SURFACE SAMPLING OF CONCRETE BUNKERS DOE/ERSP TECH NOTE NO.13.0 DATED: September 1978 AUTHOR: T. Crites, RI Introduction The Field Radiation Support Team (FRST) has made extensive surveys of bunker surfaces. This information has been summarized and diagrammed by J2. The DOE has only limited information about the radionuclide make-up of this contamination. During the 1972 survey, beta ratios reportedly were found to be higher on concrete surfaces than elsewhere. This led to a general assumption that the contamination is largely 90Sr. Recent discussions and various bunker disposal experiments have led to the decision to leave the majority of these bunkers as they are. In an effort to establish a method for future definition of the hazard involved, samples were taken of two concrete surfaces for radiochemical analysis. Sample Collection Surface samples were taken from two bunkers on Irene; a horizontal surface at Ivy Station 200, corresponding to FRST location 7 or 8, and a vertical surface on Ivy Station 600 FRST location 24. In each location a 10 em x 10 em area was marked off and a reading taken with the EIC pancake probe mode] HP-210. Readings were made on the "C" scale with the detector probe in contact with the concrete surface. A 30 em by 56 em (12 x 22 in.) plastic bag was taped on three sides of the designated area as shown in Figure B-13-1. A hammer and chisel were used to remove the concrete surface. Care was taken to make a smooth cut of uniform depth across the designated area. By controlling the direction of cut and holding the bag top open, but close to the top of the sample area, one can get nearly all of the chips and fines into the bag. Sample was chipped away and measurements made with the HP-210 until approximately half the apparent activity had been removed. At that time the bag was replaced with a new bag and a second sample taken until another half of the activity had been removed. The changein surface activity is given with sample number and location in Table B-13-1. The depth of each cut appeared to be about 1 mm, generating approximately 10 cc of sample at each point. Sample Results The concrete samples were submitted to the EIC radiochemistry laboratory for analysis. Results of their work are presented in Table B-13-2. Cobalt, cesium, and that 241A4m column so noted were analyzed by gamma counting. The other nuclides were analyzed using chemistry techniques described in the EIC laboratory manuals. Conelusions Bunker concrete contamination is largely due to 90s; and 137Cs. These two isotopes appear in similar orders of magnitude on the surface, but 99sp activity falls off much more rapidly as surface material is removed. Analysis for one of them does not give direct data for the other. HP-210 readings appear to track with the 90s, activity (beta contamination), decreasing in a similar fashion. Correlation between the two sample locations is not good (factor of nearly two in epm/pCi/g). This may indicate a sampling technique problem, but will require more than twotrials to determine. The HP-210 does not track with the total pCi/g present. If it becomes necessary to provide more complete documentation of bunker contamination in the certification phase, the hammer and chisel method appears to be a good starting point. B-13-1