**5.1. Energy security of uranium resources**

The accessibility is important from the viewpoint of energy security. Accessibility should be discussed from the viewpoint of geography and concession. The resources should be distributed widely from the viewpoint of geography, and the concession to obtain the resources should be also ensured from the viewpoint both of economy and politics.

**Figure 9** shows distribution of identified resources of conventional uranium [15]. The top three countries Australia, Kazakhstan, and the Russian Federation occupy about half of the resources of the world. By the concentration of uranium resources, the risk of damage to sustainable energy supply increases owing to natural disasters, political instability, etc. In fact, uranium price in 2007 shown in **Figure 2** soared due to the catastrophic water inflow in Cigar Lake Mine in Canada [28], even though increase of uranium demand in China and India is also affected [15]. If the production of several mines in a certain region would be damaged simultaneously by large-scale disasters or political instability, the energy sustainability cannot be achieved. It is concluded that the conventional uranium resources have a problem of geography from the viewpoint of energy security.

Moreover, the uranium requirement exceeds the production in the recent two decades as shown in **Figure 10** [15]. The mass balance has now been achieved by the stock until 1990. In addition, the 1993 US-Russia Federation highly enriched uranium (HEU) purchase agreement was terminated in 2014 [15]. According to this agreement, the Russian Federation converts the 500 t of HEU from nuclear warheads to low enriched uranium (LEU) over 20 years from 1993 to 2013. As early as June 2006, the Russian Federation indicated that the HEU agreement will not be renewed when the initial agreement expires in 2013.

In this context, to purchase the uranium securely, mining interest of uranium ore, that is, concession, should be obtained by investing in the exploration and development of the mine. Here, I discuss Japanese case as representative country, which is not uranium-producing countries and does not have enough concession to satisfy the request. Many countries can be applied the similar condition as Japan. In Japan, requirement of uranium is approximately 8000 tU (8091 tU), and the production from own concession is 663 tU in 2007 [29]. The fraction is only 8.2%. Not only companies but also governments invest in the exploration and development of the mine to obtain the uranium concession. **Table 5** [29] lists the uranium concession owned by Japanese companies for mine under operation and development in 2009. Even though all mines under development will start the operation, the production can fill only half of the requirement. It is difficult to obtain the concession corresponding to the entire requirement. It is concluded that conventional uranium resources also have a problem of concession.

To realize the ultimate energy security, the resources should be recovered within the country. Countries facing the sea can utilize seawater uranium as domestic resources. The recovery process of seawater uranium is simpler than mine uranium as shown in **Figure 11** [17]. The extraction process of the recovery system consists only of elution in acid. It can be easy to introduce without any innovative technology. The transportation of absorbent is also realistic because the concentration of uranium in the medium is on the same degree of that in uranium ore. Moreover, the radioactive tailings, which may pollute the environment, are never generated unlike the uranium from mine. The amount of the production is large enough to satisfy the requirement if the current of the sea exists in exclusive economic zone (EEZ). The seawater uranium is effectively recovered with ocean current. The recovery system with capacity of

1200 tU/year requires the ocean area of 134 km<sup>2</sup>

**Figure 11.** Process of uranium recovery.

**Table 5.** Uranium concession owned by Japanese companies.

is proper in Japan, and the ocean area of 6000 km2

and it can occupy 87% of the requirement in the world.

a conflict of the right of fishing. Annual uranium production of 53,731 tU/year is expected from this area. This is approximately 6.6 times as much as the requirement of 8091 tU in Japan,

Honeymoon Mitsui & Co. 49 Under development

**Country Mine Company Concession (%) Condition**

Development Co.

Development Co.

Kazakhstan West Mynkuduk Kansai Electric Power Co. 10 Under operation

Canada Cigar Lake Tokyo Electric Power Co. 5 Under development Idemitsu Kosan Co. 7.9 Kazakhstan Kharasan 1–2 Marubeni Co. 13 Under development Tokyo Electric Power Co. 12 Toshiba Co. 9 Chubu Electric Power Co. 4 Tohoku Electric Power Co. 2 Australia Kintyre Mitsubishi Co. 30 Under development

