Patent Application
20140005462
1. Field
Some example embodiments relate generally to a chemical separations system and/or method for processing and storing post-accident coolant, and more particularly to a chemical separations system and/or method of filtering post-accident water to remove fission products and salts for permanent disposal.
2. Related Art
After a reactor accident, efforts are typically made to have the reactor core reprocessed and/or placed in interim storage. However, the mitigation of the reactor accident may be complicated by the introduction of foreign materials. For instance, in the Fukushima Daiichi accident in 2011, seawater was used in an attempt to cool the reactors. As a consequence of the use of seawater, sea salts were deposited in the reactors. Accordingly, the integrity of metal containers intended for subsequently storing the recovered fuel from the reactor core may be compromised by the corrosive action of the sea salts.
When the reactor is operating, the radioactive soluble and/or insoluble impurities may be removed, at least in part, by one or more demineralizers, filters, ion exchangers, and/or other devices (collectively referred to in this application as a Reactor Water Cleanup Unit (“RWCU”)). For a damaged reactor core injected with off-specification water (e.g., seawater) using the normal RWCU, a relatively large volume of ion-exchange resin may be generated. Therefore, the RWCU filter beds would need to be changed frequently, thereby making the process more difficult and costly. In addition, operation of the RWCU allows for coolant (e.g., water) to be extracted from the bottom of the reactor, which may be obstructed due to damaged components and fuel. Furthermore, the spent resin is not stable enough for permanent waste storage due to relatively large amounts of radioactivity.
Some example embodiments provide a chemical separations method and/or system for processing and storing a post-accident coolant including contaminants, e.g., corium, sea salts, etc.
An example embodiment of a method for processing a coolant includes filtering a coolant using a first filtration system to generate a first filtered material, and filtering the filtered coolant using a second filtration system to generate a second filtered material. The second filtration system is different from the first filtration system. The first filtered material is transferred to a first waste treatment container to convert the first filtered material to a first waste product for permanent disposal, and the second filtered material is transferred to a second waste treatment container to convert the second filtered material to a second waste product for permanent disposal.
An example embodiment of a system includes a first filtration system configured to filter a coolant and generate a first filtered material, and a second filtration system configured to filter the filtered coolant and generate a second filtered material. The second filtration system is different from the first filtration system. A first waste treatment container is configured to convert the first filtered material to a first waste product for permanent disposal, and a second waste treatment container is configured to convert the second filtered material to a second waste product for permanent disposal.
The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the intended scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
Detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.
Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
Example embodiments are directed to an in-situ technique to remove relatively large amounts of contaminates from reactor coolant after fuel damage and off-specification coolant injection, for example, sea water. The nuclear material, e.g., corium, is removed from the coolant, and a waste is generated for permanent geologic disposal that is relatively safe, secure and stable.
The nuclear material referred to herein may be corium, although example embodiments are not limited thereto. As understood by those of ordinary skill in the art, corium is a fuel containing material (FCM) that is formed during a nuclear meltdown. In particular, corium is a lava-like molten mixture of portions of a nuclear reactor core and may include nuclear fuel, fission products, control rods, structural materials from the affected parts of the reactor, products of their chemical reaction with air, water, and steam, and/or molten concrete from the floor of the reactor room in situations where the reactor vessel is breached, and resulting from the introduction of foreign materials, such as seawater or boron injections. The composition of corium depends on the type of the reactor and, specifically, on the materials used in the control rods and the coolant. For instance, there are differences between pressurized water reactor (PWR) corium and boiling water reactor (BWR) corium. In addition to corium, it should be understood that the nuclear material referred to herein may include used nuclear fuel or other analogous materials in need of similar treatment.
The method according to an example embodiment decontaminates the coolant, e.g., water, thereby enhancing an ability to decommission the reactor and internals, and mitigates internal corrosion (e.g. stress corrosion cracking, general chloride induced corrosion, or intergranular corrosion) to the container for long-term storage of the waste.
The first filtering system 20, e.g., alumina bed, is part of a first Shielded Removable Filter (SRF) system, which shields plant personnel and equipment from accumulated radionuclides during the cleanup process. The first SRF includes the filter material included in the alumina bed, and a shielded container made of concrete or steel and optionally lined with an additional shielding material, e.g., steel, lead, or tungsten. The coolant enters and exits the first SRF through a tortuous flow path to mitigate any potential radiation streaming paths from the first SRF. The entire first SRF (e.g., container and filter material of the alumina bed) is designed to be easily inserted into and removed from the filtration process, and is designed to be easily transported due to its modular nature.
