Creating a baseline radiological standard for the waste isolation pilot plant underground

Abstract

The Waste Isolation Pilot Plant (WIPP) is a deep underground geological repository for defense transuranic wastes. The creation of a full baseline radiological standard for the WIPP underground is essential in order to evaluate and account for the influence of the naturally occurring radioactive materials, and to prepare for any suspected contamination or the very unlikely event of a real accident scenario. In this report, we describe the establishment of the baseline information using the gamma background dose rate measurements and the salt rib smears of surface removable alpha and beta activities throughout the WIPP underground. The average background gamma dose rate in the WIPP underground is 8.27 × 10⁻⁹ ± 1.65 × 10⁻⁹ Gy/h while the gamma dose rate on the WIPP surface is 3.46 × 10⁻⁸ ± 1.65 × 10⁻⁹ Gy/h. The overall surface average alpha activity in the underground is 8.52 × 10⁻⁵ ± 1.22 × 10⁻⁴ Bq/cm² (at 1σ level) with the minimum detectable activity (MDA) of 4.81 × 10⁻⁴ Bq/cm². The overall surface average beta activity is 8.25 × 10⁻⁴ ± 8.17 × 10⁻⁴ Bq/cm² (at 1σ level) with the MDA of 3.19 × 10⁻³ Bq/cm². This baseline standard will be beneficial to the overall WIPP operational facility, ensuring the worker safety and adding to public confidence in the operation of the WIPP.

Keywords:

• Background radiation
• Radiation protection
• Radiological standard
• Salt mine
• Transuranic waste
• Waste disposal

Acknowledgements

The authors would like to thank Ricky Whiteley for his generous assistance in drilling the salt samples throughout the WIPP underground and the shaft crews for their assistance in collecting salt samples from the shafts. Thanks are also extended to Pete Allen for his assistance in Figure 1 and to Marsha Beekman for her careful review and suggestions to this report. Funding and support to Hung-Cheng Chiou are provided by DOE Radiation Sciences Fellowship Program at University of Pittsburgh, DOE Carlsbad Field Office and Washington TRU Solutions.