ML20211G892

SER Accepting Amend 1 to License SNM-1097

ML20211G892
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Site:	07001113
Issue date:	09/26/1997
From:	Weber M NRC
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ML20211G885	List: ML20211G880 ML20211G888 ML20211G892
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NUDOCS 9710060040
Download: ML20211G892 (5)

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y 4 UNITED STATES g j NUCLEAR REGULATORY COMMISSION WA$HINGTON, D.C. 20656 4001 o  !

• • • • ' September 26, 1997 DOCKET: 70-1113 LICENSEE: General Electric Company Nuclear Energy Production Wilmington, North Carolina

SUBJECT:

SAFETY EVALUATION REPORT: APPLICATION DATED SEPTEMBER 19, 1997, CHANGES TO TABLE 6.0 FOR THE DRY CONVERSION PROCESS HYDROFLUORIC ACID RECOVERY AND STORAGE FACILITY  :

BACKGROUND

, On September 4, 1997, la accordance with Nuclear Regulatory Commission  !

Bulletin 91-01, " Reporting Loss of Criticality Safety Controls," the General Electric Company (GE; the licensee) reported to NRC that the Dry Conversion Process (DCP) had discharged uraniue to the atmosphere in excess of facility operating limits at GE's fuel fabrication facility in Wilmington, NC. Based on GE's review of the accident, GE concluded that the release was caused by the inadvertent introduction of unreacted UF6 from the nitrogen purge lines into the DCP conversion kiln during initial startup. Previous to the startup in which the release occurred, GE discovered that the nozzle for injecting UF 6 gas, superheated hydrolysis steam, and nitrogen gas into the reactor was clogged. During several attempts to start up the DCP and resolve the clogging, UF6 gas condensed in the nitrogen purge lines. ,

Normally, UF6 is reacted with steam to produce uranyl fluoride (U0 F ) which is prevented from being released through the stack by design featu,re,s that include filters on the conversion kiln and condensers and. vapor / liquid separators in the Hydrogen Fluoride (HF) Effluent Recovery and Storage Facility. However, when the nozzle was finally cleared and the line was aurged with nitrogen, dry unreacted UF was introduced into the conversion ciln. Because steam had not yet been introduced to the kiln, the UF6 was able to bypass the features designed to prevent uranium releases from exceeding previo aly analyzed maximum uranium release amounts; these previous analyses were based on the assumption that U0,F, particulate carryover would be the only transport mechanism and did not account for transport of unreacted UF 6 gas. For the unreacted UF6 transport, the maximum amount of uranium that could heve been introduced into the conversion kiln was conservatively calculated by GE to be approximately 500 grams of uranium. _This transport

, mechanism could have resulted in a theoretical maximum release of approximately 250 grams of uranium.

.By application dated September 19, 1997, GE Nuclear Energy Production, requested Materials License SNM-1097 be amended to authorize a change to

, Table 6.0 of the license application for the HF Effluent Recovery.and Storage Facility of the DCP. GE specifically requested that the table be amended to

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allow for single parameter control on'the mass of unreacted UF6 gas in the HF Effluent Recovery and Storage Vessels. This change was necessary to ensure nuclear safety for the DCP because previous assessments had not accounted for 9710060040 970926 " f PDR ADOCh 07001113 C PDR2 ,

. 2 the potential presence of unreacted UF 6 in the HF facility. GE discussed the ,

proposed amendment with the NRC during teleconferences on September 18 and 19,  !

1997. These teleconferences summarized GE's accident analyses and planned corrective actions. On September 23, 1997 GE faxed additional details to the NRC to support the amendment application. GE provided a hard copy of these additional details by letter dated September 25, 1997.

DISCUSSION The NRC staff reviewed the licensee's request to change the basis for l criticality safety in the DCP for the HF Effluent Recovery and Storage l Facility portion of Table 6.0, " Plant Systems and Parameter Controls," in  !

Materials License SNM-1097. Specifically, the basis for criticality safety I for an unreacted UF6 gas release into the HF Effluent Reco" ry and Storage  !

