Материал: Апсе ENVIRONMENTAL PROTECTION 2014

Risk of nuclear weapon proliferation (RP)

The RP value is high. The Nuclear Suppliers Group put an informal embargo on export of the isotope separation technologies.

4. Fabrication of nuclear fuel (fuel rods and fuel assemblies) NM vulnerability to theft (VT)

The VT value is low. One fuel assembly weighs 300-500 kg depending on the reactor type. So, a special transportation tool has to be used for theft of even one fuel assembly.

NM vulnerability to diversion (VD)

The VD value can cover the range from low to high depending on applications of the IAEA safeguards, i.e. L/H(IAEA).

Risk of nuclear weapon proliferation (RP)

The RP value can cover the range from low to high depending on the value of uranium enrichment, i.e. L/H(Enrichment).

5. Use of nuclear fuel at NPP NM vulnerability to theft (VT)

The VT value is low because of large weight, radioactivity and disposition of fuel assemblies in a nuclear reactor core.

NM vulnerability to diversion (VD)

The VD value can cover the range from low to high depending on applications of the IAEA safeguards, i.e. L/H(IAEA).

Risk of nuclear weapon proliferation (RP)

The RP value can cover the range from low to high depending on the value of uranium enrichment, i.e. L/H(Enrichment).

6. Interim storage of SNF

NM vulnerability to theft (VT)

The VT value is low because of large weight, radioactivity and residual heat generation of spent fuel assemblies.

NM vulnerability to diversion (VD)

The VD value can cover the range from low to high depending on applications of the IAEA safeguards, i.e. L/H(IAEA).

Risk of nuclear weapon proliferation (RP)

The RP value can cover the range from low to high depending on the value of uranium enrichment, i.e. L/H(Enrichment).

7. SNF reprocessing

NM vulnerability to theft (VT)

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The VT value is high. SNF reprocessing technologies deal with highly radioactive and heat-generating materials. That is why only remote equipment is used to separate spatially staff members and dangerous nuclear materials. However, at some steps of the SNF reprocessing, plutonium-containing materials may be more accessible for theft.

NM vulnerability to diversion (VD)

The VD value can cover the range from low to high depending on applications of the IAEA safeguards, i.e. L/H(IAEA).

Risk of nuclear weapon proliferation (RP)

The RP value is high. SNF reprocessing plants can produce either weapon-grade plutonium or, at least, reactor-grade plutonium with relatively worse isotope composition but also suitable for manufacturing of a nuclear explosive device with significantly lower energy yield. The Nuclear Suppliers Group put an informal embargo on export of the SNF reprocessing technologies.

8. Ultimate disposal of radioactive wastes NM vulnerability to theft (VT)

The VT value is low because of intense radioactivity, residual heat generation and small content of fissionable nuclides.

NM vulnerability to diversion (VD)

The VD value is low because of small content of fissionable nuclides.

Risk of nuclear weapon proliferation (RP)

The RP value is low because of intense radioactivity, residual heat generation and small content of fissionable nuclides.

The factors defining threats from all the NFC stages to nuclear nonproliferation regime are gathered in Table 3.1.

3.2. Comparison of reactor types from viewpoint of nuclear nonproliferation

In addition to the NFC stages, different types of nuclear reactors can be characterized by different values of NM attractiveness from nonproliferation point of view. The following fuel parameters can be helpful for estimating attractiveness of nuclear reactors from this viewpoint:

1.Quantity and quality of fresh fuel loaded into the reactor cores.

2.Quantity and quality of spent fuel unloaded from the reactor cores.

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For the beginning, the reactors fueled with highly-enriched, weapongrade uranium (above 90% 235U) are considered below.

1. Research reactors

Some research reactors are still using highly-enriched, weapon-grade uranium fuel in a very attractive form of pure metals or metal alloys. However, thermal power of the research reactors in operation now is

relatively low (at the level of several megawatts) and, therefore, total mass of 235U in their cores is well below 10 kg.

According to the IAEA recommendations, the national programs on conversion of the research reactors from highly enriched to middleenriched (below 20% 235U) uranium fuel are currently underway in some countries. By the way, critical mass of 20%-uranium is evaluated as large as 830 kg. The reduced uranium enrichment can lead to larger

sizes of the reactor core, larger amounts of loaded fresh fuel, but total mass of 235U can remain at the same or even lower level thanks to the

better neutron economy in the larger reactor cores (lower neutron leakage).

Secondary nuclear fuel is not produced practically by the research reactors in operation now because of low neutron flux and small amount of fertile nuclides.

