ML20207D016
| ML20207D016 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 05/25/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2026, NUDOCS 9906030171 | |
| Download: ML20207D016 (4) | |
Text
e 1
g f.
USEC A desbol Endrgy Company May 25,1999
' GDP 99-2026 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. '20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS) l Docket No. 70-7002' Event Report 99-08 I
Pursuant to the Safety Analysis Report Section 6.9, Table 6.9-1, J(2), Enclosure 1 provides the required 30 day Event Report for an event that resulted from the actuation of a cascade automatic data processing (CADP) smokehead in the X-330 building tails area at the Portsmouth Gaseous Diffusion Plant. There are no new commitments contained in the report.
i Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.
Sincerely,
<.Aad b Se6 J. Morris Brown i
General Manager Ponsmouth Gaseous Diffusion Plant
Enclosures:
As Stated cc:
NRC Region 111 OfTice NRC Resident inspector-PORTS
/60 h l
9906030171 990525
/
,,,,, V i
PDR ADOCK 07007002 C
,,.,10
- s United States Enrichment Corporation Portsmouth Gaseous Diffusion Plant P.O. Ilox 628, Piketon, OH 45661 f
k i
GDP 99-2026 A.
i Page1of3 Event Report 99-08 Description of Event At 1312 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.99216e-4 months <br /> on April 27,1999, the tails mezzanine smokehead SSWE alarm actuated in the X-330 process building area control room 2. The operator assigned to tails responded to the alarm equipped with appropriate personnel protective equipment (PPE). The operator did not observe any smoke, odors or abnormal conditions. Operators evaluating the cascade automatic data processing (CADP) printouts for smokehead SSWE determined from the voltage drop that an outgassing may have occurred. At 1420 hours0.0164 days <br />0.394 hours <br />0.00235 weeks <br />5.4031e-4 months <br />, the operators further investigated the valves located inside the heated tails housing and observed a trace amount of UO F on the stem of valve WL-1. Based on the observed 22 evidence, the smokehead actuation was determined to be a valid safety system actuation caused by outgassing of the WL-1 valve. Safety system actuations are reportable in accordance with the Safety Analysis Report (SAR), Section 6.9, Table 6.9-1, J(2).
' Prior to this event, smokehead SSWE had been taken out of service and replaced. During the replacement, operational coverage of the mezzanine was provided by smokehead SSWA.
Smokehead SSWE was functional and undergoing post-maintenance testing at the time of the event, but had not yet been declared operational. Printouts of smokehead SSWA also show a voltage drop which indicated that UF. was present, but below the level needed for it to activate the safety system.
The release is believed to have occurred during pigtail purging operations. The pigtail for the tails cylinder located in tails withdrawal position 1 had been purged to remove liquid and gaseous UF.6 During routine pigtail purging operations, the pigtail and associated process piping is temporarily pressurized to 40 or 50 psig with gaseous nitrogen (N ). The N and UF. mixture is vented to the 2
2 cascade and the purging operation is repeated a number of times to prepare the pigtail for disconnection.
When the pigtail at position I was purged,' a small leak on valve WL-1 caused a outgassing of UF.
during the pressure transient. The leak was not detected outside the housing, but was a sufficient quantity to actuate the smokehead inside the housing.
The material that outgassed was a small amount of depleted UF at a nominal enrichment of 0.4%
U-235. The WL-1 valve is a 1-inch Xomox Tufline plug valve. It is located inside a heated housing and is not accessible for routine visual inspections.
L Cause of Event The direct cause of the CADP actuation was a UF. telease from the valve stem seal of the WL-1 valve. Previous operating experience has indicated that the use of this type of valve in UF.
L
L y
GDP 99-2026 Page 2 of 3 r
Event Report 99-08 withdrawal station applications can result in small leaks as a result of stem seal wear due to repeated operation of the valve. In this event, the valve stem seal failure allowed a sufficient amount of UF 6 to escape to actuate the CADP smokehead SSWE and to form a small deposit of UO F on the valve 2 2 stem.
The root cause of the outgassing was that the corrective action to replace the tails valves has not been implemented yet it had previously been identified that valves incorporating stem packing may develop leaks as the stem pack.ing wears. A project was initiated to replace this type of valve with a more durable valve which utilizes a bellows seal. When installed, the bellows seal will reduce the likelihood of minor leakage.
The project to install the bellows sealed valves is part of a long-term project for upgrading t il three withdrawal stations. Currently, tails withdrawal, the final station in the project, is scheduled for completion by July 1,2001. A review of event reports for the past two years revealed only one additional instance of a safety system actuation caused by valve stem seal leaks (reference Event Report 99-04). Considering the low frequency and negligible safety consequences of these valve seal leaks, it was determined that the valve replacement project schedule did not need to be accelerated.
Valve stem seal leaks are dependent on the amount of wear the stem seal experiences during operation of the v?lve. The life of the sealis not predictable at this time. The valve sleeve, valve j
stem seal, and valve plug for valve WL-1 will be replaced prior to returning the valve to service. No other compensatory actions are required at this time. Personnel protection when responding to any similar leaks which may occur will be assured through the use of PPE.
The potential for minor leaks has been previously recognized and discussed in the SAR. This outgassing of UF,, was similar to the types ofleaks described in SAR Section 4.1.1.3.1. which states "Small amounts of UF. and other toxic materials such as llF, CIF and UO?2 can be released during 3
sampling operations, seal changes, failure to obtain sufficient cell and piping UF,, negatives, ruptured copper tubing, and possibly through buffer systems. These releases are prevented primarily by use of engineering and administrative controls. To protect the operator in the unlikely event a release does occur, operating specifications rec,uire that personnel performing operations and maintenance, where the possibility of releases exists, wear protective equipment such as an individually fitted gas mask. The releases in these cases may mean that a few grams of UF will escape to the atmosphere.
6 l
There are no TSR systems, (Safety Systems) to prevent the release of UF while performing these 6
types of operations. Engineering and administrative controls are considered adequate."
!E
r-6 4
GDP 99-2026 Page 3 of 3 s
Event Report 99-08
)
Corrective Actions i
1.
By July 1,2001, bellows scaled valves will be installed at tails withdrawal as part of the withdrawal station improvement project (project X-34470).
Extent of Exposure ofIndividuals to Radiation or Radioactive Materials l
l Four operators submitted urine samples for urinalysis. The bioassay results were less than 5 pg/l of uranium. The urinalysis program flag action level is 5 pg U/1 as specified in SAR Table 5.3-4.
Lessons Learned l
l There were no lessons learned from this event. Operations responded to this event in accordance with plant policies and procedures. No outgassing was observed. The release was small and could only be detected by the CADP smoke detector and verified by observation of hydrolyzed UF on the 1
6 surface of the valve.
l l
l' l
i l