Facility of the DCP was added. This basis relied on controlling the mass of unreacted UF 6 = To implement this control on the mass,- GE addC multiple, independent controls (software interlocks) that sensed steam flow rates to

signal block valves to close in the UF6 feed piping to the conversion kiln. A process description and a review of the safety basis supporting this request 4- are discussed below.

The DCP directly reacts uranium hexafluoride (UF 6 ) with hydrolysis steam in the DCP conversion kiln (static reactor) to form uranyl fluoride powder (VO # The UO F is then reacted with pyrohydrolysis steam in the conversion kil,F. ) .n to form ura,nIum dioxide powder 2 (U0 ).

Gaseous UF 6 feed from the Model 308 UF cylinder, which is hented inside an autoclave at a controlled temperature,6 is delivered by heat-insulated and electrically-heated piping to an injection nozzle in the conversion kiln.

Five separate block valves are located along -the delivery pipe for isolation of the UF6 feed. A nitrogen purge is provided downstream of the last block valve to purge the injection nozzle of any residual UF6 during startup of the DCP. This nitrogen purge prevents steam back-flow and plugging within the UF6 feed pipe.

UF6 gas, nitrogen gas, and superheated hydrolysis steam are simultaneously and continuously introduced into the injection nozzle of the conversion kiln. The injection nozzle is a ring-shaped injector that allows concentric flow of the UF gas, nitrogen gas, and superheated steam into the conversion kiin. The nii.rogen gas flows between the UF6gas and superheated steam to prevent them from reacting immediately at the nozzle outlet; the hydrolysis reaction that produces UO Fi powder is designed to take place in the center of the conversionkiln. The steam flow rate is independently used (through independent input / output (1/0) cards recently added by GE) to signal two

. separate block valves to close in the UF feed line to ensure that excess hydrolysis steam exists for reacting witb the UF6 gas. By closing off the feed line if sufficient steam is not present, the revised DCP should prevent unreacted UF 6 from being released into and from the conversion kiln during DCP ,

operations The U0 F powder formed from the hydrolysis" reaction falls down to the lower part of khe conversion kiln and feeds a screw conveyor which directs the U0,F,

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powder to the second part of the kiln (rotating tube) where it reacts with ,

i superheated pyrohydrolysis, steam and hydrogen gas. Hydrogen gas and- l

- superheated pyrohydrolysis steam are introduced from the rear end of the kiln  !

i tube to produce h countor-current contact flow with the U0 F, powder to j powder. f produce controlled U0,to ensure that excess hydrogen gas and steam exist for  :

powder. F i with the hydro U0 F,lyzes any residual unreacted UF gas.This helps to prevent particula and also 6 The steam flow rate independently used (through independent I/O cards recently added by GE) to i 4

signal two separate block valves to close in the UF feed line to ensure that F such that.any excess unreactedpyrohydrolysis UF 6 will not be steam released from exists the for conversion reacting kiln witb the U0,d,uring Dl i

operations and that particulate carryover of U0,F, will not occur.  !

3 The gases resulting from the conversion reactions contain excess HF, steam, hydrogen, and ..itrogen. These gases are evacuated at the-top of the conversion. kiln where they are filtered by a series of filter tubes made of t sintered Monel to remove any particulate carryo)er of uranium from an accident i before being delivered to the HF Effluent- Recovcry and Storage Facility of.the

[ DCP where HF acid solutions are recovered. M.e process contains a second

level of filtra+, ion installed downstream of the filter tubes to augment removal of the uranium particulate carryover in the event that the primary filters in the conversion kiln fail.

The HF Effluent Recovery and Storage Facility of-the DCP houses systems, structures, and components to recover HF from the conversion kiln off-gases and scrub process gases before releasing gases to the environment. This facility also serves to reduce the quantity of a release involving 00 F, 1

, carryoter. Processflowsthatmaybeexpectedtocontainuraniumduringan accident'that causes U0,F, particulate carryover are restricted to equipment and components that are favorable geometry, including the HF off-gas pipe, HF ,

j condenser, piping upstream of the vapor / liquid separator inlet, vapor / liquid

- separator, piping between the vapor / liquid separator outlet and aipe i - detectors, polluted ~ storage tank, and HF building floor sump. T1e water- ,

cooled-condenser transfers heat from the kiln off-gases, and a vapor-liquid

- separator. vents..noncondensible gases to a wash column. A single wash column 4

- is designed to prevent exceeding 11 ease-limits for the maximum expected off-

-gas flow from .two conversion lines in the DCP.

t - . t Concentrated HF flows by gravity from the condenser outlet to large 20,000 liter Concentrated Storage Tanks, and dilute HF is-automatically pumped from the wash column to large 20,000 liter Dilute Storage Tanks. Normally, .

concentrated HF flows to the unfavorable geometry Concentrated Storage Tanks.

