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Startup of the whiteshell irradiation facility
1158
Nuclear Instruments and Methods in Physics Research B40/41(1989)
1158-1161
North-Holland, Amsterdam
STARTUP
OF THE WHITESHELL
J.W. BARNARD
IRRADIATION
FACILITY
and F.W. STANLEY
Whiteshell Nuclear Research Establishment,
Pinawa, Manitoba,
Cana&
Recently, a lo-MeV, l&W electron linear accelerator was installed in a specially designed irradiation facility at the Whiteshell Nuclear Research Establishment. The facility was designed for radiation applications research in the development of new radiation processes up to the pilot scale level. The accelerator is of advanced design. Automatic startup via computer control makes it compatible with industrial processing. It has been operated successfully as a fully integrated electron irradiator for a number of applications including curing of plastics and composites, sterilization of medical disposables and animal feed irradiation. We report here on our experienceduring the first six months of operation.
1. fntraduction The Accelerator Applications Building (AAB) at the Whiteshell Nuclear Research Establishment of Atomic Energy of Canada (AECL) was designed and built to fulfill three functions: (1) to be a tool for carrying out underlying research in radiation processes; (2) to be a centre where industry could develop new processes to the pilot scale level; and (3) to provide small-scale commercial irradiation services in Western Canada. Most of the facility construction was completed by the end of 1987. The accelerator was installed in 1988 February and March. We report here on our experience for the first six months of operation.
Shielding is provided by a combination of concrete and earthworks. Approximately 2.4 m of concrete are provided to shield the operating area from directly penetrating X-rays produced in the accelerator room. Approximately 0.5 m of concrete and 3.5 m of earth berm shield the roof area outside the accelerator room from X-rays. A maze provides access for the conveyor. Scattering of neutrons and X-rays along this maze has been analysed (11 using the Monte Carlo code MCNP [2], even though neutron production is insignificant for the materials being irradiated and electron energies being used ( < 10 MeV). The shielding was designed to limit dose rates in occupiable areas to 2.5 p,Gy h-’ when the accelerator is in operation. The present accelerator is capable of producing only 1 kW of electron beam power. The facility is licensed for a IO-kW electron beam at 10 MeV.
2. The facility 3. The accelerator The facility has been previously described by Barnard and Wilkin [l]. Plan views are shown in fig. 1. The basement is the operating area with the accelerator room, shielding maze, control room, supervisor’s office, storage room, dosimetry/quality assurance room, and an experimental area. In keeping with the intent to provide an industrial environment for pilot scale processing of materials, warehouse space with a truck bay has been provided at street level. Pallets of materials for processing can be received and stored on the upper level and, by means of a conveyor system running between floors, be delivered to the lower level for irradiation. Materials and equipment can be moved about on the upper level or lowered through the conveyor hatchways to the basement using a 5-t overhead crane. 0168-583X/89/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
The accelerator presently installed in the AAB is an AECL I-10/1. This instrument is a standing wave linear accelerator driven by a 2.5~MW (peak power) magnetron (English Electric Valve) operating in the S-band. Electrons from a barium oxide cathode are injected into the accelerating structure at -42 kV, accelerated along a horizontal axis, bent through 270° in the vertical plane, where energy analysis occurs, and emerge in the downward direction through a 250~pm aluminum window. In the Whiteshell configuration, acceleration, beam bending and scanning occur in the same vertical plane, although the I-10/1 can be manufactured in other configurations. The accelerated beam current is actually somewhat greater than the nominal 100~pA value; however, the beam actually delivered to the prod-
J. W. Barnard
F. W. Stanley / Startup of the Whiteshell irradiation facility
BASEMENT FLOOR PLAN
1159
,,
Fig. 1. Plan view of the accelerator applications building.