Niger Akouta Overseas Uranium Resources

Canada McClean Lake Overseas Uranium Resources

with a proper current. The Kuroshio Current

is available to recover the uranium without

25 Under operation

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35

7.5 Under operation

Sumitomo Co. 25 Under operation

Safety and Economics of Uranium Utilization for Nuclear Power Generation

**Figure 10.** Annual world uranium requirements and production.


**Table 5.** Uranium concession owned by Japanese companies.

Moreover, the uranium requirement exceeds the production in the recent two decades as shown in **Figure 10** [15]. The mass balance has now been achieved by the stock until 1990. In addition, the 1993 US-Russia Federation highly enriched uranium (HEU) purchase agreement was terminated in 2014 [15]. According to this agreement, the Russian Federation converts the 500 t of HEU from nuclear warheads to low enriched uranium (LEU) over 20 years from 1993 to 2013. As early as June 2006, the Russian Federation indicated that the HEU agreement will

In this context, to purchase the uranium securely, mining interest of uranium ore, that is, concession, should be obtained by investing in the exploration and development of the mine. Here, I discuss Japanese case as representative country, which is not uranium-producing countries and does not have enough concession to satisfy the request. Many countries can be applied the similar condition as Japan. In Japan, requirement of uranium is approximately 8000 tU (8091 tU), and the production from own concession is 663 tU in 2007 [29]. The fraction is only 8.2%. Not only companies but also governments invest in the exploration and development of the mine to obtain the uranium concession. **Table 5** [29] lists the uranium concession owned by Japanese companies for mine under operation and development in 2009. Even though all mines under development will start the operation, the production can fill only half of the requirement. It is difficult to obtain the concession corresponding to the entire requirement. It is concluded that conventional uranium resources also have a problem of concession. To realize the ultimate energy security, the resources should be recovered within the country. Countries facing the sea can utilize seawater uranium as domestic resources. The recovery process of seawater uranium is simpler than mine uranium as shown in **Figure 11** [17]. The extraction process of the recovery system consists only of elution in acid. It can be easy to introduce without any innovative technology. The transportation of absorbent is also realistic because the concentration of uranium in the medium is on the same degree of that in uranium ore. Moreover, the radioactive tailings, which may pollute the environment, are never generated unlike the uranium from mine. The amount of the production is large enough to satisfy the requirement if the current of the sea exists in exclusive economic zone (EEZ). The seawater uranium is effectively recovered with ocean current. The recovery system with capacity of

not be renewed when the initial agreement expires in 2013.

34 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

**Figure 10.** Annual world uranium requirements and production.

1200 tU/year requires the ocean area of 134 km<sup>2</sup> with a proper current. The Kuroshio Current is proper in Japan, and the ocean area of 6000 km2 is available to recover the uranium without a conflict of the right of fishing. Annual uranium production of 53,731 tU/year is expected from this area. This is approximately 6.6 times as much as the requirement of 8091 tU in Japan, and it can occupy 87% of the requirement in the world.

**Figure 11.** Process of uranium recovery.

Thus, the problems of geography and concession from the viewpoint of energy security can be solved by using seawater uranium. Then, the seawater uranium should be utilized regardless of the exhaustion of conventional uranium.

#### **5.2. Energy security of plutonium utilization**

Plutonium composition is depending on the condition of fresh fuel composition, burnup characteristics, and storage period before and after reprocessing. Plutonium composition is always fluctuated. Therefore, in Japan, fuel composition of FBR is managed by equivalent fissile coefficient [30]. The definition is as follows:

$$\mathbf{y} \triangleq \mathbf{v} \,\mathbf{o}\_t - \mathbf{o}\_{\langle \mathbf{o}, \mathbf{y} \rangle} \tag{2}$$

migration of radioactive nuclides and is made of bentonite. The waste package, canister, and buffer material are called engineered barrier system (EBS) from the viewpoint of containment

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The safety analysis of the geological repository [33] assumes the mechanism as shown in

• The canister and waste package failed by corrosion, and the radioactive nuclides dissolve

Thus, host rock in repository works as barrier as well and is called natural geological barrier. The safety of geological repository is assessed by public exposure by assuming migration of

Moreover, transuranic (TRU) waste [34], which is categorized as low-level radioactive waste (LLW), is also generated when spent fuel is reprocessed and disposed. The dose of public exposure is evaluated for representative geological repository design for LWR wastes as

• The radioactive nuclides migrate through the host rock via groundwater.

• The radioactive nuclides flow into river and diffuse into environment.

radioactive nuclides due to the corrosion and failure of waste packages.

shown in **Figures 13** and **14**, respectively, for HLW and TRU waste.

• The radioactive nuclides migrate to aquifer through fault.

