History of the KUR and the view of operation in the near future

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  • Physica B 311 (2002) 16

    History of the KUR and the view of operationin 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, KyotoUniversity, a new key research facility for thefuture is being proposed, the accelerator-drivenssion assembly being used for basic studies inneutron-multiplication and energy-amplication.It is also intended to continue the operation of thepresent key facility, the 5MW-Kyoto UniversityResearch Reactor (KUR), until the proposedfacility is realized. The prospect of the realization,however, is not so clear at present. The KUR hasgiven an opportunity in this conference to explainits long history and its expectation for thecontinued operation in a rather short period.

    2. History

    In Japan, the construction of a research reactorshall be authorized legally in the long-range

    national plan for research and development ofatomic energy, which is decided in the JapaneseAtomic Energy Commission. The KUR was ofcourse constructed with the authorization. Theplanning, design and construction, commissioning,operation and utilization were carried out byuniversity people under the inuence of theMinistry of Education, Science and Culture.The KUR attained its rst criticality and

    reached the 1-MW nominal power in the sameyear, 1964. In 1968, the nominal power was raisedto 5MW after upgrading the cooling capability.Since that time, the KUR has been serving thecommon use for universities and public researchorganizations.

    The general-purpose critical assembly, KUCA,was also constructed in 1974. In 1978, theconstruction license of the KUR-2 was ap-proved by the regulatory body. The construc-tion plan, however, was not realized mainlybecause of the disapproval of the local govern-ment, and was nally canceled in 1991.

    *Fax: +81-724-51-2620.

    E-mail address: fujita@rri.kyoto-u.ac.jp (Y. Fujita).

    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

  • After the construction plan of the KUR-2 cameto a standstill, the staff members were devoted toenhance the utilization of the KUR, and refurbishthe KUR year by year. They also installed newlydeveloped experimental facilities such as the coldneutron source, the super-mirror neutron guide,the wide-band neutron chopper, and started thestudy of the boron neutron capture therapy.During 1990 and 1993, the KUR was reviewed

    by the Kyoto University and the related committeeof the Science Council, regarding the achievementsof their activities, the role and value, and thecontinuing operation. The second review was justnished in 2000.The KUR is now satisfactorily operating with

    minimum chance of unscheduled shutdowns underthe surroundings, which change rapidly. Thehistory of the KUR is summarized in Table 1.

    3. Developments of diverse experimental facilities

    As for a personal computer, the weight was rstattached to performance of the central processorunit, and then to the peripheral equipment and tothe software. Similarly, diverse experimental facil-ities equipped year by year raised the value of theKUR. The diversity comes from that the KUR hasbeen used by university-researchers in a variety ofresearch elds.

    Some of the experimental facilities were installedat the same time with the construction of thereactor, and others have been installed afterwardsthrough the development works of the staffmembers along with the trend of research. Figs. 1and 2 show the plan and horizontal sections of theKUR with the installation of the experimentalfacilities.The water pool is rather small and the reactor is

    called the well type. Employing the well type andlocating the spent fuel pool outside the reactorbuilding, all of the horizontal directions areeffectively opened to the installation of beamtubes and thermal columns. For the irradiationexperiments accessed vertically to the core, thesub-pool was prepared near the reactor top. Thehydraulic conveyer is equipped at the center of thecore where the fast and thermal neutron uxes arethe highest. The conveyer has a novel capabilitythat the irradiation sample can be inserted into itand extracted from it during the reactor operation.At the edge of the core or in the reector, there

    are three pneumatic tube systems and the longtime irradiation plug. The new irradiation plugwas also installed recently, in which the tempera-ture of the irradiation sample is controlled withelectrical and nuclear heating methods.Two different kinds of thermal columns are

    equipped. The graphite thermal column was usedfor neutron thermalization studies in the early