following energy analysis is about 80 PA. The I-10/1 is described in more detail elsewhere [3]. An important feature of the I-10/1 is automatic operation. The operator controls the accelerator from a keypad. Beam parameters, set points, etc., are displayed graphically on a colour monitor. At the heart of automatic control is the GEM-80 industrial controller (GEC Canada). The GEM-80 responds to inputs from the operator, manages closed-loop feedback and control of beam parameters, monitors machine functions and enunciates abnormal states. There are no accelerator setting that the operator can change without input to the GEM-80. Once the operator has cleared the interlock conditions and pressed the “auto-on” button, the GEM-80 brings the accelerator to full power. uct
4. product handlii Conveyor selection was based on the following considerations: (1) ability to deliver a package or tray squarely to the conveyor section under the beam without jamming;
(2) radiation resistance of conveyor materials; (3) capital cost; and (4) maintenance cost. Demonstrations in existing production facilities showed that live rollers would present a square package for irradiation in the correct orientation and with reasonable reliability. Sector plate or slider plate conveyors would perform this last function with better precision, but their capital and maintenance costs are considerably greater. Therefore, live roller conveyors were selected for product transport along level stretches. Rubber mat conveyor belts are used on inclines or, in one instance, where conveyance must be interrupted for “indexing” (dispensing to the beam). The conveyor section that transports the product through the beam has to fulfill special requirements. Besides withstanding the direct radiation effects of the transversely scanned beam, it must be capable of controlling the dose by transporting packages at a controlled rate under direction from the GEM-80. The speed range required to provide the needed range of doses is 600-1.0 mm s-l. Stainless steel mat was chosen for this conveyance IX. RADIATION
PROCESSING
1160
J. W. Barnar4
F. W. Stanley / Startup of the Whiteshell irradiation facility
surface for its radiation resistance. A specially wound 2-HP three-phase induction motor drives this section of conveyor through a 20.1: 1 reduction gear. The induction motor is powdered by a variable frequency ac inverter (Toshiba International). The inverter frequency, and thus conveyor speed, is controlled by an analogue signal from the GEM-80. Feedback for closed-loop speed regulation and monitoring by the GEM is provided by a toothed wheel with a proximity sensor on the motor drive shaft.
5. Radiation measurements Barnard and Wilkin [l] estimated the dose equivalent rates that might be expected in the control room from X-rays produced by an electron accelerator of the maximum licensed beam power and energy. Included in this analysis were contributions from directly penetrating radiation and radiation scattered through the maze. Estimates of dose rate were made for the northwest corner of the control room against the wall separating the control room from the maze and in the opening where the conveyor enters the maze. A dose rate of 36 /rGy h-’ was predicted at the conveyor opening for a lo-kW machine. The dose rate behind the wall was predicted to be negligible. Fig. 2 shows the distribution of dose rate, as measured using thermal luminescent dosimeters (TLDs), on the basement level while the accelerator is in operation. The dose rates along the east, north and west walls of the accelerator room are within 10% of the values estimated using data from Brynjolfsson and Martin [4] or National Council on Radiation Protection Publication No. 51 [5]. Dose rates along the south wall of the accelerator room, however, indicate that in this direction the accelerator is strongly self-shielding. Dose rates along the control room wall were indistinguishable from background, as predicted. Since the I-10/1 actually delivers a beam that is only 8% of the
I
Fig. 2. Radiation dose rates with the accelerator operating.
licensed power of the facility, it is expected that the dose rate at the conveyor opening would be about 2.9 pGy h-‘. The measured value of 0.54 uGy h-’ tends to indicate that the dose rate predictions of Barnard and Wilkins were overestimated by a factor of 5; however, the dose measured with this TLD was about the same as the statistical variation on TLD measurements.
