SE500413C2 - Methods of utilizing hydrogen-water chemistry in a boiler-water reactor plant and hydrogen-water-chemistry methods for use in a boiler-water reactor plant - Google Patents

Abstract

PURPOSE: To reduce the amount of radioactive<16> N that is discharged to a part with a low shielding degree of a reactor system by suppressing the migration of a gas-shaped nitrogen compound from a liquid phase to a steam phase. CONSTITUTION: Volatile<16> N compound mainly migrates to a steam phase at two regions in a reactor container. One of them is a reactor core region including an inchannel region where nearly all boiling occurs and the other is a region at the upper part of the reactor core where water and steam from a bypass region are mixed and the lower part of a gas separation region. For reducing the<16> N in the steam phase, the ratio of volatile<16> N compound to be generated is decreased or the migration of the volatile<16> N compound into the steam phase is suppressed or the arrival of the volatile<16> N compound in the steam phase at a turbine is delayed. For example, for reducing the ratio of the volatile<16> N to be generated, a reaction path reaching the generation of the volatile<16> N compound is changed by adding a chemical substance (especially a liberation group capturing agent), thus reducing the amount of radioactive<16> N to be discharged to a part with a low degree of shielding.

Description

Û L) fš- higher radiation levels in the main steam lines and turbine hubs have been observed. These higher radiation levels in the more heavily shielded plants have not caused any significant problems. Heavily shielded turbines, capacitors and steam lines have prevented radiation from reaching service personnel and areas where people are. Unfortunately, many plants include heavy shielding of the plant's turbine, condenser and steam line side, which is only sufficient to limit the dose rates in normal water chemistry. As this is the case, the elevated radiation levels have tended to limit the use of hydrogen-water chemistry to prevent stress corrosion.

Operation of boiling water reactors in normal water chemistry gives rise to a small proportion of N-16, which is formed by the n, p reaction of O-16 and is in a chemical form, which tends to be volatile. When this fraction is transported in the aqueous phase in the reactor and the water coolant is converted to steam, a part of the volatile fraction is wrapped in the steam phase and transported to the turbine.

N-16 is a radioactive nuclide, whose half-life is approximately 7 seconds. At its decay, high-energy gamma radiation of 6 and 7 mev was emitted. During the normal operation of the plant, a significant radiation field thus comes from the steam lines and the turbine. Due to the intensity of gamma radiation and relatively high energy, considerable shielding is required to limit the intensity of the radiation field. Despite the shielding, the impact of the N-16 source can also be measured at a significant distance from the source.

In the context of the present invention, it has been found that the observed radiation levels are at least partly caused by the conversion of N-16 to volatile nitrogen compounds, including ammonia, which are transported in the vapor phase.

Under hydrogen-water chemistry conditions, a larger proportion of N-16 is converted to volatile form. Thus, the radiation levels in the vapor phase increase considerably in comparison with the levels without the addition of hydrogen. Depending on the reactor, the levels of us have been found by measurement to increase from 1.2 to 5 times at the hydrogen concentration required to prevent intercrystalline stress corrosion cracking in the circulatory system. For some facilities, the increase is sufficient to exceed safety dose rate limits, not only near the source but also in surrounding buildings and land and at the boundaries of the site. This is perceived as one of the most detrimental aspects of hydrogen-water chemistry. Thus, it would be highly desirable to find a way to limit the volatility of N-16, i.e. the amount transported by the steam.

The present invention generally offers a method of operating boiling water reactors with hydrogen-water chemistry under conditions which limit the level of emitted radiation which has hitherto accompanied this chemistry. More specifically, by preventing the transfer of gaseous nitrogen compounds from the liquid phase to the vapor phase, the release of radioactive N-16 can. smaller shielded parts of the reactor system are reduced. Different ways of preventing such a transfer are applied in part depending on the mode of operation of the reactor. Three working methods are applied, which provide varying hydrogen protection levels.

