- Email: [email protected]
History of the KUR and the view of operation in the near future
Physica B 311 (2002) 1–6
History of the KUR and the view of operation in the near future Yoshiaki Fujita* Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka, Japan
Abstract The 37 years’ history of the Kyoto University Research Reactor is presented on the points of developments of diverse experimental facilities, and operation, maintenance and refurbishment on the reactor. The view of operation in the near future is introduced referring to the review and evaluation works. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Kyoto university research reactor; History; Experimental facilities; Extended operation; Fuel problem
1. Introductory remarks At the Research Reactor Institute, Kyoto University, a new key research facility for the future is being proposed, the accelerator-driven fission assembly being used for basic studies in neutron-multiplication and energy-amplification. It is also intended to continue the operation of the present key facility, the 5 MW-Kyoto University Research Reactor (KUR), until the proposed facility is realized. The prospect of the realization, however, is not so clear at present. The KUR has given an opportunity in this conference to explain its long history and its expectation for the continued operation in a rather short period. 2. History In Japan, the construction of a research reactor shall be authorized legally in the long-range *Fax: +81-724-51-2620. E-mail address: [email protected] (Y. Fujita).
national plan for research and development of atomic energy, which is decided in the Japanese Atomic Energy Commission. The KUR was of course constructed with the authorization. The planning, design and construction, commissioning, operation and utilization were carried out by university people under the influence of the Ministry of Education, Science and Culture. The KUR attained its first criticality and reached the 1-MW nominal power in the same year, 1964. In 1968, the nominal power was raised to 5 MW after upgrading the cooling capability. Since that time, the KUR has been serving the common use for universities and public research organizations. The general-purpose critical assembly, KUCA, was also constructed in 1974. In 1978, the construction license of the KUR-2 was approved by the regulatory body. The construction plan, however, was not realized mainly because of the disapproval of the local government, and was finally canceled in 1991.
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 0 4 7 - X
Y. Fujita / Physica B 311 (2002) 1–6
2
After the construction plan of the KUR-2 came to a standstill, the staff members were devoted to enhance the utilization of the KUR, and refurbish the KUR year by year. They also installed newly developed experimental facilities such as the cold neutron source, the super-mirror neutron guide, the wide-band neutron chopper, and started the study of the boron neutron capture therapy. During 1990 and 1993, the KUR was reviewed by the Kyoto University and the related committee of the Science Council, regarding the achievements of their activities, the role and value, and the continuing operation. The second review was just finished in 2000. The KUR is now satisfactorily operating with minimum chance of unscheduled shutdowns under the surroundings, which change rapidly. The history of the KUR is summarized in Table 1.
3. Developments of diverse experimental facilities As for a personal computer, the weight was first attached to performance of the central processor unit, and then to the peripheral equipment and to the software. Similarly, diverse experimental facilities equipped year by year raised the value of the KUR. The diversity comes from that the KUR has been used by university-researchers in a variety of research fields.
Some of the experimental facilities were installed at the same time with the construction of the reactor, and others have been installed afterwards through the development works of the staff members along with the trend of research. Figs. 1 and 2 show the plan and horizontal sections of the KUR with the installation of the experimental facilities. The water pool is rather small and the reactor is called the well type. Employing the well type and locating the spent fuel pool outside the reactor building, all of the horizontal directions are effectively opened to the installation of beam tubes and thermal columns. For the irradiation experiments accessed vertically to the core, the sub-pool was prepared near the reactor top. The hydraulic conveyer is equipped at the center of the core where the fast and thermal neutron fluxes are the highest. The conveyer has a novel capability that the irradiation sample can be inserted into it and extracted from it during the reactor operation. At the edge of the core or in the reflector, there are three pneumatic tube systems and the long time irradiation plug. The new irradiation plug was also installed recently, in which the temperature of the irradiation sample is controlled with electrical and nuclear heating methods. Two different kinds of thermal columns are equipped. The graphite thermal column was used for neutron thermalization studies in the early
Table 1 History of the KUR and experimental facilities Decade
KUR
’60
’64: Critical, 1 MW ’68: 5 MW
’70 ’80
’81–’84: 1st refurbishment ’89–’92: 2nd refurbishment ’85–’99: 3rd refurbishment ’93: Review
’90
2000
Experimental facilities installed at KUR ’68: ’73: ’77: ’84: ’85: ’86:
Low temp. irrad. loop Ni-mirror NGT Online isotope separator Wide band N-chopper Super mirror NGT Cold neutron source
’90: N. scattering analyzer ’92: Small angle N. scattering ’92: Neutron spin echo ’96: H. W. column modification 98: Temp. control irrad. loop ’00: Review
KUCA, KUR-2, others ’64: ’69: ’74: ’78:
e-LINAC Cobalt-60 KUCA completed KUR-2 license approved
’91: KUR-2 license canceled
Y. Fujita / Physica B 311 (2002) 1–6
3
ometer, the neutron radiography instrument and the iron-filtered neutron irradiation facility.
