ML20206E146
| ML20206E146 | |
| Person / Time | |
|---|---|
| Site: | 07000938 |
| Issue date: | 04/30/1999 |
| From: | NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | |
| Shared Package | |
| ML20206E123 | List: |
| References | |
| 70-0938-99-201, 70-938-99-201, NUDOCS 9905050033 | |
| Download: ML20206E146 (8) | |
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' U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS Docket No.: 70-938
- License No.: SNM 986 Report No.: 70-938/99-201 Licensee / Facility: Massachusetts institute of Technology Location: Cambridge, Massachusetts
. Inspection Dates: March 30,1999 Inspectors: Garrett Smith, Chernical Safety inspector Dennis Morey, Senior Criticality Safety inspector
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Approved By: Philip Ting, Chief Operations Branch Division of Fuel Cycle Safety and Safeguards, NMSS 4
Enclosure 4
9905050033 990430 PDR ADOCK 07000938 PDR.
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W 2-MASSACHUSETTS INSTITUTE OF TECHNOLOGY NRC INSPECTION REPORT 70-938/99-201 EXECUTIVE
SUMMARY
. This inspection was conducted per Temporary Instruction 2600/004 to ensure that programs are in place and adequately implemented to safely handle the special nuclear material (SNM) located at the Massachusetts Institute of Technology (MIT) facility. This includes SNM currently used at the MIT facility and that being stored in vaults onsite. Areas inspected included: '
Fissile Material Operations, Fissile Material Storage, and Criticality Safety Analysis.
Fissile Material Operations The inspectors concluded that licensee fissile material operations that occur or are planned will be in such smal! quantities as to be of minor safety significance with respect to criticality safety.
Fissile Material Storaae The inspectors concluded that the licensee fissile material probably could not sustain a chain reaction by itself. The inspectors concluded that the licensee storage vault conditions would assure the criticality safety of the material. Licensee operational practices such as the spacing arrangement, locked storage, and prohibition on the introduction of reactor fuel were considered adequate to assure criticality safety of the fissile materialin storage.
. Criticality Safety Anaivsis The inspectors determined that licensee criticality analysis met the license requirement to analyze fissile material operations occurring outside the reactor restricted area and was performed in accordance with the level of risk that was apparent at the facility.
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I REPORT DETAILS
- 1. Fissile Material Operations .
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- a. Inspection Seone
- The inspectors performed a walkthrough of the MIT reactor facility tc determine the location )
of fissile material,' the extent and nature of fissile material operatior.s, and to identify any )
significant criticality safety issues. !
- b. Observations and Findinas The licensee maintains the bulk of licensed fissile material at their reactor facility in a secure l storage vault outside the reactor containment building. The fissile material consists of !
sources in the form of buttons and foils and several hundred steel and aiuminum clad i uranium dioxide (UO 2) rods enriched between 1 and 2% in (Uranium 235)23sU. No f operations were observed or identified involving more than gram quantities of this fissile material, and the inspectors observed no evidence that the licensee plans to conduct any operations involving more than a critical mass of fissile material. All operations observed )
inside the reactor containment building appeared to directly involve reactor operations. The only substantial quantities of fissile material observed by the inspectors inside the containment building was reactor fuel which is not possessed or used under SNM 70-986.
Some material in gram quantities consisting of sources and fission chambers is maintained at other campus locations. Licensee documentation indicates that this material in toto is substantially less than a critical mass and is, therefore, of minor safety significance. I
- c. Conclusions
.The inspectors concluded that licensee fissile material operations that occur or are planned will be in such small quantities as to be of minor safety significance with respect to criticality safety.
- 2. Fissile Material Storage
- a. Inspection SCoDe l In order to verify criticality safety of storage conditions, the inspectors performed a ;
walkthrough of the licensee fissile material storage vault which contains the majority of fissile material covered by SNM 70-986.
- b. Observations and Findinas The inspectors observed that the licensee vault contains a locked safe and a small rack which contain foils, buttons, and fission chambers with gram quantities of fissile material.
