A^WPul^^-frli, H*Jjji^>jffl^nJfffl£tff«SWF$EftF#ii* (T319-1195 ktt9M&&[ si$m&*t) for, *D^LiBL<fc$i,\ &*>, ccon^Mcwa^AJ.-n^-yjSA^^ftW-tr/ *- (T319-H95 fc#mflWiP5fc/fettHMn-f;jffi£tffrt) xm^i-i^g'iWnsrfe- This report is issued irregularly. Inquiries about availability of the reports should be addressed to Research Information Division, Department of Intellectual Resources, Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken T319—1195, Japan. ©Japan Atomic Energy Research Institute, 2003 JAERI-Tech 2003-028 t&w&T&miz&z TRACY mmftmvwmiimmamfe *s, m-mm <&n+-=m mm (2003^1 n 31 B%M) TRACY zm^tzmmR^mz&ttg>mt)mm&m&&<ffl7£.?z>tz®\z, m^^^^m. *«H&raf: T319-H95 ^ttmajiBfiu^jswa^esw i JAERI-Tech 2003-028 Measurements of Power Profile in TRACY Supercritical Experiment by Detecting Epithermal Neutrons Ken NAKAJIMA, Hiroshi YANAGISAWA+ and Yoshinori MIYOSHI Department of Fuel Cycle Safety Research Nuclear Safety Research Center Tokai Research Establishment Japan Atomic Energy Research Institute Tokai-mura, Naka-gun, Ibaraki-ken (Received January 31,2003) We have tried to measure the power profile in the TRACY supercritical experiment with high accuracy by detecting epithermal neutrons. In order to measure the epithermal neutrons, a cadmium covered 235U fission chamber was used, and a neutron moderator of polyethylene, was set inside the cadmium to enhance the neutron detection efficiency. In addition, a lead shield was used to reduce the noise current due to gamma-rays. The measured results were compared with the ones using a thermal neutron detector, and it was found that the time delay effect in the thermal neutron detection, which was caused by the flight time of neutrons to reach the detector, distorted the power profile and reduced its peak value. The reduction ratio of peak power was about 4% for the relatively slow power change with the inserted reactivity of 1.5$, but it became more than 40% for the rapid power change with the reactivity of about 3$. Keywords: TRACY, Power Profile Measurements, Epithermal Neutron Detection, 235U Fission Chamber, Gamma-ray Shield, Time Delay Effect, Peak Power Reduction + Department of Safety Research Technical Support u JAERI-Tech 2003-028 1 . \$Vtb\z 1 2. 4"»7^;i/^-MH 3 2,111 3 2.2 7 4)\s9-%l£<DMM 3 2.3 UtflMWllZ-D^X 5 2.4 £ttb 6 3. mw&?fcmz&zmmm<DM%.u% 15 3.1 m s 15 3.2 s^nsm 15 3.3 ££:J6 16 4. ££#) 24 ##» 24 ttB 1 : TRACY (DWtM 26 tti* 2 : mm-W 28 tt^3:^4>tt^ffi»ffl££ff 29 Contents 1 . Introduction 1 2 . Effect of Neutron Filters 3 2.1 Outline 3 2.2 Measurements of Filter Effect 3 2.3 On the Power Oscillation 5 2.4 Summary 6 3 . Results of Power Profile Measurement by Detecting Epithermal Neutrons 15 3.1 Outline 15 3.2 Results of Measurement 15 3.3 Summary 16 4 . Summary 24 References 24 Appendix 1: Outline of TRACY 26 Appendix 2: List of Experiments 28 Appendix 3: Measurement Conditions of Epithermal Neutron Detection System 29 ui This is a blank page. 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