The results of using remote-controlled machinery in the disassembly of loop facilities of the MR research

reactor, which was decommissioned at the National Research Center Kurchatov Institute, are presented.

The results of an examination of the loop channels of the reactor and the handling of high-level wastes

during extraction, fragmentation and packaging are presented. Methods of remote diagnostics for

measuring the activity distribution along a channel are proposed. Means for cutting channels and methods

of lowering worker dose loads are presented.

The plan to decommission the MR and RFT research reactors in order to decrease radiation exposure of workers,

the environment and the population requires a diagnostics method and robotic means for disassembling equipment having

high levels of radioactive contamination and handling high-level wastes [1, 2]. Disassembly of equipment in the cooling loops

for secondary-loop facilities located in the central hall and basement rooms of MR began in 2011–2012. The work was per-

formed using Brokk (Sweden) remote-controlled machinery; the most strongly contaminated parts of the equipment and

pipelines are identified by radiological and spectrometric methods using systems such as Gamma-pioneer, gamma-locator

and gamma-viewer [3–5]. To sort the wastes by activity and choose transport containers, methods were developed for frag-

menting equipment using robotic means, which were aimed on intense sources of γ-radiation based on data obtained with a

gamma-viewer. Such technology makes it possible to lower worker dose loads considerably, monitor the volume activity of

aerosols in air, and prevent significant discharges of radionuclides into the environment.

To secure worker radiological safety, limit the flow of radionuclides into the environment, and reduce the effect on

the population in nearby urban areas of Moscow, the equipment in the secondary-loop facilities and structures in individual

rooms of MR were disassembled in accordance with the system developed and adopted at the National Research Center

Kurchatov Institute. This system included the following measures:

1) documentation of the organizational work order – development of a plan for each activity, technological regula-

tions, safety instructions and the order of high-hazard work;

2) use of fundamentally new technology for disassembly operations – use of remote-controlled machinery and video

systems, polymer materials for decontamination and dust suppression;

3) remote diagnostics of the radiological state of objects [5, 6];

4) equipping robotic means with a collimated remote-controlled radiation-detection system, which enables real-time

adjustment based on its indications to the technological process of disassembly, fragmentation and waste packaging;

Atomic Energy, Vol. 113, No. 5, March, 2013 (Russian Original Vol. 113, No. 5, November, 2012)

UDC 574:594.1.04+621.039.7

National Research Center Kurchatov Institute, Moscow. Translated from Atomnaya Énergiya, Vol. 113, No. 5, pp. 285–289, November, 2012.Original article submitted July 10, 2012.

1063-4258/13/11305-0357 ©2013 Springer Science+Business Media New York 357

V. G. Volkov, O. P. Ivanov,V. I. Kolyadin, A. V. Lemus,V. D. Muzrukova, V. I. Pavlenko,S. G. Semenov, S. V. Smirnov,V. E. Stepanov, S. Yu. Fadin,A. V. Chesnokov, and A. D. Shisha

USE OF REMOTE-CONTROLLED MACHINERY

TO REDUCE WORKER RADIATION EXPOSURE

5) securing the serviceability of the systems and elements of safe work execution, including special ventilation and

gas scrubbing;

6) introducing a level for each controlled radiation parameter;

7) introducing the maximum daily dose of irradiation, worker self-monitoring of the dose using an additional dosime-

ter with overdose signaling;

8) providing workers with special clothes and means for protection of the respiratory organs in accordance with the

work standards in first-class laboratories;

9) maintaining in a serviceable state the physical barriers preventing radionuclides from entering the environment;

10) radiological monitoring during loading of radioactive wastes into transport containers and vehicles as well as at

exit gates;

11) use of local ventilation facilities; and

12) dust suppression using AK-501 and SKS-501 polymer compositions, which are capable of forming a protective

film that fixes the contamination of the disassembly equipment preventing dissemination of radioactive contamination and

decreasing the deflation of aerosols from surfaces into the environment.

The work was performed in the technological rooms of the secondary-loop facilities, which are characteristically

filled with equipment, contain large-size equipment to 5 tons and high γ-ray dose rates in the rooms (to 20 mSv/h) and have

pathways of great complexity for removing containers with fragments of the disassembled equipment. The rooms where dis-

assembly work was performed in 2011–2012 are shown in Fig. 1. The following complex of work operations was performed

in them: cutting of secondary-loop channels stored in a storage pool in the reactor hall, expansion of doorways and hatch pas-

sageways in the basement rooms of building 37/1, disassembly of equipment and pipelines in corridors, including pipelines

in mezzanines, disassembly of pipelines in the subdeck space of the MR reactor hall, equipment in the steam-generator, POV

and PVO system loops and their pipelines. The fragments of the disassembled equipment and pipelines were mostly converted

to radioactive wastes and partially recycled in the form of scrap metal.