However, if the uranium concentration exceeds 10 ppm from the condenser outlet as sensed by pipe-detectors-downstream of the condenser and vapor / liquid separator, block' valves actuate to redirect flow of the concentrated HF to the

- favorable geometry Polluted Storage Tank (115 liters). A primary detector is dedicated to each conversion linet and a secondary detector common to all

. conversion lines is used to_ provide for _ control reliability.

i L - As: stated previously, 'if the hydrolysis and pyrohydrolysis superheated steam flow rates: decrease below minimum values, safety interlocks recently added by

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GE independently activate closure of a total of four separate block valves in l the UF6 feed line (i.e., two from hydrolysis steam flow rate signals and two from pyrohydrolysis steam flow rate signals) to isolate UF 6 feed flow. This ensures that excess steam exists to prevent more than a residual amount of  ;

. unreacted UF from entering the conversion kiln and subsequently being released to khe environment. Calculations by GE determined that a maximum of 477 gu per line at 5.0% U-235 enrichment could be released to the conversion kiln during an accident, which is significantly less than a safe batch of 15.9 kgU at 5.0% U-235 enrichment (based on Section 6.2.4 of the itcense application). This calculation conservatively assumed (1)-all three lines were operating normally, (2) UF6 feed rate was maximized, (3) steam flow was >

instantaneously reduced to zero after 20 seconds, (4) the steam low flow

- interlock stops UF feed, (5) the block valve leaks in the line immed4+ely '

beforetheconversionkiln,and(6)thepressuretransmitterlina and *.zzle  !

are full of UF6at the time of the accident. Only UF6gas in the static pressure line and ine gas behind.the last block valve remained avai'sble for a release, if it v.as conservatively assumed that the residual UF does not react +

with the excee.s available steam in the conversion kiln while steam is present.

GE calculations to quantify the maximum delivery of uranium to the HF recovery facility upon a total loss-of steam with the control system response resulted in a maximum release of 246 gu from unreacted UF gas. GE calculations to quantify the maximum credible holdup of uranium in the conversion kiln during

• l a DCP startup with no control system response (i.e., the Bulletin 91-01 referenced event) resulted in a much lower release than the above scenario for

[ a= total loss of steam with the control system response. 1 NRC has reviewed GE's calculations to determine the maximum credible unreacted i UFi release based on stoichiometric considerations. These calculations adequately determined the maximum credible UF6 release amounts and were conservative. Based on these reviews and the inde)endent interlocks GE s recently added to close multiple-block valves in tie feed lines to control the' mass of unreacted UF 6

, the staff has reasonable assurance that a criticality event will not occur due to an accident with unreacted UF6 in the DCP and that the'DCP can be operated safely considering the potential release of unreacted UF6 into and from the DCP conversion kiln.

< ENVI")NMENTAL REVIEW The staff has determined that the following criteria in 10 CFR 51.22(c)(ll) for categorically excluding an action from an environmental review have been met: ,

1. There.'is no significant change in the types, or significant increase in the amount, of. effluents that may be released offsite.  ;

2. There is no significant increase in individual or cumulative

- occupational radiation exposure.

3. There is no significant construction impact.

4. There is no.significant increase in the potential for, or consequences from, radiological accidents.

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5 Accordingly,_ pursuant to 10 CFR 51.22(c)(ll),_ neither an environmental assessment nor an environmental impact statement is warranted for this action.

(01(CLUSION Based on the above discussion, the staff concludes that the proposed changes are acceptable. The Region 11 inspection staff has no objection to this proposed action.

Princioal Contributors [

Crai A. Hrabal /d li Dona d E. Stout u Ig' cbp L

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