ML20216J053

Provides Response to NRC RAI on Certificate Amend Request Dealing W/Product & Tails Withdrawal Facility Criticality Accident Alarm Sys.Info Requested Provided in Encl 1

ML20216J053
Person / Time
Site:	Paducah Gaseous Diffusion Plant
Issue date:	03/13/1998
From:	Toelle S UNITED STATES ENRICHMENT CORP. (USEC)
To:	Paperiello C NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
References
GDP-98-0047, GDP-98-47, TAC-L32047, NUDOCS 9803230331
Download: ML20216J053 (17)

Text

,

y USEC A Global Energy Company March 13,1998 GDP 98-0047 Dr. Carl J. Paperiello Director, Office of Nuclear Material Safety and Safeguards Attention: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001

~ Paducah Gaseous Diffusion Plant (PGDP)

Docket No. 70-7001 Response To Request for AdditionalInformation Certificate Amendment Request - Product and Tails Withdrawal Facility Criticality Accident Alarm System

Dear Dr. Paperiello:

The purpose of this letter is to provide a response to the NRC's request for additional information (TAC. No. L32047) on the Certificate Amendment Request dealing with the Product and Tails Withdrawal Facility Criticality Accident Alarm System (Reference 1). Reference 2 identifies the additional infonnation required by NRC to allow final action to be taken on the Certificate Amendment Request.

USEC's response to the NRC's information request is provided in Enclosure 1 to this letter. This additional information should enable NRC to complete the review and approval of USEC's Certificate Amendment Request.

USEC will continue to implement the compensatory measures described in References 3 and 4 which have been implemented to minimize the consequences of postulated seismic failures in the C-310 facility until such time as the Justification for Continued Operation associated with the C-310 facility is no longer in effect and the compensatory measures are no longer required.

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9803230331 980313 PDR ADOCK 07007001 C

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Q u J ri.') a 690311ockledge Drive, Bethesda. MD 20817-1818 Telephone 301-564-3200 Fax 301-564-3201 http://www.usec.com OHices in Livermore. CA Paducah, KY Portsmouth, OH Washington, DC

- O. -

. Dr. Carl J. Paperiello March 13,1998 -

. GDP 98-0047, Page 2 Commitments contained within this submittal are identified in Enclosure 2. Any questions related '

to this subject should be directed to Mr. Mark Smith at (301)S64-3244.'

Sincerely,

.np

5. A. IdV Steven A. Toelle Nuclear Regulatory Assurance and Policy Manager -

Enclosures:

~ 1. Response to Additional Information Request (TAC No. L32047)

. cc: NRC Region 111 Office

.NRC Resident Inspector-PGDP NRC Resident Inspector - PORTS

- DOE Regulatory Oversight Manager

i 1-U

Dr. Carl J. Paperiello March 13,*1998 :

. GDP 98-0047, Page 3 REFERENCE

. 1) Letter from 'Mr. James II. Miller (USEC) to Dr. Carl J. Paperiello (NRC), Certificate Amendment Request - Product and Tails Withdrawal Facilities Criticality Accident Alarm System, USEC Letter GDP97-0061 dated September 15,1997.

2) Letter from Mr. Charles Cox (NRC) to Mr. James H. Miller (USEC), Paducah Certificate Amendment Request - Product and Tails Withdrawal Criticality Accident Alarm System (TAC -

L32047), dated February 12,1998.

. 3) Letter from Mr. James H. Miller (USEC) to Dr. Carl J. Paperiello (NRC), Request for

' Enforcement Discretion, USEC Letter GDP 98-0031, dated February 25,1998.

~

. 4) Letter from Mr. James H. Miller (USEC) to Dr. Carl J. Paperiello (NRC), Request for Enforcement Discretion-Response to NRC Request for Additional Information, USEC Letter

- GDP 98-0041, dated March 5,1998.

4 9

6-

GDP 98-0047

+

Page 1 of13 Response to AdditionalInformation Request (TAC No. L32047)

Issue 1:

- Please provide corrosion trend information and current wall thickness measurements for the accumulators and condensers in the Product Withdrawal station

' Resnonse:

The requested data is provided in the attached Figures.

Figure Number Title Figure 1 Side Withdrawal Accumulator Thickness Measurement Locations Figure 2 Product Withdrawal Accumulator Thickness Measurement Locations Figure 3 Condenser #1, #2, and #3 Thickness Measurement Locations Figure 4 C-310 Side Withdrawal Accumulator Tank Ultrasonic Thickness Measurements Figure 5 C-310 Product Accumulator Tank Ultrasonic Thickness Measurements Figure 6 C-310 UF6 Condenser #1 Ultrasonic Thickness Measurements Figure 7.

