JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
deposition, RI production rate and so on are necessary. Those are the neutron and charged
particle spectra and activation cross sections below 250 MeV.
JENDL Intermediate Files are also useful for accelerator related applications such as
accelerator driven system (ADS) for nuclear waste transmutation, International Fusion
Material Irradiation Facility (IFMIF). The neutron production cross section and neutron
spectrum are important.
2.3 Safety Researches
The safety researches can be categorized into “frontend” (Nuclear Fuel Supply),
“reactor” (Core Characteristics and Operation), “down-stream” of nuclear fuel cycle (Spent
Fuel Treatment) and “backend” (Nuclear Waste Management). At the frontend stage,
criticality safety for handling of processing, storage and transport of fuel should be considered.
If fail to control, critical accident, ex. the JCO Accident (1999.9.30), is happened. For the
reactor safety, the operation by grasping power distribution, control rod worth, reactivity
coefficients, etc. is important (ex. Chernobyl (1986.4.26), and TMI Accident (1979.3.28)).
For this purpose, the prediction of burn-up characteristics and evaluation of delayed neutron
effects should also be considered. At the down-stream stage of nuclear fuel cycle, the
criticality safety for storage, transport and reprocessing, shielding and decay heat is important.
At the backend stage, the waste management such as the long-term radio-toxicity (HLW) and
clearance level (LLW) should be considered.
The “Criticality Safety” is one of the key items for safety researches and well
established. Though recent experiments are getting more expensive relatively than before,
some databases have been prepared, ex. the OECE/NEA International Criticality Safety
Benchmark Evaluation Project (ICSBEP), the Criticality Safety Handbook (JAEA-Data/Code
2009-010) with the critical limits for minimum mass, size, concentration, etc. at keff = 0.98.
For the criticality safety research, nuclear data such as fission and capture cross sections,
fission product yields (FPY) are the most important.
Safety researches at the down-stream and backend stages are getting more important
from my point of view, since the replacement period of current nuclear power plants is
coming near future and competition of international sales of power reactors by developed
countries is harder so as to reduce CO2 emission. The critical safety is still important for
spent fuel storage and cask design; keeping “Subcritical when immersed in water” and
“Subcritical when piled up in numbers”. For this purpose, neutron absorbers, B-SUS, B-Al,
B-Resin, Cd-Alloy etc. are considered to keep keff < 0.95 even for unirradiated fuel with initial
235 U enrichment. The “Burn-up Credit” is also considered to estimate the reactivity loss and
the nuclide concentrations. The Post Irradiation Experiments (PIE) is one of the good
benchmark tests for analyzing accuracy of calculations and data (FPY, capture cross section
and decay data). Important nuclides are, for example, 12FPs ( 95 Mo, 99 Tc, 103 Rh, 133 Cs,
143,145 Nd, 147,149,150,152 Sm, 153 Eu, 155 Gd) by JAERI-Tech 2001-055, 15FPs ( 95 Mo, 99 Tc, 101 Ru,
103 Rh, 109 Ag, 133 Cs, 143,145 Nd, 147,149,150,151,152 Sm, 153 Eu, 155 Gd) by OECD BUC WG and 13FPs
( 99 Tc, 103 Rh, 131 Xe, 133 Cs, 143,145 Nd, 147 Pm, 147,149,151,152 Sm, 153 Eu, 155 Gd) by SAND87-0151 for
casks.
The clearance (= radioactive nuclide productions) level estimation is needed for
dispose waste, especially at the reactor replacement period. For this purpose, radioactive
isotope (RI) production should be estimated as accurate as possible and activation cross
sections and decay data are necessary. The nuclide list included in the IAEA Safety
Guideline for the clearance level estimation is shown in Table 3 as an example. The similar
list is also enacted in Japan and is given in Table 3. Other long-lived RIs, for example 182 Hf