ML20198Q108
| ML20198Q108 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 11/07/1997 |
| From: | Morgan J UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-97-2029, NUDOCS 9711120112 | |
| Download: ML20198Q108 (6) | |
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United St:tra Enrichment Corporttion a
2 Democracy Center 6903 Rockledge Drwe nethesda, MD 2081T
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Tel (301)564 3200 Unilesl Salca Enticinnent Corpinnioni November 7,1997 United States Nuclear Regulatory Commission GDP 97-2029 Attention: Document Control Desk Washington, D.C. 20555-0001 Portsmouth Gascous Diffusion Plant (PORTS)- Docket No. 70-7002 - Event Report 97-19 Pursucnt to Safety Analysis Report (SAR), Section 6.9, Table 6.9-1, J(2), Enclosure 1 provides the required 30 day mitten Event Report (ER) tbr an event involving an autoclave high condensate level shutolTactuation at the Portsmouth Gaseous DifTusion Plant. Enclosure 2 is a list of commitments made in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (614) 897 2373.
Sincerely, w
J m iorgan iencral Manager Portsmouth Gaseous Diffusion Plant DIA:SScholl:me t
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NRC Region 111 J
i D. Ilartland, NRC Resident inspector, PORTS 9711120112 971107 PDR ADOCK 07007002 C
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af) en Offices in Pitducah, Kentucky Portamouth. Ohio Washington. DC
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Docket No. 70-7002 Page 1 of 4 Event Report 9719 Description of Event On October 9,1997, at 0120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />, X-343 Autoclave (AC) #4 was in Mode 11, heating a 14 ton Uranium llexafluoride (UF ) cylinder when the audible alarm for steam shutdown was received.
Operators responding to the alann found the "A" and "B" condensate level probe lights on, indicating the high condensate level shutoff (llCLS) safety system had actuated. The autoclave local alarm panel indicated steam supply block valve FV-413 was closed, stopping steam flow to the autoclave as designed. Operations personnel noted iat the intemal autoclave pressure was 14.4 psia at the time of the actuation.
A second event occurred on October 9,1997. At 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br />, X-343 Autoclave (AC) #2 was also in Mode !!, heating a 14 ton Uranium 11exafluorid:(UF ) cylinder when the audible alarm for steam shutdown was received. Operators responding to the alarm found the "A" and "B" condensate level probe lights on, indicating the high condensate level shutoff (11CLS) safety system had actuated.
The autoclave local alarm panel indicated steam supply block valve FV-213 was closed, stopping steam Gow to the autoclave as designed. Operations personnel noted that the internal autoclave pressure was 13.7 psir at the time of the actuation.
In both events operators acknowledged the steam shutdown alarm, which silenced the alarm and caused the "A" and "B" condensate level probe lights to clear, if condensate had still been in contact with the probes, the lights would have remained illuminated.
Both actuations of the llCLS safety systems are reportable in accordance with the Safety Analysis Report (SAR), Table 6.9-1, J (2).
Both of the above events were associated with the heating of 14 ton cylinders in six foot diameter feed autoclaves. Discussions with Operations and Customer Order Management personnel indicated that they believe these were the first 14 ton cylinders fed to the cascade in several years. Nonnally 10 ton cylinders are used for feed, llowever, due to a drop in the number of 10 ton feed cylinders available, feeding of 14 ton cylinders was resumed to provide adequate feed to the cascade. Afler the second llCLS actuation, plant operators recognized that the heating of 14 ton cylinders could be a common cause for both actuations. As a result, heating of 14 ton cylinders was suspended until the cause of the actuations could be determined.
The condensate level shutoff system is provided to prevent over pressurization or a nuclear criticality in an autoclave following a postulated UF release. Excess water is undesirable in case of a Ull release from the cylinder that could cause either high hydrogen fluoride pressure as the resun of the reaction between UF and water or the excessive moderation of an unsafe mass of uranium, thereby causing a criticality within the autoclave.- The system function is to detect either a drain line plug or restriction and to shutoff the steam flow to the autoclave.
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Docket No. 70-7002 Page 2 of 4 Event Report 97-19 Cause of Event The direct cause for the llCLS safety system actuation on AC #4 and AC #2 was a orop in internal autoclave pressure which caused water to back up into the drain line and activate the condensate hvel the probes.
The root cause for the actuation of the llCLS safety system on AC #4 and AC #2 has been determined to be an inadequately designed condensate system on six foot autoclaves. The similarity from these llCLG actuations are that both occurred in six foot diameter autoclaves while heating 14 ton cylinders. Information obtained from operations personnel indicated that llCLS actuations have occurred in the past while heaung 14 ton cylinders in six foot autoclaves. Past operating practices allowed these actuations to be considered routine and no corrective actions were taken.
