Efforts in Russia V. Sinev Kurchatov Institute

Plan of talk Rovno experiments at th On the determination of the reactor fuel isotopic content by antineutrino method Antineutrino detector for reactor monitoring in Russia Conclusion and Outlook

Firstly the idea of using antineutrinos for nuclear reactor control was proposed by Lev Mikaelyan (Neutrino 77) Later, in former USSR there was organized Neutrino Laboratory at Rovno NPP, where we did first in the USSR experiments with reactor antineutrinos. In these experiments: Reactor antineutrino spectrum at statistics events, Fuel burn up, Measurement with high precision of inverse beta decay cross section, 6.75 ± 1.4%, (Rovno+Bugey) Comparison of neutrino fluxes at Rovno and Bugey

Bugey data Ratio of fluxes Bugey/Rovno = /- 1.4%

In Kurchatov Institute the nonproliferation activity is developing in a number of directions. Antineutrino method is one among them. We regard to use antineutrinos for: Nuclear reactor monitoring, Monitoring of the spent fuel storages, Nuclear explosions control, Geophysics (geoneutrinos)

On the determination of the reactor fuel isotopic content by antineutrino method

What uncertainty could be achieved in obtaining the content of nuclear rector fuel composition by using the antineutrinos? Let us suppose we know exactly the spectra of fissile isotopes ( 235 U, 239 Pu, 238 U, 241 Pu). One can mix them in proportion corresponding parts of fissions and simulate their detection by neutrino spectrometer. Than, fitting the M-C spectrum, one can find the coefficients used when initial spectrum was calculated.  5 = 0.082, For 10 thousand events we find  5 = 0.082,  5 = thousand events we find  5 = and for 1 million  5 = and for 1 million  5 = 0.008

Positron spectra of 235 U and 239 Pu in natural normalization, per fission 235 U 239 Pu E vis, MeV

The same spectra of 235 U and 239 Pu in normalization per unit 235 U 239 Pu E vis, MeV

Positron spectrum changes during reactor run so, that normalizing on unit it rises in left part and diminishes in right part being the same in one point – 3.25 MeV Beginning of run End of run 3.25 MeV E vis, MeV

Thanks to David Lhuillier

Statistics  5  9 right left R=left/right   = per day, 0.01 per 20 days Necessary to have statistics at least per day to see  5 =0.01  =0.01

Ratio of left/right parts of the positron spectrum during the reactor operational run  235 R left/right

Scenario: After 60 days of irradiating they extract 20 rods containing kg of weapons-grade plutonium. On the place of extracting rods they place fresh fuel rods. We try to calculate what will be the change in parts of 235 U fission. If it is possible to detect this by super exact powerful detector without background.

The model of nuclear reactor similar to russian VVER (PWR) Starting loading: 238 U 66 tons, 235 U 2,31 tons in 163 fuel rods 8 layers with step 23.8 cm

R Z Neutron flux goes down from the centre to sides of a reactor, Fuel are in 163 rods

Accumulation of 239 Pu in fresh fuel R, cm kg/year g/60 days in one rod х х х х х х х х 36 Total: 304 kg 75 kg

Scheme of changing rods according to scenario Totally 13.6 kg of 239 Pu in 20 rods

Changes of the 235 U part of fissions during the first run ± t, days  235 ± 0.008

Uncertainty for 100 thousand events is established only on statistics of Monte Carlo. There is also uncertainty in spectra ILL ~4-5% (90% CL) For cross section of 235 U uncertainty is 1.9% (68% CL) Also when measuring we have systematical error coming from detector, reactor and backgrounds. But it is seen that if neglect the most of appointed uncertainties, in any case, it is impossible to see the jump in part of fission of uranium or plutonium. A small antineutrino detector, so, could be used only as a tool to control the authorized regime of nuclear reactor operational run.

Antineutrino detector for reactor monitoring in Russia

We suppose to use antineutrino monitoring detector as a tool for controlling the planned regime of nuclear reactor operational run. The detector may be installed in the same plant where the fuel would be sold as close as possible to the reactor core. The most important to control first 60 days of fuel irradiation. The construction of a detector will be chosen after testing experiments. We think about doing liquid scintillation detector of about one cubic meter in volume. May be it would be separated in some sections.

Detector construction The target 1 m 3, LS+Gd Gamma catcher, LS PMT (40-50)

Collaboration in Russia: Kurchatov Institute – construction, assembling, testing VNIIA (All-Russian Research Institute for Automatics) - mechanical construction Institute for Physical Chemistry RAS – liquid scintillator Corporation “Marathon ” - electronics

Scintillator on base of LAB doped with Gd LAB – Linear Alkyne benzene. It is a mixture of synthetic carbohydrates C 6 H 5 R, where R=C 10,C 11,C 13 Fractions of R are: C %, C 11 – 55%, C 13 – 30% Physical properties:  = ± g/cm 3, Flash point +147°C Transparency is > 20 m, LY ~95% relative to PC+ PPO(5g/l)

Light yield as a function of Gd and PPO concentrations relatively to pure LAB scintillator Gd concentration, g/l LY,% PPO concentration, g/l

High stability in small amounts, 1 liter during 1 year doesn’t change its properties. We are preparing the mock-up containing 100 l of scintillator on base of LAB with Gd. We plan to construct the detector with a target 1 m 3 and 1 m 3 surrounding volume, that should be installed at Power Plant.

Conclusion Using of antineutrino spectrum for obtaining the fuel composition of a core is difficult for the moment. One could not see the disappearing of kg of plutonium. A small detector placed in vicinity of the core (under the core) can control the non declination from the standard regime of reactor run. In Russia we try to design a prototype of small detector placed close to the reactor core. The tests of scintillator stability are on run now. The mock-up is under construction. PMTs are bought. Electronics is under developing.

Outlook We regard a possibility to do an International experiment under the patronage of IAEA in some country. For example it may be Ukraine (Rovno) where we did the first experiments. France (Chooz, Bugey)? or Brazil (Angra)? or somewhere else ??? This experiment could demonstrate not only the possibility of the method (was done at Rovno and San-Onofre), but the opportunity of doing it for safeguard purposes.

S.N. Ketov et al. Talk at Safeguards International Symposium, Vienna, IAEA-M-293/62, v. 2, V.I. Kopeikin, L.A. Mikaelyan, V.V. Sinev, Physics of Atomic Nuclei, v. 60, No. 2, p. 172, M.D. Skorokhvatov, Talk at Safeguards International Symposium, Vienna, 2003.