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RRFM 2009 Transactions - European Nuclear Society

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Results<br />

The burn up calculations were done in 100 steps with 45 days duration but the results get<br />

continuously more uncertain after the first third of the total burn up period especially for the<br />

thermal spectrum due to limited self shielding capabilities of DARWIN. This was considered<br />

acceptable for the preliminary study in preparation for more detailed and time consuming<br />

calculations with HORUS code package. Nevertheless the results demonstrate that matching<br />

He to fission ratio and burn up vs. time is possible between fast and thermal spectra. The<br />

following three graphs show the behaviour of selected sample and flux combinations.<br />

He production<br />

1.40000E-03<br />

1.20000E-03<br />

He mass/ intitial HM mas<br />

1.00000E-03<br />

8.00000E-04<br />

6.00000E-04<br />

4.00000E-04<br />

2.00000E-04<br />

0.00000E+00<br />

0<br />

180<br />

360<br />

540<br />

720<br />

900<br />

1080<br />

1260<br />

1440<br />

1620<br />

1800<br />

1980<br />

2160<br />

time [days]<br />

2340<br />

2520<br />

2700<br />

2880<br />

3060<br />

3240<br />

3420<br />

3600<br />

3780<br />

3960<br />

4140<br />

4320<br />

4500<br />

SFR reference<br />

JHR reference<br />

JHR 20% enriched, 3% flux<br />

JHR 2.5% Am, 33% flux<br />

JHR 10% enrichted, 33% flux<br />

Fig 2: He content in the sample. Please note flux percentage given for JHR samples refers to<br />

the JHR reference flux.<br />

Because the reaction chain 241 Am (n,γ) 242 Am (d,β) 242 Cm (d,α) 238 Pu is responsible for most<br />

of the He production, the He content is only dependent on the neutron flux level and Am<br />

content of a sample for a given neutron spectrum. This means U enrichment can be used to<br />

shift the He to fission ratio curve given in figure 3 up or down without changing its shape.<br />

While allowing for a very good match between for example the SFR reference and the JHR<br />

10% enriched sample at 33% max. flux, the energy and He deposition per time differ<br />

considerable and the difference is burn up dependent. To speed up an experiment from 10<br />

years irradiation time to 5 years for the same burn up is not inconvenient, but the higher<br />

power also effects fuel behaviour. On other hand the He contends and burn up curves for the<br />

JHR 20% enriched sample with 10% max. flux are individually far closer to their counter parts<br />

of the SFR but the He to fission ratio in figure 3 is actually worse than most other examples.<br />

447 of 455

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