In step S220 of
When the cation exchange sites on the humic acid molecule are filled predominately with hydrogen cations, the material is determined to be an acid. The pH is not greatly affected, however, because the acid is insoluble in water. When the predominant cation on the exchange sites is other than hydrogen, the material is determined to be a humate. Apart from the effect on the solubility of materials and their absorption by clays, the different cations may have little effect on the humic molecules. The humic molecules have relatively low water solubility in the neutral to acidic pH range, but may be soluble at higher pH levels, e.g., greater than 10, thereby producing dark brown solutions. Humic acid of the second filtering system 30 can immobilize most of the contaminants in the coolant, e.g., water.
The fluid stream of the coolant will flow through the first and second filtering systems 20 and 30, e.g., the alumina and humate beds, until either the first or second filtering system 20 or 30 reaches its radioactive loading limit (S300). The radioactive loading limit is determined by a threshold radiation dose detected in the SRF including the first and second filtering systems 20 and 30, e.g., the alumina and humate beds, and the point in which the SRF has become chemically exhausted (e.g., filled) is determined by the second coolant monitoring system 11b positioned downstream from the second filtering system 30.
In an example embodiment, if neither the first or second filtering system 20 or 30 has reached its loading limit, the method of treating the coolant using the first and second filtering systems 20 and 30 may be repeated a number of times until undesirable levels of the harmful contaminates are removed (S330). If either of the first or second filtering system 20 or 30 have reached the loading limit, the filtered coolant may be transferred to the RWCU system 40 (S310), which may be the conventional plant system for treating the coolant, and returned to the reactor coolant system RCS 10 (S320). Alternatively, the coolant, e.g., water, may be sent directly to the plant's standard RWCU system 40 for the continued removal of solids and cations, and then returned to the reactor coolant system RCS 10. Each of the first and second filtering systems 20 and 30 (e.g., the alumina bed and the humate bed) can contain multiple lines or trains to allow for continuous operations.
A pH control unit 50 may be used to adjust the pH for optimum or improved operation of the second filtering system 30 and for removal of contaminants. During operation of the system, swings in the pH may be used to shock the system to remove contaminates from the reactor coolant system RCS 10 and place them into the SRFs of the respective first and second filtering systems.
After the water chemistry condition inside the reactor coolant system RCS 10 is improved, the corium is captured in at least one of the first and second filtering systems 20 and 30 by the respective Shielded Removable Filters (SRF). The SRF of the first filtering system, e.g., the alumina bed SRF, and the SRF of the second filtering system, e.g., the humate bed SRF, are processed by different treatment methods which will be described in detail as follows.
The SRF of the first filtering system 20 is dewatered by draining the water and then removing the water through a vacuum extraction system. The captured corium debris and fission products in the alumina bed SRF give off heat which accelerates the dewatering vacuum process. Another optional heat source may be added to the process to externally heat the alumina bed SRF, and further accelerate the dewatering process.
In step S210 of
Oxide compounds, for example, CaO and SiO2, are added to the first waste treatment container 60, e.g., ceramic crucible. A well-known Ca—Al—Si ceramic system, for example, a feldspar mineral such as anorthite, is formed within the first waste treatment container 60, e.g., ceramic crucible, from the reaction between CaO, SiO2, and Al2O3, and the corium is incorporated into a leach resistant matrix within the first waste treatment container 60, e.g., ceramic crucible, suitable for permanent disposal.
The first waste treatment container 60, e.g., ceramic crucible, containing the additives as described herein is an example embodiment of a system for processing the corium for long-term storage, but other well-known ceramic systems may also be used to contain the corium, e.g., glass-bonded sodalite, synroc, etc., depending on the process and regulatory requirements for the final waste product. This ceramic system within the first waste treatment container 60, e.g., ceramic crucible, is loaded into a waste canister (not shown) and consolidated into a monolithic first waste product 80a for long-term storage. The first waste product 80a may be evaluated for leachability, structural stability, and other regulatory checks before long-term storage. The first waste product 80a contains a majority of the soluble fission products and transuranics found in the coolant.
In step S230 of
Example embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the intended spirit and scope of example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
