ML20125D145
| ML20125D145 | |
| Person / Time | |
|---|---|
| Site: | Framatome ANP Richland |
| Issue date: | 12/07/1992 |
| From: | Maas L SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-91-004, IEB-91-4, NUDOCS 9212150025 | |
| Download: ML20125D145 (2) | |
Text
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' S1EM ENS Docomber 7,1992 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington DC 20555 Gentlemon:
Re: Follow up to NRC Bulletin 91-01 Report No 24514 - UNH Dissolver 901 Material Hold Up On 10/27/92 Slomons Power Corporation (SPC) reported a criticality safety incident to the NRC Oporations Offico por NRC Bulletin 91-01. SPC internal procodutos require a writton follow-up report of the inillal tolophone report. This lotter fulfills this requirement.
Backaround SPC has two dissolvers,901 and 902, used to dissolvo U 0 or UO with nitric acid (HNO ),
3 s 2
3 thereby producing uranyl nitrato hexahydrato (UNH). Each discolver tank is mado of a 10-inch schedulo 40 pipe about 3 foot long below an 8-inch scheduto 40 pipo section about 4 foot long, At the top of the tank is a perforated stool baskot used to mix the powder from a screw convoyor with solution recycled from the tank. Betwoon the scrow feodor and the basket is a butterfly valvo. This valvo is in placo to isolato process off-gases from the powdor food hood and direct them to tha POG scrubber system. The basket is in the nominal 8-inch diamotor section. Because the lower portion of the dissolver is not a favorable diameter, the dissolver is operated on a batch basis and is limited to one safo batch (45% of a minimum critical mass). The dissolvors are required to bo operated in a manner that provides reasonablo assuranco that powdor does not accumulato in the dissolvors from batch to batch.
The criticality safety analysis for this system demonstratos that k-off is loss than 0.92 when the dissolver contains two safe batches plus 10 kg of UO at optimum moderation and full water 2
reflection.
Description SPC has committed to upgrading its criticality safety analysos for plant operations. As part of this effort SPC engineers woro requestod to determine the amount of hool,if any, that could romain in the dissolver after pumping the dissolvers empty, p
While preparing to run tests to determine the size of any potential heels left after tank pump A
out, a 6.5 kg accumulation of UO, was found in Dissolver 901 in the 7670 cc volume between O
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Siemens Power Corporation ~
Nuclear Division Engineering and Manufacturing Facility
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2101 Horn Rapids Road. PO Box 130 Richland. WA 99352-0130 Tel: (509) 275-8100 Fax: (509) 375 8402 9212150025 921207 PDR ADOCK 07001257
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Document Control Desk Page 2 December 7,1992
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the buttorfly valvo and the scrow foodor discharge, if this ontito volumo had boon filled with powder, it could have contained 13 kgs of UO,, assuming a density of 1.7 g/cc.
SPC Process Enginooring dolormined that each dissolver has a hoolleft in the tank after each batch. The volumo of this hool varlod from 5.5 to 7.5 gallons. Tho dissolution paramotors gonorato a uranium concentration of approximately 300 gU/litor UNH. Assuming a maximum hool of 7.5 gallons, and a maximum concentration of 350 gU/litor, the hool could contain up to 10 kgs of uranium, Based on the discovery of U holdup in the system which was not adequately addressed in ~
the criticality safety analysis, SPC reported the situation to the NRC Operations Offico via tolophono at 1725 hours0.02 days <br />0.479 hours <br />0.00285 weeks <br />6.563625e-4 months <br /> on 10/27/92 (NRC Roport No. 24514).
Cause The potontlal for powdor accumulation at this location in the dissolvor oxists whenover the scrow foodor operates for any porlod of timo with the buttorfly valvo in the closed position.
The criticauty safoty analysis did not prescribo the spocific mothods of assuring that powdor accumulation did not occur. Also, the operating procoduro did not require an inspoction to detoct powdor accumulation in this area when successivo batches woro of the samo U-235 onrichmont.
Correctivo Actions An addondum was added to tho_ criticality safety analysis for the dissolvers and the required limits and controls woro changed to address the potentials for U holdup in the system. Those changes includod reducing the allowed batch sizo by 10 kg to componsato for the potential of a 7.5 gallon hool, limiting the UNH concentration result!ng from dissolution to 330 gU/litor, and inspecting the dissolvor baskot to ensure the entire batch has boon was dissolved and pumped out beforo processing another batch, ovon when the next batch is of the samo.U 235 ontichmont levol.- Tho SOP was chan00d to require a visual inspection of the dissolver baskot after each run to detect any accumulation above tho buttorfly valvo.
Quostions regarding SPC actions in responso to this situation can be directed to mo on (509) 375-8537.
Vo truly yours A
CR, i n.
Loron J, Maas, Manager Regulatory Compliance LJM:pm cc:
J. W. N. Hickey, NRC J. B Martin, NRC y
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