6. Operating experience Since installation in the AAB, the I-10/1 has been operated for more than 150 h. A variety of items have been irradiated, including animal feed for pasturization, plastic samples for cross-linking, composite materials for resin curing, and medical disposables for sterilization. A procedure has been developed for irradiating products in the AAB. The proponent fills out a materials irradiation request form (MIRF). The supervisor of the facility, upon receipt of the MIRF, gauges the safety of the proposed irradiation. He may request outside review, which may result in additional safety constraints being attached to the irradiations. Once satisfied as to safety, he assigns an event number to the irradiation and registers it in an event log. The accelerator operator attaches dosimeters according to previously established quality assurance requirements. During the irradiation, he generates a printout of machine parameters from the GEM-80. After irradiation, the dosimeters are read and results returned to the supervisor as a dosimetry report. From the machine printout and the dosimetry report the supervisor prepares an event completion report stating what was irradiated, the dose given each lot by lot number and important machine parameters including beam current and conveyor speed. The monitoring of machine parameters, trending and reporting is being automated. The live roller conveyors have performed as expected. No embrittlement of elastomeric or rubber components has been observed even on those components closest to the beam. Items too small to ride over the rollers are placed in standard 60 x 80 cm plywood totes for irradiation. Prior to installing the controlled speed conveyor, the manufacturer demonstrated its operation over two overlapping speed ranges from 0.75 to 610 mm s-l. Thus far, we have used it on the upper speed range (2.0-610 mm s-l) in the “autodose” mode, slaved to the beam power. Even at the low speeds, dynamic torque control and dose regulation are excellent. Maximum dose variation along the length of a standard tote for a range of doses from 1.4 to 5.0 kGy as measured using radiochromic films was found to be about 5%, which is about the statistical variation of the dosimeters.
J. W. Barnard
F. W. Stanley / Startup of the Whiteshell irradiation facility
7. summary Commissioning of the AAB is now complete. The accelerator runs routinely under automatic control interfaced with the conveyor. Thus, interfacing has worked very well. The dose variation over the length of the standard tote is about f 5%. Preliminary measurements indicate that the dose rates in occupied areas of the AAB with the beam on are approximately one fifth the design rates.
1161
References
111J.W. Barnard
and G.B. Wilkin, Proc. 20th Midyear Topical Meeting of the Health Physics Society, Reno Nevada, 1987, p. 287. 121 Los AIamos Radiation Transport Group, Los Alamos National Laboratory, LA-7396-M (1981). 131 G. Hare, Radiat. Phys. Chem. 31 (1988) 309. 141 A. Brynjolfsson and T.G. Martin III, Int. J. Appl. Radiat. Isopt. 22 (1971) 29. PI National Council on Radiation Protection, Report No. 51 (1977).
IX. RADIATION
PROCESSING
Nuclear Instruments and Methods in Physics Research B40/41(1989)
1158-1161
North-Holland, Amsterdam
STARTUP
OF THE WHITESHELL
J.W. BARNARD
IRRADIATION
FACILITY
and F.W. STANLEY
Whiteshell Nuclear Research Establishment,
Pinawa, Manitoba,
Cana&
Recently, a lo-MeV, l&W electron linear accelerator was installed in a specially designed irradiation facility at the Whiteshell Nuclear Research Establishment. The facility was designed for radiation applications research in the development of new radiation processes up to the pilot scale level. The accelerator is of advanced design. Automatic startup via computer control makes it compatible with industrial processing. It has been operated successfully as a fully integrated electron irradiator for a number of applications including curing of plastics and composites, sterilization of medical disposables and animal feed irradiation. We report here on our experienceduring the first six months of operation.
1. fntraduction The Accelerator Applications Building (AAB) at the Whiteshell Nuclear Research Establishment of Atomic Energy of Canada (AECL) was designed and built to fulfill three functions: (1) to be a tool for carrying out underlying research in radiation processes; (2) to be a centre where industry could develop new processes to the pilot scale level; and (3) to provide small-scale commercial irradiation services in Western Canada. Most of the facility construction was completed by the end of 1987. The accelerator was installed in 1988 February and March. We report here on our experience for the first six months of operation.
Shielding is provided by a combination of concrete and earthworks. Approximately 2.4 m of concrete are provided to shield the operating area from directly penetrating X-rays produced in the accelerator room. Approximately 0.5 m of concrete and 3.5 m of earth berm shield the roof area outside the accelerator room from X-rays. A maze provides access for the conveyor. Scattering of neutrons and X-rays along this maze has been analysed (11 using the Monte Carlo code MCNP [2], even though neutron production is insignificant for the materials being irradiated and electron energies being used ( < 10 MeV). The shielding was designed to limit dose rates in occupiable areas to 2.5 p,Gy h-’ when the accelerator is in operation. The present accelerator is capable of producing only 1 kW of electron beam power. The facility is licensed for a IO-kW electron beam at 10 MeV.
