ML20044B860
| ML20044B860 | |
| Person / Time | |
|---|---|
| Site: | Framatome ANP Richland |
| Issue date: | 03/05/1993 |
| From: | Maas L SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-91-001, IEB-91-1, NUDOCS 9303110008 | |
| Download: ML20044B860 (6) | |
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SIEMENS March 5,1993 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Gentlemen:
Re:
Follow-up to NRC Bulletin 91-01 Report No. 25038 - Powder Feeder Limit Switch Incident On February 7,1993, Siemens Power Corporation (SPC) reported a criticality safety incident to the NRC Operations Office per NRC Bulletin 91-01. SPC internal procedures require a 30-day written follow-up report of the initial telephone report. This letter fulfills this requirement.
Backaround The SPC Conversion area has three powder preparation lines. Each of these lines has a blending step which takes place inside unfavorable geometry blenders. Criticality safety in the blenders is assured by moderation controls with double contingency. After the UO2 powder is blended, it is dropped into a feed hopper and vacuum transferred to other equipment where it is further processed. Each of the three feed hoppers is located inside a blender discharge hood - a HEPA filtered, metal framed lexan enclosure. Umit switches have been installed on the ends of the three discharge tubes from the feed hoppers so that if a discharge tube becomes separated from its feed hopper, the feed screw will shut off, thereby preventing large accumulations of UO powder in the bottom of the blender discharge hood.
2 The discharge tubec were designed to separate from the hoppers to prevent damage to the feed screw and hopper if plugging occurs.
Description At 0815 hours0.00943 days <br />0.226 hours <br />0.00135 weeks <br />3.101075e-4 months <br /> on February 7,1993, the Une 3 powder prep technician discovered that the une 3 powder feeder discharge tube had separated from the powder feed hopper causing approximately 124 kgs of UO Powder to spill within the blender discharge hood. The limit 2
switch installed to shut down the feed hopper when the discharge tube becomes separated from the feed hopper had not activated. It was determined that this limit switch had been disabled so that it would not shut off the feed screw. The existence of this quantity of powder outside the normal equipment envelope was judged to be a reportable incident under Nuclear Regulatory Commission (NRC)Bulletin 91-01. However, due to other controls in place, a criticality accident was not possible. Also, since the powder was confined within the HEPA-090035 Siemens Power Corporation Nucear Dntson - Engoeenng and Manutamunng Facey 2101 Horn Ransk Road PO By 130 RcNand, WA 993520130 Te!. FJ9) 375a103 Far (509) 375 8402 9303110008 930305 V
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Page 2 March 5,1993 filtered feed hopper enclosure, no worker exposure hazards or environmental releases resulted from the powder spill.
Immediate Corrective Actions Upon discovery of the powder spillage, the following immediate response / corrective actions were undertaken:
The technician immediately shut down the une 3 powder preparation system and notified his lead technician, who in turn notified the supervisor.
The shitt supervisor called the Criticc!ity Safety Specialist who advised that the powder remain undisturbed until he could inspect the situation (0835 hours0.00966 days <br />0.232 hours <br />0.00138 weeks <br />3.177175e-4 months <br />).
The shift supervisor called the Conversion Area general supervisor, who dictated that all the powder prep lines were to be shut down. - (Une 2 powder prep was already down for enrichment cleanout). The general supervisor also notified the Plant Operations Manager.
Pictures were taken to document the material in the hood, the condition of the discharge tube, and the condition of the interlock switch (0855 hours0.0099 days <br />0.238 hours <br />0.00141 weeks <br />3.253275e-4 months <br />).
At 0950 hours0.011 days <br />0.264 hours <br />0.00157 weeks <br />3.61475e-4 months <br />, with concurrence of the general supervisor and the Criticality Safety Specialist, cleanout of the discharge hood to the central vacuum cleaner j
syrtem was initiated. The cleanout was completed at 1245 hours0.0144 days <br />0.346 hours <br />0.00206 weeks <br />4.737225e-4 months <br />.
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The telephone report to the NRC as required by NRC Bulletin 91-01 was made-at 1149 hours0.0133 days <br />0.319 hours <br />0.0019 weeks <br />4.371945e-4 months <br /> based on substantial degradation of a controlled parameter, A management team consisting of the Plant Manager, the Manufacturing Engineering Manager, the Safety, Security and Ucensing Manager, and the j
Plant Operations Manager arrived on plant during the early afternoon to review
-l the event and appoint a root cause analysis team to investigate the incident.
Cause a
A four person team representing Plant Operations, Manufacturing Engineering, and Safety, f
Security, and Ucensing was convened to investigate and determine root causes for this incident. Initialinvestigation revealed that the immediate initiating condition for this incident-.
was that the Une 3 discharge tube limit switch was jammed by a piece of tape which '
l prevented the switch from shutting off the feed screw when the discharge tube separated from the hopper. Inspection of the other two powder prep feed hoppers revealed that the-Une 1_ feeder did not have any tape on or near the switeghowever, the Une 2 limit switch was found to be disabled with tape. Using the Taproot analysis methodology, the team
.j identified the following root causes under the following categories.
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u Page 3 March 5,1993 Management System 1.
A procedural requirement to not disable interlocks was violated.
l 2.
A procedure requiring the use of an engineering change notice (ECN) to modify equipment that directly involves fissile material, was not followed, instead, the limit switch had been installed under a work order (WO).
3.
