ML20249B244
| ML20249B244 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 06/15/1998 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-2024, NUDOCS 9806220222 | |
| Download: ML20249B244 (5) | |
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USEC A ouw sn.rsy comp,y June 15,1998 GDP 98-2024 United States Nuclear Regulatory Commissien Attention: Document Control Desk Washi gton, D.C. 20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 98-09 Pursuant to Safety Analysis Report (SAR), Section 6.9, Table 6.9-1, J (2), Enclosure 1 provides the required 30 day written Event Report (ER) for an event involving a high condensate level shutoff actuation at the Portsmouth Gaseous Diffusion Plant. Investigations and testing activities are continuing to determine the cause and corrective actions for this event. The revised report is scheduled for July 16,1998. There are no new commitments contained in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (740)897-2373.
Sincerely, J. Morris Brown
' General Manager Portsmouth Gaseous Diffusion Plant i
Enclosures:
As Stated l
cc: NRC Region 111 Office NRC Resident Inspector-PORTS
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l 9906220222 990615
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PDR ADOCK 07007002 f l
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P.O. Box 800, Portsmouth, OH 45661 Telephone 614-897-2255 Fax 614-897-2644 http://www.usec.com OfIices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC
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GDP 98-2024 Page1of4 Event Report 98-09 Description of Event On May 15,1998, at 1508 hours0.0175 days <br />0.419 hours <br />0.00249 weeks <br />5.73794e-4 months <br />, X-343 Autoclave (AC) #4 was in Mode 11 heating a 48-inch Uranium Ilexafluoride (UF ) cylinder when the audible alarm for steam shutdown was received.
6 Operators responding to the alarm found the "B" condensate level probe light on, indicating the high condensate level shutofT(IICLS) safety system had actuated. The autoclave local alarm panel indicated that steam supply block valve FV-413 was closed, stopping steam flow to the autoclave as designed. A IICLS actuation is reportable in accordance with the Safety Analysis Report (SAR),
Table 6.9-1, J(2).
The condensate level shutoff system is provided to prevent over pressurization or a nuclear criticality 1
in an autoclave following a postulated UF release. Excess water is undesirable in the event of a UF.
6 release from the cylinder that could cause either high Ilydrogen Fluoride pressure as the result of the reaction between UF and water or the excessive moderation of an unsafe mass of uranium thereby 6
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.
Cause of Event The direct cause for the IICLS safety system actuation was the failure of the condensate discharge line steam trap to operate. The steam trap is a non safety related component that is located downstream of the condensate containment isolation valves. The steam trap became air bound when the continuous air vent on the steam trap inverted bucket became obstructed with a small amount of debris. The obstruction in the vent caused air to accumulate in the bucket and prevent the steam trap from discharging condensate.
Maintenance inspection of the steam trap revealed that the bucket was not the correct bucket for this trap. The installed steam trap is an Armstrong Model 814T. The bucket that was installed in the trap was a smaller bucket that is designed for an Armstrong Model 813 steam trap. The Model 813 bucket does not have a thermic air vent (bi-metallic controlled auxiliary air vent) as specified for a Model 814T trap and it has a smaller continuous air vent hole. The diameter of the continuous air vent hole on the Model 813 bucket is approximately 1/16 of an inch. The diameter of the continuous vent on the 814T bucket is approximately 1/8 of an inch.
Although the steam trap functioned correctly for a number of autoclave heating cycles with the Model 813 bucket installed, the steam trap was more susceptible to failure caused by blockage of the air vent due to debris. The Model 814T bucket, with its larger continuous air vent hole, would
GDP 98-2024 Page 2 of 4 Event Report 98-09 have a reduced probability of the hole becoming obstructed with debris that could be present in the condensate flow stream in the area of the steam trap. The condensate strainers located upstream of the steam trap have a mesh size of approximately 1/16 of an inch. This means that debris particles large enough to obstruct the continuous air vent hole of the Model 813 bucket could pass through the strainers and could increase potential for plugging the vent hole. In addition, the thermic air vent on a Model 814T allows additional air to vent from the bucket during autoclave startup, making it less likely that the steam trap could become air bound at these times.
An engineering evaluation has concluded that the combination of no thermic air vent and the plugging of the continuous vent could have contributed to air binding of the trap (in which the trap fills with air and remains in the closed position), preventing the flow of condensate through the trap and resulting in the llCLS actuation.