First, boiling water reactors can be operated with complete plant protection, whereby the hydrogen water concentration of the feed water is sufficient to prevent intercrystalline stress corrosion cracking or irradiated stress corrosion cracking in all parts of the primary reactor system, including all components of the primary reactor system. Secondly, the reactors can be operated with selective protection, whereby hydrogen is introduced only in certain critical areas in the reactor, which gives 5: 1 4. io localized protection within these areas. Operation with selective protection allows the introduction of a smaller total amount of hydrogen, so that less N-16 is generated than with full protection. Examples of the critical areas for the introduction of hydrogen are generally (a) the circulatory system, (b) the bypass area of the core, ie. the area not within the boundaries of the fuel assemblies and the area immediately above the fuel core, more specifically the area of the upper fuel control, and (c) the lower filling chamber area of the reactor tank, which includes the lower part of the tank up to the area immediately above the fuel support plate. Third, the boiling water reactor can be operated with partial protection, the hydrogen concentration being lower than that required to achieve the lowest electrochemical potential for completely preventing radiation-induced stress corrosion cracking. Such an approach partially stops the growth of cracks and reduces the proportion of volatile N-16. In the first category, either the amount of volatile N-16 species transferred to the vapor phase is chemically reduced, the quantity of volatile N-16 species transferred to the vapor phase is physically reduced, or the transport of volatile N-16 species in the vapor phase is delayed to the main steam to the turbine for a sufficient time to allow considerable decay of the radiation. In the second and third categories, less hydrogen is used and thus less volatile N-16 is formed.

Complete protection Firstly, the formation of volatile nitrogen compounds can be prevented chemically. This can be accomplished by altering pathways leading to the formation of volatile N-16. with small amounts of additives, in particular free radical cleaners, and / or by increasing the pH of the reactor feed water to an acidic level. Thus, according to the invention, trace amounts (billionths of concentrations) of a kind are introduced for inhibition, suppression or alteration of the reaction pathway for radioactive nitrogen, which leads to the formation of a ~ i o Ovøu 'OO 1 II I? W volatile species, such as ammonia, and / or enhancement of the reaction pathway leading to a non-volatile species, such as nitrite. Examples of possible additives are nitric oxide, carbon dioxide, nitrite, nitrate, low molecular weight alcohols or ketones, copper, zinc or vanadium, etc., whereby other possibilities are not excluded. Alternatively, a slight increase in pH reduces the volatility of ammonia. A change in pH can also change the pathways leading to the formation of volatile nitrogen compounds. In this latter case, the formation of volatile N-16 species is prevented.

Usually, the pH of the boiler feed water is increased to the range from about 7.0 to 8.6, measured at room temperature (normally the feed water has a pH of from about 6.1 to 8.1).

This can be accomplished by appropriately balancing the anion or cation exchange resin used in the boiling water treatment plant.

Second, the N-16 transport to the vapor phase can be limited by physical means. It is known that N-16 is formed in two areas of the core: (1) in the housing of the fuel bundle channel, i.e. in the area inside the duct, -and (2) in the area outside the fuel bundle area, ie. the bypass area. Essentially all boiling takes place in the area inside the canal and essentially none in the bypass area. In addition, the flow rate is much higher and thus the residence time is much shorter in the area inside the canal than in the bypass area, while the water volumes in both areas are comparable. Thus a considerable part of the formation of N ~ 16 takes place in the bypass area. Since the residence time of the water in the bypass area is considerable in comparison with the half-life of N-16, a decrease in the flow rate reduces the total production of N-16 at the core exit, which provides a physical control mode.

A second physical method involves limiting the time of contact between the steam and the water. This reduces the net transfer of the volatile N-16 species from the liquid to the vapor. -w, §¶ ,, _ ,, .., ß -... i-yn N ......-, -. <.- v - = - .., <-, ~ WJM .__. , v .. ~ ,, ~ ..., ..., _, phase, thereby limiting the vapor phase concentration of N-16. This method can be performed by physically changing the area above the core.