2. The facility 3. The accelerator The facility has been previously described by Barnard and Wilkin [l]. Plan views are shown in fig. 1. The basement is the operating area with the accelerator room, shielding maze, control room, supervisor’s office, storage room, dosimetry/quality assurance room, and an experimental area. In keeping with the intent to provide an industrial environment for pilot scale processing of materials, warehouse space with a truck bay has been provided at street level. Pallets of materials for processing can be received and stored on the upper level and, by means of a conveyor system running between floors, be delivered to the lower level for irradiation. Materials and equipment can be moved about on the upper level or lowered through the conveyor hatchways to the basement using a 5-t overhead crane. 0168-583X/89/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
The accelerator presently installed in the AAB is an AECL I-10/1. This instrument is a standing wave linear accelerator driven by a 2.5~MW (peak power) magnetron (English Electric Valve) operating in the S-band. Electrons from a barium oxide cathode are injected into the accelerating structure at -42 kV, accelerated along a horizontal axis, bent through 270° in the vertical plane, where energy analysis occurs, and emerge in the downward direction through a 250~pm aluminum window. In the Whiteshell configuration, acceleration, beam bending and scanning occur in the same vertical plane, although the I-10/1 can be manufactured in other configurations. The accelerated beam current is actually somewhat greater than the nominal 100~pA value; however, the beam actually delivered to the prod-
J. W. Barnard
F. W. Stanley / Startup of the Whiteshell irradiation facility
BASEMENT FLOOR PLAN
1159
,,
Fig. 1. Plan view of the accelerator applications building.
following energy analysis is about 80 PA. The I-10/1 is described in more detail elsewhere [3]. An important feature of the I-10/1 is automatic operation. The operator controls the accelerator from a keypad. Beam parameters, set points, etc., are displayed graphically on a colour monitor. At the heart of automatic control is the GEM-80 industrial controller (GEC Canada). The GEM-80 responds to inputs from the operator, manages closed-loop feedback and control of beam parameters, monitors machine functions and enunciates abnormal states. There are no accelerator setting that the operator can change without input to the GEM-80. Once the operator has cleared the interlock conditions and pressed the “auto-on” button, the GEM-80 brings the accelerator to full power. uct
4. product handlii Conveyor selection was based on the following considerations: (1) ability to deliver a package or tray squarely to the conveyor section under the beam without jamming;
(2) radiation resistance of conveyor materials; (3) capital cost; and (4) maintenance cost. Demonstrations in existing production facilities showed that live rollers would present a square package for irradiation in the correct orientation and with reasonable reliability. Sector plate or slider plate conveyors would perform this last function with better precision, but their capital and maintenance costs are considerably greater. Therefore, live roller conveyors were selected for product transport along level stretches. Rubber mat conveyor belts are used on inclines or, in one instance, where conveyance must be interrupted for “indexing” (dispensing to the beam). The conveyor section that transports the product through the beam has to fulfill special requirements. Besides withstanding the direct radiation effects of the transversely scanned beam, it must be capable of controlling the dose by transporting packages at a controlled rate under direction from the GEM-80. The speed range required to provide the needed range of doses is 600-1.0 mm s-l. Stainless steel mat was chosen for this conveyance IX. RADIATION
PROCESSING
1160
J. W. Barnar4
F. W. Stanley / Startup of the Whiteshell irradiation facility
surface for its radiation resistance. A specially wound 2-HP three-phase induction motor drives this section of conveyor through a 20.1: 1 reduction gear. The induction motor is powdered by a variable frequency ac inverter (Toshiba International). The inverter frequency, and thus conveyor speed, is controlled by an analogue signal from the GEM-80. Feedback for closed-loop speed regulation and monitoring by the GEM is provided by a toothed wheel with a proximity sensor on the motor drive shaft.
