Effect of 236U on Protected Plutoniumproduction

Effect of 236U on Protected PlutoniumProduction

H. Sagara, T. Mitsuhashi[*], K. Fukuda and M. Saito

Tokyo Institute of Technology,Tokyo, Japan

, Tel:+81-357343074, Fax: +81-357342959

Reprocessed Uranium (RepU) recovered from the spent fuel contains a small amountof 236U (0.5~1% in U) which does not exist in natural uranium. Since 236Ucan betransmuted into 238Puthrough following reactions, 236U(n,β)→237Np(n,β)→238Pu, which has 567[W/kg] decay heats and 2660[n/sec/g] spontaneous fission neutrons,Pu produced by RepU irradiation would be more proliferation resistantthan that from natural U or conventional low enrichedU(LEU). The objective of the present study is the quantitative neutronics analysis of the effect of 236Uonthe Protected Plutonium Production which is proposed by M.Saitoet al.[1],[2],[3],[4],[5].

As a methodology of re-enrichment of RepU, the centrifugetechnology is adapted to adjust 235U content to a certain level,and three-component isotope(235U, 236U, 238U) separation calculation has been performed based on the centrifuge cascade model[6] to calculate the enriched RepU(ERU) isotopic composition. Multi-cycle burnup calculation was performedin a unit pin-cell model with theSRAC(Ver.2002) code system coupled with 107-groupcross-section library generated from JENDL3.3. As a criterion to evaluate the proliferation resistance of Pu based on the nuclear material property, 6% 238Pu isotopic ratio, which would meet unsuitability of a nuclear explosive device[7], is compared with the result of burnup calculation.

From the results,in order to meet the criterion of 6% 238Pu isotopic ratio, the required isotopic ratio of 236Uin the initialERU isabout 2 %, which is corresponding to once enriched RepU isotopic ratio. The worth of this 236U quantity is equivalent to about 0.2% addition of minor actinides from spent fuel of conventional LWRs in the view point of 238Pu production(Fig.1). Since the amount of RepU stockpiled in the fuel cycle is very huge (700,000ton of U are accumulated as RepUas ofyear 2005), the utilization of RepU might lead energy resource saving, more proliferation resistant fuel than conventional low enriched U fuel, and potential cost competitiveness with natural Uin coming nuclear renascence.

[8][9][10]

Fig.1 Property of Pu discharged from differenttypes of fuels

References

[*]Present Organization: Mitsubishi Heavy Industry, Tokyo, JAPAN

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[5] M. Saito, “Protected Plutonium Production (P3) by Transmutation of Minor Actinides,”ICAPP5, Korea, (2005).

[6]Benedict, et al., “Nuclear Chemical Engineering Second Edition,”MacGraw-Hill Series in Nucl Eng, p 693-701(1981).

[7] G.Kessler,“Plutonium Denaturing by 238Pu,”Nucl Sci Eng,155, p53-73 (2007).

[8] G. Kessler, “Plutonium Denaturing by Pu-238,”Trans First Int. Sci. Technol. Forum on Protected Plutonium Utilization for Peace and Sustainable Prosperity, Tokyo, p38-39 (2004).

[9] B. Pellaud, J of Nucl Mat Management, 31[1](2002).

[10] A.N. Chebeskov, The 9-th International Conference “Nuclear Power Safety and Nuclear Education, ObninskStateTechnicalUniversity for Nuclear Power Engineering (2005).