The γ-ray dose rate during execution of individual forms of work in these rooms was characterized by the following

values:

• 1–1.5 Sv/h during cutting and fragmentation of the channels and packing into containers;

• to 10 mSv/h during disassembly of pipelines in the subdeck space, water secondary loops (KVP) on mezannine

corridors 1–3 (pipeline corridor);

• to 50 mSv/h during loading of wastes into storage facility No. 7;

• to 20 mSv/h during disassembly of equipment in secondary-loop facilities.

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Fig. 1. Technological rooms where disassembly work was performed in 2011–2012:

CD) technological passage between rooms; the numbers denote the room numbers.

The admissible γ-ray dose rate based on NRB-99/2009 was taken to be 12 μSv/h. The γ-ray dose rate in direct prox-

imity to the contaminated equipment is a factor of 103–106 higher than the admissible value. This means that the yearly dose

rate can be reached in 1 h in the secondary-loop rooms and 5 min during channel cutting.

Handling Radwastes During Disassembly. Disassembly requires preliminary examination of the technological

room using a gamma-locator and gamma-viewer in order to find the equipment surfaces with the strongest emission.

The measurements showed nonuniform contamination of the equipment; individual sections strongly contaminated with137Cs did not coincide with sections contaminated with 60Co [6]. Nonetheless, it should be noted that the intensely emit-

ting surfaces and equipment did not make the main contribution to the equivalent dose rate averaged over the entire room,

i.e., their removal did not significantly reduce the equivalent dose rate in the entire volume of a room. For this reason,

the simplest method for disassembling equipment in technological basement rooms of secondary-loop facilities of the steam

generator, POV and PVO systems was found to be staged disassembly of equipment accessible to Brokk remote-controlled

machinery, ranging from Brokk-90 to Brokk-400 [1]. The use of a large set of easily changeable mounted tools made it pos-

sible to perform the disassembly work quite rapidly without worker participation. The operators were located in exterior

decontaminated rooms, and remote-controlled machinery performed all operations inside the technological rooms. As an

example, the disassembly of equipment in room No. 66 is shown in Fig. 2.

A different situation was encountered during disassembly and cutting of the cooling loops of the secondary-loop

facilities located in the storage pool of the MR reactor hall. Here remote-controlled machinery was used for fragmentation,

sorting and packaging in high-level waste containers. The high-level wastes were long elements of the loop equipment of the

reactor and secondary-loop facilities, specifically, secondary-loop channels, and were distinguished by their construction and

structural materials. Some of these structures located in the reactor core were exposed to intense neutron irradiation; all oth-

ers were contaminated with fission products and activation. All this equipment was located in the reactor’s storage pool;

the total number of such structures was 150. The particulars of the irradiation of the elements greatly complicated their extrac-

tion from the storage pool, fragmentation and removal from the reactor hall.

The most intensely emitting parts of the secondary-loop equipment were identified using the following measuring

systems: a radiometric system placed on Brokk-90 (Gamma-pioneer), a remote-controlled system and a normative gamma-

viewer [4].

First, the loop equipment was scanned with the Gamma-pioneer radiometric system and a γ-image was obtained

simultaneously using a gamma-viewer (Fig. 3). The nuclide composition of the contamination of the scanned channels was

determined according to the radiation spectrum measured with the gamma-locator spectrometric system. Next, on the basis

of an analysis of the scanning results and the measured spectra the activity along each channel studied was determined using

specially developed methods. Analysis showed that the activity along channels is highly nonuniform; the parts of the struc-

359

Fig. 2. Use of remote-controlled machinery during disassembly of equipment in room No. 66.

tures which were located in the core showed the highest activity. The main dose-forming nuclide is 60Co, but other radionu-

clides were also found in the spectra of some channels, for example, 94Nb. These data were used to determine the optimal

site for cutting them in order to separate the highly active parts of the equipment from the less active parts.

