ML20236Q092
| ML20236Q092 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 07/13/1998 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-2033, NUDOCS 9807170308 | |
| Download: ML20236Q092 (6) | |
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CSEC A Global Energy Company July 13,1998 GDP 98-2033 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 98-09, Revision 1 Pursuant to Safety Analysis Report (SAR), Section 6.9, Table 6.9-1, J (2), Enclosure I 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. The revised event report includes the root cause and corrective actions. Changes from the previous report are marked with a vertical line in the right margin. Enclosure 2 is a list of commitments made in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.
Sincerely, l
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. Morris Brown General Manager Portsmouth Gaseous Diffusion Plant ll
Enclosures:
As Stated cc: NRC Region III Office NRC Resident Inspector - PORTS
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.,v4 J 9007170308 980713 PDR ADOCK 07007002 C
PDR P.O. Box 800, Portsmouth, Oli 45661 Telephone 740-897-2255 Fax 740-897-2644 http://ww.usec.com Omces in Livermore, CA Paducah. KY Portsmouth, Oli Washington, DC
GDP 98-2033 Page1of4 Event Report 98-09, Revision 1 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 liexafluoride (UF.) cylinder when the audible alarm for steam shutdown was received.
Operators responding to the alarm found the "B" condensate level probe light on, indicating the high condensate level shutoff (liCLS) safety system had actuated. The autoclave local alarm panel indicated that steam supply block vaive FV-413 was closed, stopping steam flow to the autoclave as designed. A 11CLS actut tion 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 in an autoclave following a postulated UForelease. Excess water is undesirable in the event of a UF.
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 causing a criticality within the autoclave. The system function is to detect either a drain li je plug or restriction and to shutofTthe steam flow to the autoclave.
Cause of Event The direct cause for the llCLS safety system actuation was the failure of the condensate discharge line steam trap to operate. The steam trap is a non-safety component that is located downstream of l
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 i
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 did 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 i
have a reduced probability of the hole becoming obstructed with debris that could be present in the 1
GDP 98-2033 Page 2 of 4 Event Report 98-09, Revision 1 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 sent 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 liCLS actuation.
The root cause for the event was the failure to maintain adequate configuration control of non-safety l
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 (NS). Ilowever, when the l
traps do not functic,n as designed,11CLS actuations can occur. The configuration management program requirements for NS equipment are not as rigorous as the requirements for safety significant l
equipment.
In 1992, the Model 814T thermic bucket steam traps were installed as a unit on the autoclaves to help prevent ilCLS actuations 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 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.110 wever, the replacement for an 813 and 814T inverted bucket is not stamped with the manufacturer model number nor is there 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 afler a replacement bucket is received from warehouse stock, l
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GDP 98-2033 Page 3 of 4 Event Report 98-09, Hevision I 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. Ilowever, 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 I
substitutions.
l Steam trap preventive maintenance work instructions that were modified on August 8,1997, require l
that the thennic element on the buckets be checked to determine ifit is distorted and the continuous vent hole to be checked, to ensare it is free of debris along with other steam trap inspection criteria.
Ilowever, they da not contain any lists for replacement parts, or diagrams to show what the parts
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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 information.
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A contributing cause for the event was a failure to detect that the incorrect trap was installed during I
a previous maintenance activity that occurred on August 19, 1997. The maintenance activity included a troubleshooting work package on AC #4 which contained the new steam trap work I
instructions. 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 perfomied since it was a troubleshooting work package and not a preventive maintenance activity. This failure to perform all steps in the instructions during troubleshooting is considered a mis!.ed 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."
Corrective Actions 1.
On June 16,1998, all in-senice autoclaves with model 814T steam traps were inspected to l
ensure that the inverted bucket inside was for an 814T trap and that it had a thermic element.
l X-342, AC #2 and X-344, AC #2 are currently shutdown and will be inspected prior to their I
being placed in senice.
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4 i-GDP 98-2033 l
Page 4 of 4 Event Report 98-09, Revision 1 2.
On June 19,1998, Daily Operating Instructions was issued to planners to revise the work i
package instructions to provide specific direction for ensuring 814T traps are fitted with the l
correct bucket with thermic element.
l 3.
By August 1,1998, an evaluation of existing procedural guidance to clarify the performance l
of work instructions during troubleshooting activities will be completed.
l 4.
By October 1,1998, revise the guidance for work instructions for troubleshooting activities l
based upon the recommendations from the maintenance evaluation.
l 5.
By September 1,1998, Engineering will develop and document design controls for l
non-safety components in the autoclave condensate system.
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6.
By October 1,1998, engineering design controls for non-safety components will be l
incorporated into the appropriate autoclave condensate system work instructions.
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By December 15,1998, Engineering will develop and implemert a system for the control l
of specific non-safety components. This system will define by what criteria components are I
determined to be in need of additional control and what additional rigor is to be taken during l
their procurement and installation.
I 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 Inadequate configuration control of certain non-safety components can result in safety system l
actuations. Appropriate control must be established for these components to ensure reliable l
operation.
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GDP 98-2033 Page1ofI Event Report 98-09,llevision 1 List of Commitments t
1.
By August 1,1998, an evaluation of existing procedural guidance to clarify the performance I
of work instructions during troubleshooting act.ivities will be completed.
I i
2.
By October 1,1998, revise the guidance for work instructions for troubleshooting activities I
based upon the recommendations from the maintenance evaluation.
l 3.
By September 1,1998, Engineering will develop and document design controls for l
j non-safety components in the autoclave condensate system.
l l
4.
By October 1,1998, engineering design controls for non-safety components will be l
I incorporated into the appropriate autoclave condensate system work instructions.
l 5.
By December 15.1998, Engineering will develop and implement a system for the control l
of specific non-safety components. This system will derme by what criteria components are l
determined to be in need of additional control and what additional rigor is to be taken during l
their procurement and installation.
l i
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