A causal factor for the event was the failure to maintain adequate configuration control of non-safety related components whose failure could result in safety system actuations. The condensate discharge steam traps do not perform a safety function and are designated as non-safety related (NS).
However, when the traps do not function as designed, HCLS actuations can occur. The configuration management program requirements for NS equipment are not as rigorous as the requirements for safety related or safety significant equipment.
In 1992, the Model 814T thermic bucket steam traps were installed as a unit on the autoclaves to help prevent HCLS alarms that had been occurring. Engineering drawings were not updated to reflect the new design. It is believed that sometime after 1992, the Autoclave #4 steam trap bucket was replaced with the incorrect Model 813 bucket. Maintenance records from January 1996 to present were reviewed to determine when the incorrect bucket was installed. The information available in these records did not indicate that the bucket was replaced. As a result, exactly how and when the wrong bucket was installed could not be determined, but is believed to have been before 1996.
The design information relating to the trap was also reviewed to determine if sufficient information existed to specify the correct bucket for the Model 814T. An engineering drawing was located that indicated that a Armstrong #800-814 trap should be used. The numbers on the drawing mean an 800 series 814 trap. The drawing did not specify an 814T where the "T" means thermic. As a result, the l
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drawing did not contain sufficient information to ensure the correct trap would be installed. The steam traps and their internal replacement parts are assigned stores stock numbers so that when replacements are needed, they can be ordered by maintenance planners. However, the replacement for an 813 and 814T inverted bucket is not stamped with the manufacturer model number nor is there
GDP 98-2024 Page 3 of 4 Event Report 98-09 any information as to which model trap they are for. The stores stock number is also not printed on the replacement parts. This means that after a replacement bucket is received from warehouse stock, there are no identification markings to indicate the correct bucket for a specific trap.
The investigation revealed that both the Model 813 and 814T traps are used at the site. Replacement buckets for the 813 and 814T traps are stocked both in stores and in the X-342 Mechanical Maintenance Area. Without some means of part identification available, it appears likely that the Model 813 bucket was inadvertently substituted for the Model 814T bucket. Maintenance personnel have been instructed to follow a "like for like" replacement policy when there are no other engineering approved documents (i.e. drawings, specifications and equipment / material lists) available. However, this policy was instituted as part of the transition from DOE to NRC regulatory oversight and may not have been in place when the substitution occurred. In addition, there are no known administrative requirements in place to formally evaluate and document all non-safety related substitutions.
Steam trap maintenance work instructions that were modified on August 8,1997, require that the thermic element on the buckets be checked to determine ifit is distorted and the continuous vent hole to be checked, to ensure it is free of debris along with other steam trap inspection criteria.
However, they do not contain any lists for replacement parts, or diagrams to show what the parts look like or dimensions to ensure that the right replacement parts are installed. Prior to August 8, 1997, the work instructions relied upon skill of the craft and available manufacturer infonnation.
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. A causal factor for the event was a failure to detect that the incorrect trap was installed during a i
previous maintenance activity that occurred on August 19, 1997. The maintenance activity concerned a troubleshooting work package on AC #4 with the new steam trap work instructions included. During the troubleshooting process maintenance mechanics found the strainer 90%
plugged and the " trap found OK with a 5/8" orifice." It is believed that the section relating to inspection of the thermic bucket was not performed since it was a troubleshooting work package and 1-not a preventive maintenance activity. This failure to perform all steps in the instructions during troubleshooting is considered a missed opportunity. It does not appear there was a comprehensive inspection of the steam trap. The work instructions did not contain any requirement for a sign-off and there were no steps marked N/A.
Investigation activities are continuing to determine the root cause of the event. An initial corrective action of checking steam traps on the condensate line of all autoclaves has been completed and resulted in no additional discrepancies being identified. Further corrective actions to correct the causes of the event will be submitted with the revised event report. A revised event report is scheduled for July 16,1998.
GDP 98-2024 Page 4 of 4 Event Report 98 Corrective Actions The corrective actions will be provided with the revised report.
Extent of Exposure ofIndividuals to Radiation or Radioactive Materials There were no exposures to individuals from this incident to radiation or radioactive materials.
Lessons Learned.
The Lessons Learned will be provided with the revised report.
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