4. Operation and maintenance
Fig. 1. Vertical section of the KUR.
stage, but in 1987, the cold neutron source with liquid deuterium of 4 l was installed in it. The heavy-water thermal column with a bismuth gamma-ray shield on the irradiation-room side provided a very pure thermal neutron field, which has been used mainly for biological irradiation studies. The thermal column was modified installing aluminum layers and cavities in the heavy water tank to provide both thermal and epithermal neutron fields, which is now used as the BNCT facility for deep-seated brain tumors. The thermal neutron guide tube using natural nickel mirrors is installed on the E-3 beam tube and the super mirror guide tube in the B-4 thermal neutron beam tube. In the four cold neutron beam tubes looking at CNS, the natural nickel guide tube, the supermirror guide tube and the VCN guide tube are installed. Other beam tubes are used for the low-temperature irradiation loop, the isotope separator on line, the four-circle neutron monochrometer, the triple axis neutron diffract-
The KUR is operated from Tuesday morning to Friday evening in a regular week. On Tuesday morning, a few hours are needed for the start-up checking and fuel shuffling. About four months in a year are allotted for overhaul maintenance and the legal inspection to obtain the 1-year operation license. Until recent years, it was the custom at the KUR that both the technicians and researchers share the duty of reactor operation and maintenance. The custom partly remains until now. For example, some of researchers of neutron physics are joined to the operation staff members. There have been a variety of opinions for the custom. Considering that the requirements of the regulatory body for the complete quality assurance system in operation and maintenance have been very strict after the criticality accident, rigorous training is needed for the operation and maintenance staff members. Therefore, the sharing of the duty for operating and maintaining the KUR between researchers and technicians has become difficult.
5. Refurbishment works and integrity inspections For the recent 20 years or after the plan of the KUR-2 construction came to a standstill, a lot of refurbishment works for the KUR were carried out year by year according to their importance order for the safety. Some reactor structures and components have been replaced many times, and others keep their integrity without any replacement. The replacement frequency depends on the surrounding conditions and materials of the structures and components. The typical causes degrading the integrity are radiation damage, mechanical fatigue and wear, and corrosion. The experience at the KUR shows that the corrosion of aluminum alloy is the most prominent.
4
Y. Fujita / Physica B 311 (2002) 1–6
Fig. 2. Horizontal section of the KUR.
The structures and components replaced until now are main heat exchangers, pumps of secondary coolant, the cooling tower, the purifying system of reactor tank water, the heavy water thermal column, the graphite in the thermal column, the emergency generator, the reactorwater supply and drain systems, the instrumentation and control system, the ventilation system and radiation monitor system. The reactor tank, the biological shield and the reactor building are not the objects of replacement. The possibility of corrosion of the aluminum-alloy lining of the reactor tank is the matter of highest concern. The inner side of the lining could be visually inspected. The outer side was inspected from the inner side using an ultrasonic thickness meter. For the shield and the building, the integrity of concrete and reinforced steel were confirmed through appropriate inspections. The recent inspection was carried out in 1999. The former one was in 1991. There was no difference between the inspections, and the institute has the prospect that the integrity of these structures may be preserved for at least the next ten years.
