Sesión 6 “RECREO RUIDOSO”
3. Conclusiones
Table 6 shows data related to the dismantling work for the biological shield concrete. The diamond sawing and coring technique and the water jet cutting technique both were able to remotely cut blocks from the planned location. In cutting by the water jet technique, the cutting slits were wider than those of the diamond sawing and coring system.
Furthermore, since the nozzle had to be repeatedly moved over the same path to cut the embedded reinforcing bars, the cutting slits in the concrete were deeper than planned.
This increased the production of sludge.
The cutting speed of the diamond sawing and coring system was strongly influenced by the material being cut. For example, the blade traveling speed was slower for the steel liner and the embedded reinforcing bars than for concrete. Also, the coring procedure needed much time to bore adjacent holes at the back of the concrete blocks being - data on waste generation weight of waste : 178.7 tons (concrete)
removed.
Generally, the cutting time per unit of weight of dismantled concrete needed by the diamond sawing and coring system was longer than the time needed by the abrasive water jet system. In addition, diamond sawing could not be used for the thick lead tubes covering the neutron detector guide tubes. However, the abrasive water jet cutting system cut the concrete, embedded reinforcing bars, and the lead tubes. This resulted in a higher cutting efficiency in total. Although the controlled blasting can demolish the reinforced concrete most effectively, it is not suitable for demolishing the highly activated shield concrete.
5 Management data
Various management data on the dismantling work have been accumulated since the start of the JPDR dismantling. These data are stored in the decommissioning data base and used for future commercial power reactor decommissioning as well as for the management of JPDR dismantling activities. Typical management data collected during the JPDR dismantling activities are illustrated in Fig. 11.
Table 6 Data related to the dismantling work
Cutting operation : Diamond sawing and coring
: Abrasive water jet
: Controlled blasting Manpower
expenditure
: 2,300 man-days : 5,400 man-days : 3,700 man-days
Radiation exposure : 7.40 man-mSv : 8.80 man-mSv : 2.07 man-mSv
Duration : 107 days : 190 days : 153 days
Cut blocks : 9.3 tons : 29 tons : 200 tons
Cutting time : 260 hours : 120 hour : —
Fig. 11 APPENDIX:—Dismantling schedule, manpower expenditure, radiation exposure to workers, and decommissioning waste produced during JPDR dismantling activties (through September 1992)
(1) Manpower expenditure
The cumulative manpower expenditure from the start of the dismantling through December 1992 was 77,000 man-days. During this period, approximately 45 workers per day and 140 workers at the peak time have been engaged in this dismantling. In the JPDR dismantling, the approximate job analysis consists of 21% for the supervising, 65% for the site work and 14% for the radiation control. The percentage of workers for dismantling of the biological shield concrete is found to be larger than that of other dismantling item. This high value resulted f from applying three kinds of dismantling techniques, diamond sawing and coring, water jet cutting and controlled blasting to accumulate reactor decommissioning experience.
(2) Radiation exposure
The cumulative radiation exposure to workers and maximum cumulative personal radiation exposure from the start of the JPDR dismantling through December, 1992 were 300 man-mSv and 9 mSv, respectively. Dismantling of the activated and/or contaminated components were almost completed, therefore the exposure to workers will not increase any more.
The dismantling work accompanied with high-level radiation exposure was as follows:
the decontamination of the spent fuel storage pool, the installation of the water tank for cutting the RPV, and the other preparatory work such as the installation of the remotely controlled devices. Since the highly activated components such as the reactor internals, the RPV and the biological shield concrete were dismantled remotely, the cumulative radiation exposure to workers during the cutting work for these components was found to be less than those for preparatory work.
(3) Radioactive waste
The cumulative amount of the solid radioactive waste as of Dec. 1992 was 1800 tons.
Various types of containers have been used for storage of the radioactive waste during the decommissioning of the JPDR. Selection of the type of container is based on the material, size and radioactivity of the waste. High level radioactivity waste was placed in shield containers which have different wall thickness. As of December 1992, 34 shield containers, 43×3 m3 containers, 438×1 m3 containers and 4083×200 liter drums were used for the storage of the solid radioactive waste. These containers have been transferred to the new radioactive waste storage building in the JAERI site.
6 Concluding remarks
The JPDR decommissioning program is proceeding satisfactorily without any problems about safety, radiological and environmental matters. Various cutting tools with remote operation developed in the early stage of the program have been applied successfully in dismantling the highly activated components such as the reactor internals, the RPV and the biological shield concrete. These techniques were proved to be useful to minimize the radiation exposure to workers and to prevent contamination. The wide variety of the results obtained through the JPDR dismantling are expected to make a valuable contribution to decommissioning of commercial power reactors.