ML20138B760
| ML20138B760 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 04/24/1997 |
| From: | Allen D UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-97-2002, NUDOCS 9704290266 | |
| Download: ML20138B760 (5) | |
Text
i United States Enrichment Corporation 2 Democracy Center a
6903 Rockledge Drive Bethesda. MD 20817 Tel (301)564-3200 au 01) 564-3201 l'niteil %tes Enriclunent Corpondion April 24,1997 GDP 97-2002 i
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 97-02 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. There are no commitments being made with this report.
Should you require additional information regarding this event, please contact Scott Scholl at (614) 897-2373.
Sincerely, 4
N i
Dale Allen General Manager Portsmouth Gaseous Diffusion Plant DIA:Scholl:me i
Enclosures d,gg cc:
C. Cox/D. Hartland, NRC Resident Inspectors
/
NRC Region III
',\\f,d ;l\\ b;d i, '.
9704290266 970424 s
J PDR ADOCK 07007002 C
PDR Offices in Paducah. Kentucky Por tsmouth. Ohio Washington DC
United States Nuclear Regulatory Commission April 24,1997 Page Two 1
Distribution Robert L. Woolley bec:
J. Adkins,IlQ J. Anzelmo, PORTS J. Bolling, PORTS M. Boren, PGDP l
S. Brawmer, PGDP D. Davidson, PORTS J. Dietrich, LMUS L. Fink, PORTS
- R. Gaston, PORTS M. Ilasty, PORTS J. Labarraque, PGDP B. Lantz, PORTS R. Lipfert, PORTS A. Rebuck-Main, liq R. D. McDermott PORTS J. Miller, IIQ J. Mize, PCDP J. Morgan PORTS J. Oppy, PORTS R. Robinson, PORTS S. Routh, liq S. Scholl, PORTS B. Sykes, PGDP D. Thompson, PORTS R. Wells, HQ PORTS Records Management R.M: PORTS 97-890-081
Docket No. 70-7002 Page1of3 Event Report 97-02 Description of Event On March 25,1997, at 0120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />, X-342 autoclave (AC) #2 was in Mode II heating a 48-inch uranium hexafluoride (UF ) cylinder when the audible alarm for steam shutdown was received.
6 Operators responding to the alarm noted that both "A" and "B" condensate probe lights were on, indicating the high condensate level shutoff (IICLS) safety system had actuated. Steam supply block valve FV-1613, was verified to be in the closed position, stopping steam flow to the autoclave as designed. A HCLS safety system actuation is reportable in accordance with the Safety Analysis Report (SAR) Table 6.9-1, J (2).
Operators responding to the alarm also noted that the roll motor buffer air light was off, indicating that buffer air to the roll motor enclosure was low. This was unusual since the rcll motor buffer air light normally remains on anytime the autoclave shell is closed. The roll motor enclosure is located inside the autoclave and is buffered with a minimum of 15 psig dry air to prevent steam in-leakage during normal operations. A pressure switch monitors the air pressure inside the roll motor box.
When the pressure drops below 15 psig, steam shutdown is initiated and FV-1613 closes. The buffer air system for the roll motor box is a non-safety related system.
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 the event of a UF6 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 of the HCLS actuation was low roll motor buffer air pressure which caused the steam supply block valve FV-1613 to close. The closure of this valve resulted in an immediate drop in internal autoclave pressure. This sudden loss of pressure reduced the motive force necessary to properly expel condensate through the autoclave steam trap. The condensate subsequently accumulated in the drain line causing the condensate level probes to actuate.
At the time the IICLS actuation occurred, the autoclave was approximately 25 minutes into the heating cycle. At this time cylinder pressure was near its triple point, where steam demand is at its highest and the largest amount of condensate is generated due to the change of state from solid to liquid UF.
6 Following the IICLS actuation, a maintenance inspection of the condensate drain line, in line strainer and steam trap determined there was no restriction or buildup of debris. The temperature control
Docket No. 70-7002 Page 2 of 3 Event Report 97-02 valve (TCV), which allows steam to bypass the steam trap until the autoclave temperature reaches 200 F, was also determined to be working properly. The condensate level probes were also tested and determined to be working properly.
Since this was the first cylinder to be heated in AC #2 for approximately two weeks, the shell and head of the autoclave were cold, which would have created more condensate than normal.
Operations and Engineering performed a test attempting to duplicate the IICLS actuation by heating the autoclave for two hours. During this test the HCLS did not actuate. The buffer air supply pressure was monitored every 15 minutes. The results of this monitoring indicated that the buffer air pressure remained at acceptable levels during the two hour test.
Additional testing of the autoclave was performed to determine if the loss of buffer air pressure could result in a HCLS actuation. Prior to performing the test, AC #2 was allowed to cool to simulate the steam condensing conditions present during the March 25,1997, event. With the autoclave empty, the steam heating cycle was initiated. After approximately 5 minutes, the buffer air supply was closed to simulate loss of buffer air. After an additional 5 minutes, tbc buffer air light went out and steam shutdown occurred closing steam supply block valve FV-1613. One minute later condensate probe B actuated and two minutes later condensate probe A actuated. Based on the above findings, engineering determined that the most likely cause for the HCLS actuation was inadequate air pressure in the non-safety related buffer air system.
The root cause for the loss of buffer air was determined to be air leakage through the roll motor packing. Although this condition could not be reproduced during the investigation, air leakage is believed to be the most likely cause. The roll motor packing is subjected to temperature changes during autoclave startup that may have affected its sealing capability. Operators reported that air leakage from the packing was audible before the autoclave was placed into service. However, the roll motor buffer air light came on almost immediately after closing the autoclave shell, which indicated that the buffer air supply was adequate to overcome existing leakage. It is suspected that the leak may have increased enough to cause the buffer air pressure to drop below the pressure switch set point.
Prior to returning the autoclave to service the buffer air switch was calibrated and found to be within allowable tolerance. The roll motor buffer air packing was also replaced.
Corrective Actions 1.
On March 25,1997, in X-342, AC #2 condensate strainer and steam trap were inspected for debris and determined to be free from plugging. The TCV was also removed for verification of proper operation by Instrument Maintenance.
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i Docket No. 70-7002 4
Page 3 of 3 l
Event Report 97-02 2
1 2.
On March 25,1997, Instrument maintenance verified the proper operation of the TCV on AC 3
- 2 in X-342.
3.
On March 25,1997, the "A" and "B" condensate probes on AC #2 in X-342 were verified
{
to be functioning properly.
i 4.
On March 31,1997, maintenance personnel inspected the condensate line from the TCV well j
to the bottom of AC #2 in X-342. No obstructions or debris were found in the condensate j
line.
5.
On April 2,1997, maintenance personnel repacked the roll motor shaft on the buffer air box on AC #2 in X-342.
i 6.
On April 3,1997, Instrument Maintenance checked the buffer air pressure switch for the l
proper set point on AC #2 in X-342. The set point was found within tolerance.
Extent of Exposure ofIndividuals to Radiation or Radioactive Materials i
There were no exposures to individuals from this incident to radiation or radioactive materials.
i Lessons Learned J
h Loss of the non-safety related buffer air pressure and subsequent steam shutdown can result in a j
HCLS actuation due to the reduction in internal autoclave pressure.
j s
l