A third method means that the time for the retention of N-16 in the steam is increased by several seconds, which is significant in comparison with the half-life. This can be achieved physically by arranging an increased volume of the steam as close to the reactor tank as possible. This volume could be screened. An alternative method may involve chemical adsorption on a matrix material for a sufficiently long time (seconds) to provide a significant delay relative to the half-life.

Selective and partial protection The hydrogen concentration required to protect the components of the stainless steel circulation system varies considerably among plants. (See Fig. 2). This variation is attributed to differences in the ability of the hydrogen used to promote hydrogen-oxygen recombination in the drop gap area. Thus, methods which can promote the efficiency of hydrogen use reduce the total hydrogen use and reduce the amount of volatile N-16 generated and transported to the vapor phase. Reduction of the required hydrogen concentration may be beneficial in reducing the N-16 vapor phase activity, depending on the required final hydrogen concentration (see Fig. 3). This can be accomplished by such methods as catalyzing the hydrogen-oxygen recombination reaction, for example by increasing the radiation in the fall gap area or possibly by surface catalysis.

It is also known that hydrogen, which is injected into the feed water, the usual nuisance for injection, is only partially available for the fall gap area, ie. the hydrogen-carrying water is divided at the top of the jet pump, so that a part enters the jet pump and from there directly into the hearth and goes past the fall gap area. Thus, if the hydrogen is injected under the inlet to the jet pumps, the entire amount is available for the fall gap area. Since this can lead to a corresponding reduction in the total amount of hydrogen added (and that it enters the curing area), less volatile N-16 is formed.

To ensure a sufficient concentration of hydrogen in the bypass area of the core, while limiting the production of volatile N-16, hydrogen can be injected directly into the bypass areas. This hydrogen injection in combination with the methods described for enhancing the utilization of hydrogen in the trap gap area reduces the total addition of hydrogen and thereby reduces the concentration of volatile N-16.

In this case, both the circulatory system and the bypass area of the core are protected from intercrystalline stress corrosion cracking and radiation-assisted stress corrosion cracking with only a relatively small increase in the concentration of volatile N-16.

In the lower filling chamber area a sufficiently low oxygen concentration can be achieved by adding hydrogen, for example via feed water addition, and catalyzing the recombination reaction by either increased radiation in this area or in the vicinity of the jet pumps or by surface catalysis or in the drop gap area as described above .

To provide partial protection, it is possible to work at a slightly higher electrochemical potential, so that the rate of crack growth is reduced but not stopped. This would require less hydrogen and thus reduced formation of volatile N-16.

During complete or partial suppression, it also seems probable that the proportion of ammonia (N-16) that is transferred to the vapor phase can be affected by other changes in physical parameters. Among these may be changes in an 'OI sin; ,, I. . , ¿,,. '' oo 0 coon øaoo m ~ ,. na .. 401 4 ~ -1 oo »- now 00" in CZ * ._ 'lb- .... I »r.¿ reactor core water level reduce the N-16 level in the vapor phase, so that at least partial compensation is obtained for the increase in radiation levels, which is brought about by working under hydrogen-water chemistry, Other parameters include the circulation flow rate, axial power distribution and axial distribution of efficient steam space.

In the accompanying drawings Fig. 1 schematically shows a boiling water reactor plant and illustrates the primary components of a boiling water reactor, Fig. 2 is a diagram showing the differences in oxygen concentration in the recirculation system between seven plants as a function of the hydrogen concentration, Fig. 3 is a diagram illustrating the effect of hydrogen injection on elevated levels of N-16 radioactivity for a number of jet pumped boiler water reactor plants, and fig; 4 shows a probable reaction sequence for the N-16 species in a boiling water reactor plant.

