«L. Frank-Supka, D. J. Harward, S. C. Casey May 2005 INTRODUCTION This document provides an overview of the effluent air monitoring activities at the ...»
Overview of the WIPP Effluent Monitoring Program
Compliance with Title 40 CFR Part 191, Subpart A
Environmental Standards for Management and Storage
L. Frank-Supka, D. J. Harward, S. C. Casey
This document provides an overview of the effluent air monitoring activities at the Waste Isolation Pilot Plant
(WIPP), in Carlsbad, New Mexico. The WIPP Effluent Monitoring Program is designed to comply with the U.S.
Environmental Protection Agency (EPA) radiation protection standards for management and storage of spent nuclear fuel, high-level radioactive waste and transuranic (TRU)-waste at the WIPP. The standards issued by the EPA are contained in Title 40 Code of Federal Regulations (CFR), Part 191, Subpart A. The standards require the U.S. Department of Energy (DOE) to minimize radiation doses to any member of the public within the surrounding vicinity of the facility. This document includes the regulatory history of the program, a description of the sampling and analysis process, accomplishments and improvements to the effluent monitoring system, and perspectives from independent evaluations of WIPP’s effluent monitoring compliance.
The WIPP facility is now in its seventh year of operation. The first shipment of TRU waste was safely transported, delivered, and emplaced on March 26, 1999. As of March 26, 2005, the WIPP has safely handled 3,480 shipments and emplaced approximately 27,500 m3 of contact-handled (CH) TRU waste in the repository.
BACKGROUND The WIPP Facility is located in southeastern New Mexico about 26 miles east of Carlsbad, New Mexico. The WIPP is located on approximately 10,244 acres in Eddy County (See Figure 1). The land has been withdrawn from public use by Public Law 102-579, referred to as the WIPP Land Withdrawal Act (WIPP LWA). The WIPP Project is authorized to demonstrate the safe disposal of radioactive waste materials generated by atomic energy defense activities. The DOE is the owner of the WIPP facility. The facility is designed for the disposal of TRU mixedwaste (a combination of hazardous and radioactive waste).
The WIPP underground repository is excavated in the middle of a massive bedded salt formation located 2,150 feet below the land surface (See Figure 2). The WIPP repository utilizes a “room and pillar” design that allows containerized solids or solidified waste to be placed in the underground excavations called panels. Each waste panel consists of seven rooms and two access drifts. Each room is approximately 300 feet (91 meters) long, 33 feet (10 meters) wide. There are a total of ten panels planned and three of the panels have already been excavated; of the excavated panels the first one has been closed, the second is nearly filled to capacity, and the third has started the process of filling with TRU waste. The excavations of the panels are coordinated with waste receipt, minimizing the number of panels that are opened at any one time.
Figure 1. The Waste Isolation Pilot Plant Located in Eddy County (New Mexico) The underground ventilation system is split into four separate ventilation circuits.
A dedicated ventilation circuit (or air flow pathway) provides air to the disposal panels inhibiting the spread of contamination in the unlikely event radioactive material becomes airborne. Separation of the air flows is maintained by the use of a series of ventilation bulkheads until all air flows are recombined at the bottom of the exhaust shaft. A pressure differential (separating low and high pressures) is maintained between the ventilation circuits to ensure that air will flow from the nonradiation areas (locations where radioactive waste is prohibited, and the least contamination potential) to the radioactive materials areas (locations immediately next to the waste that have the highest contamination potential).
Figure 2. WIPP Layout
High efficiency particulate air (HEPA) filtration maintains a negative pressure differential between the outside environment and the waste handling environment. This provides a secondary confinement barrier against the release of radionuclides to the environment, where the waste containers themselves are considered the primary barrier. The negative pressure differential ensures that any leaks into the WHB structure will result in an inflow of outside air, which inhibits the release of airborne contamination from inside the WHB to the environment.
During the operational period, WIPP is subject to regulation under Title 40 CFR, Part 191, Subpart A, per the enactment of the WIPP LWA in October 1992 (PL 102-579). The WIPP LWA was amended in September 1996 (PL 104-201, Subtitle F). Section 9(a)(1) states the applicability requirements, “Beginning on the date of the enactment of this Act, the Secretary [the Secretary of DOE] shall comply with respect to WIPP, with: (A) the regulations issued by the Administrator [of the EPA] establishing the generally applicable environmental standards for the management and storage of spent nuclear fuel, high-level radioactive waste, and transuranic radioactive waste and contained in Subpart A of Part 191 of Title 40, Code of Federal Regulations.” Section 9(a)(2) describes the periodic oversight duties of the administrator and state, “The Secretary shall, not later than 2 years after the date of the enactment of this Act, and biennially thereafter, submit documentation of continued compliance with the laws, regulations, and permit requirements described in paragraph (1) to the Administrator, and with the law described in paragraph (1) (C), to the State.” The DOE is in compliance with the WIPP LWA requirements.
The DOE continues to comply with the EPA radiation protection standards for management and storage of TRU mixed-waste at the WIPP. The standard relevant to this document was issued by the EPA in 1985 and is contained in Title 40 CFR, Section 191.03(b). The standard requires the DOE to provide both whole body radiation dose and critical organ radiation dose for the maximally exposed individual. The standard states that “The combined annual dose equivalent to any member of the public in the general environment resulting from discharges of radioactive material and direct radiation from such management and storage shall not exceed 25 millirems (mrem) to the whole body and 75 millirems to any critical organ. The combined annual dose equivalent to any member of the public is calculated by using a combination of the site-specific data and the EPA CAP88-PC computer model output data for the maximally exposed individual (EPA, 2000).
