ML20094B737

Responds to Ramos Request for Addl Info Re Expected Radioactivity Levels in Aerotest Research & Radiography Reactor Tank & Concrete Walls After Assumed 10 Yr Decay Period

ML20094B737
Person / Time
Site:	Aerotest
Issue date:	04/28/1980
From:	Newacheck R AEROTEST OPERATIONS, INC.
To:	John Miller NRC
References
NUDOCS 9511010239
Download: ML20094B737 (2)

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e AE ROTEST OPER ATIONS, INC.

AD 3455 FOSTORIA WAY SAN RAMON. CALIFORNIA 94583 .(415) 837 4248 xM 28 April 1980 James R. Miller Chief, Special Projects Branch Division of Operating Reactors Nuclear Regulatory Commission Washington, D.C. 20545

Reference:

Docket No. 50-228 License No. R-98

Dear Mr. Miller:

This letter is in response to a request by Mr. Rams to provide additional information regarding the expected radioactivity levels in the Aerotest Research and Radiography Reactor tank and concrete walls af ter an assumed 10 year decay period.

The request for license transfer dated 11 April 1980 provides as a part of the financial responsibility presentation inclusion of a plan to decommission the reactor. This plan proposes to remove all radioactive materials inside the tank and dispose of these items through appropriate methods; i.e. reprocess the fuel and package the other radioactive materials for approved burial. The remaining radioactive materials would include the tank, concrete, dirt and reinforcing steel adjacent to the reactor core location. Although these materials would be only mildly radioactive af ter a few montis decay time, it would be safer and more economical to consider an extended decay period before they are removed. Our decommissioning plan assumed a 10 year decay period.

This plan would meet the requirements of ANS 15.10 (proposed) options for decommissioning by initial entombment and delayed removal / dismantling.

Initially, af ter removal of all material inside the reactor tank, the tank will be filled with sand and a cover will be welded near the top. Concrete will be paved over the top and floor level to prepare the building for unrestricted use during the 10 year decay period. Radioactivity or radiation levels for any accessible area would meet the requirements of Table 5 in ANS 15.10 for unrestricted use. After the desired decay period, the sand will be removed and all radioactive materials will be removed if necessary until the levels prescribed by ANS 15.10 or Regulatory Guide 1.86 are attained. The assumed 10 year decay period will eliminate or greatly reduce the amount of material that must be removed.

The reactor tank is 10 feet diameter by 23 feet deep. The reactor core center is 3 feet from the nearest wall and also 3 feet from the tank bottom. The tank is surrounded by reinforced concrete with varying thickness from 6 inches to 2 feet. The closest distance f rom the fuel to the tank wall is 27 inches.

N durance fr om the fuel to the tank bottom is nearly 30 inches. Based on 9511010239 800428 PDR ADOCK 05000228

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Nuclear Rsgulatory Commission 28 April 1980 Docket 50-228 this geometrical configuration, assuming consecutive reactor operation of 1040 hours0.012 days <br />0.289 hours <br />0.00172 weeks <br />3.9572e-4 months <br /> per hour for 10 years and the typical elemental composition of aluminum, conc' rete and reinforcing bar, we have made a best estimate calcu-lation of the maximum induced activity. We would expect the results to be very conservative (high) because of the consecutive reactor operation assumption.

At the end of the 10 year operating period there would be a total of approxi-mately one microcurie per gram of rebar of radioactive iron-55 and -59. After a 10 year decay period the only significant activities in rebar would be less than 0.07 microcurie per gram. The activity from all elements in the aluminum and concrete would be below the limits established by ANS 15.10 and Regulatory Guide 1.86 2 The proposed ANS 15.10 places limits on allowable microcuries per 100 cm surface area. On this basis, we feel confident that measurements i taken as prescribed in ANS 15.10 at the internal wall of the aluminum tank i would, in effect, allow unrestricted use without removal after the 10 year l decay period. However, the rebar wf11 have a peak iron-55 activity of about l 0.07 microcuries per gram at that time. Because of the wide spacing of the l rebar it is difficult if not impossible to convert the microcurfes per gram j Talue into microcuries per 100 cm2 terms. This is further complicated by the j fact that iron-55 is a pure beta emitter (of course, with its ever present l 1 remsstrahlung radiation. ) We believe that under the worst conditions the rebar j might be up to 10 times the allowable concentration at the highest point of 1 activation. In any case, if it is considered appropriate to remove the robar in the area where it exceeds the allowable activity, the total amount of #4 rebar would be less than 50 feet. The concrete would be acceptable for unrestricted disposal, so the overall cost would be a few thousand dollars.

We suggest that it_may well be safer for all concerned to leave the tank, rebar and concrete buried in place if the interior of the tank indicates no l detectable radiation as we suspect it will be. I I

In general, we have analyzed the isotopes as given in Appendix B of ANS 15.10 for concrete, carbon eteel (rebar) and aluninum. However, we did not include cobalt in our analysis in that we can find no indication that cobalt is an l alloying element in the aluminum or rebar. If in the rebar, it would be a j trace element of about .005% and would not result in any significant activity. '

These calculated values seem to be in line with the preliminary data available from the decommissioning of the Harry Diamond Laboratory 250 KW TRIGA reactor. l They found that most of their pool structure was not very radioactive even at the core level and immediately beneath the core. However, they did have to do some concrete removal from those areas to meet the unrestricted access criteria of ANS 15.10 and Regulatory Guide 1.86.

If we can provide any further information, please contact me at your convenience.

Very truly yours, AER0 TEST OPERATIONS INC.

& Q' Richar L. Newacheck President RLN:be cc: Steve Ramos, NRC