure at 45.0 psis which was higher than what is normally expected afler 19 minutes of heating, in accordance with procedure XP4-TE-FD2701, "X-343 and X-342 Autoclave Operat!on," the operator prepared to hot bum (vent to the cascade) enough UF. to reduce cylinder pressure. One minute later, at 0125 hours0.00145 days <br />0.0347 hours <br />2.066799e-4 weeks <br />4.75625e-5 months <br />, before the operator could hot burp the cylinder the autoclave alarmed at 115 psia due to

• pylinder high pressure. The operator responded according to procedure and immediately hot bu the cylinder The cylinder pressure following the hot burp was 9.0 psia. At 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br />, although the steam supply was isolated from the autoclave, the operator noticed the cylinder pressure had increased to 70 psia and rising. While the operator was proceeding to hot burp the cylinder for the second time the autoclave alarmed again due to high cylinder pressure. He operator responded and immediately hot burped the cylinder reducing the pressure to approximately 50 psia. The cylinder pressure then dropped to approximately 20.0 psia and stabilized. The highest pressure observed durina this event was approximately 130 psia which is less than the 214.4 psia maximum allowable working pressure (MAWP) of 2.5 ton cylinders. Approximately thirty three lbs of material was removed from the cylinder during the two burps.

The UF. cylinder high pressure autoclave steam shutoff system is provided to prevent internal cylinder over pressurization caused by normal heating of a UF cylinder containing excessive 6

amounts of" light" gases. In r,ddition, in the event an over filled cylinder is heated in an autoclave i

the UF. cylinder high pressure autoclave steam shutoff system pre,ents the intemal cylinder pressure from exceeding the hydrostatic test pressure of the cylinder.

4 Cause of Event

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a The direct cause of the UF cylinder high pressure alarm is believed to be the unequal distribution of UP. behind the cylinder valve or trapped gases being released from within solid UF..

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t Docket No. 70 7002

. Enclosure 1 Page 2 0f 4

- Event Report 9710 Hevl lon 2 Similar pressure increases have occurred previously while heating 2.5 ton cylinders. One event 1"

occurred September 9,1995 while heating two Commomvealth Edison cylinders filled in Russia and i

other occurred October 24,1996, while heating three cylinders containing blended UF. filled in

' Russia. 'Ihese pressure increases were similar to pressure increases experienced when heating 14 ton Tails cylinders filled at FORTS and cylinders filled at PGDP during cold weather, it is believed that

< rapid cylinder cooling causes a build up of solid UP. to form near the valve, separating it from the larger cylinder void volume.

Corrective actions resulting from these previous events inchuled revising operating procedures to give the operator the authority to hot burp a cylinder when cylinder pressure is rising rapidly or has exceeded 90 psia. Ilowever, in this event the pressure rise occurred more rapidly than expected,

~ preventing the operator from relieving the cylinder pressure before the 115 psia set point was 1

L exceeded.

Other factors that could have produced the type of pressure increase were climinated by weight data and the analysis oflaboratory samples following the event. Weight data showed that the cylinder was filled to 4994 pounds, which was below the 5020 pound maximum cylinder fill limit. The L

amount of weight lost during the two hot burps indicates that liquid UF. was evacuated from the cylinder md not " light" gases. The laboratory samples taken following hot burping indicate that no excessive " light" gases were present in the cylinder.

On May 23,19", Customer Services and Product Scheduling put a hold on heating 2.5 ton Russian cylinders until an engineering evaluation could be completed to determine corrective actions to

- prevent a recurrence of this event.- On May 29,1997, the cylinder hold was modified to allow

- heating of the Russian cylinders that have previously been through a heating cycle at PORTS.

L On July 9,1997, heating of Russian cylinders was resumed following implementation of temporary i

procedural ~ controls. The procedural controls included an enhanced valve clarity check to identify a

whether unequal distribution of UF existed behind the cylinder valve. The new controls also i

provided a modified heating process that reduced the rate that heat was added to the cylinders and i

an alternate valving coniiguration that reduced the time needed to burp cylinders to avoid cylinder i

high pressure alarms. Additional cylinder void space ps samples were also taken afler modified i

heating to allow analysis of trapped gases. These dions were taken to reduce the probability of a i

recurrence of this event and allow additiond.iata to be gathered to determine the root cause of the i

pressure spikes, i

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Since the implementation of temporary procedure controls described above,47 cylinders have been i

processed and gas sampled using temporary procedure XP4-TE-FD2791 TMP, "Special llandling i

of Russian 2.5 Ton Cylinders." Analyses of the gas samples after controlled initial heating were i

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Page 3 of 4 1

Event Report 9710 1,

Revision 2

' similar io other samples analyzed in the past with no indication of non typical gases being emitted i

fkom solid 1)F. upon heating, i

lOn Augdst 23,1997, two cylinders experienced pressure spikes within the first IS minute heating cycle.1ne peak pressures were well below the alarm setpoint of the autoclaves. Enhanced valve i

clarity.' checks.sho.wed no indications of UF crusting behind either cylinder valve. Oas samples i

c obtained on the trapped pressure indicated typical composition results. The substantial weight of i

the' material collectaid in the sample containers for these two cylinders indicated that the high i

pressure spikes were caused by the formation ofliquid UF. In the pigtall Upon resumption of i

~, Jheating' on both cylinders, pressure spikes again occurred after approximately five minutes and i

required hot burping to prevent alarm activation.

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- The root cause of preswre spikes has not yet been determined. There is evidence that suggests i

' controlling the cylinder heating process by reducing the rate of heat applied to the cylinders has i

w reduced the_ magnitude of the pressure spikes. Additional testing is required to determine the i

appropriate controlled heating rates.-

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W 10n September 17,1997, temporary procedure XP4 TE FD2791-TMP was resised to gather new data i

to find the root cause. This event report will be revised when the root cause and corrective actions i

have been determined. ne revised event report is scheduled for February 16,1998.-

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Corrective Actions 1 -

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_On July 8,1997, temporary procedure XP4 TE FD2791-TMP was implemented to provide;

-.1) a new method ofidentifying the existence of unequal distribution of UF. behind the

. cylinder valves,2) a modification to the cylinder heating process, reducing the rate of heat f

T applied to the cylinders,3) an alternate valving configurction reducing the time required to

' burp cylinders to an evacuation header and 4) cellection of cylinder void space gas samples i

after modified heating for analysis of trapped gases, n

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l $ffective SeptembeE 17,1997, temporary procedure XP4 TE FD2791-TMP was revised to; i

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f 1) delete fuither requirement for gas sampling after initial controlled heating,2) change i

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. Tcontrolled heating conditions, i

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s Extent of Exposure ofIndividuals to Radiation or Radioactive Materials These were no exposures to individuals from this incident to radiation or radioactive materials.

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Docket No. 70-7007,

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. The event demonstrated that pressure rises experienced while heating Russian cylinders can occur

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more rapidly than previously believed. Cylinder heating procedures need to be strengthened to s

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l improve i.iperator ability to control premire increases and provide a means to detect an unequal f?>

idistdbution of UFi.

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