ML20249B431
| ML20249B431 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 06/17/1998 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-2026, NUDOCS 9806230090 | |
| Download: ML20249B431 (6) | |
Text
4 h
s USEC A Global Energy Company June 17,1998 j
GDP 98-2026 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 98-05, Revision 1 Pursuant to the 10CFR 76.120(d)(2), Enclosure 1 provides a revised 30-day Event Report for an event that resulted from the discovery that some autoclave containment isolation valves were not capable of closing when relying on their safety related backup air supply reservoirs. Enclosure 2 is
'a list of commitments contained in the report. Due to the extensive number of revisions made throughout the report, the vertical line in the margin has been omitted. This report replaces the previous report in its entirety.
Should you require additional information regarding this event, please contact Scott Scholl at
'(740) 897-2373.
Sincerely, I
. Morris own General Manager Portsmouth Gaseous Diffusion Plant
Enclosures:
As Stated l
\\
cc:
NRC Region Ill Office.
NRC Resident Inspector-PORTS
.._f
\\
l 9006230090 990617
/
I PDR ADOCK 07007002 r
{
C PDR
,,' j.y [,j 7 r
!!O Box 800, Portsmouth,OH 45661 Telephone 614-897-2255 Fax 614-897 2644 harp://www.usec.com Offices in Livermore, CA Paducah, KY Pommouth, OH Washington, DC L____________-
4 GDP 98-2026 Page 1 of 4 Event Report 98-05, Revision 1 Description of Event On April 9,1998, at 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br />, while in Mode VII Shutdown, Operations personnel were performing a functional check on Autoclaves #1 and #2 in the X-342 facility. In response to a NRC j
inquiry concerning the adequacy of containment valve surveillance testing, the operator performed a containment isolation valve closure functional check with the normal plant air supply isolated. The purpose of this functional check was to verify that containment isolation valves were capable of closing with the safety related backup air supply. The checks demonstrated that several valves on Autoclave #1 and #2 failed to close as designed when the normal plant air supply was valved off.
At the time of this discovery, it was not known if the redundant containment isolation valves in the affected penetrations were operable during the time period that the backup air supply was degraded.
As a result, the failure of the containment isolation valves to close on demand under a simulated loss of the non-safety related plant air supply was reported in accordance with 10CFR76.120 (c)(2)(i).
The containment valves that failed to close use air-to-open, air-to-close actuators. These actuators are connected to air reservoirs that supply closing air pressure if the normal plant air supply is lost.
Air leaks within the containment valve air reservoir systems allowed the backup air pressure to fall below the pressure required to close the valves. Both of these autoclaves were inoperable at the time of discovery. All autoclaves on plantsite were declared inoperable until Operations could determine whether this condition existed on other autoclaves in the X-343 and X-344 Buildings.
I The X-342, X-343, and X-344A autoclave facilities are equipped with a total of 13 autoclaves. The X-342 is equipped with two feed and sample (84-inch) autoclaves. The X-343 is equipped with four feed (72-inch) autoclaves and three feed and sample (84-inch) autoclaves. The X-344A is equipped with four sample and transfer (96-inch) autoclaves. Each of these autoclaves is equipped with an Autoclave High Pressure Containment Shutdown System (AllPCSS), as described in TSR Section 2.1.3.5. The autoclave facilities are equipped with a total of 233 AllPCSS containment isolation valves. Actuation systems for these containment valves can be divided into two different types:
spring-to-close and air-to-close. Spring-to-close actuation systems are employed on 160 of the 233 AHPCSS containment isolation valves. The remaining 73 AllPCSS containment isolation valves are air-to-close (ATC) and rely on " backup" air systems to close the valve on loss of plant air or on loss of plant air and receipt of a containment signal. The actuation systems for the ATC valves can I.
further be divided into three types based on design and service, including: pilot operated, shell vent, and parent cylinder safety valve (PCSV).
l l
L
l
{
j GDP 98-2026 Page 2 0f 4 Event Report 98-05, Revision 1 A test procedure was initiated to determine if any other air-to-close autoclave containment valves would fail to close without normal plant air pressure available. As of June 1,1998,55 of the 73 containment isolation valves have been tested on ten different autoclaves. Three as-found tests were performed on the pilot operated actuation systems. These systems were functionally tested under normal plant air conditions, closure with loss of air, and containment with low air pressure (55 psig).
Valve closure and closure times were noted or recorded for each test. Any leaking components were replaced and as-left data was taken. For acceptance, valves were required to close in less than 15 seconds for containment at normal air pressure, close in less than 15 seconds for containment with low air pressure, and close with loss of air. Components of the actuation air system were tested for zero leakage, including the removal and leak testing of the check valve. As-found testing for the shell vent and PCSV actuation systems involved testing for containment at low air pressure (55 and 45 psig, respectively). The components of these actuation systems were checked for leakage, including the removal and leak testing of check valves. Acceptance criteria for these systems were based on their ability to close within 15 seconds repeatedly. Any leaking components were replaced and as-left data was taken. Of the 55 valves tested to date,31 of these valves have passed and 24 valves failed either the loss of air, the low air pressure test, or both tests.
The backup air systems have been repaired and the failed valves have been tested satisfactorily for all autoclaves that have been retumed to service. The backup air systems will be tested and repaired prior to returning the remaining autoclaves to service.
