(Unofficial translation by Green Action)
This document analyses 8 areas concerning safety of MOX fuel use. It presents arguments of both anti and pro MOX sides, and gives Saga Prefecture’s conclusions. For all items, Saga Prefecture agrees with the pro MOX argument.
The 8 areas:
- 1. Control of Reactor
- (1) Efficacy of Control Rods and Boron
- (2) Concerning Self-regulating characteristics
- (3) Characteristics of Output Distribution
- 2. Safety of the Fuel
- (1) Melting Point of Fuel
- (2) Internal Pressure of Fuel (Plutonium Spots)
- 3. Experience with MOX Fuel Performance
- (1) Experience concerning Plutonium Enrichment Levels and Burn Up
- 4. Radioactive Dose During Normal Operation
- (1) Worker Dose
- 5. Effects Due to Accidents
- (1) Possibility of Reactor Containment Vessel Rupture
- (2) Areas Affected as a Result of Accident
- 6. Spent MOX Fuel
- (1) Spent Fuel Storage
- 7. Possibility of Terrorism
- (1) Possibility of Terrorism
- 8. Measures Related to Earthquakes
- (1) Measures Related to Earthquakes
1. CONTROL OF REACTOR
(1) Efficacy of Control Rods and Boron
- PRO: (Entire text.)
- When MOX fuel is used, the control efficacy of control rods and boron is reduced slightly, in other words there is a tendency for the efficacy to be lowered.
- However, under the safety licensing procedure a margin is placed over and above the capability “necessary to shut down the reactor”. Moveover, when assessing control rod efficacy, the analysis is conducted subtracting 10% from capability. Moreover, the analysis is conducted in a very conservative manner by which it is postulated that one control rod will not work. It has been confirmed that the criteria is met even under these conditions. Therefore, there is no problem with safety since the necessary conditions to shut the reactor down safely are met with plenty of margin.
- Also, vis-a-vis boron, it has been confirmed that the reactor can be shut down safely even after taking into consideration the unique characteristics of MOX fuel.
- PREFECTURE:
- [ Prefecture states ” ‘the ability necessary to shut down the reactor under all manner of reactor operating conditions and anomalous situations’ has been considered.”]
(2) Concerning Self-Regulating Characteristics
- PREFECTURE: (Entire response.)
- Concerning self-regulating characteristics, the characteristic of maintaining the reactor at steady output levels is enhanced with MOX fuel as compared with uranium fuel. This is a positive characteristic for safety. If and when conditions arise in which reactor output (power) starts to increase for some reason, the ability to autonomously lower output is enhanced even without the operation of control rods.
- On the other hand, if and when the temperature of the reactor is lowered for reasons such as low temperature coolant water mistakenly entering (the reactor), although the characteristic to autonomously increase output is enhanced, analyses have been undertaken to take these conditions under consideration. We understand and are convinced that even under these conditions the control rods and boron will safely shut down the reactor as indicated in (1).
(3) Characteristics of Output Distribution
- PREFECTURE: (Entire response.)
- The issue is whether fuel damage might occur where output is highest.
- According to the plans, MOX fuel with lower plutonium enrichment will be used in assemblies where output can easily become high. In other words by placing MOX fuel rods which burn less in these areas, this will even out output.
- Moreover, analyses have been conducted for the MOX fuel rods which will have the highest output. Safety of this fuel has been confirmed and therefore we understand and are convinced that safety can be ensured.
2. SAFETY OF THE FUEL
(1) Melting Point of fuel
- PRO: (Entire Text)
- The melting point of MOX fuel pellet when the temperature in the center of the fuel rod becomes the severest is, with maximum enrichment of 13%wt approximately 2720 degrees C. This is approximately 70 degrees lower than uranium fuel. Compared to this the melting point of the MOX fuel pellet is approximately 1820 degrees under normal output and under abnormal conditions the maximum temperature is approximately 2280 degrees. There is plenty of safety margin and therefore no safety problem.
- PREFECTURE: (Entire text)
- Even when taking into consideration abnormal conditions, there is approximately 440 degrees C difference between the highest temperature of the fuel and the fuel’s melting point. Therefore we understand and are convinced that safety can be maintained.
- On the other hand, fuel melted during the 1979 Three Mile Island accident. However, this occurred when human error involving mistaken operation of the equipment coincided with break-down of equipment. Since then, based on the experience gained from the accident, countermeasures to maintain safety have been put in place such as changes in design of facility, regulatory guidelines, operational management etc. and we understand and are convinced that safety can now be ensured.
(2) Internal Pressure of Fuel (Plutonium Spots)
- PRO: (Entire text.)
- With regards to fuel rod design, considering the possibility of increased release of fission gases, by taking the countermeasurr of reducing helium gas pressure in the fuel rod as compared to uranium fuel, it is confirmed that the fuel rod internal pressure standard is met.
- With regard to plutonium spots, as a result of experimental results under conditions more severe than could be thought to occur realistically, it has been confirmed that it is not necessary to pay special consideration to the effects of fuel damage.
- PREFECTURE: (Entire text.)
- The original gas pressure in the fuel rods has been reduced taking into consideration increase in the release of fission gases. As a result, it has been confirmed that the fuel rod pressure meets the standard.
- Also, as a result of experiments using fuel with plutonium spots larger than can be thought to be realistically possible, it has been confirmed that the effects of fuel damage do not have to be specially taken into consideration. Therefore we understand and are convinced that safety will be ensured.