6. Review and evaluation works In recent years, there were several committee works for review and evaluation of the activities of the institute, where the reconsideration of the continued operation of the KUR was one of the main subjects. Several points are extracted, by the author’s valuation, from the results of the works: (1) The KUR has made an acceptable contribution to the basic researches and the cultivation of human resources in the process of the developments of applications of nuclear energy and nuclear radiations. (2) The KUR still has the role and value as a university reactor where many kinds of experiments of trial or sprout step are carried out by researchers and students in diverse research fields. (3) Full core conversion to low enriched uranium fuel is encouraged for the extended operation. (4) The research activity is rather too all-round. The concentration on the limited research subjects is recommended. Most of the
Y. Fujita / Physica B 311 (2002) 1–6
reviewers recommend the research subjects that visibly contribute to the welfare of mankind. (5) Promotions of activities in education and cultivation, cooperation with industries, and international cooperation are recommended. (6) Further cooperation is recommended with such institutes as Japan Atomic Energy Research Institute and Japan Nuclear Cycle Development Institute. (7) Ensuring the safety and reliability is the premise for the continued operation. As for item 4, the institute selected the following five subjects in 1993. Their attainments were evaluated in 2000. They generally received favorable evaluations: (1) production and utilization of very cold and ultra cold neutrons; (2) radiation damage studies under controlled irradiation conditions; (3) studies of Characteristics of transuranic elements; (4) separation and utilization of short-lived isotopes; and (5) biological and medical basic studies for the advanced medical uses of particle radiation.
7. Fuel problems and future operation For the extended operation beyond April 2004, the institute should first renew the approvals of the local governments. The most important matter in the renewal process may be that the institute presents the procedure to evacuate the spent fuel produced in the extended operation from the site. The spent fuel problem may decide the feasibility of the extended operation of the KUR. The KUR is now operated using the fuel elements of highly enriched uranium–aluminum alloy. The stock of the fabricated elements will be allotted for the coming three-year operation. The full core conversion to the low enriched silicide fuel was not finished with the reason that the raw
5
uranium fuel of high enrichment prepared for the KUR-2 operation was requested to be used up in the KUR. It will take about three years between the preparation of the application to the fuel conversion license and the procurement of new elements. The preparation needs to be started without delay. There are difficult problems before them. As is well known, the USA government will not accept the spent fuel from the foreign research reactors, which are produced with the operation after May 2006. In addition, the COGEMA, France reported two years ago their experience that the silicide fuel cannot be reprocessed under the commercial base. After the report, there started the development of uranium– molybdenum fuel in several countries. The new fuel can be reprocessed and the flexibility in the final disposal can be retained. Irradiation tests of the new fuel are under going or planned in several reactors. The matter of concern of research reactor people is the completion of the development and safety assessment of the new fuel before May 2006 with three years leading time for preparations. At the KUR, they anticipate the insufficiency of years considering the former experience for the case of silicide fuel in Japan. The institute should select one from two possibilities for the extended operation of the KUR. One is to employ the silicide fuel and start the preparation for licensing without any delay. In this case, some spent fuel that cannot be reprocessed should be stored in the spent fuel pool at the site for a long period. The other is to wait until the new type fuel is completely developed. In this case, the operation of the KUR may probably be stopped for a considerable period.
8. Concluding remarks The reactor operator, the institute, is primarily responsible for the fuel problems. The surrounding situations for the extended operation of the KUR are very severe and are rapidly changing. The institute is going to make its best efforts toward
6
Y. Fujita / Physica B 311 (2002) 1–6
the continued operation, including the set of a study table under the framework of the newly rearranged governmental structure. From the author’s opinion and standpoint of hardware at least, a research reactor is one of the
most excellent neutron sources. The overall nuclear technology requires to support research reactors and the inverse relation may be true.
