The ebullient water reactor or REB (in English BWR for Boiling Toilets Reactor ) is a technology of Nuclear reactor currently used in certain nuclear plants generating American, Japanese, German, Swedish, Finnish, Russian, Swiss…

The world park of REB is approximately one the third of the world park of REFERENCE MARK, for the following primary reasons:

• the REFERENCE MARKS derive directly from the engines of submarines, consequently corresponding technology was definitely more mature than that of the REB in years 1960 and 70 of strong development of the nuclear power in the world,

• the REB had a bound slower development, inter alia with the difficulty in obtaining a sleeving of fuel seals durably under operation. It resulted from this in particular a negative radiological assessment in exploitation, the irradiation of the personnel was more important than in the case of the REFERENCE MARKS. This point is besides one of the reasons of the choice of the die REFERENCE MARK in France in the middle of the years 1970. That being this situation is not any more topicality; today thanks to the progress made by the REB in particular on the level of the sealing of the sleeving of fuel the radiological assessment is even rather in favor of the REB.

The power (electric) unit of the REFERENCE MARKS is rather higher than that of the REB but the variation is not very important and does not exceed 15% (for example 1550 MWe for the ESBWR and 1650 MWe for EPR European pressurized Réacteur - with possible option to 1800 MWe)

Without one being able to affirm it is rather probable that the proportion of the working installed capacity of die REB increases compared to the die REFERENCE MARK in the next years; this certainly at slow rate/rhythm because the electricians will seek to maintain the homogeneity of their park of power stations to limit the costs of exploitation and training of the operators

The question to know if it would not be indicated that EDF is equipped with some engines of type REB (a series of 4 for example) at the time of the renewal of the current park is put de facto being given the advantages which this die gets compared to the die REFERENCE MARK. In addition to the advantages to wait for the electrician, this choice would place French industry in very favorable situation with respect to world competition in the field of the light water reactors.

General presentation of the concept of ebullient water reactor

With the difference of the Pressurized water reactor, the ebullient water reactor has one primary education vapor and food water circuit produced after evaporation in the tank. Water boils, and this in normal exploitation, in the higher zone of the heart of the engine, water and the vapor are then separate in the upper part of the tank. The outgoing vapor of the partly high tank goes directly in the turbine, undergoes a condensation and turns over in the engine. Thus, there is no heat exchange between a primary education liquid water circuit and a secondary water vapor circuit as in REFERENCE MARK the Pressurized water reactor. This cycle and the higher operating temperature ensures a thermal efficiency a little better than that of the REFERENCE MARK. On the other hand, the form partially vapor of the regulator (of liquid water in the course of evaporation in the higher zone of the heart) is less favorable (and less easy to control and model) from the point of view of the negative feedbacks with an excursion.

From a strictly functional point of view for the generation of vapor, the tank and the heart of the REB are compared rather directly with a steam generator to tubes out of U vertical and recirculation of the type of those used on the engine REFERENCE MARK. Indeed a recirculation of food water is organized in the tank: The mass throughput of water and nucleate vapor in boiling passing in the heart is typically 7 times superior with the produced vapor nominal capacity. Above the heart a separation (static gravitating and by centrifugation) of saturated water and the vapor is organized in a way very similar to the stage of separation of a steam generator of REFERENCE MARK The Fuel nuclear used in the heart of a REB is Uranium enriched, and the Coolant which circulates in the single primary education circuit is ordinary Eau under pressure. The rates of enrichment used in the REB are the same ones with the 1st order as those used in the REFERENCE MARKS.

Like any type of thermal reactor (nuclear or with flame), the condenser of a REB is cooled by a great quantity of cool water pumped in a river or a sea. Near a REB, one finds also sometimes a Tower cooling to cool the water used in the circuit of the condensers of the turbines. The thermodynamic output of a REB is rather higher than that of a REFERENCE MARK while remaining very close for the following reasons:

• the two types of engine produce dry saturated vapor; the possibility of overheating the vapor to increase the thermodynamic output was implemented in an industrial way neither by the REFERENCE MARKS nor by the REB whereas in this last case the conditions of heat exchange lend themselves to it better a priori

• the produced saturated steam pressure is more easily adjustable with the optimal value is around 80 bar in the case of the REB since this pressure is that to which the engine functions while at the same time in the case of the REFERENCE MARK to obtain the same steam pressure it is necessary to make function the primary education circuit of the reactor at a higher temperature (typically from 25 to 30 °C approximately) and thus to a primary pressure definitely higher so that the aforementioned circuit is liquid at the temperatures in question. Typically the pressure of operation of the primary education circuit of a REFERENCE MARK (160 bar) is thus double of that of a REB.