As a resuit, no contmls were put in place to prevent 14 ton cylinders from being heated in six foot autoclaves.
The actuations occur because the steam supply to the six foot autoclaves is not adequate to prevent the internal autoclave pressure from going to a vacuum. Aner the 14 tons of solid UF. is heated to 147' F and 22 psia nressure, the entire mass of UF. begins to liquefy. This liquefaction proceeds at a rate which is comparable to the rate of energy supplied to the cylinder contents. In the case of steam supply to a six foot diameter autoclave, the energy available from the steam is not enough to both liquefy the UF and maintain 9 positive pressure inside the autoclave. The energy demands of the UF. phase change to liquid absorbs enough cnergy from the steam to cause the intemal autoclave pressure to drop below atmospheric pressure. Without this positive pressure to force the condensae out of the autoclave, the condensate remains in the piping and is believed to actually backup iri the piping activating the condensate level probes.
This phenomena has not been observed in the seven foot diameter autoclaves because the larger volume provides a greater heat reservoir for the UF phase change to draw from. This reservoir is apparently large enough to allow the solid to liquid phase change to occur without a drop in pressure.
The autoclave condensate system was designed to operate at an autoclave internal pressure of approximately 2.5 psig (16.95 psia). This pr ssure is necessary to drive the condensate out of the autoclave, through the piping and out of the system through the steam trap. The steam trap must have at least 2 psi difTe ential pressure to be able to move the amount of condensate produced during the UF. phase change. This was previously recognized as an autoclave design inadequacy and was included as a non conformance in the Plan for Achieving Compliance with NRC Regulations at the Portsmouth Gascous Diffusion Plant (Issue 3, item no. 7). This design deficiency will be corrected as part of the Autoclave Nuclear Safety Upgrade Project which is scheduled to be completed by February 1,2001.
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Docket No. 70-7002 Page 3 of 4 Event Report 9719 Until the autoclaves can be upgraded, a hose is being used upstream of the steam trap to help alleviate problems with condensate flow through the trap. Unfortunately, the hose does not help r9 move condensate when the internal autoclave pressure is below atmosphere. With autoclave pressure below atmosphere, the entire condensate system acts as a large straw, drawing condensate back into the condensate dmin line and activating the probes. The combination ofliquid being retained in the piping e nd the continuous addition of condensate from the liquefaction of the UF 6 causes the water level to rise and activate the probes.
Following the llCLS actuations approximately two quarts of condensate was drained from the AC #4 condensate drain line and approximately one gallon of condensate was drained from the AC #2 condensate drain line. The presence of this water indicated that water had backed up in the drain.
Following the HCLS actuations the both autoclaves were inspected for obstructions which could have restricted the flow of condensate. Maintenance removed the in-line strainer screens from both autoclaves and determined that there was no accumulation of debris that could contribute to restricting condensate flow Maintenance personnel did note that both screens were coated with a film of rust. Ilowever, the rust film is not believed to have blocked condensate flow because the condensate drain system was working properly until the autoclave intemal pressure went to a vacuum. Further maintenance inspection of both condensate drains did detect one pigtail gasket and a small piece of wire in the AC #2 drain line. Ilowever, these items were not large enough to obstruct condensate flow.
Corrective Actions 1.
On October 9,1997, administrative controls were put in place to prevent heating of 14 ton cylinders in six foot diameter autoclaves. These controls will remain in place until procedures can be revised.
'2.
By January 15,1998, autoclave operating procedures will be revised to prohibit heating of 14 ton feed cylinders in 6 foot diameter autoclaves. These controls will remain in place until modifications can be made to correct this autoclave design deficiency.
Extent of Exposure ofIndividuals to Radiation or Radioactive Materials There were no exposures to individuals from this incident to radiation or radioactive materials.
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. Docket No.- 70-7002 4 11
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- Enclosure 1=
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Event Report E79-
- Lessons Lierned.
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- 7he design of the six foot autoclaves does not provide.for enough steam flow to maintain positive -
- pressure during the heating of 14 ton cylinders. This design deficiency was known as a result ofe actuations that occurred several years ago. Ilowever, there were no controls put in place ~at that time -
to prevent heating of 14 ton' cylinders in six foot diameter autoclaves.
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Docket No. 70-70021 blosure 2l-
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-Page. l'of 17
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Event. Report 97-19.
List of Commitments.
h By January 15,1998, autoclave operating procedures will be revised to prohibit heating of---
~ 14 ton feed cylinders in 6 foot diameter autoclaves. These controls will remain in place until modifications can be made to correct this autoclave design deficiencyc a
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