The formation of N-16 takes place by an energetic neutron reacting with O-16 in the water. The energy ethics of the reaction are sufficient to completely break all chemical bonds and lead to the formation of a nitrogen atom with a high positive charge immediately after formation with a significant kinetic energy (approximately 0.4 meV). When the charged ion is thermalized, electrons are recaptured, so that an approach to a more neutral state takes place. During the process, chemical bonds of the surrounding medium (primarily water) and other species are also broken down in dilute concentrations.

Near the end of the thermalization process, the nitrogen species and Cflñ A '! É surrounding molecular fragments are highly reactive. The subsequent radiation chemistry reactions can be affected by the behavior of the species present, for example the species' affinity for electrons, the tendency to form free radicals, their chemical reactivity, etc. It is during this period of intense chemical reactions that the chemical end product species are formed. For example, the transition from normal water chemistry in the reactor water with about 200 ppm oxygen and 10 ppm hydrogen to hydrogen-water chemistry at 15 ppm oxygen or less and about 100 ppm hydrogen results in N-16 being chemically altered from the primarily non-volatile form such as a nitrate or nitrite to a volatile form such as ammonia.

Generally, two ways are offered to suppress the formation of volatile N-16 ammonia compounds, which arise as a result. The methods can be applied independently of hydrogen-water-chemical conditions. dependent on each other or in combination. plant protection, the chemistry can be changed to suppress or inhibit the reaction pathway for the formation of the volatile radioactive N-16 species or to enhance the reaction pathway leading to non-volatile species, for example nitrite or nitrate. Alternatively, physical parameters such as the internal components of the reactor vessel or the plant operation can be manipulated within the limits of normal operating conditions to reduce the transfer of radioactive volatile compounds to the vapor phase. In selective or partial protection, methods of enhancing the use of hydrogen to reduce oxygen concentrations (thereby preventing intercrystalline stress corrosion cracking in the recirculation system) can be utilized and include either chemical or radiological or physical methods. To protect the bypass area of the hearth, the physical method of supplemental injection of hydrogen directly into the area can be applied. To protect the lower filling chamber area of the reactor vessel, methods of enhancing the hydrogen-oxygen recombination reaction by chemical or radiation chemical methods can be applied. For operation below the electrochemical potential required to completely stop the crack growth, and to only delay the crack growth (ie conditions of partial protection), less hydrogen is required. The main purpose of all these methods is to reduce the total hydrogen use and thus the formation of volatile N-16.

Under normal water chemistry conditions, the oxygen concentration, measured in the recirculation lines of a boiling water reactor, is in the range 18G-300 ppm with a corresponding electrochemical corrosion potential of 0 to 0.1 V. The reactor's sensitized (or exhibiting cracking and / or difficult cold working ) stainless steel components or nickel-based alloys are prone to intercrystalline stress corrosion cracking. The driving force of intercrystalline stress corrosion cracking can be eliminated if the electrochemical corrosion potential of the stainless steel is reduced to below a critical value.

It is known that the addition of hydrogen to the feed water of a boiling water reactor can lead to a decrease in the concentration of oxidizing radiolysis products (O 2, H 2 O 2, etc.), leading to a reactor water chemistry with an electrochemical corrosion potential below the potential at which intercrystalline stress corrosion cracking occurs.

When hydrogen is added, the reactor water becomes less oxidizing, and this chemical change affects the distribution of N-16 in the refrigerant. N-16 is formed by a (n, p) reaction in the core with the refrigerant in the reactor core O-16 and decomposes with a half-life of approximately 7 seconds. Upon decay, high-energy gamma radiation of approximately 6 and 7 meV was emitted.

During normal plant operation, a significant radiation field thus emanates from the steam lines and turbines.

Under normal operating conditions, the more oxidized 11 chemical forms of N-16 are formed, such as nitrite and nitrate.