History of the KUR and the view of operation in the near future Yoshiaki Fujita* Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka, Japan
Abstract The 37 years’ history of the Kyoto University Research Reactor is presented on the points of developments of diverse experimental facilities, and operation, maintenance and refurbishment on the reactor. The view of operation in the near future is introduced referring to the review and evaluation works. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Kyoto university research reactor; History; Experimental facilities; Extended operation; Fuel problem
1. Introductory remarks At the Research Reactor Institute, Kyoto University, a new key research facility for the future is being proposed, the accelerator-driven fission assembly being used for basic studies in neutron-multiplication and energy-amplification. It is also intended to continue the operation of the present key facility, the 5 MW-Kyoto University Research Reactor (KUR), until the proposed facility is realized. The prospect of the realization, however, is not so clear at present. The KUR has given an opportunity in this conference to explain its long history and its expectation for the continued operation in a rather short period. 2. History In Japan, the construction of a research reactor shall be authorized legally in the long-range *Fax: +81-724-51-2620. E-mail address: [email protected] (Y. Fujita).
national plan for research and development of atomic energy, which is decided in the Japanese Atomic Energy Commission. The KUR was of course constructed with the authorization. The planning, design and construction, commissioning, operation and utilization were carried out by university people under the influence of the Ministry of Education, Science and Culture. The KUR attained its first criticality and reached the 1-MW nominal power in the same year, 1964. In 1968, the nominal power was raised to 5 MW after upgrading the cooling capability. Since that time, the KUR has been serving the common use for universities and public research organizations. The general-purpose critical assembly, KUCA, was also constructed in 1974. In 1978, the construction license of the KUR-2 was approved by the regulatory body. The construction plan, however, was not realized mainly because of the disapproval of the local government, and was finally canceled in 1991.
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 0 4 7 - X
Y. Fujita / Physica B 311 (2002) 1–6
2
After the construction plan of the KUR-2 came to a standstill, the staff members were devoted to enhance the utilization of the KUR, and refurbish the KUR year by year. They also installed newly developed experimental facilities such as the cold neutron source, the super-mirror neutron guide, the wide-band neutron chopper, and started the study of the boron neutron capture therapy. During 1990 and 1993, the KUR was reviewed by the Kyoto University and the related committee of the Science Council, regarding the achievements of their activities, the role and value, and the continuing operation. The second review was just finished in 2000. The KUR is now satisfactorily operating with minimum chance of unscheduled shutdowns under the surroundings, which change rapidly. The history of the KUR is summarized in Table 1.
3. Developments of diverse experimental facilities As for a personal computer, the weight was first attached to performance of the central processor unit, and then to the peripheral equipment and to the software. Similarly, diverse experimental facilities equipped year by year raised the value of the KUR. The diversity comes from that the KUR has been used by university-researchers in a variety of research fields.
Some of the experimental facilities were installed at the same time with the construction of the reactor, and others have been installed afterwards through the development works of the staff members along with the trend of research. Figs. 1 and 2 show the plan and horizontal sections of the KUR with the installation of the experimental facilities. The water pool is rather small and the reactor is called the well type. Employing the well type and locating the spent fuel pool outside the reactor building, all of the horizontal directions are effectively opened to the installation of beam tubes and thermal columns. For the irradiation experiments accessed vertically to the core, the sub-pool was prepared near the reactor top. The hydraulic conveyer is equipped at the center of the core where the fast and thermal neutron fluxes are the highest. The conveyer has a novel capability that the irradiation sample can be inserted into it and extracted from it during the reactor operation. At the edge of the core or in the reflector, there are three pneumatic tube systems and the long time irradiation plug. The new irradiation plug was also installed recently, in which the temperature of the irradiation sample is controlled with electrical and nuclear heating methods. Two different kinds of thermal columns are equipped. The graphite thermal column was used for neutron thermalization studies in the early
Table 1 History of the KUR and experimental facilities Decade
KUR
’60
’64: Critical, 1 MW ’68: 5 MW
’70 ’80
’81–’84: 1st refurbishment ’89–’92: 2nd refurbishment ’85–’99: 3rd refurbishment ’93: Review
’90
2000
Experimental facilities installed at KUR ’68: ’73: ’77: ’84: ’85: ’86:
Low temp. irrad. loop Ni-mirror NGT Online isotope separator Wide band N-chopper Super mirror NGT Cold neutron source
’90: N. scattering analyzer ’92: Small angle N. scattering ’92: Neutron spin echo ’96: H. W. column modification 98: Temp. control irrad. loop ’00: Review
KUCA, KUR-2, others ’64: ’69: ’74: ’78:
e-LINAC Cobalt-60 KUCA completed KUR-2 license approved
’91: KUR-2 license canceled
Y. Fujita / Physica B 311 (2002) 1–6
3
ometer, the neutron radiography instrument and the iron-filtered neutron irradiation facility.