5. Radiation measurements Barnard and Wilkin [l] estimated the dose equivalent rates that might be expected in the control room from X-rays produced by an electron accelerator of the maximum licensed beam power and energy. Included in this analysis were contributions from directly penetrating radiation and radiation scattered through the maze. Estimates of dose rate were made for the northwest corner of the control room against the wall separating the control room from the maze and in the opening where the conveyor enters the maze. A dose rate of 36 /rGy h-’ was predicted at the conveyor opening for a lo-kW machine. The dose rate behind the wall was predicted to be negligible. Fig. 2 shows the distribution of dose rate, as measured using thermal luminescent dosimeters (TLDs), on the basement level while the accelerator is in operation. The dose rates along the east, north and west walls of the accelerator room are within 10% of the values estimated using data from Brynjolfsson and Martin [4] or National Council on Radiation Protection Publication No. 51 [5]. Dose rates along the south wall of the accelerator room, however, indicate that in this direction the accelerator is strongly self-shielding. Dose rates along the control room wall were indistinguishable from background, as predicted. Since the I-10/1 actually delivers a beam that is only 8% of the
I
Fig. 2. Radiation dose rates with the accelerator operating.
licensed power of the facility, it is expected that the dose rate at the conveyor opening would be about 2.9 pGy h-‘. The measured value of 0.54 uGy h-’ tends to indicate that the dose rate predictions of Barnard and Wilkins were overestimated by a factor of 5; however, the dose measured with this TLD was about the same as the statistical variation on TLD measurements.
6. Operating experience Since installation in the AAB, the I-10/1 has been operated for more than 150 h. A variety of items have been irradiated, including animal feed for pasturization, plastic samples for cross-linking, composite materials for resin curing, and medical disposables for sterilization. A procedure has been developed for irradiating products in the AAB. The proponent fills out a materials irradiation request form (MIRF). The supervisor of the facility, upon receipt of the MIRF, gauges the safety of the proposed irradiation. He may request outside review, which may result in additional safety constraints being attached to the irradiations. Once satisfied as to safety, he assigns an event number to the irradiation and registers it in an event log. The accelerator operator attaches dosimeters according to previously established quality assurance requirements. During the irradiation, he generates a printout of machine parameters from the GEM-80. After irradiation, the dosimeters are read and results returned to the supervisor as a dosimetry report. From the machine printout and the dosimetry report the supervisor prepares an event completion report stating what was irradiated, the dose given each lot by lot number and important machine parameters including beam current and conveyor speed. The monitoring of machine parameters, trending and reporting is being automated. The live roller conveyors have performed as expected. No embrittlement of elastomeric or rubber components has been observed even on those components closest to the beam. Items too small to ride over the rollers are placed in standard 60 x 80 cm plywood totes for irradiation. Prior to installing the controlled speed conveyor, the manufacturer demonstrated its operation over two overlapping speed ranges from 0.75 to 610 mm s-l. Thus far, we have used it on the upper speed range (2.0-610 mm s-l) in the “autodose” mode, slaved to the beam power. Even at the low speeds, dynamic torque control and dose regulation are excellent. Maximum dose variation along the length of a standard tote for a range of doses from 1.4 to 5.0 kGy as measured using radiochromic films was found to be about 5%, which is about the statistical variation of the dosimeters.
J. W. Barnard
F. W. Stanley / Startup of the Whiteshell irradiation facility
7. summary Commissioning of the AAB is now complete. The accelerator runs routinely under automatic control interfaced with the conveyor. Thus, interfacing has worked very well. The dose variation over the length of the standard tote is about f 5%. Preliminary measurements indicate that the dose rates in occupied areas of the AAB with the beam on are approximately one fifth the design rates.
1161
References
111J.W. Barnard
and G.B. Wilkin, Proc. 20th Midyear Topical Meeting of the Health Physics Society, Reno Nevada, 1987, p. 287. 121 Los AIamos Radiation Transport Group, Los Alamos National Laboratory, LA-7396-M (1981). 131 G. Hare, Radiat. Phys. Chem. 31 (1988) 309. 141 A. Brynjolfsson and T.G. Martin III, Int. J. Appl. Radiat. Isopt. 22 (1971) 29. PI National Council on Radiation Protection, Report No. 51 (1977).
IX. RADIATION
PROCESSING