ML20137Z083
| ML20137Z083 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 03/21/1997 |
| From: | Cahill T AFFILIATION NOT ASSIGNED |
| To: | |
| Shared Package | |
| ML20013B314 | List: |
| References | |
| KY-G-632, KY-G-632-R01, KY-G-632-R1, NUDOCS 9704230346 | |
| Download: ML20137Z083 (9) | |
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DATE OF ISSUE: March 21,1997.
DOCUMENTNUMBER: KYlG-632 4
Rev.1 i
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JUSTIFICATION THAT OPERATIONS WITH LESS THAN 15 GRAMS 2"U DO NOT REQUIRE A NUrLEAR CRITICALITY SAFETY APPROVAL (NCSA) OR A CRITICALITY ACCIDENT l
ALARM SYSTEM (CAAS)
T.J. Cahill j
Lockheed Martin Utility Services, Incorporated
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TABLE OF CONTENTS 1.0 I n trod u c tio n.................................................................. I 2.0 Proces s Descriptio n.......................................................... I 3.0 Technical Justification......................................................... I 4.0 Nucler.r Criticality Parameter Discussion.......................................... 4 5.0 Conclusions and Recommendations............................................ 4 5.1 Evaluation S ummary.................................................. 5 5.2 Conditions of Approval................
6 5.3 Limits of Applicability................................................. 6 5.4 Criticality Safety Related Items......................................... 6 6.0 Re fe re n c es.................................................................. 7 i
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1.0 INTRODUCTION
The purpose of this document is to demonstrate that neither a Nuclear Criticality Safety Approval (NCSA) nor Criticality Accident Alarm System (CAAS) coverage is necessary for all operations involving small masses of fissionable materials at the Paducah Gaseous Diffusion Plant (PGDP).
Specifa, isotopes of U, Np, Pu, Am, Cm, Cf, Th, Pa, and Es are addressed in this report.
2.0 PROCESS DEFINITION l
A process boundary considered for the CAAS at PGDP is defined as the boundary between two unrelated areas. An unrelated area is defined as an area in which there can be no interchange of material across boundaries.m At PGDP, unrelated areas include processes performed in different rooms, or within the same room with immovable physical barriers for which there is no need to transfer fissionable material into or out of the area.
Each process or operation within the scope of this justification must be capable of measuring or conservatively estimating the isotopic mass present. Controls must be in place to assure that the mass limits on the fissionable isotopes which could be transferred into the process are not violated. Such i
controls include equipment decontamination requirements or operational limitations restricting the accumulation of fissile /potentially fissile materials.
3.0 TECHNICAL JUSTIFICATION Figure Ill.B.6(100)-2 of ARH-600m specifies the minimum critical mass for "'U at 100 wt.% to be approximately 830 grams. However, a more conservative mass of 15 grams usU is considered in this report to be consistent with the Department of Transportation (DOT) fissile exempt quantities for j
packaging and transporting radioactive material.m It would require a substantial violation of the 15 gram "5U mass limit in order to approach the minimum critical mass of 830 grams (an increase in mass by j
approximately a factor of 55). In addition, a potential criticality would require the optimization of all other parameters associated with this minimum critical mass (e.g., geometry, moderation, reflection, etc.)
and such a condition is not credible. Based on USEC-01,W a 15 gram mass of"'U does not require CAAS coverage and does not require specific handling or storage requirements to be established in an NCSA.
Specific mass limits for other isotopes are not directly available and therefore must be established.
However, the cross section libraries are not available for several actinides considered in this report and the computer code validation does not bound uranium enrichments greater than 5.5 wt% usU. Therefore, conservative estimates for the mass limits of these isotopes have been established such that neither specific NCSA restrictions nor CAAS coverage is required.
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March 1997 KY/G-632 Rev.1 The method for determining acceptable mass limits for the other fissionable isotopes discussed in this report uses the ratio of the mass limit forusU to its minimum critical mass. For"'U, this ratio is 15/840 or 1.8%. This ratio can also be used to estimate a similar mass limit for each of the other fissionable isotopes addressed in this report as discussed in ANSI /ANS 8.15.m The minimum critical mass for each isotope is also provided in ANSI /ANS 8.15. The mass limit v f isotopes aggregated together can also be estimated using this ratio. This combined mass limit is based u, the total mass of the mixture together with the mass limit of the most reactive isotope (i.e., the isotope with the lowest mass limit); however, the sum of the ratios of the mass of each isotope to its mass limit must not exceed unity.
A separate analysis completed at PGDP used a similar methodology to determine the safe handling and storage requirements for the same isotopes considered in this report
- in the form of sources and standards. This analysis established a value of the ratio for the mass limit to the minimum critical mass of 1.6% assuming worst-case accident conditions (e.g., double batching, spacing violations, etc.). This value is more conservative than the value of 1.8% discussed above and therefore is used in establishing the mass limits in this report.
The values for the minimum critical mass and the mass limit for each isotope are presented in the following table of CAAS/NCS Mass Limits. The minimum critical mass values were obtained from ANSI /ANS standards
- as identified in the table. Each of these values was then multiplied by 1.6% to obtain the mass limit for each isotope which will not require a NCSA or CAAS coverage for handling or storage.
