ML20237C699
| ML20237C699 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 08/18/1998 |
| 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-98-0172, GDP-98-172, TAC-L32047, NUDOCS 9808240077 | |
| Download: ML20237C699 (4) | |
Text
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August 18,1998 GDP 98-0172 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 Criticality Accident Alarm System (TAC No. L32047)
Dear Dr. Paperiello:
The purpose of this letter is to provide a response to the NRC's request (TAC No. L32047) for i
additional information on the Certificate Amendment Request (CAR) dealing with revision of Technical Safety Requirement (TSR) 2.3.4.7, Product and Tails Withdrawal Criticality Accident Alarm System. The request for additional information was provided to USEC in Reference 1 and identified additional information required by NRC to allow final action to be taken on the subject Certificate Amendment Request. Enclosure 1 to this letter provides USEC's response to the request for additionalinformation.
I Should you have any questions related to this subject, please contact Mark Smith at (301) 564-3244.
There are no new commitments contained in this submittal.
Sincerely, D
- 5. B.
1 I),
Steven A.Toelle Nuclear Regulatory Assurance and Policy Manager k
Enclosures:
- 1. Response to Request for Additional Information, Product and Tails Withdrawal Criticality Accident Alarm System - TSR 2.3.4.7 cc: Mr. Robert C. Pierson, NRC NRC Region III Office NRC Resident Inspector - PGDP i
NRC Resident Inspector - PORTS f
Mr. Randall M. DeVault, DOE 9808240077 900818 PDR ADOCK 07007001 C
PDR m
6903 Rockledge Drive, Bethesda, MD 20817-1818 Telephone 301-564-3200 Fax 301-564-3201 http://www.usec.com Offices in 1.ivermore, CA Paduce,ti, KY Portsmouth, OH Washington, DC
Dr. Carl J. Paperiello August 18, l'998 GDP 98-0172, Page 2 References
- 1. Letter from Merri llorn (NRC) to James II. Miller (USEC), Paducah Certificate Amendment Request - Product and Tails Withdrawal Criticality Accident Alarm System,(TAC No. L32047),
dated July 9,1998.
- 2. Letter from James II. Miller (USEC) to Dr. Carl Paperiello (NRC), Certificate Amendment Request - Product and Tails Withdrawal Facilities Criticality Accident Alarm System, USEC Letter GDP 97-0061, September 15,1997.
GDP 98-0172 l
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Response to Request for AdditionalInformation (TAC No. L32047)
Product and Tails Withdrawal Criticality Accident Alarm System - TSR 2.3.4.7 Ouestion 1
Currently, the TSR would allow the in-progress cylinder to complete the filling cycle; it would not allow stopping and restarting of the filling process. As proposed, the TSR would allow stopping and/or restarting as necessary to complete the filling cycle. The staffis concerned that allowing stopping and re.staning the process introduces human interactions and/or active engineered control imut which would increase the probability of maloperation. Please provide justification for why j
L' EC believes it should be allowed to restart the cylinder filling operation once stopped. The staff has the same concern with " normal" operation of withdrawal compressors, condensers, and accumulators. Please provide additional justification for why these operations can be stopped and restarted while the CAAS is inoperable.
Response
A Nuclear Cdticality Safety Evaluation (NCSE) has been performed and the related Nuclear Criticality Safety Approval (NCSA) has established the necessary controls for operating the product withdrawal process in C-310, including operation of product condenser, accumulators, and fill stations. The NCSA established the controls to ensure that the processes are doubly contingent. The nuclear criticality controls required by the NCSA are implemented in the C-310 operating procedures. The above described NCSE/A and implementing procedures comply with TSR 3.11.
i The initiating condition that could result in an inadvertent criticality during the cylinder filling process is the introduction of UF into a cylinder that contains moderator (i.e., oil, water, etc.). The 6
NCSA controls are in place to prevent the introduction of UF. into a cylinder that contains moderator. In addition, once UF has been introduced into a cylinder in the withdrawal station, the 6
absence of moderator is demonstrated by a lack of chemical reaction between the UF and the moderator. Having demonstrated the absence of moderator at the beginning of the filling cycle, it poses no additional nuclear criticality hazard to stop and/or restart cylinder filling that is being conducted as part of a normal cylinder filling evolution under the normal procedural controls.
