ML19220C864
| ML19220C864 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/30/1979 |
| From: | NRC COMMISSION (OCM) |
| To: | |
| References | |
| NUDOCS 7905160008 | |
| Download: ML19220C864 (6) | |
Text
e fp -) tb April 1979 REACTOR DECOM'4ISSIONING - A SU":!ARY Starting in FY 1975 studies were initiated through our contractor Battelle Pacific Northwest Laboratory on nuclear fuel cycle facilities and in FY 1976 on light-water reactors. To date, detailed reports have been received on an annotated bibliography, NUREG/CR-0131, a fuel reprocessing plant, NUREG-0278, a small oxide fabrication plant, NUREG/CR-0129, and a large pressurized water reactor, NUREG/CR-0130.
Studies are still underway on other fuel cycle facilities and on a large boiling water reactor.
It was planned to conduct decommissioning studies for reactor plants that have been in accidents, but those studies have not been initiated yet.
The study of the pressurized water reactor may have some applicability to the Three Mile Island situation. However, it must be remembered that the study was for a reactor plant that had experienced a normal lifetime of 40 years without an accident.
It was assumed that the core was intact and that contamination inside and outside of the building was typical of normal operation, that is a person could walk right into the containment building.
For a facility that had experienced an accident additional work will be required if the core is damaged and there is a higher than normal level of contamination in the buildings. 'When it is possible to determine the cost of this additional work a good estimate of the decommissioning cost can be made by adding it to the costs from the Battelle report.
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_2-To repeat, we do not have estimates for an accident situation but will review here the results we have for a non-accident case.
In this case a large pressurized water reactor power station like the Trojan plant in Oregon, having a capacity of 1175 MW electrical compared to 906 MW electrical for Three Mile Island, was conceptually decommissioned by three dif ferent modes.
These included:
1.
Immediate dismantlement; 2.
Safe storage for 30 years to allow for some decay of the radioactivity follcwed ay dismantlement and, 3.
Entombment.
The ground rules for conducting the study wer'e:
1.
Methods used to acccmplish the decommissioning must utilize presently available technology; 2.
The effort was carried out within the framework of existing regulations; 3.
The decommissioning staff was drawn largely from the operating personnel of the station; 4.
Decontamination of the dismantled facilities was to achieve a level to permit unrestricted use of the property; 5.
Decommissfor.ing was to be conducted to provide the required safety for the decommissioning worker and the public; 6.
All radioactive materials except the fuel were to be shipped to a licensed burial site for disposal;
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Decommissioning took place 40 years a f ter the start of construction of the plant.
Of this period, 30 years involved active operations; 8.
The facility and its site were to have radioactive contamination typical of plant that had been in operation for 30 years.
Starting with detailed drawings of the facility, highly detailed step-by-step plans were developed for decommissioning it.
Estimates of the radiation expisurcs to war!<nen and public and of the costs of labor, materials and services including such things as insurance were made.
These various estimates were then summed to obtain estimates of the safety and costs for the various parts of the facility and for the total plant.
The immediate dismantlement mode consists of those actions required to remove all radioactive or contaminated materials from the facility, thus permitting unrestricted release of the property. This mode required six years to complete starting with detailed plans and preparation two years before reactor shutdown. The major steps consist of:
1.
Defuel the reactor and ship fuel to storage or a high-level repository; 2.
Make a detailed radiation survey of the whole facility and its equipment to establish decontamination requirements; 3.
Chemically decontaminate as much of the equipment and facility as possible;
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. 4 Segment and package for disposal all remaining radioactive componet 's such as reactor pressure vessel and its internals, steam g erators and piping; 5.
Mechani ally decontaminate any remaining conta-if nated surfaces such concrete shielding walls; 6.
Evaporate and/or solidify all radioactive liquids and process solutions and package for disposal; 7.
Ship all radioactive wastes to licensed disposal burial grounds; 8.
Demolish remaining non-radioactive structures if required; 9.
Backfill and landscape.
The safety evaluation of dismantlement showed c very small public exposure during the deccamissioning operaticas of 22 man-rem, mainly associated with the transportation of die radioactive wastes.
The occupational exposure was 1200 man-rem spread over the four years of the decommissioning operatica.
The estimated costs for this mode was $42 million.
The safe storage mode follcwed by deferred dismantlement allcws a reduction in the occupational and public exposures by a factor of over 2.5.
This mode consists of:
1.
Refueling and snipping the fuel to storage or repository; 2.
Chemical decontamination and/or immobilization of accessible contamination in the facility; 3.
Solidification and packaging of all radioactive liquid wastes; nC
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Disposal of all processed radioactive wastes at a licensed burial facility; 5.
Erection of physical barriers to prevent entry into radioactive and/or contaminated areas; o.
Operation and maintenance of protective systems such as radiation, intrusion, and fire detection systems as well as electrical pcwer distribution systems; 7.
Periodic surveys and inspections of the facility and site.
The safe storage period would be folicwed by dismantlement much as indicated above under immediate dismantienent. The reduction in occupational exposure is about optimal after 30 years of safe storage since there is little further decrease thereafter.
The safety and costs esticates are as follows for safe storage with deferred dismantlement:
Exposure, Man-Rem Costs Public Occupational
$ Millions Preparations for Safe Storage tk g.
450 12.6 Surveillance for 30 Years Neg.
14 2.2 Deferred Dismantlement 3.5 24 37.0 Totals 3.5 488
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. Entombment is a mode of decommissioning used in the past for relatively small reactors. It consists of placing the majority of the highly radioactive materials from the facility in the containment building and sealing it in concrete.
Although this allows a reduction in occupational exposure, it results in sealing up some radionuclides 94 (Nb and Ni S9) that have very long half lives, 20,000 and 80,000.
The major problem here is that it is difficult to assure the integrity of any structure for hundreds of thousands of years, the time required for the decay of these nuclides.
A preliminary cost estimate for entombment is $30 million and the associated occupational dose is 900 man-rem.
Entombment might require 5 years, the first two of which would take place prior to reactor shutdown.
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