The monitoring of the WO program for incorrect usage was less than
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adequate.
Communications
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No formal method was available to notify Operations that a modification to process equipment was performed by a WO.
5.
Shift turnover was less than adequate in informing followup shifts of the equipment modification by WO.
Training 6.
Instruction in following the standard operating procedure (SOP) requirement to not disable interlocks was less than adequate.
Procedures 7.
The existence of the powder feeder interlocks and their operation were not identified in a procedure.
Equipment Reliability i
8.
The design / installation of the interlock switch was less than adequate because frequent and spurious trips occurred, inviting the switch to be disabled.
l The team also identified two other conditions which were judged to have possibly contributed indirectly to the incident, as follows:
The " maintenance required" section of the powdor prep logs (filled out by the
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powder prep technician) was being used to report process test results, thereby making it difficult to use the section to report maintenance problems or if used, not making the item visible enough to be easily recognized.
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Page 4 March 5,1993 The shift schedule worked by the Conversion area crew can cause communication to be more difficult between the shifts and other support personnel.
Corrective Actions Actions Reauired Prior to Restart of Powder Feeders on Prep Une -
r 1.
Modify limit switches so that incidental movement of feeder discharge tube does not activate the interlock. (Plant Engineering) 2.
Functionally test all three intericcks on powder feeders for proper operation. (Plant Engineering) 3.
Conduct an independent walk through of the Conversion area to assure that all limit switches and interlocks are functional. (Plant Engineering) 4.
Revise the applicable SOP's to include all pertinent interlocks in the powder prep areas. (Plant Operations) 5.
Conduct an incident critique and retrain all Chemical Operations technicians on the function of interlocks or limit switches and state they.
are not to be disabled or bypassed unless for a defined purpose and in accordance with an approved procedure. Plant Operations to complete before each crew is allowed to start their shift.
6.
Review all outstanding WO's to assure that equipment modifications per ECN Procedure EMF-8581.13 are being done on a ECN. (Plant Engineering) 7.
Specify the use of the ECN procedure for modifications; reserve WO's for repair or replacement work. (Manufacturing Engineering)
All corrective actions in this category have been completed.
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Follow-up Actions l
1.
Prepare and implement a Work Station Training and Operator Qualification Guide. (Plant Operations) i 2.
Provide training / audit of ECN and work order procedures (EMF-8581.13 and 1.21) to re-emphasize the criteria used for determining ECN versus WO usage. (Manufacturing Engineering)
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Page 5 March 5,1993 3.
Re emphasize to all Manufacturing personnel the importance/ requirement for not disabling any interlock or limit switch r
except for a defined purpose and in accordance with an approved procedure. (Plant Manager) 4.
Revise " Plant Operations Rules", EMF-221.1.1 (P66,318),
- Master Safety Rules", EMF-30 Chapter One (P65,501), and " Criticality Safety Guide Rules", EMF-30 Chapter Three Appendix 9, to dictate that interlocks are not to be disabled or by-passed, with the only exception being for a defined purpose and in accordance with an approved procedure. (Plant Operations and Safety, Security, and Ucensing) 5.
Assure that all pertinent interlocks are described in respective Plant Operations SOP's. (Plant Engineering and Plant Operations) -
6.
Review alternate designs for the powder feeder discharge tube system for possible improvements or simplification to assure that the design prevents the discharging UO powder into the bottom of the Blender g
Discharge Hoods. (Plant Engineering) 7.
Revise the Powder Prep Logs to provide a separate section to record all required information. This will allow equipment problems to be highlighted in the " maintenance required" section. (Plant Operations) 8.
Form an independent task force to review the operation and condition of other interlock / limit switches in the plant. (Plant Engineering) l 9.
Review the 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> shift implementation. (Plant Operations)
Follow-up corrective action numbers 3,7, and 8 have been completed. Work is in progress l
on all other follow-up corrective actions with specific scheduled completion dates on or before April 15,1993.
" Generic implications" Corrective Actions
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To assure proper application of " lessons learned" from this particular incident to the balance of the plant, the Richland Plant Manager commissioned a " Generic implications" team to investigate interlock-related issues plantwide. The team included representation from both Manufacturing Engineering and Plant Operations and worked independently from the root cause investigative team and the Startup Council. The generic implications study recommended a number.of improvement initiatives focusing on how interlocks are installed, documented, communicated, and maintained. The initiatives validate, strengthen, and in some cases expand on corrective actions recommended by the root cause team and will be independently tracked to completion.
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Confirmatory Action Letter i
This incident was investigated by an NRC Augmented Inspection Team (AIT) over February 9-12,1993. Over the course of their investigation the AIT identified a generic criticality safety issue not directly related to this event i.e. the potential for moderator intrusion into the area of powder preparation lines 2 and 3. On February 12 NRC Region V issued a Confirmatory Action Letter (CAL) requiring SPC to perform an engineering evaluation of this potential, including defining any needed control measures. The CAL provided SPC with two options by which the powder prep lines could be operated pending cornpletion of the engineering evaluation. SPC is currently operating within the limitations prescribed in the CAL Results of the engineering evalus. on, which is ongoing, will be provided to NRC Region V.
Questions regarding SPC actions in response to this incident can be directed to me on 509-375-8537.
Very truly yours, a
U W
Loren J. Maas, Manager Regulatory Compliance LJM:pm cc:
J. B. Martin, NRC E. G. Adonsam, NRC HQ a
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