Pressurized water reactors primary loop

Most nuclear reactors use a heat exchanger to transfer heat from a primary coolant loop through the reactor core to a secondary loop that suppHes steam (qv) to a turbine (see HeaT-EXCHANGETECHNOLOGy). The pressurized water reactor is the most common example. The boiling water reactor, however, generates steam in the core. 

The primary coolant circuit of a PWR is shown in schematic form in Fig. 36. In this particular circuit, there are four loops between the reactor and the steam generators. The pressurizer is also shown, which maintains the pressure in the primary loop at a sufficiently high value (typically 150 bar) such that sustained boiling does not occur and maintains the desired concentration of hydrogen in the coolant. The reactor heat removal system (RHRS) and the reactor water cleanup system are not shown. The general operating conditions in a PWR primary loop are summarized in Table 2. 

Elearochemistiy of Pressurized Water Reactors 713 Tab. 2 Typical conditions that exist in the main loop of the primary coolant circuit of a PWR... 

The hot/cold intraface level in the upper density lock is determined by the total volume of the primary loop water mass, when the position of the interface level in the lower density lock is kept constant. The temperature measurements for the interface level in the upper lock are basically used for reactor pool volume control purposes. (The reactor primary loop volume control utilizes level measurements in the pressurizer.)... 

The reactor system is pressurized by means of steam supplied from an electrically heated recirculation boiler, drawing water from the water volume of the pressurizer. The steam volume of the pressurizer is comparatively large and, together with its volume of saturated water, the reactor system can accommodate pressure and level variations that may occur during operational transients and accident situations. The pressurizer is connected to the reactor pool via funnels up into the steam volume, and to the reactor primary loop via open passages from the pressurizer "poor. 

Figure 1.1. Four-loop primary coolant system of a 1300 MWe pressurized water reactor a) Reactor pressure vessel b) Steam generator c) Reactor coolant pump d) Pressurizer e) Pressurizer relief tank (Meyer, 1991)...

The HTTR is an experimental helium-cooled 30 MW(t) reactor. The HTTR is not designed for electrical power production, but its high temperature process heat capability makes it worthy of inclusion here. Construction started in March 1991 [47] and first criticality is expected in 1998 [48]. The prismatic graphite core of the HTTR is contained in a steel pressure vessel 13.3 m in height and 5.5 m in diameter. The reactor outlet coolant temperature is 850°C under normal rated operation and 950°C under high temperature test operation. The HTTR has a primary helium coolant loop with an intermediate helium-helium heat exchanger and a pressurized water cooler in parallel. The reactor is thus capable of providing... 

In the other design, PWRs have two closed loops of water circulating in the plant plus a third, external loop to remove the waste heat. Water is pumped through the reactor core in the primary coolant loop to moderate the neutrons and to remove the heat from the core as in the BWR. However, the reactor vessel is pressurized so that the water does not boil. Steam is necessary to run the turbines, so the primary loop transfers the heat to a secondary loop. The water in the secondary loop is allowed to boil, producing steam that is isolated from both the core and the outside. The water in the primary loop usually contains boron (as boric acid H3BO3 0.025 M) to control the reactivity of the reactor. The steam in the secondary loop is allowed to expand and cool through a set of turbines as in the BWR the cold steam condenses and is returned to the primary heat exchanger. A third loop of water is used to maintain the low-temperature end of the expansion near room temperature and remove the waste heat. 

The operating temperatures of the water in the main inlet and outlet tubes, the UOj in the center of the fuel rod, the water between the TFCs, and the fuel element cladding at one-half of maximum power were 26TC, 313 C, 1400 C, 280 C, and 700 C, respectively. Water flow rates in the N2 reactor primary circuit bow and stem loops were 458 and 407 tonne-h" , respectively, and the operating pressure was 180 kg-cm. ... 

Various methods of on-line reactor surveillance have been used, including neutron noise monitoring in boiling water reactors (BWRs) to detect internals vibration, and pressure noise surveillance at TMI-2 to monitor primary loop degasification. On-line surveillance data has been used in the assessment of loose thermal shields. 

The supercritical water-cooled reactor is a normal light water reactor (LWR) that has increased temperature and pressure. The purpose is to place the water in the primary coolant loop into a supercritical state, which would dramatically increase operating efficiency. 

Most of the heat generated by the reactor Is removed by the primary loop cooling water. In order to ensure efficient 1 safe, heat removal, reliable Instrumentation for measurement and control of the flow, temperature and pressure of the coolant have been provided. 

There is a capability to isolate each primary loop from the reactor using two gate valves on the suction and pressure pipelines of the circuit. On the pressure pipeline of each loop downstream of the PSP a flap-type check valve is provided eliminating coolant backflow in the event of a PSP trip in one loop when the other PSPs are operative. The secondary sodium circuits comprise EHX heat transfer tubes, pipelines, secondary sodium pumps and steam generators. Due to utilization of the reactor energy for fresh water production the steam-water system has some specific features. Steam from the SG is supplied to turbines of two types a condensing turbine (K-100-45) and a back-pressure turbine (K-50-45). Exhaust steam flows from the back-pressure turbine and from intermediate bleeds of K-100-45 turbine are supplied to the water desalination facilities. At a heat output of 750 MW the reactor produces ... 

During reactor operation, the secondary system is operated as a steam condensate system to transfer heat removed from the primary loop to the circulating raw water system. Heat transfer from the primary loop results in boiling on the secondary side of the ten main heat exchangers. This steam then flows to the main 46 steam header atop the 109 Building. Sufficient steam to drive the six drive turbines and to supply auxiliary areas uses flows to the turbine supply header the remainder is condensed in the dump condensers, completing the heat transfer to the circulating raw water system. Secondary coolant pressures, flow rates and Inventory are directly controlled coolant temperatures are dependent variables. 

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