To notice that engine EPR (REP) increased - by report/ratio with the generations of REFERENCE MARK former the value of the steam pressure produced to full power up to 78 bar what corresponds appreciably to the optimal value for the output of a saturated vapor cycle, as rather usually do it one will be able to say " naturellement" - the whole of engines REB

Comparison REP/REB

Advantages of the ebullient water reactor

1°) a REB has only one circuit, which is pledge of simplicity compared to a REFERENCE MARK. For example, a REFERENCE MARK 4 loops (standard N4 or Konvoy or EPR) requires 5 large capacities cauldronfuls (4 Steam Generator + the pressurisor). In a REB, the tank larger but is certainly dimensioned with a pressure appreciably 2 times less. In addition, because of the least number of large components, for the same electric output, the containment of a REB is of less scale that of a REFERENCE MARK.

2°) This is translated on the capital cost of the whole of the section (nuclear small island + left known as traditional) (civil engineering and components) which is about 18% less low for a REB compared to a REFERENCE MARK of equivalent power. The costs of fuel and exploitation being close, the cost of electricity resulting from a REB is slightly lower than that of electricity resulting from a REFERENCE MARK. The difference remains weak.

3°) the primary pressure of operation of a REB is appreciably half less than that of a REFERENCE MARK (typically 155 to 160 bar against 78 to 80 bar). The operating temperature of a REB is lower by 25 to 30 °C compared to that of the REFERENCE MARK on the level of the primary education circuit as a whole and of more than 50 °C if one compares to the pressurisor. This operation range of the REB is more favorable than that of the REFERENCE MARK with respect to the water corrosion demineralized of the primary education circuits.

4°) the consumption of electricity necessary to the operation of a REB is appreciably the half of that necessary to the operation of a REFERENCE MARK (the variation comes mainly from the consumption by the primary education pumps of the REFERENCE MARK). The power necessary to the section is about 8% of the output capacity delivered with the network for a REFERENCE MARK whereas it is only of 4% in the case of a REB.

By the fact, the net yield of the installation is increased by 1,4% coarsely, not considerable

5°) In variation of the existence of only one circuit instead of two, the instrumentation of the REB is rather less consequent than that of the REFERENCE MARK; for example: there are 5 principal measurements of level in 1 REFERENCE MARK with 4 loops (4 measurements of level Steam Generator + 1 with the pressurisor) against only one - very useful in the event of accident in the REB.

6°) In the course of the normal functioning of the installation a water level is established in the tank of the REB which is measured permanently and contributes to the overall regulation of the system. This measurement of water level in the tank which does not exist under normal functioning in the REFERENCE MARK is of a capital interest in the management of a possible accident of water loss which can lead to the transitory unwatering of the heart. For example in the case of the accident of TMI2 (accident affecting a REFERENCE MARK) the operators were deluded on the quantity with water indeed present in the tank by measurement with level with water in the pressurisor of which reliability is debatable in accidental situation.

7°) the REB are not controlled with soluble boron, which:

• eliminates the problem from the management of the acid content boric of the primary education circuit, source of important concern on the engines controlled with the dissolved boric acid.

• reduces considerably the liquid effluents emitted by the installation.

• eliminates the primary source from production of tritium in the REFERENCE MARKS which constitutes the first source of radioactive rejections of these engines.

• corresponds to a sourer design since in the analyzes of safety the risks of loss of control of the boron concentration in the case of the REFERENCE MARKS belong to the events considered to be dominating in term of risk; in the case of the REB an addition of clear water in the tank in the course of an accident is without consequences; in the same way the risks of crystallization of the boric acid are not to consider.

• reduces the risks of corrosion brought by the boric acid which were at the origin of serious vexations on certain REFERENCE MARKS.

8°) In the case of the REB the water injection in the tank intended to permanently ensure the underwater maintenance of fuel in 1st place is made by the feed-water pumps of the installation which are under operation permanently and of which the availability is thus controlled permanently.

The risk of fall of the level in the tank which can lead to the unwatering of the heart is thus a priori higher in the case of the REFERENCE MARKS than of the REB

9°) the principal primary loops of a REFERENCE MARK connected to the tank and pipings of vapor extraction of the REB are of diameter rather comparable, but:

• on the one hand in the event of rupture of a loop of REFERENCE MARK the mass throughput during the initial phases of the accident (out of diphasic water then mixture) is much higher than the case of the REB or the flow is initially out of vapor and or piping is located partly higher tank

• in addition it is much easier in the case of to practice a restriction on the level of the exit vapor on the tank the REB than on the water loops of the REFERENCE MARK still reducing to the mass throughput vapor to be considered in the event of rupture.