1 Engineering performed a review to determine if there were any other plant systems which utilize the
{
air-to-close valve design in "Q" safety system applications. The review identified that similar air-to-
]
close valves were installed in the ERP, LAW and Tails Withdrawal stations. Testing was conducted j
on these valves and all passed satisfactorily. There were two additional valves identified in the X-705 calciner system. Following an extended outage, the calciner valves were tested on June 8, 1998, prior to str.rtup and passed satisfactorily. Engineering has also initiated a review to verify that other TSR safety systems and their supporting systems are adequately tested to verify performance of their intended safety function.
An engineering evaluation of the event was performed. The evaluation found there was no impact to safety since with a loss of plant air, the autoclave automatically shuts down and containment is not required. With normal plant air available, the containment system would have closed the valves.
There was no credit taken in the TSR bases statements for closure of valves on loss of normal air.
No design basis accident assumes loss of air concurrent with a cylinder rupture in an autoclave.
GDP 98-2026 Page 3 of 4 Event Report 98-05, Revision 1 Cause of Event The direct cause of the event was leaking autoclave backup air reservoir systems. When the plant air supply was valved off during testing, leaks in the air reservoir systems allowed the air pressure to drop on some of the systems to the point where the valves would no longer close.
The root cause of the event was failure to identify and develop testing and surveillance that verify the intended safety functions of the airtanks. During the development of the SAR, personnel identified testing and surveillance for those safety systems identified in the SAR and TSR. During this effort, the testing and surveillance for the autoclave backup air reservoir systems were not identified. A review of testing performed on air-to-close containment isolation valves indicated that quarterly surveillance testing only verified that at normal operating air pressure containment valves close upon receipt of a containment signal. The simulated loss of the non safety related plant air system was not included in the quarterly surveillance testing.
A contributing cause of the failure to properly test and maintain the air-to-close containment valves was failure to develop and implement appropriate coirective actions for an event which occurred in 1996 during the transition from DOE to NRC regulation. Event Report PTS-1996-0023,
" Performance Degradation of Autoclave Safety Valves at X-344 Toll Enrichment Facility," describes an event where two PCSV failed to close during an inadvertent containment actuation on Autoclaves
- 2 and #3 in X-344 Building. As part of the corrective action plan, Engineering was tasked to review the actuator / air supply system and develop a corrective action plan to track implementation of any required changes. The engineering evaluation provided recommendations for only the autoclave actuator / air supply systems. It did not evaluate the actuator / air supplies across the plant.
i The corrective action plan did not specifically address the ability of the supporting air reservoir l
system to perform its intended safety function to fail safe on loss of air and was focused narrowly on the failed PCSV air supplies.
A contributing cause was inadequate preventative maintenance (PM) for a back-up air supply supporting a safety system. The backup air supply was not identified as equipment requiring PM during the February 1997, review of the "Q" system boundaries. Therefore, no PM task or frequency was defined for the backup air supply. The original boundary definition for high-pressure containment shutdown did not specifically include the air reservoir, because the air tanks were thought of as part of the containment valve assembly. They were described in Boundary Definition
- 9 as," Valve assemblies with air reserve tanks also include a pilot valve and check valve." The l
l l
GDP 98-2026 Page 4 of 4 Event Report 98-05, Revision I boundary manual was updated on April 29,1998, and now states," Valves with air reservoir backups (necessary to close the valve on loss of air) also include any necessary pilot valves, check valves, air reservoir tanks, low air pressure switches and switch over solenoid valves...." The effect on the PM program of this change to the "Q" boundary was not evaluated. Currently, there is no process in place that ensures PM requirements are evaluated when changes are made to safety significant documents.
Corrective Actions 1.
Issue formal testing criteria by June 17,1998, for surveillance testing of the backup air reservoir tanks. Testing will be conducted via work packages. Completed June 16,1998.
2.
An action plan will be developed by July 10,1998, that verifies SAR design bases systems credited for backup are being properly tested.
3.
Testing of backup air reservoirs will be scheduled to be performed on a quarterly basis. This testing will be initiated on June 28,1998.
- 4.
By August 5,1998, Engineering will perform a PM evaluation to determine if periodic maintenance is required to ensure safety related air-to-close valves with backup air reservoir tanks are capable of closing containment valves on loss of air at ERP, LAW, Tails, X-705, and X-340 complex.
5.
By September 16,1998, Engineering will perform an evaluation and develop an action plan that ensures any changes to the plant and safety related documents are flowed into the PM l
program.
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 There is a need to become more proactive in identifying systems requiring testing and maintenance.
Support systems that have inputs to safety related systems might impact system reliability if they do not perform as designed.
L I
GDP 98-2026 Page1of1 Event Report 98-05, Revision I List of Commitments 1.
An action plan will be developed by July 10,1998, that verifies SAR design bases systems
. credited for backup are being properly tested.
2.
' Testing of backup air reservoirs will be scheduled to be performed on a quarterly basis. This testing will be initiated on June 28,1998.
3.
By August 5,1998. Engineering will perform a PM evaluation to determine if periodic maintenance is required to ensure safety related air-to-close valves with backup air reservoir
' tanks are capable of closing containment valves on loss of air at ERP, LAW, Tails, X-705, and X-340 complex.
4.
By September 16,1998, Engineering will perform an evaluation and develop an action plan that ensures any changes to the plant and safety related documents are flowed into the PM program.
l J
b
_-__-____:____-_-_-_