ML20036B261
| ML20036B261 | |
| Person / Time | |
|---|---|
| Site: | Framatome ANP Richland |
| Issue date: | 05/10/1993 |
| From: | Maas L SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER |
| To: | Hooker C, Karsch R NRC, NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| IEB-91-001, IEB-91-1, NUDOCS 9305180393 | |
| Download: ML20036B261 (3) | |
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Date: May 10,1993 To:
U.S. Nuclear Regulatory Commission Operations Center Attention: Rudy.Karsch)
U.S. Nuclear Regulatory Commission Region V Attention: Chtek Hooker From: L J. Maas (A
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Manager, Regulatory Compliance Siemens Power Corporation
Subject:
Follow Up To NRC Bulletin 91-01 Report No. 25458 on incinerator Ash Buildup Introduction and Summary On April 28,1993 Siemens Power Corporation (SPC) reported per the requirements of NRC Bulletin 91-01 a buildup of ash in the primary and secondary chambers and flue of our incinerator used to burn uranium-contaminated combustible waste. SPC internal procedures require a written follow-up report of the initial telephone report. This letter fulfills this requirement.
SPC had recently replaced portions of the incinerator and prior to authorizing the restart of l
this equipment, SPC management directed a Start-up Council to review the incinerator operation. This review included a review of the criticality safety controls used on this batch-operated process. The method of accounting for the heel remaining in the incinerator was challenged during this review. It was decided to change the method of accounting for the heel by requiring a mass balance to be done using analytical results instead of the empirically-determined heel. To start using this new method required that the incinerator be cleaned out (zeroed out). This was completed April 24,1993. The ash removed from the incinerator was sampled and analyzed for uranium content. Review of the results of these laboratory analyses on April 27,1993 indicated that the allowed U-235 mass had been exceeded. However due to the form and distribution of the material a nuclear criticality accident was not possible.
This accumulation of ash was assessed as reportable to NRC headquarters under requirements of NRC Bulletin 91-01 and was recorded as report number 25458. The report was also forwarded to Region V of the NRC.
17004S Siemens Nuclear Power Corporation Enginoenng and Manufactonng Facety fh 2101 Horn Ranids Road PO Bcx 130 Rch!and. WA 99352 4130 Tet (509) 375-8100 Fax. (509) 3758402 l
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The incinerator is used to burn low enriched uranium-contaminated combustible waste. The incinerator ash contains recoverable amounts of uranium and is removed from the incinerator, placed into 30-gallon drums and stored.
l The Criticality Safety Umit on the incinerator is 793 grams U-235. This value is based on 45%
of a minimum critical mass (optimally moderated and reflected) of 5 wt.% enriched UO, The mass is monitored by computer based on assays of material fed into the incinerator. This single limit meets the required double contingency principle because the system design and operation minimizes the probability of liquid water mixing with the ash in the incinerator and in the collection container. That is, neither double batching nor flooding the incinerator as single events could cause a criticality accident.
Cardboard boxes are used to feed the chemically nonhazardous uranium-contaminated combustible waste into the incinerator. The waste is placed in the cardboard boxes in a j
manual sorting hood near the incinerator. The waste placed into the sorting hood comes from 55-gallon drums. Each 55-gallon drum contains waste that was pre-sorted at the point of generation to exclude non-combustibles and hazardous chemicals. Each drum is assayed and verified to contain less than 100 grams U-235 before it is dumped into the sorting hood.
One drum is sorted at a time and the contents of 1 drum will typically fill two cardboard boxes. This final sorting provides a second check that the wastes do not contain a significant mass of uranium.
The cardboard boxes of waste are also assayed just before they enter the incinerator. The U-235 assay value for the box contents is automatically added to the incinerator inventory by computer with the assumption that the incinerator already contained a heel of 206 grams U-235 (26% of 793). This assumed constant heel in the incinerator was based upon the amount of heel t, leaned out of the first 10 runs with the incinerator and was periodically verified.
When the computer indicates that the incinerator inventory reaches 713.7 grams U-235 (90%
of the allowed 793 grams), the feed is automatically stopped, the material is burned down and the ash is pushed out into a 30-gallon drum. In the past after an ash push, the computer system reset the incinerator U-235 inventory back to 206 grams U-235.
In February of 1989, after six months of operation, Corporate Ucensing personnelincluding the criticality safety specialist reviewed the operating experience of the incinerator. They concluded that the existing Criticality Safety Specifications for the facility were adequate but recommended improvements to the U-235 accountability system. The Criticality Safety Specialist reviewed and concurred with the implementation of these recommendations.
As a result of the recent Start-up Council review of the incinerator operation, one of the C
operatione' changes scheduled to be put in p! ace prior to restarting operations consisted of instituting a mass balance inventory system. That is, the actual amount of U-235 removed from the incinerator as analyzed in the ash would be removed from the inventory and the empirically-determined heel size would not be used.
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Current Status The SPC incinerator was shut down on October 7,1992 for modifications and remains shut l
down.
A total of 242 Kg of ash has been removed from three different sections of the incinerator and is in a total of five 30-gallon drums. Each of these drums contains less than 500 grams U-235 and is safely stored within criticality safety limits.
Assessment The average enrichment of the uranium in the 242 Kg of incinerator ash is about 3.25 wt.% U-l 235 based upon analytical results. A safe mass (defined as 45% of the minimum critical mass) of U in UO2 at this enrichment is about 31.75 kg. The total mass of uranium removed from three separate areas of the incinerator as a heel was measured to be 35.57 kg which corresponds to 1.12 times a safe mass. This value is substantially less than the 53 kg of U originally estimated which was based on preliminary laboratory results.
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About 29 of the 35.57 kg of the uranium was removed from the primary chamber.
Approximately hatf of the ash removed was uniformly distributed on the floor about 1 inch deep and the other half accumulated near the primary chamber door. The last batch of ash processed out of the incinerator contained about 15 kg uranium at 3.25 wt.% U-235 which indicates that before shut down the total amount of uranium (ash and heel) in the incinerator i
was about 50.57 kg or 1.6 times a safe mass. Therefore, a criticality accident was not possible because there was insufficient uranium in the incinerator, the uranium was dispersed, the uranium-bearing ash was dry, and the system is enpineered to prevent the ash i
from getting wet.
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Cause l
The empirically-determined heel was based on historical engineering and production data and was not reviewed frequently enough to assure continued validity for increased run times, changes in feed materials, etc.
Corrective Actions The incinerator will remain out-of-service and under the formal control of a Start-up Council.
As previously scheduled, the inventory system will be changed to calculate the actual heel remaining in the incinerator.
SPC will provide a description of the revised Criticality Safety Limits and Controls for the incinerator operation to Region V for review and approval before the system is restarted.
I If further information is needed I can be reached at (509) 375-8537.
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