ML20196A169
| ML20196A169 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 06/16/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2032, NUDOCS 9906220143 | |
| Download: ML20196A169 (4) | |
Text
i USEC A Global Energy Company l
4 June 16,1999 GDP 99-2032 U. S. Nuclear. Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 99-11 i
Pursuant to Safety Analysis Report, Section 6.9, Table 6.9-1, J.2, Enclosure I provides the required 30-day written Event Report for an event involving a high condensate level shutoff actuation at the l
Portsmouth Gaseous Diffusion 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 (740) 897-2373.
Sincerely, Vh W
J. Morris Brown General Manager Portsmouth Gaseous Diffusion Plant
Enclosures:
As Stated I
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NRC Region Ill Office NRC R-sident Inspectors - PORTS
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United S "es Enrichment Corporation Portsmouth Gaseous Difrusion Plant P.O. Box 628, Piketon, OH 45661
,m GDP 99-2032 Page1of2 Event Report 99-11
- Description of Event
- On May 17,1999, at approximately 1605 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.107025e-4 months <br />, X-344 autoclave (AC) #2 was in Mode 11 heating a 48" uranium hexaficaride (UF ) cylinder when operators near the autoclave heard the steam supply 6
block valve on AC #2 close, indicating that steam shutdown had been initiated. Operators responding to the valve closure found the general condensate alarm light illuminated indicating the high condensate level shutoff (HCLS) safety system had actuated. Steam supply block valve PSV-133 was verified to be in the closed position, stopping steam flow to the autoclave as designed.
A HCLS acmation is reportable in accordance with the Safety Analysis Report, Table 6.9-1, J.2.
Prior to this event, AC #2 experienced a steam. shutdown that was caused by a low buffer air pressure condition. Approximately ten minutes after neam had been restored, the HCLS actuation occurred.
As noted above, operators responding to the valve closure found that the general condensate alarm
. light was illuminated, but the individual alarm lights that indicate which condensate probe had fired were not illuminated. Since the audible alarm for HCLS ectuation and individual lights for each condensate probe are only illuminated when a high condensate level condition exists, the lack of individual alarm lights indicates the high condensate level condition existed for only a short duration.
The condensate 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 the event of a UF 6
6 release from the cylinder that could cause either high Hydrogen 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 actuation of the HCLS safety system was a momentary rise in the condensate level that occurred approximately ten minutes after the autoclave was restarted following a steam shutdown. In this event, steam was on for approximately 12 minutes and off for approximately 18 minutes before the steam was restarted. This brief time interval did not allow enough time for the existing condensate to drain from the autoclave before new condensate was added.
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The autoclave steam supply and condensate removal systems are not designed to prevent excess
. con ensate rom co ect ng n t e autoc ave w en t e autoc ave s cyc el d off then on. At the d
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i beginning of a heat cycle, the rate of condensate formation is at its vaatest due to the large cold mass l
presented by the UF cylinder Since the autoclave vessels are not vented Ibr drainage, condensate 6
drainage depends on sufficient steam pressure in the vessel to force the condensate out. When steam is cut off shortly after starting a heat cycle, condensate famiation continues, which causes the vessel pressure to drop as the vessel inventory of steam is used up. This results in a loss of motive force
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GDP 99-2032 Page 2 of 2 Event Report 99-11 to drive the condensate out. In this case, hydrostatic head replaces vessel pressure as the motive force and condensate will remain in the autoclave without sufficient force to expel it. Valving the steam back in increases condensate formation without an immediate rise in internal autoclave pressure. The lack of motive force allows the condensate to accumulate and increase the chances for an HCLS actuation to occur.
The root cause for the event was the lack of procedural controls to ensure the autoclaves are drained of condensate prior to restarting the autoclaves following a short duration shutdown. When an unexpected autoclave shutdown occurs, the investigation into the cause of the shutdown normally requires the autoclave to remain out of service for an extended period of time. This amount of time is normally sufficient to allow condensate to drain from the autoclave, which helps prevent high condensate conditions from occurring when the autoclave is restarted. This event has demonstrated that in instances where the cruse for an autoclave shutdown is quickly detemlined, additional controls are needed to prevent restarting the autoclaves ur.til accumulated condensate is drained from the autoclave. Following the event, an inspection of the condensate strainer and drain system piping confirmed that there were no obstructions that could have caused the HCLS actuation.
Corrective Actions 1.
On June 14,1999, a section policy for the X-344 building was issued which requires that any time an AC heating cycle is interrupted the Plant Shift Superintendent is to be notified, a Problem Report initiated, and requires that the system will not be returned to service after a short duration shutdown until the autoclave shell is opened to ensure that condensate drains from the autoclave.
2.
By September 30,1999, change / develop.X-344 procedures that require any time an AC heating cycle is interrupted, actions are taken to ensure the AC shell is drained of condensate prior to restarting the AC.
3.
By December 15,1999, engineering will review the X-344 autoclave condensate problems that have been experienced and determine appropriate corrective actions.
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 Steam supply interruption during periods of high condensate generation rates can inhibit proper condensate drainage from the vessel and cause an IICLS actuation. Re-initiating steam supply can further aggravate this condition.
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GDP 99-2032 l
Page1of1 i
i Event Report 99-11 List of Commitments i
1.
By September 30,1999, change / develop X-344 procedures that require any time an AC heating cycle is interrupted, actions are taken to ensure the AC shell is drained of condensate prior to restarting the AC.
2.
By December 15,1999, engineering will review the X-344 autoclave condensate problems 1
that have been experienced and determine appropriate corrective actions.
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- Regulatory commitments contained in this document are listed here. Other actions listed in this submittal are not considered reb atory commitments in that they are either statements or actions l
completed, or they are considered enhancements to USEC's investigation, procedures, or operations, i
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