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Rev.1 CAAS/NCS Mass Limits t
Nuclide Suberitical Mass Mas'. Limit (Mixture ofNuclides)
(g)
-(g)
U-233 540*
8.64' i
U-235 with enrichments greater than 760*
15d i
t or equal to 1.0 wt.%
Combination of U 233 and U-235 540' 8.64' Pu-238 3000' 48
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Pu-239 450' 7.2
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Pu-240 3000*
48 i
Pu-241 2006 3.2 Pu-242 3000*
48 Am-241 3000' 48
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Am-242m 135 0.208
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Am-243 30005 48 Cm-243 90*
1.44 l
Cm-244 30005 48 Cm-245 30' O.48
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Cm-247 9006 14.4 Np-237 3000' 48 Cf-249 106 0.16 Cf 251 55 0.08 Cf 252 58 0.08 Cf-250 Sd 0.08 Th-228 58 0.08 Pa-231 3000' 48 Cm-246 58 0.08 Es 254 0
0 Combination of any two or more m-
' ANSI /ANS 8.1 1983 (uranium isotopes are bound by *U and SU)
- ANSI /ANS-8.151981 Table 2
' ANSI /ANS-8.15-1981 Table 1 (requires the lowest value in Table I for mixtures) dA 5 gram limit was used for Cf-252 based on the Cf-251 limit since a computed value is not available. This is a conservative value to use since these nuclides are not fissile while Cf 251 is fissile and based upon several comparisons between thermal and fast systems, fast fission systems are less reactive than thermal systems.
'This limit is based on 10 CFR 71 requirements.
%his mass limit bounds uranium and its daughter products. This is a conservative value to use since the daughter
. products are not fissile while U-235 and U 233 are fissile and based upon several comparisons between thermal and fast systems, fact fission systems are less reactive than thermal systems.
- The mau limit for combinations of nuclides shall be based on the nuclide with the lowest mass limit. This does not apply to the combination of uranium with its daughter products.
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March 1997 KY/G-632 Rev.1 4.0 NUCLEAR CRITICALITY PARAMETER DISCUSSION This section provides a discussion of the parameters that can afTect criticality safety during the handling and use of the sources and standards.
M ass:
The masses for each isotope in any mixture acc controlled with mass limits that have been shown to be equivalent to 15 grvns of 2"U.
Enrichment:
Not controlled Volume:
Not controlled.
Geometry:
Not controlled.
Concentration:
Not controlled.
Density:
Not controlled.
Moderation:
Not controlled.
Interaction:
Not controlled Reflection:
Not controlled.
Neutron Absorption:
Not controlled.
5.0 CONCLUSION
S AND RECOMMENDATIONS 5.1 Evaluation Summary There are adequate safeguards to ensure that the mass of any isotope identified in Section 3.0 will not exceed their respective mass limits which ensure safe operations without relying on the CAAS or specific NCSA requirements. This analysis assumed an enrichment of 100 wt.% for "U and therefore 2
can be implemented for plant operation at any assay.
5.2 Conditions of Approval In order for a process to be exempted from requiring an NCSA or CAAS coverage, it is necessary for measurements to be taken or conservative estimates to be made to assure the mass limits presented in Section 3.0 are not exceeded. In addition, each process must be separated by a process boundary to prevent the transference of materials which could result in the mass limits being exceeded.
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March 1997 KYlG-6n Rev.1 5.3 Limits of Applicability The conclusions of this evaluation are applicable to processes which satisfy the isotopic mass limits in Section 3.0 assuming that the isotopic mass values can be accurately measured or conservatively estimated.' Such processes will be designated as not requiring an NCSA or CAAS coverage.
5.4 Criticality Safety Related Items There are no items related to criticality safety which need to be implemented.
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6.0 REFERENCES
I.
ANSilANS-8.3 1986, Criticality Accident Alarm System.
2.
ARP-600, Vol. II, Criticality Handbook, Atlantic Richfield Hanford Co., S/23/69.
3.
10 CFR 71.53, Packaging and Transportation ofRadioactive Material-Fissile Material Exemptions, Nuclear Regulatory Commission,4/30/92.
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4.
USEC-0l, Applicationfor UnitedStates Nuclear Regulatory Commission Certification. Paducch Gaseous Difusion Plant, updated through 3/7/97.
S.
. ANSIIANS-8.1S-l981, American NationalStandardfor Nuclear Criticality ControlofSpecial Actinide Elements.
6.
NCSE GEN-24, Request 1744, Nuclear Criticality Safety Evaluationfor the Storage and U Standards and Sources at the Paducah Gaseous Difusion Plant.
7.
ANS11ANS 8.1-1983, American NationalStandardforNuclear CriticalitySafetyin Operations with Fissionable Materials Outside Reactors.
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ENCLOSURE 1 l
Technical Justification for the Exemption of C-746-A, C-733, C-754, C-754-A, C-333 and C-757 Waste Storage Facilities from Criticality Alarm Requirements, KY/S-267, Revision 1, dated March 10,1997 i
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