Survey on actual practices of radiation dose control at the TEPCO Fukushima Daiichi Nuclear Power Plant
- Directions to prevent a recurrence provided to TEPCO and its primary contractors -
The Ministry of Health, Labour and Welfare (MHLW) summarized the results of surveys on improper measurement of radiation exposure doses using a lead plate at the TEPCO Fukushima Daiichi Nuclear Power Plant. Based on the results, The MHLW provided directions to TEPCO and its primary contractors to prevent a recurrence on 30 October 2012.
Key points of the survey results:
- No intentional improper cases like using the lead plate were identified, however, some improper cases were identified; e.g. dose data that were not correct, a case which no PAD (*1) was worn when waiting/operating at the high dose area in seismically isolated building, and a case with improper dose measurement.
- Cases requiring improvement in terms of radiation dose control were identified; e.g. shared use of PADs in the group, and PADs with too high alarm set point.
- Good employment situation; e.g. currently, there are a sufficient number of workers, and job transfer to conventional construction work for workers whose radiation exposure dose has reached to the upper limit is smoothly implementing.
*1: Personal alarm dosimeter (To be distributed for each person to identify the dose in each operation)
Based on the survey result, the MHLW provided the following instructions to TEPCO and its primary contractors, with emphasis on preventing recurrence of similar cases.
- Inspection of radiation exposure dose data management methods and implementation of recurrence prevention measures
- Promotion of personally-allocated use of PADs, and facilitating use of protecting clothing with a clear window on the chest enabling to confirm the PAD from outside (Tyvek suit)
- Improve accuracy of dose measurement by restricting the wearing of glass badge (*2) during the operation
- While measurement by the glass badge should in principle be recorded, however, when the PAD reads a somewhat higher level than the glass badge, the measurement by the PAD should be recorded.
- Set a warning level close to the daily maximum allowable radiation exposure dose.
- The dose notification should be given in writing to the workers.
- Implement rotation among low-dose work and high-dose work, and enhance communication between employers and workers whose radiation dose reached to the upper limit.
*2: Cumulative personal dosimeter (Distributed individually, possible to measure monthly cumulative dose)
- Attachment 1: The results of the survey on the conduct of radiation dose control at the TEPCO Fukushima Daiichi Nuclear Power Plant (Overview) PDF 40KB
- Attachment 2: The results of the survey on the conduct of radiation dose control at the TEPCO Fukushima Daiichi Nuclear Power Plant PDF 668KB
- Reference: Actions in response to improper radiation dose measurement at the
TEPCO Fukushima Daiichi Nuclear Power Plant, Press release (24 July 2012) PDF 204KB