Search - OECD Nuclear Energy Agency

Table 2. One-group effective cross-sections of boron and plutonium isotopes in the HYPER core
σ ( n , γ ) , barn ( , α)
σ n , barn σ f , barn
10 B
11 B
7 Li
238 Pu
239 Pu
240 Pu
241 Pu-
2.978E-4
4.468E-5
3.097E-5
0.631
0.397
0.427
0.375
2.307
–
–
–
–
–
–
–
–
–
1.089
1.693
0.358
2.296
The ( n , α)
reaction of 10 B is exothermic and produces helium gas as well as Li-7. Therefore, care
must be taken, when using 10 B as a burnable absorber in nuclear reactors. It is well known that direct
mixing 10 B with fuel impairs the fuel integrity since the fuel swelling is enhanced due to helium gas
and liquid-phase Li-7. To overcome this limitation, Westinghouse has developed a burnable absorber
technology for PWRs, where the fuel rod is coated with ZrB 2 [2], and achieved successful
performance. Thickness of the ZrB 2 layer is about 0.002 cm.
Unfortunately, it is not easy to use the Westinghouse approach directly for HYPER, since the
TRU fuel of HYPER is very radioactive. Therefore, we have used a slightly different option, i.e.
B 4 C-coated cladding, where the inner surface of cladding is coated with B 4 C. In the present work, B 4 C
is used, instead of ZrB 2 , since it is easily available and has more boron elements than ZrB 2 . Thickness
of the B 4 C layer is 0.0009 cm or 0.0012 cm. In the natural boron, abundances of 10 B and 11 B are 19.8%
and 80.2%, respectively. In order to maximise the 10 B loading, it is assumed that 10 B is enriched up to
90% atomic percent in this paper. Figure 2 shows the burnable absorber rod for the HYPER core. It
should be noted that two cutback regions, where the absorber is not applied, are adopted to flatten the
axial power distribution.
Figure 2. Fuel rod with B4C-coated cladding in HYPER
785