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Radiotoxicity and spent fuel. 237 Np case. (n, γ ). (n, γ ). β. (n, 2n). β. 238 U 237 U 237 Np . Tovesson & Hill, PRC 75 034610 (2007) . 235 U 236 U 237 U 237 Np. Motivations.

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237 np case
237Np case

(n,γ)

(n,γ)

β

(n,2n)

β

238U 237U 237Np

Tovesson & Hill, PRC 75 034610 (2007)

  • 235U 236U 237U 237Np
motivations
Motivations
  • Transmutation and incineration of long-lived nuclear wastes : Np, Am, Cm, (Pu ?)
  • Higher concentration of minor actinides in reactor cores
  • Need of accurate cross section of actinides
uranium cycle

Neutron

Capture

 decay

β-

Uranium cycle

β-

Thorium cycle

β-

β-

232Th + n  233Th  233Pa  233U (fissile)

238U + n  239U  239Np  239Pu (fissile)

232U

233U

234U

235U

236U

237U

238U

231Pa

232Pa

233Pa

234Pa

235Pa

230Th

231Th

232Th

233Th

234Th

  • Lower production of minor actinides
  • Thermal breeder possible, with low fissile inventory
slide5

Neutron balance for breeding

of fissile nucleus only (capture/fission)

We start with 1 fission :

-number of destroyed fissile nuclei: 1+a (fission+capture)

  • neutrons needed for next fission: 1+a(fission+capture)
  • neutrons needed to restore the fissile nucleus (breeding): 1+a
  • neutrons released by fission:
  • available additional neutrons:
motivations for fission cross section measurements
Motivations for fission cross section measurements
  • Need of accurate fission cross sections for actinides

- candidates to incineration : 237Np

- involved in the 232Th/233U : 232Th, 233U, 234U

  • Broad neutron energy spectrum (ADS) up to spallation domain
slide11

Fission detection : coincidence method

  • Détection of the 2 fission fragments
  • High level of rejection for alphas and high energy reactions (>10 MeV) : spallation
  • Severe constraint : detectors and target backings very thin
slide17

Neutron

Capture

 decay

Future : f of 231Pa

232U

233U

234U

235U

236U

237U

238U

231Pa

232Pa

233Pa

234Pa

235Pa

230Th

231Th

232Th

233Th

234Th

angular distribution combination of spins
Angular distribution : combination of spins

Basically :

J combines incident spins and orbital momentum

K projection along fission axis

If K << J forward peaking

If K ~ J sideward peaking (even-even target nucleus)

The angular distribution may vary quickly with the energy according to (J,K) of the vibrational resonances

poor knowledge above 10 mev
Poor knowledge above 10 MeV

237Np

232Th

nTOF well suited for describing the quick variations with energy

spallation domain
Spallation domain ?

Tutin et al., NIM A457 (2001) 646

Need to confirm the high anisotropy of 232Th at high energy