2. High-Temperature Gas-Cooled Reactors (HTGR)

These reactors are fueled with highly enriched uranium (93% 235U) as a fissile material and natural thorium as a fertile material. HTGR-

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type reactors use the dispersed fuel in form of spherical micro-particles (500-800 microns in diameter) inside of multi-layer cladding made of pyrolytic carbon and silicon carbide. The fuel micro-particles are uniformly dispersed in graphite matrix that is used further to fabricate spherical (~6 cm in diameter) or prismatic fuel elements.

TRISO-type micro-particles consist of fuel kernel coated with three-layer cladding (low-density pyrolytic carbon, silicon carbon and high-density pyrolytic carbon).

BISO-type micro-particles consist of fuel kernel coated with twolayer cladding (low-density pyrolytic carbon and high-density pyrolytic carbon).

The HTGR-770 project presumes that initial fuel loading consists of 8100 kg 232Th as thorium dioxide in BISO-type micro-particles and 700 kg 235U as uranium carbide in TRISO-type micro-particles. By the end of irradiation cycle the reactor core contains about 7500 kg 232Th, 40 kg 235U and 180 kg 233U (secondary fuel), or ~230 kg 233U/GWe×year.

3. Light-water reactors (LWR)

3a. VVER-type reactors

Power VVER-type reactors are fueled with low-enriched (4-5% 235U) uranium dioxide. As a rule, initial fuel loading of VVER-1000 is equal to about 100 t UO2. Secondary fuel is produced with a specific rate ~200 kg Pu/GWe·year.

However, isotope composition of the produced plutonium extracted from spent fuel is far from optimal suitability for manufacturing of a nuclear explosive device. Typical weapon-grade plutonium contains mainly 239Pu and below 7% 240Pu. Typical plutonium extracted from

spent fuel of VVER-type reactors (reactor-grade plutonium) contains about 2% 238Pu, 58% 239Pu, 25% 240Pu, 11% 241Pu and 4% 242Pu, i.e.

~71% of fissile plutonium isotopes. Critical mass of metal reactor-grade plutonium is larger on 50% than critical mass of metal weapon-grade plutonium (23 kg via 15 kg). But this is not the most major aspect. Re- actor-grade plutonium contains larger 240Pu quantity (by a factor of 4) than weapon-grade plutonium. The larger quantity of 240Pu can sharply reduce (roughly by a factor of 30) energy yield of nuclear explosive devices because 240Pu is an intense emitter of spontaneous fission neutrons. These neutrons can cause untimely premature initiation of the

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chain fission reaction in a nuclear charge (the pre-detonation effect) and, thus, energy yield of nuclear explosion will not exceed 3% of nominal energy yield. According to some numerical evaluations, if Hi- roshima-type atomic bomb (nominal energy yield - 20 kt TNT) would be made of the reactor-grade plutonium, then the most probable energy yield would be about 600 t TNT. Nevertheless, this value is a high enough energy equivalent. As is known, masses of usual explosives exploded in Moscow and caused many human victims were well below 100 kg TNT.

3b. RBMK-type reactors

In some publications the RBMK reactors are named as Chernobyltype reactors because the world-wide known Chernobyl accident (1986) occurred in the RBMK reactor. The RBMK reactors use reactor-grade graphite as a neutron moderator, and boiling light water as a coolant. The light-water coolant circulates in vertical technological channels that transpierce through the graphite stack of the reactor core (diameter of the graphite stack - ~12 m, height - ~8 m). The heat-generating cassettes consisting of two consecutively coupled fuel assemblies (length – 3,5 m each) are inserted into the technological channels.

RBMK-type reactors are fueled with low-enriched (1,8-2% 235U) uranium dioxide. As a rule, initial fuel loading of RBMK-1000 is equal to about 150-180 t UO2. Secondary fuel is produced with a specific rate ~250 kg Pu/GWe·year. Isotope composition of reactor-grade plutonium extracted from SNF of the RBMK-type reactors is inferior to reactorgrade plutonium extracted from SNF of the VVER-type reactors in respect of fissile isotopes content and in respect of 240Pu content. Typical

plutonium extracted from spent fuel of RBMK-type reactors contains about 45% 239Pu, 36% 240Pu, 11% 241Pu and 8% 242Pu, i.e. ~56% of fis-

sile plutonium isotopes.

A particular threat of the RBMK-type reactors to nuclear nonproliferation is caused by their principal capability to work in the continuous refueling operation mode without reactor outages for refueling. Under this operation mode, fuel exposure time may be chosen short enough to produce plutonium with isotope composition very suitable for manufacturing of a nuclear explosive device.

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