These elements make for example that the accumulators under gas pressure necessary on the REFERENCE MARKS for renoyer quickly the heart in the event of rupture of the primary loops, are not necessary on the REB.

The food water piping of a REB - of diameter much lower than the vapor collector can comprise a non-return valve placed in the vicinity of the wall of tank, practically eliminating the risks from unwatering of the heart in the event of rupture.

10°) In addition to the systems under operation in normal situation as evoked at the preceding point (in the case of the REB food water constitute de facto a system of water injection of safety in the tank under permanent operation) there exist in the case of the REB as well as REFERENCE MARKS of the back-up systems on standby available of injection of safety in the tank whose levels of reliability are rather equivalent of one die to the other.

However:

• on the one hand in the case of the REFERENCE MARKS the pressure to which these systems must drive back to obtain the injection is a priori higher than the case of the REB, even if in the course of the accident the pressure tank at least in the case of varies and lowers the important breaches

• in addition in the case of the REB these systems inject directly in the tank (for the simple reason that it there not the choice.) and not in another point of the primary education circuit and typically in the loops as in a good number of REFERENCE MARKS; the provision of direct injection out of tank is higher in the sense that it in particular in the case of removes a rather great number of common modes break in the circuit related to the primary loops principal (a certain number of REFERENCE MARKS such as for example those of Babcok technology or derived (ABB) have however an injection of direct safety out of tanks)

11°) the containment of the REB is generally under inert atmosphere what eliminates any fire hazard in normal service and any chemical reaction with the hydrogen emitted by reaction zirconium water in the event of serious accident

12°) a penalty of the REB comes from the need for having a sleeving of particularly tight fuel, that being since the density of power of the heart of the REB is approximately twice less than that of the REFERENCE MARKS this sealing is ensured de facto under normal functioning; The temperature in heart of fuel is less in a REB than in a REFERENCE MARK

Moreover, if a loss of sealing of sleeving is noted in service implying the potential presence of PF (in particular gas, but not only) in the part harnesses circuit conveying water and the primary education vapor this does not have on a terrestrial engine generating of immediate serious consequences, it is however necessary to quickly isolate the extraction from vapor what can be made by means of a sufficient number of isolating valves on the vapor - which could be of big number if it were necessary it without important penalty on the normal functioning of the installation.

13°) the possibilities of varying moderation in the hearts of REB are potentially higher than the case of the REFERENCE MARKS. Consequently the possibilities of increase in the convertion rate of fissile plutonium 239 uranium 238 are potentially more important in the case of the REB than in the case of the REFERENCE MARKS. Generally the REB use uranium best that the REFERENCE MARKS, which can appear interesting on the assumption of a rarefaction - in the long term of the sources of natural uranium The implementation of cyle of thorium 232 // uranium 233 is potentially possible with an engine of type REB

14°) to announce the interesting evolution of the concept of REB is currently in study by various manufacturers consisting in simplifying the system more by removing the primary pumps of recirculation and the loops or outgrowths of associated tanks (ESBWR in particular). It is a generating important simplification of one economy to the considerable additional investment

Disadvantages of the ebullient water reactor

In counterpoint of the advantages evoked above the REB present several disadvantages compared to the REFERENCE MARKS:

1°) the produced vapor is active what complicates the access to the hall harnesses under operation; however post stop since the principal bodies formed by irradiation of water are at very short period (less than 10 seconds), it does not have there a real problem for the maintenance actions. This, except in the incidental cases where the sealing of the sleeving of fuel would have been affected and where for example gas fission products would then be transferred towards the turbine and the condenser. That being, the hall turbine is consequently a nuclear controlled zone in a more strict and more complex way of access and ventilation that the hall machine of a REFERENCE MARK

2°) has power equalizes given, a REB comprises a greater number of combustible matter (typically 4 times more) and absorbents of control. The recharging of a heart of REB is thus longer than that of a heart of REFERENCE MARK

3°) the operating machineries of the absorbents of control of the reactivity are placed partly lower of the tank than the image of what is made in many piles swimming pools; the insertion of the absorbents in the heart in the event of emergency stop is not simply gravitating like in the case of the REFERENCE MARKS or typically the power dump of an electromagnet is enough to cause the fall. Each absorbent is equipped with a system oelopneumatic of insertion in the heart, of which reliability is high (it is a system " passif") but which is more complex than system PWR.