C-310 UF6 Condenser #2 Ultrasonic Thickness Measurements Figure 8 C-310 UF6 Condenser #3 Ultrasonic Thickness Measurements Note that some measurement locations have no data. This is due either to (1) the selected location was fabricated out of monel and does not require monitoring, or (2) the selected location had such a small radius that the curvature of the material made obtaining accurate and repeatable thickness measurements impossible. The second reason relates primarily to attached piping and not to the vessel itself.

Issue 2:

Please provide a brief discussion of the control specifics to accomplish a controlled cascade recycle mode (i.e., specifically indicate the level of human action necessary to maintain this state versus automatic engineered control).'

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GDP 98-0047 Page 2 of 13 -

Response to AdditionalInformation Request (TAC No. L32047)

. Ecsponse:

The main control concem is the top assay. Once product withdrawal ceases, the top product assay

- will start to rise. Starting from 1.9% assay, the top product would rise to approximately 2.5% in about 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Controlling the cascade' assays below approved levels would require additional

- steps. The preferred method to control the assay would be to withdraw " product" from the cascade and temporarily store this in surge drums, if available. Procedures are in place to manually set up.

valving and withdraw product into both the C-331 and C-335 surge drums. Withdrawing material from the top'of C-335 and storing it in surge drums would serve the same purpose. As long as the

~ withdraw rate matches the U-235 upflow rate, no assay increase will occur. During this evolution,

' the assay in C-310 can be monitored using the on-line mass spectrometers (assay machines) and the flow rates can be manually adjusted to maintain product assay. This is very similar to the way that product assay is typically controlled, by making manual adjustments to the product withdrawal rate in response to assay changes indicated by the assay machines.

If empty surge drums are not available, however, additional methods must be taken to control the j

assay. Procedures are in place that give the cascade controller several options in setting up assay I

mixing in the top of the cascade which will result in assay control. These options involve either misfe'eding normal assay feed or Bottom Overlap (BOL) feed into the top of the cascade. One of the

- preferred methods would be to manually valve the BOL feed into the top of C-335. Even after 3 days in this mode, the top assay will be blended down to acceptable levels. Controlling the assay while operating in this mode would involve continuously monitoring the cascade assay machines (or lab samples, if needed) and manually adjusting the amount of mixing flow to maintain the desired assay.

If the top of the cascade is on recycle but tails withdrawal and feeding is still operable, feeds could be manually valved off and tails withdrawal rate could be manually increased (as well as maximum Freezer Sublimer use) to drop cascade load. This would make controlling the assay easier since, at the lower power levels, less product would need to be diverted or mixed. However, during tails cylinder change-out, this would increase the rate of C-315 accumulator filling.

In conclusion, the amount of human interaction needed to operate the cascade in recycle mode involves additional manual valving to set-up the cascade in recycle mode, which could result in mis-valving of higher assay material to areas that are not approved, if not done correctly. Once set up, the mixing control req" ires manual set po_ int changes in response to assay machine (or lab sample) results. Also, the' control could require manual re-valving to reset-up the cascade with different BOL feed points as operational parameters and assay levels dictate.

Procedures referenced in the response to this issue are available at the site for review,

GDP 98-0047 Page 3 of13 Response to AdditionalInformation Request (TAC No. L32047)

Issue 3:

Please provide a brief discussion of the number of Normetex pump failures associated with the withdrawal station or, if no pump failures occurred, provide a brief discussion of the number of automatic activations of safety systems to preclude over pressurization or other failures in the pump.

Conservative estimates are acceptable.

Resnonse:

Normally, one pump in C-310 and two in C-315 are continuously in operation. Use of Normetex

. pumps as primary withdrawal compressors has been in place since about 1987 in C-310 and 1990 in C-315. Normetex pumps have operated a total of 274,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> at PGDP.

Failures resulting in a breach of UF, envelone: None.

Failures resulting in degradation of numning spiral interior surface: One. The first pump placed in operation had inferior pump spiral nickel plating technology and experienced some de-bonding of plating aller about 7000 hours0.081 days <br />1.944 hours <br />0.0116 weeks <br />0.00266 months <br /> of use. This resulted in minor damage to the spiral surface from crosion caused by plating particles between close-tolerance moving parts. Newer design spirals on all existing PGDP pumps use an improved plating method that has performed without incident.

Failures of the precision bearing assembiv: There have been five failures of the precision bearings requiring replacement or repair of a pump (bearing replacement is a shop overhaul task). All have been progressive events that were detected by plugging of the pump oil filter with metallic dust / flakes. All failures have been confined to one of the three crankshafts. During these failures, instability or impairment of UF pumping function was not evident, and no damage to the UF 6

6 pressure boundary resulted.

