Estimation of Exposure Dose Due to Radon in Radioactive Spring Water

—Case study of a hot spring facility in Mie prefecture—

Abstract

  In Japan, the Hot Springs Law and the Guideline of Analytical Methods of Mineral Springs (revised) classify springs containing 74 Bq/kg of radon as “hot springs” and those with radon levels exceeding 111 Bq/kg as “medical springs” called “radioactive spring”. Radon is a noble gas that easily diffuses in air.
  This study evaluates exposure dose due to radon when using a radioactive spring at a spa in the Toriido area, Komono town, Mie district, Mie prefecture.
  After bath water was supplied through a pipe from hot spring storage tanks to bathtubs, only 5.3-18.0% of radon remained in the water. Two days later, only 0.3-0.4% of the radon remained in the bath water due to radioactive decay and diffusion into air being increased by bathing and recirculation filtering.
  The calculated effective dose from bathing in radioactive hot spring was 2.8-12.0 nSv, and that from drinking radioactive hot spring water was 5.1-23.3 nSv. To determine the total effective dose from use of the hot spring facility that may effects on human health, it is necessary to analyze radon concentrations not only in the water but also the surrounding air.