Architectures of REB under studies eliminate these penalties by envisaging absorbents operations through the lid from tank and with gravitating fall such as Russian engine VK300 under development, for example.

4°) the internal preparings of tank are rather more complex than those of a REFERENCE MARK primarily owing to the fact that it is necessary to organize;

• the separation of the vapor
• recirculation of saturated water

To however notice that this relative complexity of the interns tank becomes an advantage when it is a question of managing the first moments of an accident of rupture of piping related to the tank because on this assumption the entirety of the interior volume of the tank is ipso-facto in broad communication and balance of pressure, which is not the case of many REFERENCE MARKS or these cases of different accidents according to if the breach considered is related to the loop " chaude" or " froide" (the rupture in cold loop is more penalizing)

5°) the instrumentation out of tank is a little more complicated in the case of the REB than of the REFERENCE MARKS

6°) the crossings in bottom of tank which the crossings for operating machineries represent constitute a weakness of the system larger than in the case of the REFERENCE MARKS because an important escape or breach on this level increases the risk of unwatering of the heart

To announce that REB in studies remove this defect (Russian project VK300)

7°) the management of gases of radiolyse of water in the heart (production of hydrogen) is more malcommode in a REB that in a REFERENCE MARK, which historically led to various incidents; this point related inter alia to the detailed drawing of the interns upper shaft is adjustable however without major difficulties

8°) the management of the water on the side harnesses and more strict and complex that in the case of a REFERENCE MARK since it is about primary water; for example:

• filtration purification of water before return to the tank is more strict than in the case of the secondary water of REFERENCE MARKS the

• the turbines must be with total or controlled sealing (incondensable gases potentially active extracts of the turbine, etc)

9°) the modeling of the thermohydraulic and neutron phenomena in the case of the REB is more complicated than in the case of the REFERENCE MARKS, this handicap the REB in particular when one seeks to increase the power

10°) Although the neutronics and the thermohydraulics of a REB are a priori more complex than that REFERENCE MARKS the burnup rates of fuel reached by the REB are almost the same ones de facto as those of the REFERENCE MARKS

Comments on comparison REB // REFERENCE MARK

Although the exercise of comparison is very difficult because both dies have advantages and disadvantages;

• acting of a generating application (and only in this case of application)
• since the sealing of the sleeving of the fuel is assured,
• taking account of the whole of the recent developments of the die REB which progressed much these 20 last years,
• the question of the system of operation of the absorbents, which remains a strong penalty, being put aside because in evolution of design c% manufacturers,
• the management of the resumption of reactivity related to the collapse of the vapor contained in the heart under operation being supposed controlled

the other disadvantages of die REB, for important that they are, are not really major and to the assessment the comparison turns rather to the advantage of the REB .

Development of the die

To notice that the concept of supercritical water reactor is de facto an evolution of engine REB towards the high temperatures and thus towards the best thermodynamic outputs since it is then possible to function out of overheated vapor.

The International forum Generation IV retained the concept of " water reactor supercritique" like one of the concepts to be developed. The technology of water/supercritical vapor for the electrical production is already developed since strong a long time for the thermo plants with coal. Within the framework of the nuclear production, the RESC (supercritical water reactor) aims at taking best technologies REB (control of moderation, thermodynamic output) and REFERENCE MARK (negative void coefficient, but not exaggeratedly not to risk of resumption of important reactivity in the event of collapse of the bubbles present in the heart). In prospect it is necessary to indicate the possibility of increasing the convertion rate into Pu 239 of the fuel U 238 with can be the attack of the Iso-generation.

Internal bond

• nuclear Nuclear plant
• Die
• Pressurized water reactor
• European pressurized Engine

History of the modifications of " Water reactor bouillante"

Preliminary: I am Internovice: Not knowing how one creates a history in Wikipedia I add some elements following the article

I found a little by chance an outline of article on the BWR in very thin Wikipedia really, approximately 1,5 years ago

Since I stuck to the comléter elements which I believe important of which in particular the comparison PWR // BWR which without being certainly complete is objective It must make reflect the French nuclear community because over the long period it is the sourest technology and least expensive which will be essential, but there is no REB of strong power which aity and accepted by the Authority of French Safety what is very regrettable.

I practiced a rather great number of various final improvements in order to at least improve clearness of the text I hope for it

A certain number of other speakers also improved the article since what is very well

Cordially