The DOE has implemented radiation protection standards for the management and storage of transuranic waste at the WIPP. On December 30, 1994, the EPA granted approval to the WIPP on use of the shrouded probe technology for effluent monitoring (U.S. EPA, 1994). This approval letter was received from the EPA Assistant Administrator for Air and Radiation and grants DOE the approval to use the alternate approach based single-point sampling and the shrouded probe. The original shrouded probes and their transport assemblies were installed in 1988 by Westinghouse Electric Corporation personnel. The shrouded probes sample effluent air as it exhausted from the WIPP underground repository.
The DOE directed the cooperative effort of the Los Alamos National Laboratory and Texas A&M University in spear-heading the initial research and development of the shrouded probe technology, as well as being instrumental in developing the technical documentation necessary for a regulatory evaluation.
WIPP EFFLUENT MONITORING PROGRAM
The WIPP facility has three effluent air monitoring stations. These are known as Stations A, B, and C (see Figure 3). At Station A, unfiltered air is exhausted from the repository to the atmosphere. At Station B, HEPA filters are first used to filter the exhaust from the repository. When in filtration mode, Stations A and B are mutually exclusive (i.e., when air is exhausted from one Station, none is exhausted from the other Station). Stations A and B sample the same air when operating in the maintenance bypass, reduced, or minimum mode. Station C is used to sample the exhaust from the WHB. Prior to sampling activities at Station C and then venting to the atmosphere, the collective air passes through HEPA filters.
Figure 3. WIPP Effluent Air Monitoring Stations (Station A, Station B, and Station C) Station A is located at the top of the exhaust shaft and contains openings in the floor to permit access to the exhaust shaft.
The openings are designated A1, A2, A3, and A4, which contains the weather probe. The three sampling lines (A1, A2, and A3) extract air from the exhaust shaft as illustrated in Figure 4. The sampling lines are fitted with shrouded probes, which has an inner probe located concentrically within a cylindrically shaft shroud (see Figure 5).
Additional fixed-air samplers (FASs) and continuous air monitors (CAMs) are maintained at strategic locations in the WHB and in the underground repository to monitor the levels of airborne radioactivity for operational purposes.
Readouts from the underground CAMs are displayed in the Central Monitoring Room, a continuously occupied location from which WIPP facility operations are monitored.
Figure 4. Top and Side View of Exhaust Shaft and Station A
The WIPP facility uses skid-mounted FASs at each effluent air monitoring station (Stations A, B, and C) to collect representative samples of airborne particulates (See Figure 6). A FAS consists of two independent vacuum pumps;
one vacuum pump supplies the vacuum and the other functions as a backup. In the event of an external power failure, an uninterruptible power supply provides sufficient power to operate all FASs for approximately 30 minutes.
Diesel generators are available to supply electrical power should the electrical outage last longer than 30 minutes. A formal preventive maintenance program includes monthly shrouded probe cleaning activities, and when necessary, a more extensive transport line inspection and cleaning in-place. The monthly preventive maintenance and the shrouded probe conditions are observed, reviewed and evaluated by the WIPP oversight groups. Non-routine maintenance is also performed during the months when salt encrustation and moisture is most prominent. The inspection and maintenance activities, and the pass/fail criteria are described in the Station A preventive maintenance procedure. The criteria of the salt buildup on the Station A probes is stated in the WTS Preventive Maintenance procedure, PM364005, Inspection and Cleaning of Station “A” Sample Probes BLDG. 364 that states, “The limit of salt buildup at the probe inlet should be no more than 2/3 of that area. The buildup of salt blocking the shroud exhaust should be limited to no more than 1/3 of that area.” The “as found” and “as left” conditions of the shrouded probe are documented after each preventive maintenance activity. The shrouded probe that provides the sample of record for Station A has always been found “acceptable,” per the technical basis used to ensure a representative sample at the exhaust discharge (DOE/WIPP 93-043, 1993).
Controlled operating procedures are used at the WIPP facility to ensure uniform methods are used to collect, package, and transport FAS filters. The use of such procedures provides a means for demonstrating quality assurance of air emission data. At Station A, a FAS filter sample is collected, each working shift or more frequently as needed in order to assure a representative sample. At Station B, a FAS filter sample is collected weekly or as needed. At Station C, a FAS filter sample is collected weekly or as needed. Appropriate chain of custody is established and implemented for each filter sample to record sample traceability throughout the sampling and analysis process.
Filter samples from all three stations are routinely analyzed for 238Pu, 239/240Pu, 241Am, and 90Sr. The filter samples are composited each quarter for Stations B and C. Because of the large number of samples from Station A, these samples are composited monthly. Prior to the samples being submitted for composite isotopic analysis, all compliance filter samples undergo an initial gross alpha and gross beta analysis. The processing and documentation time for a gross alpha and gross beta analysis averages one week. After review and validation of the analytical data package for the filter samples, the samples are resubmitted to the WIPP Laboratories for a composite isotopic analysis to be performed. The WIPP Laboratories processing and documentation time is typically 30 to 35 business days.
The DOE is also receiving data and information from the independent sample collection and monitoring of Station A performed by the Carlsbad Environmental Monitoring and Research Center (CEMRC).
Based on the WIPP monitoring results for calendar year (CY) 1999 through 2003, a summary of WIPP’s annual effective dose equivalents is contained in Table 1 (DOE/WIPP 02-2171, 2002 and DOE/WIPP 00-2171, 2000).
These results are well below the 25 mrem per year limit to the whole body, and the 75 mrem per year limit to any critical organ as required by 40 CFR 191, Subpart A, Section 191.03(b). To provide perspective, the BEIR V Report documents (Biological Effects of Ionizing Radiation V, 1990) that the average person in the United States receives 360 mrem/year of radiation exposure.