Under the more reducing chemical conditions in hydrogen-water chemistry (HWC), N-16 primarily forms volatile chemical species, such as ammonia. Since the ammonia form is much more volatile than oxidized species, a switch to hydrogen-water chemistry conditions at a hydrogen concentration required to prevent intercrystalline stress corrosion cracking can lead to a significant increase in the presence of N-16 in the vapor phase increase. of the gamma radiation emitted along the main steam lines and elsewhere on the steam side of the installation devices.

The magnitude and consequences of the radiation increase are different for each boiling water reactor plant, since the reduction in the oxygen concentration and the corresponding protection potential against intercrystalline stress corrosion cracking for the circulation is achieved at different degrees of hydrogen injection. In addition, with different building and equipment arrangements, the consequences and the actual size of the radiation increase inside and outside the facility can vary considerably. Since hydrogen-water chemistry offers such an increased margin to intercrystalline stress corrosion cracking for both the plant's pressure-enclosing components and internal parts, for many boiling water reactor plants, the introduction of hydrogen-water chemistry could be planned as part of the overall planning to increase plant availability. small and the service life of the plant. However, many boiling water reactors lack sufficient shielding in and around the plants to tolerate the increased radiation levels that result from the increased production of volatile N-16. Thus, reducing the production of volatile N-16 would facilitate the application of hydrogen-water chemistry to boiling water reactor plants.

Pig. 1 schematically shows the hardware for the water flow paths through the reactor tank 10. Jet pumps 20 draw in 12 water from the upper part of the trap gap area 30 and in combination with the drive flow water 40, 50 provide the cooling flow to the lower part of the reactor tank. The water rises in the lower filling chamber area 150 and up through the hearth support plate 160 and into the fuel area 170. The water which does not enter the jet pumps flows downwards along the drop gap area 30 and supplies the water for the circulation loops. The circulation pumps 60, 70 and the flow control valves 80 regulate the circulation flow rate. The hydrogen gas is introduced into the reactor tank with the main feed water flow from the water condensate from the turbine at 100. Steam generated by the fission heat passes through the steam separators 110, upwards and past the steam separators 120 and out of the tank at 130 as the main 90 steam flow to drive plant turbines .

Various physical parameters can be manipulated to reduce the N-16 levels, which reach the steam side of the plant. The transfer of the volatile N-16 species to the vapor phase takes place primarily in two areas of the reactor tank: (a) in the core area, where essentially all boiling takes place within the fuel channel, and (b) in the area above the core, where the water from the bypass area is brought together with the water and steam from the inner channel area and in the lower part of the steam separator area.

The present proposals for regulating N-16 in the vapor phase include two general methods: (a) in view of complete oxygen suppression and thus protection in all parts of the primary system, which require higher hydrogen concentration, the N-16 levels in the vapor phase may be in significantly higher. In this case, two general methods are possible. One method is to change the pathways that lead to the formation of volatile species of N-16, so that the volatile species are formed to a lesser extent and thus less 13 volatilize. The alternative to this is to reduce the concentration of volatile N-16 in the vapor phase, before it flows to the turbine. (b) With a view to selective oxygen suppression, i.e. oxygen suppression and thus protection in selected areas of the primary system or partial suppression_ whereby the rate of crack growth is stopped but not completely suppressed, the purpose is to minimize the total use of hydrogen and thereby limit the amount of volatile N-16 formed (in the core area) .

Each of these methods of execution is described in the following paragraphs. Even if each is described separately, one or more may be used together. early, so that flexibility is obtained in the application and so that optimization for each plant is allowed.

Complete protection V This operation maintains a sufficient hydrogen concentration in the feed water and throughout the primary system to reduce the oxygen concentration to a level at which corrosion, such as intercrystalline stress corrosion cracking, is halted. This hydrogen concentration is probably high enough to cause a significant increase in the N-16 concentration in the main vapor with a corresponding increase in the dose rate (Fig. 3).

