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Journal Articles

Mechanisms of positive temperature reactivity coefficients of dilute plutonium solutions

Yamamoto, Toshihiro; Miyoshi, Yoshinori

Nuclear Science and Engineering, 142(3), p.305 - 314, 2002/11

Times Cited Count：2 Percentile：10.15(Nuclear Science & Technology)

Mechanisms of a positive temperature reactivity coefficient that occurs in a dilute plutonium solution are investigated based on the perturbation theory and the four-factor formula. The temperature coefficient of a solution fuel is positive if the adjoint flux or f between 0.05eV and 0.2eV increases with neutron energy. As compared to Pu-239, Pu-241 has a tendency to make the temperature coefficient of a plutonium solution. As Pu-241 in a plutonium solution decays into Am-241 with time, the temperature coefficient becomes more positive. Since the capture cross sections of most neutron absorbers such as boron and gadolinium decreases with increasing neutron energy, soluble absorbers make the temperature coefficient positive for higher concentration plutonium solution. Cadmium and samarium solved in a dilute plutonium solution exceptionally can keep the temperature coefficient. A fixed neutron absorber generally makes the temperature coefficient negative regardless of the property of absorber materials.

JAEA Reports

Development and the results for the control rods in MK-II core of experimental fast reactor JOYO

Miyakawa, Shunichi; ; Soga, Tomonori

PNC TN9410 97-068, 113 Pages, 1997/07

PNC-TN9410-97-068.pdf:3.97MB

Since the first control rod design for the Joyo Mk-II core (about twenty years ago), there have been several challenging improvements; for example, a helium venting mechanism and a flow induced vibration prevention mechanism. Forty-four control rods with these various modifications have been fabricated. To date, thirty-four have been irradiated and the sixteen have been examined, This experience and effort has produced fruitful results: (1)Efficiency and reliability of the diving-bell type Helium venting mechanism (2)Efficiency of the flow induced vibration prevention mechanism (3)Efficiency of the improvement for scram damping mechanism (4)Clarification of absorvber-pellet-cladding-mechanical-interaction (ACMI)phenomena and preventive methods The fourth result listed above has been a subject of investigation for fifteen years in several countries, that is a main phenomena to dominate control rod life time. The results of this investigation of ACMI in absorber elements are summarized below: (a)In five of Joyo Mk-II control rods, cladding cracks were found in fifteen of the elements. These cracks were caused by a acceleration ACMI, due to B $_{4}$ C fragments relocation. They occurred over a wide burnup range from 5E+26 Cap./m $^{3}$ to 45E+26Cap./m $^{3}$ in a nearly typical provability distribution. The cladding cracked because of its low ductility (approximately 1/4 lower than the uniform elongation of usual tensile testing for irradiated 316SS cladding) due to neutron irradiation and the ultra slow ACMI induced strain rate. (b)In this case the crack growth rate is extremely slow and the ACMI induced cracking in absorber elements do not influence either the reactor or plant operations. It is on this basis that a strict limitation to avoid the cladding crack is not necessary. According1y, it is suggested that a realistic design standard should consider the ACMI phenomena and the burnup limit be based on the nominal base calculation for average plastic strain use ...

JAEA Reports

None

Power Reactor and Nuclear Fuel Development Corporation

PNC TN9360 95-002, 98 Pages, 1995/11

PNC-TN9360-95-002.pdf:4.61MB

no abstracts in English

JAEA Reports

None

Power Reactor and Nuclear Fuel Development Corporation

PNC TN9360 95-001, 104 Pages, 1995/11

PNC-TN9360-95-001.pdf:4.23MB

no abstracts in English

JAEA Reports

Report of phase I program (19891993) on nuclear material crossover research

Kano, Shigeki; Tachi, Yoshiaki; ; ; Yoshida, Eiichi; Hirakawa, Yasushi

PNC TN9410 94-113, 70 Pages, 1994/04

PNC-TN9410-94-113.pdf:3.67MB

(Purpose) This report describes the outline, research results obtained, interchange activities, etc. of the Phase I Program on the Nuclear Material Crossover Research, which has been conducted by related research institutes including PNC/OEC from 1989 through 1993 fiscal year, and shows the Phase II Program to be started from 1994 fiscal year. (Method) Crossover research programs, research results and interchange methods were decided through discussions at the crossover research comittee (chairman : Prof.M.Okamoto, TIT) in which PNC, JAERI, NRIM, NIRIM and NCLI were participated as main members. Forums, seminars, symposiums and workshops with domestic and foreign experts on materials research were set up as the opportunities for interchange. (Results) (1)As secretary institutes, PNC and JAERl planned eight times of forums, 3 times of seminars, twice of domestic symposiums, once of international symposium, five workshops with research institutes in France, Germany, Italy and the Netherland. The contacts with outside experts, collection of new information on advanced materials, receipt of test samples, achievement of collaborative research, etc. through these interchanges were much valuable for effective performance of PNC research. (2)The following results were obtained on PNC research. The prospects on creation of following advanced materials were obtained through these interchanges: (a)advanced ceramics having excellent corrosion resistance to sodium, (b)longer life neutron absorbing materials having higher resistance to cracking than B $_{4}$ C, (c)high performance shielding materials having higher heat resistance than conventional materials. (3)Phase II Program to be started from 1994 fiscal year has been planned by main five institutes and authorized through the evaluation by two evaluation comittees organized separately by the crossover research comittee and PNC. (Conclusion) The prospects on creation of several advanced materials were obtained through ...

JAEA Reports