• The radioactive nuclides are exposed to the public.

and delayed function of radioactive nuclides.

**Figure 12**:

in groundwater.

**Figure 12.** Process of public exposure.

$$\eta\_i = \mathbf{y}\_i / \mathbf{y}\_{\text{:} \mathbf{y}\_{\text{:}}} \tag{3}$$

where y is the equivalent fissile value (cm−2), <sup>ν</sup> <sup>σ</sup><sup>f</sup> is the microscopic production cross section (cm−2), σ(n,γ) is the microscopic radioactive capture cross section (cm−2), y*<sup>i</sup>* is the equivalent fissile value of ith nuclide (cm−2), y239*Pu* is the equivalent fissile value of <sup>239</sup>Pu (cm−2), and η*<sup>i</sup>* is the equivalent fissile coefficient ith nuclide (−).

To reserve the product of fuel composition and the equivalent fissile coefficients, plutonium enrichment is determined. However, if fuel loading and/or operation of reactor would be significantly delayed, the fuel should be refabricated and reloaded because of the change on reactivity worth due to the decay of 241Pu, whose half-life is 14.4 years, to 241Am. In Monju, where sodium leakage accident occurred on December 1995 and start-up test is performed on May 2010, the depletion of criticality was observed [31] in the test. After the test, fuel reloading was performed on August 2010 to compensate the reactivity worth. The resilience of fuel cycle system with plutonium is weaker than that of uranium.

Moreover, there is a threat that the spent fuel would be seized in FBR cycle. In general, the Puf ratio of spent fuel is around 60% for LWR and FBR. However, that of FBR blanket is over 90%, that is, weapon-grade plutonium. In this context, the concept of protected plutonium production (PPP) [32] is proposed as an option. By addition of 237Np and/or <sup>241</sup>Am, the Puf ratio can be reduced, and the dose rate of spent fuel can increase due to the converted 238Pu in this concept. However, it should be noted that the doping MAs in fuel make working environment severe.

#### **6. Environmental burden and significance of P&T**

#### **6.1. Geological disposal and safety**

Along with electricity generation, radioactive wastes are generated. Especially, high-level radioactive wastes (HLWs) will be disposed in a deep geological repository. The HLWs, which are spent fuels for direct disposal and vitrified wastes for disposal with reprocessing, are contained into steel canisters and disposed by surrounding buffer material, which delays migration of radioactive nuclides and is made of bentonite. The waste package, canister, and buffer material are called engineered barrier system (EBS) from the viewpoint of containment and delayed function of radioactive nuclides.

The safety analysis of the geological repository [33] assumes the mechanism as shown in **Figure 12**:


Thus, the problems of geography and concession from the viewpoint of energy security can be solved by using seawater uranium. Then, the seawater uranium should be utilized regard-

Plutonium composition is depending on the condition of fresh fuel composition, burnup characteristics, and storage period before and after reprocessing. Plutonium composition is always fluctuated. Therefore, in Japan, fuel composition of FBR is managed by equivalent fis-

is the microscopic radioactive capture cross section (cm−2), y*<sup>i</sup>*

sile value of ith nuclide (cm−2), y239*Pu* is the equivalent fissile value of <sup>239</sup>Pu (cm−2), and η*<sup>i</sup>*

To reserve the product of fuel composition and the equivalent fissile coefficients, plutonium enrichment is determined. However, if fuel loading and/or operation of reactor would be significantly delayed, the fuel should be refabricated and reloaded because of the change on reactivity worth due to the decay of 241Pu, whose half-life is 14.4 years, to 241Am. In Monju, where sodium leakage accident occurred on December 1995 and start-up test is performed on May 2010, the depletion of criticality was observed [31] in the test. After the test, fuel reloading was performed on August 2010 to compensate the reactivity worth. The resilience of fuel

Moreover, there is a threat that the spent fuel would be seized in FBR cycle. In general, the Puf ratio of spent fuel is around 60% for LWR and FBR. However, that of FBR blanket is over 90%, that is, weapon-grade plutonium. In this context, the concept of protected plutonium production (PPP) [32] is proposed as an option. By addition of 237Np and/or <sup>241</sup>Am, the Puf ratio can be reduced, and the dose rate of spent fuel can increase due to the converted 238Pu in this concept. However, it should be noted that the doping MAs in fuel make working environment severe.