This is caused by the N-16 species produced by the n, p reaction on O-16 being subjected to a series of reactions with the surrounding medium and leading to the formation of a volatile species, for example ammonia, which is rapidly washed from the water by the action of the steam in the boiling areas of the reactor. The N-16 concentration in the vapor phase can be reduced by either forming the fraction of volatile N-16 formed, limiting the transfer of volatile N-16 to the vapor phase or delaying the volatile N-16 species in the vapor phase before being fed 14 to the turbines.

The fraction of volatile N-16 formed can be reduced by the addition of chemical species, especially free radical cleaners, so that the path of reaction leading to the formation of the volatile N-16 species formed by the n, p reaction is changed. formed the "hot" radiation chemistry reaction of the N-16 atom and the subsequent reactions in the radiation field of the reactor core. The formation of volatile N-16 occurs through a series of reactions, some of which undoubtedly involve free radicals. A probable reaction sequence for the N-16 species in the reaction refrigerant is shown in Figs. 4.

If a detergent is added to react with the free radicals, for example, the reaction pathway leading to the formation of ammonia can be altered (inhibited) and the formation of another product enhanced. These detergents can be nitric oxide, low molecular weight alcohols and ketones, carbon dioxide, nitrite or nitrate or the addition of metal ions, such as copper zinc or vanadium to name several possible candidates without ruling out other possibilities. The detergent concentration need not be high, usually from about 5 to 100 ppm, more usually from about 20 to 30 ppm. Furthermore, a small change in the pH of the reactor water can change the reaction paths for the formation of the volatile species.

The reactor water normally has a pH of from about 6.1 'to 8.1, measured at 25 ° C, and by adjusting the pH in the range of from about 7.0 to 8.6 and usually between 6.5 and 8.0 inhibits the production of volatile N-16. The pH can be adjusted by changing the anion cation reaction in the ion exchange resin in the feedwater treatment plant. An increase in the pH value also seems to reduce the volatility of ammonia. The idea of limiting the transfer of ammonia from the liquid to the vapor phase can be realized by physical methods. These methods are given by way of example and include but are not limited to the following. (a) Since the transfer takes place in the inner channel area and in the area above the core and takes up a limited time, a reduction in the contact time between the steam and the liquid phase reduces the fraction of volatile N-16 species transferred to the steam. This can be done in several ways, for example: 1. reduction of the volume and thus the contact time in the mixing filling chamber area above the hearth, which includes the area between the upper part of the hearth and the steam separators; 2. increasing the circulation flow rate, which reduces the content of efficient vapor space and reduces the contact time between the liquid and vapor phases. This also means that the ammonia tends to remain in the liquid phase and to be "carried under" in the water reflux to the trap gap area, during which the N-16 with its half-life of 7 seconds decomposes to a significant extent. Since the residence time in this area is long compared to the half-life, an increase in the residence time further reduces the total production.

Another way involves delaying the volatile N-16 species after they have been transferred to the vapor phase. Thus, the steam in the main area of the reactor tank can be passed through a medium, which preferentially delays the volatile species, for example by adsorption, for at least several seconds, so that N-16 is allowed to decompose before transport to the steam line and turbine. The delay can also (get) (f) C.) x .r ~ J 16 be achieved physically by introducing the steam into the expanded volume, before it is transported to the turbine. For example, a volume of approximately the size of the main tank area of the reactor tank would provide a residence time of approximately one half-life, during which the N-16 concentration would decrease twice.

The manipulation of the physical parameters to reduce the amount of N-16 entering the vapor phase, as described in the example given above, is necessarily limited by the physical conditions of the reactor and the hydraulics of the reactor system.

The boiling water system is very dynamic and is limited by the requirements to generate a sufficient amount of steam for power to be obtained to the calculated capacity and for this to be done as safely as possible without any increased risk.

Selective protection in specific areas This method is based on operation at a lower total hydrogen concentration in the primary system, especially the hardening area. Pig. 3 indicates that different plants show greater differences in the oxygen concentration in the circulation system at given feed-water-hydrogen concentrations. For example, at a feedwater-hydrogen concentration of 0.3 ppm, the circulating oxygen concentration is less than 1 ppm for plant 5, while that for plant 4 is still relatively high at about 100 ppm.