3. EXPERIENCE WITH MOX FUEL PERFORMANCE
(1) Experience concerning Plutonium Enrichment Levels and Burn Up
- ANTI:
- There is no commercial experience with 9% Pu (assembly average), and Pu fissile enrichment of maximum 8% (pellet). These are figures for Genkai Unit 3 pluthermal. Even France’s experience is with 900 megawatt reactors and not 1180 megawatt like Genkai. There is data regarding fissile gas build up with high burn up fuel.
- PRO: (Entire text)
- There is lots of experience in German reactors (1000 megawatt size). Also Germany already has experience with maximum burn up of 50,000 MWd/t.
- There have been many experiments and analyses including for high enrichment and burn-up. We have undertaken safety analyses and examination taking into consideration changes to conduct of fuel rod/boron, reduction of melting point of the fuel, characteristics of output distribution, and other changes that could be thought to occur.
- Even though there is no experience in commercial reactors, the reliability of analytical methods with experiments etc has been confirmed and therefore it is possible to make accurate assessments.
- There is data with high burn up fuel in which the amount of fissile gases shot up, but this is because it was high burn up fuel and not because the fuel was MOX.
- PREFECTURE: (Entire Text)
- There is experience of burning plutonium in commercial reactors [referring to plutonium created in reactors burning uranium fuel], and based on experiments and analyses conducted in Japan and abroad, we understand and agree that the analyses has been undertaken regarding enrichment and burn up of MOX fuel for use at Genkai Unit 3.
- As for no reactor experience in France over 900 megawatt, this is because the amount of plutonium coming out of reprocessing and the capacity of the 900 megawatt reactors in France are almost the same [almost same supply/demand], and therefore it has been judged that there is no need to implement MOX use in reactors larger than 900 megawatt in France.
5. EFFECTS DUE TO ACCIDENT
(1) Possibility of Reactor Containment Vessel Rupture
- PRO: (Entire text.)
- A safety assessment of the frequency of a reactor containment vessel rupture has been undertaken for Genkai Nuclear Power Plant Unit 3 using probabilistic safety assessment. The frequency is once in 70 million years. This is substantially lower than the IAEA international target value of “once in 100,000 years” and is something that realistically cannot be considered to occur.
- PREFECTURE: (Entire text.)
- The possibility of a reactor containment vessel rupture occurring at Genkai Unit 3 is, having taken into consideration the probability of each type of equipment breaking down, human error, etc., assessed to be once in 70 million years. Although the figure is not zero, considering the fact that the risk of using scientific technology cannot be zero, the probability is substantially small and we understand and are convinced that it cannot be considered to occur realistically.
(2)Areas Affected as a Result of Accident
- PRO:
- [States the boiling point of plutonium dioxide is high (approximately 3230 degrees C)…no big change in noble gases and iodine release with MOX fuel….plutonium intake through respiration is almost totally improbable…even with the Chernobyl accident, damage from plutonium has not been confirmed.]
- PREFECTURE: (Entire text.)
- If MOX fuel is used, there is more plutonium in the reactor than if uranium fuel is used. Also, if plutonium is respired, it is confirmed that the toxicity is especially high.
- However, it is difficult for plutonium to become a vapor, and also, there are multiple barriers to keep radioactive materials inside the power plant, and therefore it is almost unthinkable that plutonium would be released to the external environment. Therefore we understand and are convinced that the effects due to radioactive materials going outside of the nuclear power plant are no different from uranium fuel.
- There is talk that, “if one wants to hypothesize an accident, any accident could be hypothesized”. For example it is assessed that the probability of the reactor containment vessel rupturing is once in 70 million years. Although this is not zero, when considering that the risk of using scientific technology cannot be zero, the probability is substantially small and we understand and are convinced that it cannot be considered to occur realistically.
7. POSSIBILITY OF TERRORISM
(1) Possibility of Terrorism
- PRO: (Entire text.)
- Although the possibility of a terrorist attach on a nuclear power plant is not zero, it is difficult to think that it will become easier to be subject to a terrorist attach just because MOX fuel use is being implemented. The security at nuclear power plants is greater than at general facilities and the building itself is more solid. Many other facilities beside nuclear power plants could be considered to be targets for terrorist attach.
- Although there cannot be sweeping mention regarding the kind of damage that might or might not occur or the degree of damage if a nuclear power plant were to come under a missile attach, considering the fact nuclear power plants are built to withstand earthquakes, and from the aspect of shielding, it is a solid building with plenty of strength and thickness, and has considerable resistance toward attack from the outside.
- [Diagram titled “Attach from the Outside” indicates thickness of concrete walls etc, various barriers, statement saying “under abnormal conditions, the reactor is designed to immediately stop automatically.” Boxed in text: “We consider that terrorist activity or military attach from a foreign country is an issue which necessitates broad-based measures from the standpoint of national security.”]
- PREFECTURE: (Entire text.)
- Although the possibility of a terrorist attach on a nuclear power plant cannot be considered to be zero, it is not that there will be any changes to such things as the security and precautionary preparedness and the facilities construction and structural strength, and therefore we understand and are convinced that it will be difficult to think that the possibility of being attached will increase in any big way.
- Even if the pluthermal program is not implemented, terrorist attachs etc. of nuclear power plants is a threat and we believe that it is necessary to make all sorts of diplomatic and political efforts to reduce their possibility.
- On the other hand, the government has established a national emergency law, and also the prefecture this January 20th (2006) drew up the “Saga Prefecture National Citizens Protection Plan” to deal with any situations that might arise so that the safety of prefectural citizens can be secured and every effort is being undertaken among related agencies to cooperate and establish a system to deal with this matter.
End