Failures due to seizine of nump snirals: The plant has experienced three cases where formation of chemical deposits in the discharge region of the spiral vanes has caused enough interference that the spiral vanes would not move freely, necessitating replacement of the pump. These failures have been unique to the C-310 West pump position. Inspections to date of these failures have not revealed evidence of damage to the spiral vanes.

Failures of pump internal discharge check valve: There have been two types of failures associated with the internal check valve. The first failure involved long temi degradation of the pump internal discharge check valve resulting in the pump's inability to restrict back flow. This type of failure is not significant for normal on-stream withdrawal operation as it only degrades pump maximum compression ratio. Pump compression ratio is not significant to on stream withdrawal operation (it

1 GDP 98-0047 Page 4 of13 Response to AdditionalInformation Request (TAC No. L32047) becomes significant only when using the pump as a vacuum pump). There have been several instances of this type of failure, estimated at 10 events. The second failure, which has occurred once, involved failure of the check valve support assembly such that portions of the assembly fell away from their normal location. As a consequence of this failure, parts can be swept downstream, and

' flow of UF can agitate these parts, or those left in the pump itself, potentially leading to piping 6

damage or debris which obstructs a valve seat. The event ofconcern did not result in damage to any components other than the check valve assembly ( support plate, tie rods, pins, bushings, seat, etc.)

itself. The check valve was repaired and the pump returned to normal service.

Trinping of Pump on High Discharge Pressure: There are several types of events that have resulted in shut down of a Normetex pump on high discharge pressure: 1) operator error causing too-rapid pressure increase while equalizing across closed discharge block valve during placement of a pump on stream,2) failure of discharge block valve solenoids (2 "Q" solenoids,1 non-safety solenoid) any of which closes the discharge block valve and back-pressures the pump, 3) interruption of downstream flow (frozen UF in piping and/or condenser or else a full accumulator and partially full 6

condenser due to prolonged cylinder filling interruptions),4) operator error in valving too much flow through a pump, discharging through the smaller vent line, and 5) operator error involving inadvertent closure of a valve downstream of the pump discharge. Note that all events are not necessarily recorded, due to variations in reporting requirements over the years. The following discussion attempts to estimate some of these failure frequencies. No discharge pressure excursion event has resulted in pump or UF. piping envelope damage. (Note: New restrictions associated with J

limitations on accumulator filling, that have been recently put in place to resolve the C-310/C-315 seismic analysis issue, will likely increase the number of Normetex Pump High Discharge Pressure Trips due to more occurrences of prolonged cylinder filling interruptions.)

1, The operator error events have been largely minimized through operator training, experience, and minor modifications to circuitry that improve operator interaction with opening of the discharge block valve. Placing a pump on stream is an infrequent operation (estimated at 2/ month for each of the 5 operating positions). Over-pressurization due to operator error is estimated to occur 1-2 times per facility (C-310 or C-315) per year.

2. Failures of a discharge block valve solenoid have occurred on two (potentially three) instances.

)

These have all resulted in high discharge pressure trips of the pumps. The last instance of this type of failure was 1996, and improved surveillance practices may have minimized this failure due to changing out of valves that exhibit problems (chattering, leaks, etc.) before complete failure occurs.

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GDP 98-0047 Page 5 of 13 Response to AdditionalInformation Request (TAC No. L32047)

3. Failures due to obstructed discharge lines are somewhat difficult to predict, since they are a combination of equipment failures and operator error. These events are less frequent in C-315, where accumulator capacity is larger, the steam / condensate system is more reliable, there are more withdrawal position options, and tails withdrawal rate is more readily controlled due to less NCS concems. This failure mte is estimated at once per year in C-315 and twice per year in C-310.

Issue 4:

Please provide information concerning the discharge location / vessel of the scale pit sump pumps.

Response

The discharge from the C-310 scale pit sump pumps goes directly to the storm sewers at the C-310 building.

GDP 98-0047 Page 6 of13 1

Response to AdditionalInformation Request (TAC No. L32047) 22 18 21 g

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GDP 98-0047 Page 7 of 13 Response to AdditionalInformation Request (TAC No. L32047)

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GDP 98-0047 Page 8 of13 Response to AdditionalInformation Request (TAC No. L32047)

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j GDP 98-0047 Page1ofI List of Commitments li. USEC will continue to implement the compensatory measures described in References 3 and 4 which have been implemented to minimize the consequences of postulated seismic failures in the C-310 facility until such time as the Justification for Continued Operation associated with the C-310 facilitj is no longer in effect and the compensatory measures are no longer required.

-.