This presentation describes the measurement method developed in the study as
well as the future measurement plan in JAEA.
Keywords Fission products • Isotopic composition • Post-irradiation examinations
6.1 Introduction
In fission products in used nuclear fuel, there are several stable isotopes that have a
large neutron absorption effect. For evaluation of the neutronics characteristics of a
nuclear reactor, the amounts of such isotopes should be evaluated by using burn-up
calculation codes. For this purpose, a quantitative analytical method of uranium,
plutonium, and fission products of spent fuels has been studied [1, 2]. However, it is
known that there are several barely measurable elements in such important fission
products.
To assay the amount of many fission products, radiation measurement is widely
used. Cesium-134 and -137 are typical examples. However, this method is not
applicable for isotopes that are important from the aspect of reactivity assessment
because they are stable isotopes. For such isotopes, there is the possibility of
adopting the isotopic dilution method (IDM), which has been used for measurement
of actinides and a few fission products such as neodymium.
In the Japan Atomic Energy Agency (JAEA), thermal ionization mass spectrometry (TIMS) has been used for IDM to evaluate the burn-up value of the used fuel.
TIMS is one of the most reliable instruments to determine the isotopic ratio and the
obtained result is considered to be the reference. However, TIMS needs relatively
large amounts of the fuel solution sample and a long time is required to obtain the
final results after dissolution of the fuel and preparation of the measurement sample.
The most serious problem is that the important fission isotopes for the reactivity
assessment belong to the rare earth elements. Because many of these have the same
mass number, we need an efficient chemical separation method and highperformance instruments for measuring the isotopic composition that which should
have high sensitivity and resolution. For this reason, the fission products important
for reactivity assessment are barely measurable and available data for such fission
products are scarce.
JAEA has been active in measuring the isotopic composition of the spent nuclear
fuel from the 1980s and the obtained data have been archived in the SFCOMPO
database [3], which has been supported by the OECD/NEA databank. Based on this
past experience, JAEA launched a development program [4] of measurement of the
fission products important for reactivity assessment under the auspices of the Japan
Nuclear Energy Safety Organization (JNES) in 2008 and successfully finalized the
program in 2012.
In this program, a combined method of chromatographic separation of uranium,
plutonium, and fission products from irradiated nuclear fuels was developed.
Furthermore, by the introduction of high-resolution inductively coupled plasma
48
K. Suyama et al.
well as the future measurement plan in JAEA.
Keywords Fission products • Isotopic composition • Post-irradiation examinations
6.1 Introduction
In fission products in used nuclear fuel, there are several stable isotopes that have a
large neutron absorption effect. For evaluation of the neutronics characteristics of a
nuclear reactor, the amounts of such isotopes should be evaluated by using burn-up
calculation codes. For this purpose, a quantitative analytical method of uranium,
plutonium, and fission products of spent fuels has been studied [1, 2]. However, it is
known that there are several barely measurable elements in such important fission
products.
To assay the amount of many fission products, radiation measurement is widely
used. Cesium-134 and -137 are typical examples. However, this method is not
applicable for isotopes that are important from the aspect of reactivity assessment
because they are stable isotopes. For such isotopes, there is the possibility of
adopting the isotopic dilution method (IDM), which has been used for measurement
of actinides and a few fission products such as neodymium.
In the Japan Atomic Energy Agency (JAEA), thermal ionization mass spectrometry (TIMS) has been used for IDM to evaluate the burn-up value of the used fuel.
TIMS is one of the most reliable instruments to determine the isotopic ratio and the
obtained result is considered to be the reference. However, TIMS needs relatively
large amounts of the fuel solution sample and a long time is required to obtain the
final results after dissolution of the fuel and preparation of the measurement sample.
The most serious problem is that the important fission isotopes for the reactivity
assessment belong to the rare earth elements. Because many of these have the same
mass number, we need an efficient chemical separation method and highperformance instruments for measuring the isotopic composition that which should
have high sensitivity and resolution. For this reason, the fission products important
for reactivity assessment are barely measurable and available data for such fission
products are scarce.
JAEA has been active in measuring the isotopic composition of the spent nuclear
fuel from the 1980s and the obtained data have been archived in the SFCOMPO
database [3], which has been supported by the OECD/NEA databank. Based on this
past experience, JAEA launched a development program [4] of measurement of the
fission products important for reactivity assessment under the auspices of the Japan
Nuclear Energy Safety Organization (JNES) in 2008 and successfully finalized the
program in 2012.
In this program, a combined method of chromatographic separation of uranium,
plutonium, and fission products from irradiated nuclear fuels was developed.
Furthermore, by the introduction of high-resolution inductively coupled plasma
48
K. Suyama et al.