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' This fissile material is in gram quantities which cannot be configured to support a chain reaction. l The inspectors also observed several hundred UO2 rods stored in a wall rack and in three DOT shipping containers. These rods contained UO, enriched between 1 and 2% 23sU, w5re--
clad in steel or aluminum, were of various diameters from 1/4 to 5/8 inch, and were varicus lengths from approximately 20 to 40 inches. The rods were previously used in a reactor experiment and are slightly contaminated to that they cannot be easily transferred out of the
- facility. The normal storage condition, which is analyzed in the license and supporting
- documents, maintains the rods in bundles of 100 or less spaced 12 inches or more apart.
The licensee criticality safety evaluation for this material concluded that the effective neutron 0 multiplication factor (k ) for this configuration was less than 0.90 which precludes criticality risk due to storage.
The licensee analysis had been performed on a deterministic code called CITATION that is resident on the MIT computer. This methodology was not accessible to the inspectors for dstalled examination during a one-day inspection. The inspectors performed confirmatory calculations with KENO to examine the licensee's analytical assumptions and confirm ;
i licensee results. The Nuclear Regulatory Commission (NRC) analysis was based on the licensee supplied description of a typical 2% enriched aluminum clad rod.
I An infinite array of fully moderated rods results in a k,, of about 0.93. This result supports i the licensee conclusion that the 2% fuel elements will not be capable of supporting criticality in any configuration due to inability to obtain optimal H/X. The inspectors determined that increasing the pitch in the infinite model does not increase multiplication. The NRC KENO '
model for the infinite case is listed below.
- CSAS25 INFINITE ARRAY oF FUEL ELEMENTS j l
27GRoUPNDF4 LATTICECELL l Uo2 1 1.0 293 92235 2 92238 98 END ALUMINUM 2 1.0 293 END H2o 3 1.0 293 END END COMP SQUAREPITCH .5 .431 1 3 .52 .444 0 END 2% ALUMINUM RODS READ PARM RUN=YES PLT =YES END PARM READ GEOM GLOBAL UNIT 1 J
CoM=! ALUMINUM CLAD FUEL ELEMENT IN WATER!
CYLINDER 11 .2155 122 0
' CYLINDER 01 .222 122 0 CYLINDER 21 .25 122 0 CUBOID 31 .25 .25 .25 .25 152 -30 END GEOM j READ ARRAY
. ARA =1 NUX=1 NUY-1 NUZ=1 l
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COM=! INFINITE ARRAY!
FILL F1 END FILL.
END ARRAY READ BNDS +XB= REFLECT -XB= REFLECT +YB= REFLECT
-YB= REFLECT +ZB= VACUUM
-ZB= VACUUM END BNDS END DATA l
'END.
The licensee analysis indicated that a fully flooded array with bundles of 150 rods on a 12-inch
' pitch resulted in a kg of 0.90. For simplicity, the inspectors modeled bundles of 144 rods on a 12 inch pitch in a 12 X12 array using an optimal water density of 0.1. This model resulted in a k, of about 0.66. This result is similar to the licensee's stated result and indicates that the storage configuration is more strongly subcritical under full flooding canditions. Subsequent discussion with the licensee regarding the slight difference in the result indicated that the CITATION calculation was performed using an infinite two dimensional model and a
. deterministic methodology and would be expected to produce a more conservative result. No additionalinformation regarding how the licensee analysis was performed is available. The NRC KENO model for the lumped array case'is listed below.
.#CSAS25 10 X 10 ARRAY OF 144 rod GROUPS '!
27GROUPNDF4 LATTICECELL UO2 1 1.0 293 92235 2 92238 98 END 3
ALUMINUM 2 1.0 293 END H2O 3 1.0 293 END H2O' 4 .10 293 END END COMP SQUAREPITCH .5 .431 1 3 .5 2 .444 0 END 2% ALUMINUM RODS READ PARM RUN=YES PLT =YES END PARM READ GEOM UNIT 1 COM=1 ALUMINUM CLAD CYLINDER IN WATER!
CYLINDER 11 .2155 122 0 CYLINDER 01 .222 122 0 CYLINDER 21 .25 122 0 CUBOID- 31 .25 .25 .25 .25 122 0 UNIT ~ 2 ,
COM=! WATER REFLECTED ARRAY!