For other passive components, such as the accumulators and condensers, in the withdrawal process which contains liquid or gaseous UF. in normal operating evolutions, the NCSA identifies two controls required to ensure double contingency. These two controls ensure that gaseous hydrogen fluoride (HF) entrained in the withdrawal stream does not condense into a liquid which could act as a moderator. One control is to maintain the temperature of the UF. at a rninimum of 147 F. Due to the physical properties of UF., the temperature must always exceed 147 F during condensing or the withdrawal process will be stopped by solidification of the process stream. The second is that the system pressure shall not exceed 50 psia in order to prevent the condensation ofIIF vapors which could act as a moderator. This control is ensured by virtue of TSRs for the Normetex pump operation. The Normetex pump discharge pressure has a TSR Safety Limit of 45 psia, a safety system trip at 42 psia and an operational trip at 39 psia. (Safety L imit 2.3.2.1 and LCS/LCO 2.3.3.1).
This is analyzed in SAR Section 4.4.3.5.
q GDP 98-0172 Page 2 of 2 4
Response to Request for Additional Information (TAC No. L32047)
Product and Tails Withdrawal Criticality Accident Alarm System - TSR 2.3.4.7 Normal operation of the Normetex Pumps (i.e., withdrawal compressors) satisfies the double contingency principle for nuclear criticality safety. Two NCS parameters, moderation and mass, i
associated with operation of the Normetex pumps are controlled. Moderation is controlled by maintaining the integrity of the UF / oil barrier in the pump. The pump is designed such that the i
6 process gas and oil regions are separate. A failure of this barrier is required to result in the potential for mixing the uranium with a moderating material. (See SAR Section 4.4.3.7) Uranium mass is controlled through the actions of the automatic and manual pump shutdown and isolation systems.
Any maleperation/ operator error which might occur during the stopping and/or restarting of cylinder filling, could possibly result in a release of UF, but does not pose an increased likelihood of an 6
inadvertent nuclear criticality as long as the NCSA controls are met. Since normal operation of the withdrawal process is conducted at pressures significantly higher than atmospheric pressure, any accidental breach of the UF boundary would result in out-leakage of UF and could not result in the 6
6 in-leakage of moderator. The only exception to this is the postulated leakage of UF into the 6
Normetex pump housing. Pooled at the bottom of this housing is the oil reservoir. Much of the UF6 leaking into the pump housing would react with mois;ure in the air and be exhausted out the oil sump vent. As a result, this scenario is automatically detected and mitigated by the Normetex Pump UF6 leak detection system, the operation of which is ensured by TSR 2.3.4.3. This postulated scenario is addressed in SAR Section 4.4.3.7.
The only postulated scenario in which the out-leakage of UF could result in an inadvertent criticality 6
4 is a pigtail or product cylinder rupture that results in the leakage ofliquid UF. The liquid UF could 6
6 drain to the C-310 Scale Pits. A potentially critical configuration could exist if a uranium solution accumulated to a depth equal to or greater than 5 inches. This postulated scenario has been analyzed in SAR Section 4.4.3.6 and NCSA controls prevent the introduction or accumulation of moderator in the scale pit.
The NCS controls described or referenced above, coupled with the fact that UF or UO F enriched 6
2 2 to less than approximately 6 % require moderation to achieve criticality (SAR Section 4.4.3.5) and the relatively short time frame over which cylinder filling operations would continue with a CAAS outage (i.e., less than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> per TSR 2.3.4.7), makes stopping and/or restarting a cylinder filling cycle during CAAS inoperability a very low risk activity.
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