Along with electricity generation, radioactive wastes are generated. Especially, high-level radioactive wastes (HLWs) will be disposed in a deep geological repository. The HLWs, which are spent fuels for direct disposal and vitrified wastes for disposal with reprocessing, are contained into steel canisters and disposed by surrounding buffer material, which delays

(n,γ) (2)

/y239*Pu* (3)

is the microscopic production cross section

is the equivalent fis-

is the

less of the exhaustion of conventional uranium.

36 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

**5.2. Energy security of plutonium utilization**

sile coefficient [30]. The definition is as follows:

y = ν σ<sup>f</sup> − σ

η*<sup>i</sup>* = y*<sup>i</sup>*

where y is the equivalent fissile value (cm−2), <sup>ν</sup> <sup>σ</sup><sup>f</sup>

cycle system with plutonium is weaker than that of uranium.

**6. Environmental burden and significance of P&T**

**6.1. Geological disposal and safety**

equivalent fissile coefficient ith nuclide (−).

(cm−2), σ(n,γ)

Thus, host rock in repository works as barrier as well and is called natural geological barrier. The safety of geological repository is assessed by public exposure by assuming migration of radioactive nuclides due to the corrosion and failure of waste packages.

Moreover, transuranic (TRU) waste [34], which is categorized as low-level radioactive waste (LLW), is also generated when spent fuel is reprocessed and disposed. The dose of public exposure is evaluated for representative geological repository design for LWR wastes as shown in **Figures 13** and **14**, respectively, for HLW and TRU waste.

**Figure 12.** Process of public exposure.

**6.2. Potential toxicity and significance of P&T**

required for the fuel fabrication.

**Figure 15.** Potential toxicity of LWR spent fuel.

Potential toxicity is often used as a hazard index to assess environmental burden. Therefore, it is set up for the objective of nuclear transmutation to reduce the potential toxicity. The definition of potential toxicity is dose of internal exposure by ingestion when all radioactive nuclides are intaken. It is believed that the dose should be lower than that of natural uranium

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The potential toxicity of LWR spent fuel is shown in **Figure 15** for each element. The burnup is 45 GWd/t, and the enrichment is 4.5 wt%. To fabricate fuel of 1 t with the enrichment of 4.5 wt%, natural uranium of 9 t is necessary. The toxicity of uranium and plutonium, that is almost composed only of plutoniums, needs 100,000 years to decay to the natural uranium level. With reprocessing, uranium and plutonium are recovered, and the toxicity is not problematic. Next, americium needs 2000 years of cooling. If americium is converted by P&T, the cooling time can

From the viewpoint of the potential toxicity reduction under the natural uranium level, it is not necessary for neptunium and curium to convert to FPs. The FPs are composed of long-lived

to 100,000 years. The toxicity of LLFPs is not problematic as well. In addition, the nuclides contributed to the toxicity are different from that contributed to the public exposure described in the previous section. From this comparison, it is found that the actual public exposure strongly depends on mobility characteristics of the nuclides compering with the inventory of the toxicity. Furthermore, the assumption of intaking all radioactive nuclides is not reasonable as a hazard index. In this context, an alternative index of "environmental impact" [37] is proposed by a specialist of geological disposal safety. That is defined as toxicity flowed out from the EBS. The potential toxicity has also attracted a lot of attention after the Fukushima Daiichi accident in Japan to reconsider the significance of the utilization of nuclear technology. The graph of the potential toxicity is often shown even in television report. Then, nuclear conversion by

Sv/tIHM is observed from 1

be reduced to 300 years, by which the dose of FPs decays lower than natural uranium.

FPs (LLFPs) and other FPs. The toxicity of LLFPs around 1.0 × 10<sup>3</sup>

**Figure 13.** Public exposure from HLW [33].

Basically, the dose rate is limited by the guideline, which is deployed at approximately one order of magnitude lower than the level of natural background. The peak from HLW is composed of <sup>135</sup>Cs and four to five orders of magnitude lower than the guideline. The peak from TRU waste is composed of 129I and two to three orders of magnitude lower than the guideline. In addition, the dose rate of HLW for direct disposal of LWR spent fuel was also reported [35]. The peak is composed of 14C and one to two orders of magnitude lower than the guideline. The safety guideline is satisfied enough for exiting LWR waste disposal plans. Especially for HLW disposal with reprocessing, where MA transmutation has been often researched, the safety margin is huge.

