ML20195C689

Forwards Required 30-day Event Rept ER-98-27 Re Actuation of Autoclave Position 4 South Steam Pressure Control Safety Sys in Bldg C-333-A.No Commitments Are Contained in Rept Since All Corrective Actions Have Been Completed

ML20195C689
Person / Time
Site:	Paducah Gaseous Diffusion Plant
Issue date:	11/13/1998
From:	Pulley H UNITED STATES ENRICHMENT CORP. (USEC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GDP-98-1075, NUDOCS 9811170195
Download: ML20195C689 (4)

Text

.

USEC A Global Energy Company November 13,1998

' GDP 98-1075 United States Nuclear Regulatory Commission Attention: Document Centrol Desk Washington, DC 20555-0001 Paducah Gaseous Diffusion Plant (PGDP)

Docket No. 70-7001 Event Report ER-98-27 i.

Pursuant to SAR Section 6.9, Table 1, Criteria J2, enclosed is the required 30-day written event report covering the actuation of autoclave position 4 South steam pressure control safety rystem in Building C-333-A. The Nuclear Regulatory Commission (NRC) was notified of the event on October 23,1998 (NRC No. 34953). All corrective actions are completed; therefore, there are no l

commitments in this report.

l l

Any questions regarding this matter should be directed to Larry Jackson at (502) 441.-6796.

Sincerely, owa

'ulle ~

General Manager Paducah Gaseous Diffusion Plant

\\

/} g'7h.'

Enclosure:

As Stated cc: NRC Region Ill OfEce NRC Resident inspector, PGDP 9811170195 981113 U"'

PDR ADOCK 07007001' C

PDR; Telephone 502-441-5803 Fax 502-441-5801 http://www.us,:c.com P.O. Box 1410, Paducah, KY 42001 Offices m Livermore, CA Paducah, KY Portsmouth, OH Washington, DC

L

/

Docket No. 70-7001 GDP 98-1075 Page1of3 l

i EVENT REPORT ER-98-27 DESCRIPTION OF EVENT -

On October 23,1998, at approximately 0900 hrs., while heating a cylinder (Mode 5) the autoclave pressure increased to approximately 6.6 psig on autoclave position 4 South, Building C-333-A. A high autoclave steam pressure alarm was received in the Operations Monitoring Room (OMR) and the steam pressure control safety system actuated, as designed. The steam pressure digital reading was 6.6 psig on the steam controller; the strip chart recorder read approximately 7 psig (alarm s:t-point range 6.5 psig-7.5 psig); and the control valve was fully open. The Plant Shift Superintendent (PSS) was notified and declared the autoclave inoperable. According to procedure the cylinder valve was closed and purged; the autoclave was jetted and opened; and the pigtail was disconnected. The autoclave was removed from service and placed in Mode 2, as required by the Technical Safety Requirements. All safety systems performed, as designed, to place the autoclave in a safe condition. On October 23,1998, at 1542 hrs., the Nuclear Regulatory Commission l

Headquarters (NRC-IIQ) operations office was notified of this event in accordance with the Safety Analysis Report (SAR), Section 6.9, Table 1, Criteria J.2 (NRC No. 34953).

At the time of the event, the Systems Engineer was in the OMR; troubleshooting was initiated immediately; and a determination made that the temperature indicating controller (TIC-523) failed, causing the temperature control valve (TCV-523) to fully open. When the TCV-523 fully opened, uncontrolled steam entered the autoclave causing the steam pressure safety system trip. The TIC-523 is a Single Station Micro Controller (SSMC), manufactured by Foxboro (model no. 761 CNA). A diagnostic digital read-out from the SSMC confirmed a TIC-523 failure. The TIC-523 experienced a memory module failure which changed the original operational settings for the autoclave allowing the TIC-523 to open and input steam into the autoclave. On October 28,1998, the memory module failure was confirmed and the module replaced.

The Systems Engineer contacted Foxboro and determined that a memory module failure seldom occurs unless under undue stress, such as from a large electromagnetic field or from unusual circumstances. Neither a large electromagnetic field nor unusual circumstance is applicable to this event. Foxboro expressed the opinion that a periodic change-out of the memory module or other preventive maintenance was not necessary. Also, the failure was random because of is absence of other problems at the time of the event.

d' Docket No. 70-7001 GDP 98-1075 Page 2 of 3 The safety significance of this event is considered low. The pressure control system has two independent channels at which increasing pressure in the autoclaves will isolate the steam supply before exceeding the safety limit for cylinder temperature / pressure. This first alarm and actuation occurs at <8 psig and isolates the steam supply. The autoclave shell pressure safety limit is 220 psig.

CAUSE OF Tile EVENT A. Direct Cause The direct cause for this event was the failure of a memory module located in the temperature indicating controller (TIC-523). The module failure disrupted the TIC-523 operational settings which allowed uncontrolled steam into the autoclave resulting in a steam pressure safety system trip.

B. Root Cause The root cause of this event was an unexpected equipment failure. There are no records to indicate that failure of an operating TIC memory module has previously occurred at the Paducah Gaseous Diffusion Plant. Additionally, the manufacturer indicated that a memory module failure is not a common failure.

CORRECTIVE ACTIONS A. Completed Corrective Actions

1. On October 28,1998, the memory module within the TIC-523, autoclaw position 4 South, was replaced.

EXTENT EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERIALS 1

None I

l I

i d

..... ~.

l.~

L Enclosure I f

t a'

' Docket No. 70-7001 GDP 98-1075 Page 3 of 3 i

LESSONS LEARNED Although the memory module failure was determined to be an isolated occurrence, any further memory module failures will be evaluated to determine whether an adverse trend is developing.

i I

P i

i t

t e

I e

h i

e L

.i 1.

i i

n 1

J J

_,