To prevent the zirconium cladding of the channels from heating up, the loop equipment was cut and the high-activ-

ity fragments removed by remote-controlled means under water using Brokk-180 and Brokk-330 robotic machines equipped

with the required mounted equipment. For this, a special water-filled stand was developed and placed in the reactor hall.

Fragmented equipment was placed on special stands under water, and hydraulic shears were used to separate the high-activity

parts (Fig. 4). The high-activity fragments were placed into special boxes and deposited in a high-level waste repository, while

all other fragments were packed in concrete or metal containers and shipped to the Moscow Scientific and Production

Association Radon for long-term storage.

The flow of aerosols into room air was evaluated during disassembly. This made it possible to evaluate the effective

internal irradiation dose to workers. The volume activity of the aerosols at disassembly work sites is lower that the level rec-

ommended in NRB-99/2009 but does not secure the established control levels (Table 1).

Optimization of Worker Radiological Protection. The preparation of MR for decommissioning coincided with the

introduction in 2000 of a fundamentally new concept for radiological protection, on the basis of which new radiation safety

norms NRB-99 and OSPORB-99 were developed and put into effect. Since 2000, tougher hygienic norms for dose loads have

360

Fig. 3. Image of a channel, obtained with a gamma-viewer.

Fig. 4. Scheme of the stand used to cut channels using robotic means under water:

1) water; 2) fragmented channel; 3) housing.

been established: 20 mSv/yr for workers and 1 mSv/yr for the general population. Radiological protection for workers was

optimized in accordance with the normative documentation. Following the principles of the ICRP Publications No. 60 and

103 the National Research Center Kurchatov Institute started to use remote methods for diagnostics of the radiation condi-

tions as well as remote-controlled machinery for operations with high-level wastes and disassembly of equipment in the tech-

nological rooms of secondary-loop facilities. In addition, the maximum admissible daily dose and individual self-monitoring

by workers using DKG-05D individual electronic dosimeters were introduced (Table 2). This made it possible to decrease the

number of workers brought into the work in the course of a year to 34 individuals (the core team did not exceed 20 individ-

uals), secure a yearly average individual dose 1.9 mSv and collective dose 0.0645 individuals·Sv/yr. The average volume

aerosol activities of 137Cs, 60Co, and 90Sr at the disassembly sites in 2011 comprised 3.4, 1.5, and 1.6 Bq/m3, respectively;

the effective internal irradiation dose levels were 39.2, 100.5, and 653 μSv/yr, respectively; and the total effective dose was

792.7 μSv/yr.

In 2011–2012, 110 tons of equipment in the basement technological rooms of the secondary-loop facilities of the

steam generator, POV and PVO systems (rooms No. 66, 66A, 66B, 72, 64, and 63) were disassembled during decommission-

ing of the MR and RFT research reactors, of which 53 tons were prepared to shipment as radwastes with total activity 50 GBq.

Ninety three channels with total 60Co activity 26 TBq and 137Cs activity 15 TBq were removed, fragmented and packed into

boxes and containers. The use of remote-controlled machinery made it possible to decrease worker radiation exposure.

REFERENCES

1. V. G. Volkov, Yu. A. Zverkov, V. I. Kolyadin, et al., “Preparation of the research reactor MR at the National Research

Center Kurchatov Institute for decommissioning,” At. Énerg., 104, No. 5, 259–264 (2008).

Type of work Number of workersAverage individual

effective dose, mSv/yrCollective individual

dose, mSv/yr

Diagnostics of the radiation state of an object to be disassembled,determination of radwastes characteristics

8 1.15 9. 25

Equipment disassembly, safety system maintenance in a serviceable state 14 2.2 30.7

Waste handling, decontamination 8 1.97 15.7

Radiological safety service 4 2.2 8.8

Work siteAvol, Bq/m3 Internal irradiation, effective dose rate, μSv Total yearly

effective dose,mSv137Cs 60Co 90Sr 137Cs 60Co 90Sr

Channel cutting 38.6 2.25 17.3 443.6 52.2 996.6 1.5

Subdeck space 20.9 11.84 12.3 240.7 272.3 708.5 1.2

Pipeline corridor 59. 3 3.1 16 682.1 75.9 921.6 1.7

Room No. 66 6.5 2.4 0.49 75.1 55.2 28.3 0.19

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TABLE 1. Aerosol Volume Activity in the Disassembly Zone and Worker Irradiation Dose

TABLE 2. Individual Dosimetric Monitoring Results

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