The NRC staff is in the process of reappraising its regulatory position relative to the decommissioning of nuclear facilities.^ ' As a part of this activity NRC has initiated two series of studies through technical assistance contracts. These contracts are being undertaken to develop information to support the preparation of new standards covering decommissioning. The basic series of studies will cover the technology, safety and costs of decommissioning reference nuclear facilities. Light water reactors, fuel cycle facilities and byproduct utilization facilities are included. Facilities of current design on typical sites are selected for the studies. Separate reports will be prepared as the studies of the various facilities are completed. The first report in this series was published in FY 1977 and covered a fuel reprocessing plant;^ ' the second was published in FY 1978 and covered a pressurized water reactor, ' the third and fourth of the series were (4) published in FY 1979 and deal with a small mixed oxide fuel fabrication plant^ ' (5) and a low-level waste burial ground.^ ' This report is an Addendum to the report on the pressurized water reactor. It supplements that report by providing information on the technology, safety and costs of the entombment mode (l)Plan for Reevaluation of NRC Policy on Decommissioning of Nuclear Facilities. NUREG-0436, Office of Standards Development, U.S. Nuclear Regulatory Commission, March 1978.

On the average, days per year have maximum temperatures of 32°C and above. Annually, an average of 168 days have minimum temperatures of 0°C and below, with 40 of them at -18°C or below. The January average relative humidities at 7:00 a.m., 1:00 p.m., and 7:00 p.m. are 76, 68, and 70%, respectively. The corresponding humidities for July are 86, 55, and 55%.The average annual rainfall in the area is 610 mm. The months of May through September have the greatest amounts of rainfall, with an average during this period of 432 to 457 mm (70% of the annual total). The maximum 24-hr total rainfall for the period 1894 through 1965 was 127 mm and occurred in May. Thunderstorms, with an average annual frequency of 36, are the chief source of rain from May through September. Snowfall in the area averages 1070 mm annually, with occurrences recorded in all months except June, July, and August. The extremes in annual snowfall of record are 152 mm minimum and 2235 mm maximum.Annually, the winds are predominantly bimodal. This bimodal distribution is characteristic of the seasonal wind distributions as well. The average wind speed for spring is 11 km/hr and for the other seasons is about 16 km/hr. The maximum reported wind speed of 148 km/hr was associated with a tornado. Tornadoes and other severe storms occur occasionally. Eight tornadoes were reported from 1916 through 1967 in the county where the site is located. The probability of a tornado striking a given point in this area is about 5 X 10~ per year. For design purposes a wind velocity of 480 km/hr is assumed to be associated with tornadoes.Natural fog that restricts visibility to 0.4 km or less occurs about 30 hr/yr. Icing caused by freezing rain can occur between October and April, with an average of one to two storms per year. The mean duration of icing on utility lines is 36 hr. Diffusion climatology comparisons with other locations indicate that the site is typical of the region, with relatively favorable atmospheric dilution conditions prevailing. Thermal inversions occur about 32% of the year, and the frequency of thermal stabilities is 19% slightly stable, 27% stable, 20% neutral, and 34% unstable. B-4Data from a number of river sites used for nuclear power reactors are used to calculate the "typical" annual atmospheric dispersion pattern in an average 22.5-degree sector around the site. Dispersion factors at selected distances for the average sector are determined from joint-frequency distributions for each site.

The results reported here establish the relevance and propose a method for including biotic transport in the assess111ent and 1 icensing process for commercial low-level waste disposal sites. Earlier work identified the biotic transport mechanisms and process scenarios linking biotic transport with does to man, and developed models for assessment of impacts. !n this, the second phase of the project, we focused on a review of the sub-models of the B!OPORT computer code and scenarios that were developed in Fhase I. Also site specific assessments of the relevance of biotic transport were conducted for two commercial low-level waste disposal facilities. The resulting Case calculotions indicate that the current BIOPORT/f•1AXI1 models predict lower doses than the previous ordPr-of-magnitude estimates developed in Phase I. However, the resulting doses, depending on model and scenario assumptions, range from the same order-of-magnitude to an order-of-magnitude lower than the doses from the comparable intruder-agriculture scenaric. The efforts to review and enhance the BIOPORT model resulted in the following: • no change in the sub-model representing waste package form de campo~. it ion 4.4.1 Cover Cor1figuration 4.4.2 Erosion Rates. .. . 4.4.3 Plant Populations. . 4.4.4 Animal Populations o o 0 0 4o4o5 ~Jaste-Package Form Integrity \' 1 •i iii 1.1 1.1 2.1 2 .I 2.2 2.4 2.5 2.5 2.7

We greatly appreciate the guidance, assistance, technical review, and encouragement offered by these individuals in the development of the methods and philosophy applied in this report. We would like to thank Jaime Lara for converting the ONSITE program for execution on a personal computer, and for updating, enhancing, and testing the computer program. We would like to thank Gus Rodriguez for his careful checking of dose conversion factors included in this software package and Joe Soldat and Bill Farris for their helpful technical review of the mathematical models contained in this document. We would also like to thank Kay Hopkins and Carolyn Schauls for their contributions in typing, organizing, and correcting the draft and final manuscripts. Finally, we would like to thank Virginia Brauns for her editorial assistance in the preparation of the manuscript.

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither The United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability of responsibility for any third party's use, or the results of such use, of any information, apparatus, product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights. DO NOi m,:^:Ji-llM' m ^^fcKi II-u'l.- .