Andrew J. Lombardo, CHP Vice President Safety & Ecology Corp. April 2011

Transcription

1 Andrew J. Lombardo, CHP Vice President Safety & Ecology Corp. April 2011

2 Completed Project 1 Overview 14 acre impacted soil area 6 million ft 3 of thorium contaminated soil Traditional approach DCGL = 3 pci/g Th-232 New segregation threshold = 30 pci/g Th-232 Traditional TEDE = 0.25 msv (25 mrem) New TEDE = 0.02 msv (2 mrem)

3 Completed Project 1 Overview

4 Completed Project 1 Overview

5 Completed Project 1 Overview Old T & D Volume = 5 million ft3 New T & D Volume = 2 million ft3 Same residential farmer exposure scenario used for both old and new dose assessment Average activity concentration of < 30 pci/g material is 18 pci/g Old Cost = $120 million, new cost = $20 million

6 Completed Project 2 Overview Elevated levels of radioactivity were discovered in soils and sediments at a former NASA test reactor site undergoing decommissioning DCGL values (cleanup standards) derived and NRC approved Surrogate (Cs-137) radionuclide DCGL 0.38 Bq/g (10.3 pci/g) At this cleanup level, using a traditional remediation approach, approx 51,700 MTs of material slated for offsite disposal

7 Completed Project 2 Overview Over-excavation of the impacted area MACTEC s Orion ScanSortSM Radiological Soil Sorting Survey System: Detects gamma-emitting radionuclides as the soil on the conveyor belt moves past the active area of a fixed platform radiation detection system Assayed material is separated into two piles: Above criteria - Offsite disposal Below criteria - Re-use as onsite backfill

8 Completed Project 2 Overview Segregation System Layout

9 Completed Project 2 Overview Soil segregation system calibrated using large-volume soil calibration standards prepared at the site NIST traceable standards Stockpiled material loaded into a rotating trommel discharged to the survey conveyor mounted with a strikeoff bar which maintained a max belt fill depth of 15cm Typically conveyor speeds ranged from cm/s beneath suspended NaI detectors Gamma spectrum collected for 122cm of travel (observation) and isotropically compared to segregation

10 Completed Project 2 Overview Additional inputs/outputs helped manage the assay and sorting process Belt speed, depth, density, and weight are monitored for consistency Audio and visual alarms for system status Control of additional material conveyors

11 Completed Project 2 Overview Segregation System and Conveyor Belts

12 Completed Project 2 Overview

13 Completed Project 2 Overview The 211 batches had an average Cs-137 concentration only slightly higher than background levels Maximum mean concentration of Bq/g (0.4 pci/g) Less than 1% of material was diverted due to elevated radioactivity Over 88,000 MTs of material was excavated and sorted during the project More than 1,636,000 measurements taken by the primary soil segregation system, assaying 211 batches

14 Completed Project 2 Overview Segregation System Output and Lab QC Data

15 New Project Overview SEC has been awarded soil remediation of an approximate 100 acre site with 50,000 tons of impacted soil identified during characterization. The radioactivity present at the site resulted from the use of contaminated scrap ferrous metal to scrub chlorine gas released during the magnesium production process. The impacted soil resides in 4 separate areas of the site. However the impacted material is distributed some what randomly through the surface to depths of 20+ feet.

16 Project Overview SEC s excavation approach includes an iterative process for surveying, delineating, and excavating areas of contamination as well as an innovative approach to segregating excavated material to minimize volumes for off-site disposal. SEC anticipates this approach will reduce the overall volume for off-site disposal by approximately 74%, resulting in approximately $10M in savings. SEC has implemented this approach at Plum Brook Station in Sandusky, OH, and has received NRC approval of the approach.

17 Excavation/Survey Process Prior to each excavation iteration, a 100% coverage gamma/global positioning system (GPS) walk-over survey is performed to map the floors and walls of each excavation. A Trimble GPS unit coupled to a Ludlum Model inch by 2-inch sodium iodide (NaI) detector, Large Area GPS Survey System (LAGSS), is used. The results of the survey are downloaded and plotted to provide a visual map of areas for excavation and the areas of the floor and walls with residual contamination are marked.

18 Excavation/Survey Process The gamma survey threshold for excavation will be results greater than the gamma background count rate. The gamma background count rate will be determined prior to the survey as well as the threshold for count rates significantly above background at the 95% confidence interval. Based on the results of the survey and historical characterization data, excavation depths will initially be a minimum of 1 foot in impacted areas.

19 Excavation Survey Process Impacted material is excavated and dewatered as necessary to reduce moisture to < 30%. Dewatering is performed along the banks of the excavation on poly liners or soil is transported to the soil preparation area and dewatered. Large debris is removed and stockpiled separately. After initial excavation is complete, the new surface area is surveyed using the same technique.

20 Excavation Overview Excavation continues until the gamma surveys indicate the entire surface area is below derived concentration guideline levels (DCGLs). At this point, SEC will perform a pre-final and FSS of the excavation. Following FSS and independent verification, SEC will backfill the areas, restoring the ditch to original contours and finishes.

21 Debris Segregation In addition to segregating and minimizing soil volumes, SEC will minimize volumes of debris requiring disposal. Debris will be segregated, surveyed, managed, and disposed of as follows: Clean debris will be released for unrestricted use and sent to a local recycler or C&D Landfill for inexpensive disposal. Contaminated debris that meets the acceptance for BSFR will be size reduced using an excavator and shear, packaged and shipped to Impact Services, Inc. (Impact) in Tennessee for processing and disposal at Chestnut Ridge Landfill.

22 Soil Acceptance Criteria COC BKG DCGLw DCGLemc (pci/g) (pci/g) (pci/g) Ra Th Th Total U

23 Soil Acceptance Criteria Sum of Ratios Apply as follows: SSSSSS = RRRR TTh TTh UU238 + UU235 + UU Using gross activity in pci/g.

24 Soil Segregation The MACTEC Orion Series SS Soil Segregation System will be used to segregate soil. The segregation system combines gamma scanning (rolling detection) with gamma spectrometry, the two features of Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM)-based FSS. The conveyor counter utilizes a fixed platform radiation detection system mounted over a rubber belt conveyor.

25 Soil Segregation As excavated soil is ready, the soil will be placed on the vibrating screen to further remove debris and large pieces greater than 6 inches in diameter and then placed on the segregation belt. The segregation system will be set to sort the soil into stockpiles of greater than and less than the DCGL/SOR. All of the material passing through the segregation system as < DCGL/SOR will be stockpiled, sampled, and set aside for use as backfill on-site.

26 Soil Segregation The material passing through the segregation system as > DCGL/SOR material will be stockpiled in several stockpiles. Each stockpile will be characterized by volume and average activity concentration. The availability of various activity concentration stockpiles will allow the volumetric averaging of each container or conveyance volume to an activity concentration less than the disposal facility waste acceptance criteria (WAC) to ensure WAC compliance while maximizing the activity allowed in each conveyance to achieve the most cost-effective disposal options.

27 MACTEC SS Series System SEC has selected the MACTEC soil segregation system based on the excellent performance and service MACTEC has provided on previous soil segregation projects. In order to maximize the effectiveness of the soil segregation process several key inputs are determined prior to operation. The MACTEC system will be presented next. By understanding the process the system uses to determine the activity concentration of a set volume of soil we can determine the best set of inputs to achieve the objectives of the project.