ARRAY 1' OOO REPLICATE 4 1 12.24 12.24 12.24 12.24 30 30 1 GLOBAL UNIT 3 I
COM=! ARRAY OF ARRAYS 1 MMY 2 000 ;
END GEOM !
READ ARRAY
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L ARA =1 NUX=12 NUY=12 NUZ-1' )
CoM=112 X 12 ARRAYl FILL'F1 END FILL ARA =2 NUX=12 NUY=12 NUZ-1 CoM= t10 X 10 ARRAY. oF ARRAYS!
. FILL F2 END FILL-END ARRAY READ BNDS +XB= REFLECT -XB= REFLECT +YB= REFLECT
-YB= REFLECT +ZB= VACUUM
-ZB VACUUM ~END BNDS END DATA )
END I
- c. Conclusions -
' The inspectors concluded that, under credible conditions, the licensee fissile material could not sustain a chain reaction by itself. The inspectors concluded that the licensee storage vault conditions would Ossure the criticality safety of the material. Licensee operational practices such as the spacing arrangement, locked storage, and prohibition on the j introduction of reactor fuel were considered adequate to assure criticality safety of the fissile
- material in storage.-
- 3. Criticality Safety Analysis
- a. Inspection Scope l The inspectors reviewed licensee criticality safety documentation to determine whether analysis of fissile material operations was performed in accordance with license commitments'and is commensurate with risk of criticality at the facility.
- b. Observations and Findinas License.SNM 70-986 Section 4' .1 requires that fissile material handled outside the reactor 1 restricted area be subjected to a criticality review. The inspectors reviewed Criticality Safety l Review 0-80-13 which covered the criticality safety of fuel elements. The inspectors also
. reviewed a prior license submittal which analyzed UO2 rod storage. The licensee analysis was thorough, employed conservative assumptions, and produced reasonable results.~ As j l
- noted above, the licensee based their conclusions in part upon computer code calculations
.which cannot be duplicated by the inspectors and appeared overly conservative. Licensee !
analysis supports the overall conclusions regarding the low risk of criticality at the facility. !
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- No licensee document contained identifiable double contingency analysis. The inspectors determined that documentation of double contingency analysis was not specifically required
' by the license, but double contingency was adequately implemented. The inspectors determined that multiple failures would be required for a criticality at the licensee facility !
including the introduction of additional fissile material, loss of geometry control, and flooding.
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.The inspectors determined that double contingency is met through the combination of licensee procedures, training, and engineered safety features. Licensee criticality safety analysis would be strengthened by development and retention of analytical assumptions, double contingency analysis and parametric study of relevant parameters.
- c. Conclusions The inspectors determined that licensee criticality analysis met the license requirement to analyze fissile material operations occurring outside the reactor restricted area and was performed in accordance with the level of risk that was apparent at the facility.
- 4. Exit Meetina The inspectors met with MIT management and representatives throughout the inspection.
The inspectors presented the inspection findings to members of the licensee management and staff during the exit meeting on March 30,1999. No classified or proprietary information was discussed. At the exit meeting, MIT management and staff acknowledged the findings presented. Because initial NRC calculations produced a substantially different result than the licensee had indicated, a telephone re-exit meeting was conducted on April 14,1999, to review NRC calculations and obtain additionalinformation from MIT staff. Subsequent to the re-exit meeting, the inspectors were able to successfully demonstrate the conservative nature of the licensee calculations.
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PARTIAL LIST OF PERSONS CONTACTED
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MIT
- Frank Mass 6, Radiation Protection Officer
- Edward Lau, NRL Assistant Superintendent
- Lin-Wen Ho, MITR Relicensing Engineer
- John Bernard, Director, NRC
- Thomas Newton, NRL Assistant Superintendent
- Fred McWilliams, Reactor Radiation Protection Officer NRC
- Garrett Smith, NRC Chemical Safety inspector
- Dennis Morey, NRC Senior Criticality Safety inspector
- Attended exit meeting ACRONYMS USED Kg,, Effective Neutron Multiplication Factor MIT Massachusetts Institute of Technology NRC Nuclear Regulatory Commission UO 2 Uranium Dioxide SNM Special Nuclear Material assU Uranium 235 4
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