Coolant reactor

Fig. 1. Pressurized water reactor (PWR) coolant system having U-tube steam generators typical of the 3—4 loops in nuclear power plants. PWR plants having once-through steam generators contain two reactor coolant pump-steam generator loops. CVCS = chemical and volume-control system.

The primary water specifications for a PWR are given in Table 1 (4). Rigid controls are appHed to the primary water makeup to minimise contaminant ingress into the system. In addition, a bypass stream of reactor coolant is processed continuously through a purification system to maintain primary coolant chemistry specifications. This system provides for removal of impurities plus fission and activated products from the primary coolant by a combination of filtration (qv) and ion exchange (qv). The bypass stream also is used both to reduce the primary coolant boron as fuel consumption progresses, and to control the Li concentrations. 

The quantity of boric acid maintained in the reactor coolant is usually plant specific. In general, it ranges from ca 2000 ppm boron or less at the start of a fuel cycle to ca 0 ppm boron at the end. Most plants initially used 12-month fuel cycles, but have been extended to 18- and 24-month fuel cycles, exposing the materials of constmction of the fuel elements to longer operating times. Consequendy concern over corrosion problems has increased. 

The reactor coolant pH is controlled using lithium-7 hydroxide [72255-97-17, LiOH. Reactor coolant pH at 300°C, as a function of boric acid and lithium hydroxide concentrations, is shown in Figure 3 (4). A pure boric acid solution is only slightly more acidic than pure water, 5.6 at 300°C, because of the relatively low ionisation of boric acid at operating primary temperatures (see Boron COMPOUNDS). Thus the presence of lithium hydroxide, which has a much higher ionisation, increases the pH ca 1—2 units above that of pure water at operating temperatures. This leads to a reduction in corrosion rates of system materials (see Hydrogen-ION activity). 

The second important component is the cooling agent or reactor coolant which extracts the heat of fission for some usefiil purpose and prevents melting of the reactor materials. The most common coolant is ordinary water at high temperature and high pressure to limit the extent of boiling. Other coolants that have been used are Hquid sodium, sodium—potassium alloy, helium, air, and carbon dioxide (qv). Surface cooling by air is limited to unreflected test reactors or experimental reactors operated at very low power. 

Fig. 21. Schematic of a pressurized-water-loop reactor coolant system.

In some BWR transient scenarios, the high pressure injection systems are postulated to fail. To make use of the low pressure injection system, it is necessary to depressurize the reactor coolant system, a function performed by the automatic depressurization system (ADS). In the scenario considered, ADS actuation is manual because the signals for automatic initiation of the system are not present. 

A first attempt to estimate the potential consequences from severe LWRs accidents was the BNL report WASH-740 (1957). The authors of WASH-740, to overcome the lack of information and methods, estimated "Hazard States based on the core state, radioactive inventory, fuel cladding, reactor coolant system, and containment conditions. 

The assumed form of iodine is not substantially retained in early containment failure, but may be retained in the reactor coolant system, where cesium iodide is more strongly retained than the elemental iodine assumed by the RSS. 

An accident sequence source term requires calculating temperatures, pressures, and fluid flow rates in the reactor coolant system and the containment to determine the chemical environment to which fission products are exposed to determine the rates of fission product release and deposition and to assess the performance of the containment. All of these features are addressed in the... 

Overall behav<4 of reactor coolant system, mrilten core, and containmerf... 

Heatup of the reactor coolant inventory and pressure rise to the relief or safety valve settings with subsequent boiloff. 

Initial blowdown of the coolant from the reactor coolant system. 

Instrumentation level instrumentation for MLO (standpipe level and ultrasonic) has limited use in a shutdown accident. Standpipe level is correct in the absence pressure m the system Ulirti sonic is correct only when the level is within the reactor coolant loops. 

Reactor coolant pump (RCP) seal failures that lead to a loss of coolant accident (LOCA)... 

ATWS A Reappraisal, Part 3 Frequency of Unanticipated Transients Nuclear 200 pump failure events from Arkansas Nuclear Unit 1, Calvert Cliff Unit 1, and Indian Point Unit 3 nuclear plants Nuclear reactor coolant pump seals 102. 

DATA BOUNDARY Nuclear reactor coolant pump seals... 

Most of the controlled corrosion studies on beryllium have been carried out in the USA in simulated reactor coolants. The latter have usually been water, aerated and de-aerated, containing small amounts of hydrogen peroxide and at temperatures up to 300-350°C. Many variables have been examined, covering surface condition, chemical composition, temperature, pH, galvanic effects and mechanical stress . 

Much of the recent research on stress-corrosion cracking of austenitic stainless steels has been stimulated by their use in nuclear reactor coolant circuits. The occurrence of stress-corrosion cracking in boiling water reactors (BWR) has been documented by Fox . A major cause for concern was the pipe cracking that occurred in the sensitised HAZ of the Type 304 pipework, which is reported to have been responsible for about 3% of all outages of more than 100 h from the period January 1971 to June 1977. 

Reactor coolant primary circulation system Depending on design, this closed-loop cooling system may recirculate high-purity treated water or other fluid at 300,000 to 450,000 US gpm (1,136-1,704 m3/m), and at velocities of 15 to 16 ft/s 4.5 to 4.9 m/s. 

Where continuous demineralization of reactor coolant is provided, premature degradation of the strong base anion (SBA) resins may occur. To avoid this, oxygen removal by use of anion resin in the sulfite form is employed. 

Reactor trip signal reactor coolant pumps tripped 4,685... 

Maurer, G. W., 1960, A Method of Predicting Steady State Boiling Vapor Fraction in Reactor Coolant Channels, Bettis Technical Review, USAEC Rep. WARD-BT-19, pp. 59-70. (3)... 

Spiegler, P., J. Hopenfeld, M. Silverberg, and C. F. Bumpus, Jr., 1964, In-Pile Experimental Studies of Transient Boiling with Organic Reactor Coolant, USAEC Rep. NAA-SR-9010, North American Aviation, Rockwell Int., Inc., Canoga Park, CA. (5)... 

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