With MA transmutation, the electricity generation cost increases as described in Section 4.2. "As low as reasonably achievable (ALARA) principal" [36], which was revised from as low as practical (ALAP), is known as radiation safety policy. Obviously, the necessity to reduce the public exposure is poor because of the huge safety margin. In this situation, the nuclear transmutation with significant cost increases against the ALARA principal. If the nuclear transmutation is plant, we should judge the "reasonability" by considering the benefit and cost.

**Figure 14.** Public exposure from TRU waste [34].

#### **6.2. Potential toxicity and significance of P&T**

**Figure 13.** Public exposure from HLW [33].

38 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

Basically, the dose rate is limited by the guideline, which is deployed at approximately one order of magnitude lower than the level of natural background. The peak from HLW is composed of <sup>135</sup>Cs and four to five orders of magnitude lower than the guideline. The peak from TRU waste is composed of 129I and two to three orders of magnitude lower than the guideline. In addition, the dose rate of HLW for direct disposal of LWR spent fuel was also reported [35]. The peak is composed of 14C and one to two orders of magnitude lower than the guideline. The safety guideline is satisfied enough for exiting LWR waste disposal plans. Especially for HLW disposal with reprocessing, where MA transmutation has been often researched, the safety margin is huge.

With MA transmutation, the electricity generation cost increases as described in Section 4.2. "As low as reasonably achievable (ALARA) principal" [36], which was revised from as low as practical (ALAP), is known as radiation safety policy. Obviously, the necessity to reduce the public exposure is poor because of the huge safety margin. In this situation, the nuclear transmutation with significant cost increases against the ALARA principal. If the nuclear transmutation is

plant, we should judge the "reasonability" by considering the benefit and cost.

**Figure 14.** Public exposure from TRU waste [34].

Potential toxicity is often used as a hazard index to assess environmental burden. Therefore, it is set up for the objective of nuclear transmutation to reduce the potential toxicity. The definition of potential toxicity is dose of internal exposure by ingestion when all radioactive nuclides are intaken. It is believed that the dose should be lower than that of natural uranium required for the fuel fabrication.

The potential toxicity of LWR spent fuel is shown in **Figure 15** for each element. The burnup is 45 GWd/t, and the enrichment is 4.5 wt%. To fabricate fuel of 1 t with the enrichment of 4.5 wt%, natural uranium of 9 t is necessary. The toxicity of uranium and plutonium, that is almost composed only of plutoniums, needs 100,000 years to decay to the natural uranium level. With reprocessing, uranium and plutonium are recovered, and the toxicity is not problematic. Next, americium needs 2000 years of cooling. If americium is converted by P&T, the cooling time can be reduced to 300 years, by which the dose of FPs decays lower than natural uranium.

From the viewpoint of the potential toxicity reduction under the natural uranium level, it is not necessary for neptunium and curium to convert to FPs. The FPs are composed of long-lived FPs (LLFPs) and other FPs. The toxicity of LLFPs around 1.0 × 10<sup>3</sup> Sv/tIHM is observed from 1 to 100,000 years. The toxicity of LLFPs is not problematic as well. In addition, the nuclides contributed to the toxicity are different from that contributed to the public exposure described in the previous section. From this comparison, it is found that the actual public exposure strongly depends on mobility characteristics of the nuclides compering with the inventory of the toxicity. Furthermore, the assumption of intaking all radioactive nuclides is not reasonable as a hazard index. In this context, an alternative index of "environmental impact" [37] is proposed by a specialist of geological disposal safety. That is defined as toxicity flowed out from the EBS.

The potential toxicity has also attracted a lot of attention after the Fukushima Daiichi accident in Japan to reconsider the significance of the utilization of nuclear technology. The graph of the potential toxicity is often shown even in television report. Then, nuclear conversion by

**Figure 15.** Potential toxicity of LWR spent fuel.

ADS also attracted a lot of attention. In this situation, an expert committee of Atomic Energy Society of Japan (AESJ) published the report for direct disposal [35]. In this report, the safety of geological disposal and public opinion were researched and discussed. It is emphasized that the potential toxicity cannot be the index directly to assess the safety, and the safety of geological disposal should be assessed by public exposure. The expert committee states its own view that the safety of geological disposal tends to be assessed by the potential toxicity in the recent society because it is easy to understand intuitively.

If the potential toxicity would be gotten public support as the hazard index and all MAs and LLFPs would be transmutated, the waste should be managed at least 300 years. Furthermore, if all radioactive nuclides would be transmutated to stable nuclides, the waste should be managed due to the toxicity of heavy metal.