    Table 1

    History of the KUR and experimental facilities

    Decade KUR Experimental facilities installed at KUR KUCA, KUR-2, others

    60 64: Critical, 1MW 64: e-LINAC

    68: 5MW 68: Low temp. irrad. loop 69: Cobalt-60

    70 73: Ni-mirror NGT 74: KUCA completed

    77: Online isotope separator 78: KUR-2 license approved

    80 8184: 1st refurbishment 84: Wide band N-chopper

    8992: 2nd refurbishment 85: Super mirror NGT

    8599: 3rd refurbishment 86: Cold neutron source

    93: Review

    90 90: N. scattering analyzer 91: KUR-2 license canceled

    92: Small angle N. scattering

    92: Neutron spin echo

    96: H. W. column modication

    98: Temp. control irrad. loop

    2000 00: Review

    Y. Fujita / Physica B 311 (2002) 162

  • stage, but in 1987, the cold neutron source withliquid deuterium of 4 l was installed in it.The heavy-water thermal column with a bis-

    muth gamma-ray shield on the irradiation-roomside provided a very pure thermal neutron eld,which has been used mainly for biological irradia-tion studies. The thermal column was modiedinstalling aluminum layers and cavities in theheavy water tank to provide both thermal and epi-thermal neutron elds, which is now used as theBNCT facility for deep-seated brain tumors.The thermal neutron guide tube using natural

    nickel mirrors is installed on the E-3 beam tubeand the super mirror guide tube in the B-4 thermalneutron beam tube. In the four cold neutron beamtubes looking at CNS, the natural nickel guidetube, the supermirror guide tube and the VCNguide tube are installed. Other beam tubes are usedfor the low-temperature irradiation loop, theisotope separator on line, the four-circle neutronmonochrometer, the triple axis neutron diffract-

    ometer, the neutron radiography instrument andthe iron-ltered neutron irradiation facility.

    4. Operation and maintenance

    The KUR is operated from Tuesday morning toFriday evening in a regular week. On Tuesdaymorning, a few hours are needed for the start-upchecking and fuel shufing. About four months ina year are allotted for overhaul maintenance andthe legal inspection to obtain the 1-year operationlicense.Until recent years, it was the custom at the

    KUR that both the technicians and researchersshare the duty of reactor operation and main-tenance. The custom partly remains until now. Forexample, some of researchers of neutron physicsare joined to the operation staff members. Therehave been a variety of opinions for the custom.Considering that the requirements of the regula-tory body for the complete quality assurancesystem in operation and maintenance have beenvery strict after the criticality accident, rigoroustraining is needed for the operation and main-tenance staff members. Therefore, the sharing ofthe duty for operating and maintaining the KURbetween researchers and technicians has becomedifcult.

    5. Refurbishment works and integrity inspections

    For the recent 20 years or after the plan of theKUR-2 construction came to a standstill, a lot ofrefurbishment works for the KUR were carriedout year by year according to their importanceorder for the safety. Some reactor structures andcomponents have been replaced many times, andothers keep their integrity without any replace-ment. The replacement frequency depends on thesurrounding conditions and materials of thestructures and components.The typical causes degrading the integrity are

    radiation damage, mechanical fatigue and wear,and corrosion. The experience at the KUR showsthat the corrosion of aluminum alloy is the mostprominent.

    Fig. 1. Vertical section of the KUR.

    Y. Fujita / Physica B 311 (2002) 16 3

  • The structures and components replaced untilnow are main heat exchangers, pumps of second-ary coolant, the cooling tower, the purifyingsystem of reactor tank water, the heavy waterthermal column, the graphite in the thermalcolumn, the emergency generator, the reactor-water supply and drain systems, the instrumenta-tion and control system, the ventilation system andradiation 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-alloylining of the reactor tank is the matter of highestconcern. The inner side of the lining could bevisually inspected. The outer side was inspectedfrom the inner side using an ultrasonic thicknessmeter. For the shield and the building, theintegrity of concrete and reinforced steel wereconrmed through appropriate inspections. Therecent inspection was carried out in 1999. Theformer one was in 1991. There was no differencebetween the inspections, and the institutehas the prospect that the integrity of thesestructures may be preserved for at least the nextten years.

    6. Review and evaluation works

    In recent years, there were several committeeworks for review and evaluation of the activities ofthe institute, where the reconsideration of thecontinued operation of the KUR was one of themain subjects. Several points are extracted, by theauthors valuation, from the results of the works:

    (1) The KUR has made an acceptable contribu-tion to the basic researches and the cultivationof human resources in the process of thedevelopments of applications of nuclear en-ergy and nuclear radiations.