It is observed (Fig. 3) that at this hydrogen concentration the main steam activity has not risen significantly for any of the plants. This difference of almost two orders of magnitude can be explained on the basis of the rate at which the hydrogen-hydrogen combination reaction takes place in the column gap area. For those plants where the oxygen concentration decreases more rapidly as a function of hydrogen addition, the recombination is catalyzed. It has been found that this difference among the plants is correlated with the dose rate to which the water is subjected when it flows through in the fall gap area 30 in the vicinity of the hearth, i.e., the area outside the jet pumps. The plants with a higher dose rate can be considered as utilizing the hydrogen more efficiently (for recombination), at least in the fall gap and circulation area. Thus, any method that can be used to improve the use of the hydrogen leads to the use of less hydrogen and in less formation of volatile N-16. This is the premise on which this part of the patent is based.

Protection of the circulatory system can be achieved by two general means: catalysis of the recombination reaction or change of the hydrogen introduction point. As already described, catalysis of the recombination reaction can be accomplished with increasing dose rate. One possibility is thus to increase the intensity of the radiation field and / or to increase the rate of energy deposition in the water in the fall gap area of these plants, where a greater concentration of hydrogen is required, for example plant 4. Another possibility is to catalyze the recombination reaction by surface reaction of an added material. Such a surface may be the stainless steel itself.

The hydrogen has been introduced into the feed water for both the plant 4 and for other plants, in which tests (not included in Fig. 3) have been performed. After mixing with the water from the hearth outlet, the feed water is divided at the top of the jet pumps.

Approximately 2/3 enters the jet pumps and is pumped directly to the core, so that 1/3 remains for reaction with oxygen in the drop gap area. If the hydrogen feed point is moved to a location in the drop gap area during the jet pump intake, the effective concentration is increased approximately three times. Thus, the total concentration can be reduced by a similar factor. Referring to Fig. 3, a three-fold reduction in the hydrogen concentration from the feed water concentration is currently required to provide sufficient suppression, i.e. about 1.2 ppm with approximately a 4.6-fold increase in the main vapor radiation level relative to normal water chemistry to a 1.6-fold increase 18 at the equivalent feedwater-hydrogen concentration of 0.4 ppm.

The problem of intercrystalline stress corrosion cracking of stainless steel components in the reactor core has been identified. These components have been found to be located primarily in the bypass area of the hearth, the area where there is no boiling, such as in the fall gap area. On the basis of the premise that a sufficient dose rate can sufficiently catalyze the recombination reaction, it is highly probable that due to the higher dose rate in the bypass areas of the core relative to the gap gap area in each reactor as well as the longer residence time of an even higher absorbed dose, the oxygen can be suppressed a lot by minimum concentrations of hydrogen. The amount of hydrogen that is added to the slurry efficiently in the presence is possible that that area may be sufficient to reduce the oxygen concentration to a sufficiently low level in the vaporization area.

If this is not the case, hydrogen could be added directly to the bypass water in a sufficient concentration and still be significantly less than the equivalent feed water concentration, where an increase of a large factor in the main vapor radiation level occurs. In this case, it is highly probable that protection against stress corrosion cracking is obtained not only for components in the bypass area but also for stainless steel components, for example the upper fuel control, which is located at the top of the bypass area but below the area where mixing takes place. with water from the inon canal council.

The second area, where there is a possibility of intercrystalline stress corrosion cracking and where the suppression of oxygen vessels is located, is in the area below the core, ie. the lower filling chamber of the reactor tank. In this case, the addition of hydrogen, possibly via the feed water, would be required for this disposal. Since the dose rate has been identified as a critical factor affecting the hydrogen-oxygen combination (throughput times of from two to five seconds in the case of the CU CU rs-low ml 19 gap range), it is possible that these reactors with a a sufficiently high dose rate for effective recombination in the downhole can also show effective recombination within the water flow time in the jet pump before delivery to the lower filling chamber. If it is not sufficient, the recombination reaction may require an increase in the rate using the catalytic methods described previously, i.e. surface radiation catalysis.

