ML20234E403
| ML20234E403 | |
| Person / Time | |
|---|---|
| Issue date: | 10/15/1987 |
| From: | Tokar M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Ebenhack D CHEM-NUCLEAR SYSTEMS, INC. |
| References | |
| REF-WM-93 NUDOCS 8801080057 | |
| Download: ML20234E403 (2) | |
Text
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00T 151987
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David Ebenhack, Vice President - _ -
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Regulatory Affairs v --
Chem-Nuclear Systems, Inc. L - . - -
220 Stoneridge Drive o< __.
Columbia, SC 29210 , _ _ _ _
Dear Mr. Ebenback:
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As a result of concerns regarding the long-term stability of High Density Polyethylene (HDPE) High Integrity Containers (HICs), the Nuclear Regulatory Comission (NRC) contracted Brookhaven National Laboratory (BNL) to (1) develop criteria for HDPE HIC structural stability, (2) analyze existing data on the creep of polyethylene, and (3) develop a computer model to use in evaluating the structural stability of these HICs. A draft methodology report has been written that describes the development of the BNL model and recommends proposed design review criteria for HDPE HICs in the form of maximum allowable values for membrane stresses, creep, and buckling stress. The criteria recommended in the report are being used to aid the NRC staff in formulating the NRC's acceptance criteria for HDPE HICs. These acceptance criteria will also be included in the NRC's Regulatory Guide on Waste Form, which is under development.
The BNL computer model determines the membrane, buckling and creep stresses for HIC geometries through a finite element analysis for time periods up to 300 years. The HICs are modeled as axisymmetric shells of revolution, corresponding to the actual design configurations. Polyethylene is modeled as a viscoelastic material, and membrane, creep, and buckling stresses are calculated for the various loads and load combinations acting on the HICs during their service life. The model compares these stresses with the recommended allowable stress values that are developed in the methodology report, and output from the computer modeling lists the finite elements where allowable stress values are exceeded.
The maximum allowable stress values developed in the BNL model methodology report are determined such that an HDPE HIC designed to specifications that will prevent the HIC from experiencing the maximum stress values will meet the requirements of NRC's Technical Position Paper on Waste Form (May,1983). The '
maximum allowable membrane stress and bending plus membrane stress reported in the methodology report are 1400 psi and 1876 psi, respectively. The maximum allowable buckling stress is determined for each HIC individually by the expressions that are explained in the appropriate sections of the methodology report. The maximum allowable creep stress is listed in the report as 765 psi.
However, after additional discussions with BNL regarding the conservatism inherent ,
in the proposed 765 psi value for maximum allowable creep stress, and taking i into consideration new data generated by BNL, the NRC has established that 1100 psi can serve as the maximum allowable creep stress value considered by the NRC ,
in qualifying HDPE HICs. l The BNL model has been run on several actual HDPE HIC designs using information l from Topical Reports submitted to the NRC for review. Results of the computer modeling analyses indicate that there may be a potential for large polyethylene containers to experience excessive membrane stresses and to exceed the proposed maximum allowable buckling stress. The BNL model also suggests that HDPE HICs could potentially exceed the proposed maximum allowable creep stress. As a 8801080057 071015 PDR WASTE WM-93 PDR: , p lffkiO lh(* .0 N /
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-n OCT 15 W e ,- I) avid Ebenhack 2 result of the work just described, it is the NRC's position that HDPE HICs-should be designed so that they do not experience excessive membrane stresses, buckling, or tertiary creep.
Therefore, to aid in expediting our review of your HDPE HIC Topical Report, we request that you submit complete information that demonstrates that your HDPE HIC design will ensure long-term structural stability as required by 10 CFR Part 61 and in a manner that is consistent with the BNL/NRC findings. This can be accomplished by demonstrating that either by (1) modification to your current designs, (2) your own analysis, and/or (3) administrative procedures, you can show that the HIC acceptance criteria will be met. The requested information must be submitted to the NRC by January 31, 1988. Failure to submit complete information-by this date would leave the NRC without the necessary bases to confirm approval or disapproval of your HDPE HIC Topical Report, and, therefore, would result in the d* continuance of the NRC review of your Topical Report.
In order to continue the expedited review of your Topical Report, the NRC staff-will complete an evaluation of your submittal by April 30, 1988.
Enclosed is a copy, of the draft BNL methodology report, entitled, " Review of the High Integrity Cask Structural Evaluation Program (HICSEP)," dated April 6, 1987. Also enclosed is a copy of the BNL computer model HICSEP, and the input and output from a sample problem used to assist in implementing the model on the NRC computer.
If you require any further information regarding this letter, the BNL methodology, the structural analysis model, or'the NRC's position regarding High Density Polyethylene High Integrity Containers, please phone me at (301) 427-4748.
Sincerely, Michael Tokar, Section Leader Technical Branch Division of Low-Level Waste Management and Decommissioning, NMSS
Enclosures:
- 1. Draft CNL Report i
- 2. Computer Listings DISTRIBUTION: (w/o encl.)
- LLW4/SF2 NMSS r/f KMcDaniel RPerson .
LLTB r/f MTokar JGreeves DAWidmayer JJSurmeier
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OFFICIAL RECORD COPY
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