    (2) The KUR still has the role and value as auniversity reactor where many kinds of experi-ments of trial or sprout step are carried out byresearchers and students in diverse researchelds.

    (3) Full core conversion to low enriched ura-nium fuel is encouraged for the extendedoperation.

    (4) The research activity is rather too all-round.The concentration on the limited researchsubjects is recommended. Most of the

    Fig. 2. Horizontal section of the KUR.

    Y. Fujita / Physica B 311 (2002) 164

  • reviewers recommend the research subjectsthat visibly contribute to the welfare ofmankind.

    (5) Promotions of activities in education andcultivation, cooperation with industries,and international cooperation are recom-mended.

    (6) Further cooperation is recommended withsuch institutes as Japan Atomic EnergyResearch Institute and Japan Nuclear CycleDevelopment Institute.

    (7) Ensuring the safety and reliability is thepremise for the continued operation.

    As for item 4, the institute selected the followingve subjects in 1993. Their attainments wereevaluated in 2000. They generally received favor-able evaluations:

    (1) production and utilization of very cold andultra cold neutrons;

    (2) radiation damage studies under controlledirradiation conditions;

    (3) studies of Characteristics of transuranic ele-ments;

    (4) separation and utilization of short-lived iso-topes; and

    (5) biological and medical basic studies for theadvanced medical uses of particle radiation.

    7. Fuel problems and future operation

    For the extended operation beyond April 2004,the institute should rst renew the approvals of thelocal governments. The most important matter inthe renewal process may be that the institutepresents the procedure to evacuate the spent fuelproduced in the extended operation from the site.The spent fuel problem may decide the feasibilityof the extended operation of the KUR.The KUR is now operated using the fuel

    elements of highly enriched uraniumaluminumalloy. The stock of the fabricated elements will beallotted for the coming three-year operation. Thefull core conversion to the low enriched silicidefuel was not nished with the reason that the raw

    uranium fuel of high enrichment prepared for theKUR-2 operation was requested to be used up inthe KUR. It will take about three years betweenthe preparation of the application to the fuelconversion license and the procurement of newelements. The preparation needs to be startedwithout delay.

    There are difcult problems before them. As iswell known, the USA government will notaccept the spent fuel from the foreign researchreactors, which are produced with the operationafter May 2006. In addition, the COGEMA,France reported two years ago their experiencethat the silicide fuel cannot be reprocessedunder the commercial base. After the report,there started the development of uraniummolybdenum fuel in several countries. Thenew fuel can be reprocessed and the exibilityin the nal disposal can be retained. Irradiationtests of the new fuel are under going or plannedin several reactors. The matter of concern ofresearch reactor people is the completion of thedevelopment and safety assessment of the newfuel before May 2006 with three years leadingtime for preparations. At the KUR, theyanticipate the insufciency of years consideringthe former experience for the case of silicide fuelin Japan.

    The institute should select one from twopossibilities for the extended operation of theKUR. One is to employ the silicide fuel and startthe preparation for licensing without any delay. Inthis case, some spent fuel that cannot be repro-cessed should be stored in the spent fuel pool at thesite for a long period. The other is to wait until thenew type fuel is completely developed. In this case,the operation of the KUR may probably bestopped for a considerable period.

    8. Concluding remarks

    The reactor operator, the institute, is primarilyresponsible for the fuel problems. The surroundingsituations for the extended operation of the KURare very severe and are rapidly changing. Theinstitute is going to make its best efforts toward

    Y. Fujita / Physica B 311 (2002) 16 5

  • the continued operation, including the set of astudy table under the framework of the newlyrearranged governmental structure.From the authors opinion and standpoint of

    hardware at least, a research reactor is one of the

    most excellent neutron sources. The overallnuclear technology requires to support researchreactors and the inverse relation may be true.

    Y. Fujita / Physica B 311 (2002) 166

    History of the KUR and the view of operation in the near futureIntroductory remarksHistoryDevelopments of diverse experimental facilitiesOperation and maintenanceRef...

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