The invention has been fully described above, but the description and drawing figures may not be construed as limiting the invention, which is set out in the appended claims.

Claims (19)

10 Patent claims A method of utilizing hydrogen-water chemistry in a boiling water reactor plant comprising a reactor in which water is boiled to a liquid phase and a steam phase, a turbine for extracting power, a condenser for condensing steam, from which power has been extracted, as well as a feed water circulation system which returns the condensed steam as feed water to the reactor steam boiler, whereby injection of hydrogen into the feed water is used to reduce the stress corrosion, characterized by the transfer of the radioactive gaseous nitrogen from the liquid phase to the vapor phase is reduced by inhibiting the formation of such nitrogen compounds in the liquid phase. A method according to claim 1, characterized in that said inhibiting step comprises chemically inhibiting the formation of volatile N-16 species in the liquid phase. IN 3. A method according to claim 2, characterized in that the inhibiting step comprises adding at least one free radical cleaner to the feed water, thereby inhibiting the development of gaseous nitrogen compounds. 4. A method according to claim 3, characterized in that said detergent is selected from the group consisting of nitric oxide, zinc, alcohols and low molecular weight ketones, carbon monoxide, nitrite or nitrate. 5. A method according to claim 1, characterized in that said inhibiting step comprises adjusting the pH of the water to a basic level in the range from about 7 to 8.6, thereby inhibiting the development of volatile hydrogen compounds. Lw CD I; 2! 6. A method according to claim 1, characterized in that said inhibition step comprises the use of reduced sprinkling in the reactor core. 7. A method according to claim 1, characterized in that said inhibiting step comprises increasing the circulating rate of feed water effluent. 8. A method according to claim 1, characterized in that said inhibiting step comprises adjusting the control rod pattern. 9. A method according to claim 1, characterized in that said inhibition step comprises raising the reactor water level. 10. A method according to claim 1, characterized in that said inhibiting step comprises introducing the hydrogen into a preselected area in the circulatory system, which area is selected to allow reduced hydrogen utilization, whereby less radioactive volatile nitrogen is evolved. 11. A method according to claim 10, characterized in that hydrogen is introduced into an area below the jet pump inlet of the circulation system. 12. A method according to claim 11, characterized in that hydrogen is introduced into a bypass area in the core inlet. 13. A method according to claim 1, characterized in that the transfer of radioactive, volatile nitrogen compounds is inhibited by the use of a selective adsorbent to increase the storage time of the nitrogen compounds with regard to further decomposition. 14. A method according to claim 1, characterized in that ÜÜÜ 4113 1: 2. the transmission of radioactive, volatile nitrogen compounds is inhibited by increasing the storage time in the steam lines. 15. A method according to claim 1, characterized in that the transfer of radioactive, volatile nitrogen compounds is inhibited by the use of surface catalysis to improve the utilization of hydrogen, thereby reducing the evolution of gaseous nitrogen. The method of claim 1, wherein the transfer of radioactive volatile nitrogen compounds is inhibited by the use of increased radiation to enhance the hydrogen-oxygen recombination. 17. A method according to claim 1, characterized in that the transfer of radioactive, volatile nitrogen compounds is inhibited by operation at a more positive electropotential, which allows less addition of hydrogen. Hydrogen-water chemistry method for use in a boiling water reactor plant with a reactor having a liquid phase and a vapor phase, characterized in that a free radical scavenger is added to the liquid phase to inhibit the transfer of gaseous nitrogen compounds from the liquid phase phase . 19. A method according to claim 18, characterized in that said detergent is selected from the group consisting of nitric oxide, copper, zinc, alcohols and low molecular weight ketones, carbon dioxide, nitrite or nitrate.