Supervised areas

Rooms are classified according to the activities permitted, e.g. controlled areas and supervised areas, a laboratories and P laboratories. 

To facilitate the control of doses to persons, the Regulations specify criteria for designating areas as controlled or supervised areas. The underlying basis of designation is to define areas where doses may exceed 3/10 or 1/10, respectively, of the annual dose limit for employees. Areas are designated on the basis of dose rate, total activity being handled, air activity concentration and surface contamination levels. 

A supervised area is any area where occupational exposure conditions need to be kept under review even though specific protection measures are not normally needed. A controlled area is any area in which such specific protection measures are or could be required. The boundaries of a controlled area depend on the magnitudes of the expected normal exposures, the likelihood and magnitude of potential exposures, and the nature and extent of the required protection and safety procedures. 

One important issue of this phase was the conversion of the major part ( 80%) of the controlled area inside the safe enclosed plant into an operational supervised area with a dose level less than 2/ Sv, which can be entered for maintenance purposes without health physics monitoring. This area is the area outside the envelope of safe enclosure but inside the safe enclosed plant (FIG. 4), 141. 

Extensive measurements had to be carried out on the dismotmting and inspection equipment which had been mostly already in use during the 3 year time of operation. As a result 3 Mg had to be stored in the remaining controlled area, app. 183 Mg were stored within the supervised area and app. 49 Mg were released as fi ee of contamination. 

Another interesting aspect of the low contamination level of the THTR 300 plant was the release of buildings from the restrictions of the Atomic Energy Act and reduction of the controlled area to a supervised area. Based on statistical methods we were able to prove the low-level contamination statu. with an acceptable amoxmt of measurements. 

With a second amendment to the core unloading license (7/12a), no-contamination-measurements of components in the turbine hall and in the adjacent feedwater tank building and the disassembly of the steam-feedwater-cycle mufflers on the roof of the reactor hall were permitted. Only the waste water discharge station in the supervised area of the turbine hall continued to be subject to measurement after having achieved the state of safe enclosure. 

The components to be removed were installed in the supervised area of the plant. Thus they actually had to be non-contaminated. It was known, however, that certain inner surfaces of pipes had been slightly contaminated due to back streaming gas during plant operation. 

Parts of the system for which no-contamination-measurements were easy, ware brought to closed containers installed outside and stored there until approval by the authorities had been obtained. Parts for which the state of no-contamination was to difficult to prove, were packed into 2001-barrels and stored in the supervised area for the time of safe enclosure. 

Bq/cm were stored within the remaining controlled area parts witii contamination between 5 and 0.5 Bq/cm were stored in the supervised area of the remaining plant and parts with a contamination level below 0.5 Bq/cm were unconditionally released for scrapping. 

Downgrading from controlled area to supervised area... 

With the first amendment to license 7/12b (establishment of the safe enclosure) issued on July 15, 1996 HKG was allowed to change the status of rooms outside the cover of tihe safe enclosure from controlled to supervised area. Therefore it had to be proved that the surface contamination of the buildings and components did not exceed 5 Bq/cm and that the dose rate did not exceed 7.5 iSv/h in this area. In addition, HKG demanded that in rooms which should be accessible without any restrictions to persons who are not occupationally exposed to radiation, the dose rate should not exceed 2 pSv/h. 

Due to the low-level contamination of the former controlled area the change to a supervised area was achieved with a relatively small amount of measurements. The total number of contamination measurements was 2316. Only 87 measurements showed values higher than 0.5 Bq/cm. All measurements were taken in the presence of members of the Technical Inspection Service. 

All buildings outside the supervised area belonged to class CE. The turbine hall and the feedwater tank building belonged to class BE just as the health physics laboratory and some rooms of the access and safety building. Only the waste water disposal duct and parts of the waste water discharge station in the turbine hall were known to be contaminated and therefore allocated to class AE. 

In general, exposure to radiation during all activities for the establishment of the safe enclosure was significantly lower than expected. Due to the low level of contamination in the controlled and supervised areas, it was possible to furnish the radiological proof required for downgrading of the controlled area to the supervised area and for release of buildings from the supervision under nuclear law by means of a relatively small number of measurements. 

The requirements for the classification of areas as controlled areas and supervised areas are established in the BSS, Appendix I, paras I.21-I.25 [2]. Each controlled area should have a minimum number of access and exit points for personnel and for materials and equipment. 

Extension of the outer boundary of a supervised area to the site fence so as to facilitate effective management of the RPP should be considered. 

Records documenting the designation and location of controlled and supervised areas should be kept. Records should also be kept of radiation surveys, including the date, time, location, and the radiation levels measured, and any comments relevant to the measurements made. Records should identify the instrument(s) used and the individual performing the survey. 

Supervised area An area where occupational exposure conditions need to be kept under review even though specific protective measures and safety provisions are not normally needed. 

For any worker who is regularly employed in a supervised area or who enters a controlled area only occasionally, individual monitoring shall not be required but the occupational exposure of the worker shall be assessed. This assessment shall be on the basis of the results of monitoring the workplace or individual monitoring (Ret [2], para. 1.34). 

Hot water layer system instrumentation Reactor water treatment system instrumentation Demineralized water system instrumentation Active effluents system instrumentation Supervised area ventilation system instrumentation Reactor hall ventilation system instrumentation Non restricted area ventilation system instrumentation Ventilation system water supply instrumentation Pneumatic transport system instrumentation... 

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