4. Operation and maintenance
Fig. 1. Vertical section of the KUR.
stage, but in 1987, the cold neutron source with liquid deuterium of 4 l was installed in it. The heavy-water thermal column with a bismuth gamma-ray shield on the irradiation-room side provided a very pure thermal neutron field, which has been used mainly for biological irradiation studies. The thermal column was modified installing aluminum layers and cavities in the heavy water tank to provide both thermal and epithermal neutron fields, which is now used as the BNCT facility for deep-seated brain tumors. The thermal neutron guide tube using natural nickel mirrors is installed on the E-3 beam tube and the super mirror guide tube in the B-4 thermal neutron beam tube. In the four cold neutron beam tubes looking at CNS, the natural nickel guide tube, the supermirror guide tube and the VCN guide tube are installed. Other beam tubes are used for the low-temperature irradiation loop, the isotope separator on line, the four-circle neutron monochrometer, the triple axis neutron diffract-
The KUR is operated from Tuesday morning to Friday evening in a regular week. On Tuesday morning, a few hours are needed for the start-up checking and fuel shuffling. About four months in a year are allotted for overhaul maintenance and the legal inspection to obtain the 1-year operation license. Until recent years, it was the custom at the KUR that both the technicians and researchers share the duty of reactor operation and maintenance. The custom partly remains until now. For example, some of researchers of neutron physics are joined to the operation staff members. There have been a variety of opinions for the custom. Considering that the requirements of the regulatory body for the complete quality assurance system in operation and maintenance have been very strict after the criticality accident, rigorous training is needed for the operation and maintenance staff members. Therefore, the sharing of the duty for operating and maintaining the KUR between researchers and technicians has become difficult.
5. Refurbishment works and integrity inspections For the recent 20 years or after the plan of the KUR-2 construction came to a standstill, a lot of refurbishment works for the KUR were carried out year by year according to their importance order for the safety. Some reactor structures and components have been replaced many times, and others keep their integrity without any replacement. The replacement frequency depends on the surrounding conditions and materials of the structures and components. The typical causes degrading the integrity are radiation damage, mechanical fatigue and wear, and corrosion. The experience at the KUR shows that the corrosion of aluminum alloy is the most prominent.
4
Y. Fujita / Physica B 311 (2002) 1–6
Fig. 2. Horizontal section of the KUR.
The structures and components replaced until now are main heat exchangers, pumps of secondary coolant, the cooling tower, the purifying system of reactor tank water, the heavy water thermal column, the graphite in the thermal column, the emergency generator, the reactorwater supply and drain systems, the instrumentation and control system, the ventilation system and radiation monitor system. The reactor tank, the biological shield and the reactor building are not the objects of replacement. The possibility of corrosion of the aluminum-alloy lining of the reactor tank is the matter of highest concern. The inner side of the lining could be visually inspected. The outer side was inspected from the inner side using an ultrasonic thickness meter. For the shield and the building, the integrity of concrete and reinforced steel were confirmed through appropriate inspections. The recent inspection was carried out in 1999. The former one was in 1991. There was no difference between the inspections, and the institute has the prospect that the integrity of these structures may be preserved for at least the next ten years.
