ML20216D785

Compliance Evaluation Rept Approving Amend to Coc GDP-2, Revising SAR Section 4.1.1.2.3.5,to Provide for Addl Identified Criticality Accident Case for X-333 Cascade Bldg Re Previously Approved Increase in Assay Limit to 3 Percent

ML20216D785
Person / Time
Site:	Portsmouth Gaseous Diffusion Plant
Issue date:	04/09/1998
From:	NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:
Shared Package
ML20216D783	List: ML20216D779 ML20216D785 ML20216D801
References
NUDOCS 9804160009
Download: ML20216D785 (2)

Text

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l DOCKET: 70-7002 l

l CERTIFICATE HOLDER: United States Enrienment Corporation Portsmouth Gaseous Diffusion Plant Portsmouth, Ohio 1

1

SUBJECT:

COMPLIANCE EVALUATION REPORT: APPLICATION DATED FEBRUARY W 1997, ADDITIONAL HYPOTHETICAL CRITICALIT' . ,ASE FOR X-333 BACKGROUND By letter dated February 25,1997, United States Enrichment Corporation (USEC) requested an amendment to the certificate of compliance for the Portsmouth Gaseous Diffusion Plant (PORTS). The request is to revise the Safety Analysis Report (SAR) Section 4.1.1.2.3.5 to provide for an additional identified criticality accident case for the X-333 cascade building related to the previcusly cpproved increase in assay lindt to 3 percent. By letter dated July 8,1997, the staff requestad additionalinformation. USEC responded to the request by letter dated August 7, 1997.

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USEC's certificate amendment request involves changing the hypothetical criticality case for the X-333 cascade building in the SAR Section 4.1.1.2.3.5, " Estimated Radiation Doses Resulting l from a Criticality in the X-330 and X-333 Buildings." The need for this amendment arose out of an increase iri the maxirnum enrichment at which the X-333 cascade building was to be i operated. The Department of Energy (DOE) approved an increase in the maximum enrichment l suel from 1.33 percent to 3 percent prior to certification by the NRC. The 3 percent limit was accepted by the NRC during the certification process. In reviewing the SAR dated November 8, 1993, USEC determined that the X-333 cascade building had not been analyzed to determine the imp.4t of the 3 percent enrichment on the hypothetical criticality cases for that facility. This l

analysis was performed by USEC and the amendment request provides the update for the SAR

( to reflect that ana!ysis.

l l An enrichment of at least 1 percent is required for criticality in the cascade. During operations at l 1.33 percent, the closest cell to the area control room (ACR-1) that could have 1 percent

! enrichment was determined to be Unit X-33-8 at a distance of 240 feet from ACR-1. At the maximum gradient, the enrichment in this unit would be 1.2 percent. For these conditions, and an exposure period of 50 minutes, a hypothetical criticalit/ accident in Unit X-33-8 was calculated to produce a dose of 0.005 rem to operators in ACR-1. The magnitude of the criticality event

, was estimated in the SAR to be 2x10 " fissions. Eight inches of concrete provide some shielding to personnel in ACR-1. During regular shift there are about 50 individuals present in the X-333 cascade building, mostly in ACR-1. During off-ahift hours there are about 10 individuals present.

The increase in enrichment to 3 percent meant the closest unit having enrichment exceeding 1 percent was now Unit X-33-6 at a distance of 40 feet from A%-1. A' this shorter distance and enrichment, the dose to personnel in the event of an inadverent cridcdity was calculated to be 49 rem. This high dose results not only from the clowr distance, bf, also the fact that the higher enrichment can produce a criticality with different configuration having greater neutron leakage.

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Tha hypoth:ticel criticality scan:rio involvts Irakage of w t cir into ths ciscida producing a slow I build-up of a UO2 F2 deposit. USEC has calculated that once criticality is achieved, the nuclear j reaction from such an event is a protracted pulse of 50 minutes duration. Personnel would only l recpive the 49 rem dose if they remained in ACR-1 for the entire 50 minutes. USEC estimates that the criticality alarm system would activate 10 minuter 'nto the transient. This late detection l

l is expected due to the low power levels early in this slow transient. Personnel evacuating at this l l 10 minute point would have received only 5 rem. l l Due to allowed higher enrichment levels in the X 330 casccde building, the same hypothetical l criticality scenario could occur right above the ACR. The dose to personnelin the ACR from this I hypothetical criticality scenario would be 124 rem. Therefore, this type of accident with a higher dose had already been described in the approved certification SAR. The probability of such events, though, in either the X-333 or the X-330 cascade buildings remains highly unlikely since these operations are conducted in accordanca with either the double contingency principle, where two unlikely, independent, and concurrent changes in process conditions would be required before a criticality accident would be possible, or in accordance with the Technical Safety Requirement for operations where only a single contingency is relied upon.

A criticality event in the X 333 cascade building has minimal impact offsite. Figure 4.1.1-3, page 4.1-80, of the SAR indicates that a criticality of 2x10 " fissions could produce a dose from direct radiation about 0.03 rem at 1200 feet. At its closest point, the site fence line is over 1000 feet from the X-333 cascade building. Thus the direct dose to any person offsite is smallin comparison with NRC's public dose limit in 10 CFR 20.1301.

The amendment application was determined to be significant pursuant to 10 CFR 76.45. That determination was based upon the increase in consequences in ACR-1 from 0.005 rem to 49 l l rem. A thirty day comment period was noticed on January 5,1998 in the Federal Reaister l (63 FR 274). No comments were received by the end of the comment period on February 5, l 1998. l ENVIRONMENTAL REVIG lssuance of the recWted amendment to the Portsmouth Certificate of Compliance (GDP-2), to amend the SAR, S6 %n 4.1.1.2.3.5, is suDject to the categorical exclusion provided in 10 CFR 51.22(c)(19) and will not have a significant impact on the human environment. Therefore, in accordance with 10 CFR 51.22(b), neither an environmental assessment nor an environmental impact statement is required for the proposed action.

CONCLUSION The estimates underlying the criticality dose calculations were reviev/ed by NRC staff and found to be reasonable and with a degree of conservatism consistent with the remainder of the

accident analysis in the SAR. The increased consequences in the hypothetical criticality l scenario for the X-333 cascade building are bounded by the same hypothetical criticality scenario l in the X-330 cascade building. The NRC staff feels that sufficiently adequate safety centrols are l currently in place at PORTS to prevent and mitigate this accident. Other than the proposed l modification to the PORTS SAR, this amendment would likely not require any other changes to plant operations. The NRC staff recommends approval of this amendment Region lll staff have no objection to this proposed action.

Pnncioal Contributors Charles Cox Yawar Faraz Dennis Darnon DISTRIBUTION Docket 747002 NRC FILE CD TER PUBLIC NMSS r# NMSS Dir Off r# FCSS r# SPBrn "See prewous concurrence CCm WSchenk FCOL PHdand RHf DHamand RHf OFC *SPB *SPR *SPH "SPD *SPB NAME CCmg VFarar DHmdicy DMamn RPierson DATE M3 M M4% M5M Wrm wrm