Asse health monitoring

The assessed radiation exposure in the Asse repository is too low for there to be a proven link to cancer among members of staff. That is the result of the first step of the Asse health monitoring (GM Asse) which was presented by the Federal Office for Radiation Protection (BfS) on 10 February 2011. The BfS has assessed in retrospect the radiation exposure to the members of staff for the period from 1967 until 2008. For this purpose available measuring and employment data of the former operator Helmholtz Zentrum München (HMGU) was verified with regard to its completeness and comprehensibility and compared with data from other sources. Furthermore members of staff were interviewed on a random basis.

Reliable documentation of radiation exposure

Thus, there is for the first time a comprehensive, reliable documentation available of the radiation exposure to all 700 members of staff who had been employed at the Asse II mine during the period from 1967 until 2008. Since the beginning of radioactive waste emplacement in 1967, the Radiation Protection Ordinance in force and the licences issued by the competent federal state authorities regulated the requirements on the radiation protection monitoring of members of staff and the documentation of this data. The BfS has evaluated all available data relevant to radiation protection.

However, it cannot be ruled out that in individual cases people were exposed to higher levels of radiation that were not documented. This can only be clarified by examining in more detail the individual cases in the second step of the Asse health monitoring. For the total number of employees, though, the available database is informative and scientifically reliable.

At the beginning of 2012, also the second part of the Asse health monitoring concluded, namely the individual evaluation of the radiation exposure to the members of the Asse repository staff. For the participants of this monitoring the result of the first part is confirmed: According to the state of the art of science and technology, their individual radiation exposure on account of their occupation in the Asse mine was too low for there to be a proven link to cancer. However, it can still not entirely be ruled out that those employees who had not made use of the offer of an individual evaluation may have been exposed to higher levels of radiation that were not documented.

Objective of health monitoring

The objective of the health monitoring was to document comprehensively the radiation exposure to all 700 members of staff who were employed in the Asse repository between 1967 and 2008. Furthermore, the individual radiation exposure to the members of staff was to be assessed and the associated risk of cancer was to be evaluated.

At the beginning of 2009, a few former staff members of the Asse II mine went public. They had suffered from cancer and have been considering their work in the Asse II mine to be the cause of this. In addition to this, former employees have filed applications for recognition of the occupational origin of their diseases to the statutory accident insurances. Besides, complaints have been lodged at the offices of the senior public prosecutor in Braunschweig against the former operator.

The BfS started the health monitoring in order to accept its responsibility as the new operator of the Asse repository for the employees and to provide for the employees’ concerns. With the health monitoring the BfS also wished to address the contradictions that had been indicated by the employees in terms of their radiation exposure. The results of the health monitoring can be used by those affected in their respective proceedings.

First step of the health monitoring

Chronological sequence of the average and maximum estimated annual effective overall dose in millisieverts for the GM Asse group of employees

In the first step of the health monitoring the BfS determined a total dose for each employee. That is the radiation dose each employee was exposed to over the entire time of his occupation in the Asse mine. On average, this total dose was 12 millisievert for individual employees and maximum 115 millisievert for one employee.

For the total dose, all estimated dose values are below the limit value of 400 millisievert for the occupational life dose and, considering individual occupational years, below the limit value of 20 millisievert per calendar year for occupationally exposed persons. However, for reasons of principle in terms of radiation protection, one needs to take into account that each radiation exposure is associated with a certain cancer risk.

The radiation exposure of 12 millisievert on average and maximum 115 millisievert determined for the approximately 700 employees in the course of their occupation in the Asse mine is in a dose range which is much lower up to about the same level as the natural radiation exposure in the same period. The assessed radiation exposure in the Asse repository is too low for there to be a proven link to cancer among members of staff.

Database

All available measured data of the former operator HMGU for the time waste was emplaced (1967 – 1978), its relocation (until 1980) and for the subsequent phase (1981 – 2008) was viewed by the BfS, examined for reliability and evaluated in order to determine the occupational radiation exposure. The BfS has also used other accessible sources. Altogether the following data has gone into the health monitoring:

• The personal data of the official and operational personal dosimetry (“film badges”),
• The personal data of the monitoring of radioactive materials being taken up in the body (incorporation monitoring),
• Radiological measurement values in the mine (local dose and local dose rate),
• Radiological measurement values of the mine air,
• Radiological measurement values of the exhaust air,
• Radiological measurement values of saline solutions, and
• Notes relating to about 200 cases of contamination documented by the former operator HMGU, in particular about events occurred in December 1973, in November 1974, in December 1978 and in September 1980.

Altogether the Asse health monitoring comprises 692 persons. Among those are 433 members of staff who had been employed at the Asse II mine between April 1967 and December 2008 and for whom the possibility of occupational radiation exposure existed. For precautionary reasons, 188 employees were taken into account, as well, for whom it could not be clarified in retrospect whether they had ever worked underground. Additionally, 71 employees from external companies were included in the Asse health monitoring.

For each employee, the BfS assessed the annual dose and the total dose for the entire time of occupation in the Asse II mine. They were calculated as effective dose in the unit millisievert. The external exposure (radiation from the environment or through radionuclides on the skin) and the internal exposure (radiation through inhalation and swallowing) have been included in these values. In cases where data relating to places and times of occupation or measurement values of radiation exposure was lacking or was uncertain, conservative procedures were used, i.e. the levels of radiation exposure were assumed to be so high that – according to the best expert evaluation – the actual level of radiation exposure was safely covered.

Second step of the health monitoring

In the second step of the health monitoring, the Asse-GmbH, which was tasked by the BfS with the operation of the mine, sent letters to all former and current employees, informing them about the results of the first step. In this second step all employees were offered to be about their individual radiation dose upon request.

Applicants were requested to fill in a questionnaire. In addition to the findings of the first part, data about the handling of possibly radioactively contaminated brines, involvement in contamination cases or participation in scientific tests with radioactive sources were queried, in order for these aspects to be evaluated for each employee in the most realistic manner. Although it was not possible to close all information gaps with the help of the questionnaires and although uncertainties remained, assumptions for the assessment were made in such a way that one tried to avoid an underestimation of the radiation exposure where this was possible.

Of the about 700 members of staff taken into account in the health monitoring, 33 employees took advantage of the offer and had their personal radiation exposure determined. 22 employees filled in the questionnaire required for the assessment. Among those were also persons who had already worked in the Asse mine during the emplacement phase.

Results

Altogether the assessments of radiation exposure of individual employees confirmed the results gained in the first part of the Asse health monitoring. The second part did not indicate clearly higher exposures than were indicated in the first part. Rather, the majority of the values in the second partial step were lower, as there was now more exact data available about periods of employment, shifts underground and activities, so that uncertainties in the assessment could be reduced. Only in individual cases was the radiation exposure higher than in the first part of the health monitoring. Higher values were found for employees who had also worked for external companies in the Asse mine, apart from their work for the operator of the Asse II mine, so that they spent more working hours in the Asse mine as had been known before.

For 80 per cent of the participants of the second part of the Asse health monitoring the determined values for the occupational life dose – i.e. the radiation they were exposed to during their entire working life – were below ten mSv and only in one case slightly above 100 mSv. All values are below the respective effective limit values for occupationally exposed persons per year (20 mSv) and the entire occupational life (400 mSv).