6. Review and evaluation works In recent years, there were several committee works for review and evaluation of the activities of the institute, where the reconsideration of the continued operation of the KUR was one of the main subjects. Several points are extracted, by the author’s valuation, from the results of the works: (1) The KUR has made an acceptable contribution to the basic researches and the cultivation of human resources in the process of the developments of applications of nuclear energy and nuclear radiations. (2) The KUR still has the role and value as a university reactor where many kinds of experiments of trial or sprout step are carried out by researchers and students in diverse research fields. (3) Full core conversion to low enriched uranium fuel is encouraged for the extended operation. (4) The research activity is rather too all-round. The concentration on the limited research subjects is recommended. Most of the
Y. Fujita / Physica B 311 (2002) 1–6
reviewers recommend the research subjects that visibly contribute to the welfare of mankind. (5) Promotions of activities in education and cultivation, cooperation with industries, and international cooperation are recommended. (6) Further cooperation is recommended with such institutes as Japan Atomic Energy Research Institute and Japan Nuclear Cycle Development Institute. (7) Ensuring the safety and reliability is the premise for the continued operation. As for item 4, the institute selected the following five subjects in 1993. Their attainments were evaluated in 2000. They generally received favorable evaluations: (1) production and utilization of very cold and ultra cold neutrons; (2) radiation damage studies under controlled irradiation conditions; (3) studies of Characteristics of transuranic elements; (4) separation and utilization of short-lived isotopes; and (5) biological and medical basic studies for the advanced medical uses of particle radiation.
7. Fuel problems and future operation For the extended operation beyond April 2004, the institute should first renew the approvals of the local governments. The most important matter in the renewal process may be that the institute presents the procedure to evacuate the spent fuel produced in the extended operation from the site. The spent fuel problem may decide the feasibility of the extended operation of the KUR. The KUR is now operated using the fuel elements of highly enriched uranium–aluminum alloy. The stock of the fabricated elements will be allotted for the coming three-year operation. The full core conversion to the low enriched silicide fuel was not finished with the reason that the raw
5
uranium fuel of high enrichment prepared for the KUR-2 operation was requested to be used up in the KUR. It will take about three years between the preparation of the application to the fuel conversion license and the procurement of new elements. The preparation needs to be started without delay. There are difficult problems before them. As is well known, the USA government will not accept the spent fuel from the foreign research reactors, which are produced with the operation after May 2006. In addition, the COGEMA, France reported two years ago their experience that the silicide fuel cannot be reprocessed under the commercial base. After the report, there started the development of uranium– molybdenum fuel in several countries. The new fuel can be reprocessed and the flexibility in the final disposal can be retained. Irradiation tests of the new fuel are under going or planned in several reactors. The matter of concern of research reactor people is the completion of the development and safety assessment of the new fuel before May 2006 with three years leading time for preparations. At the KUR, they anticipate the insufficiency of years considering the former experience for the case of silicide fuel in Japan. The institute should select one from two possibilities for the extended operation of the KUR. One is to employ the silicide fuel and start the preparation for licensing without any delay. In this case, some spent fuel that cannot be reprocessed should be stored in the spent fuel pool at the site for a long period. The other is to wait until the new type fuel is completely developed. In this case, the operation of the KUR may probably be stopped for a considerable period.
8. Concluding remarks The reactor operator, the institute, is primarily responsible for the fuel problems. The surrounding situations for the extended operation of the KUR are very severe and are rapidly changing. The institute is going to make its best efforts toward
6
Y. Fujita / Physica B 311 (2002) 1–6
the continued operation, including the set of a study table under the framework of the newly rearranged governmental structure. From the author’s opinion and standpoint of hardware at least, a research reactor is one of the
most excellent neutron sources. The overall nuclear technology requires to support research reactors and the inverse relation may be true.