Primary coolant loops

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. 

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 PWR is more expensive to build because the reactor vessel must be stronger to withstand the higher water pressure, and there is a secondary coolant loop with pumps and so on. The BWR, while less expensive to build, is more complicated to service since the turbines are part of the primary coolant loop. The details of the core design are different as well. Approximately twice as many PWRs have been constructed as BWRs. 

Primary coolant loop enclosed in a hermetically sealed safety containment... 

Fig. 41 ECP versus distance for the main primary coolant loop in a PWR under full Normal power operation.

Sound Pressure Design Levels for the Primary Coolant Loop... 

SOUND PRESSURE DESIGN LEVELS FOR THE PRIMARY COOLANT LOOP... 

A Re dual Heat Removal system brings the plant to cold conditions during a normal plant shutdown. This system is connected to the primary coolant loop through two low-diameter tines of the Chemical and Volumetric Control System. 

The acceptance criterion for the resolution of USI A-02 (documented in NUREG-0609) is that the design of the reactor primary coolant system shall demonstrate that the asymmetric loads on the reactor vessel, internals, primary coolant loop, and components shall not exceed the limits imposed by the applicable codes and standards. 

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. 

The sodium-cooled fast reactor (SFR) uses liquefied sodium as the primary coolant. The major advantage is that the reactor can operate at atmospheric pressure in the primary coolant loop. The ultimate inherent safety of this reactor, when using metallic (not oxide) uranium fuel, was demonstrated in 1986 with the Experimental Breeder Reactor 11 at the Idaho National Laboratory, under the direction of Argonne National Laboratory. 

The lead-cooled fast reactor uses either lead or lead-bismuth eutectic in the primary coolant loop. This gives similar advantages as with the SFR in terms of operational safety. Several of these reactor designs were built and operated on Russian submarines. 

Beslu, R, Masse, F., Anthoni, S., Brissaud, A., Ridoux, R, Saurin, R, Weber, C. (b) Corrosion ion release from stainless steel and higher nickel alloys under PWR conditions Experimental and theoretical conditions. Proc. 5. BNES Conf. Water Chemistry of Nuclear Reactor Systems, Bournemouth, UK, 1889, Vol. 1, p. 77—80 Bishop, W. N., Stagg, W. R. Effects of shutdown/cooldown techniques on radiation fields in PWR primary coolant loops. Report EPRI NP-346I (1984)... 

Both the primary coolant loop and the moderator coolant system have a role in the confinement system. Check valves have been installed in the primary loop on the inlet supply lines and on the return lines Just downstrecun of the dump valves, as shown in Figure 7-5 In case of a line rupture and failure of the last-ditch coolant systems, these valves will force a portion of the water in the loop to flow through the reactor before leaving the break. lhis point is critical. It is necessary that Interim cooling be provided to prevent fuel melting until steam venting is completed. 

The moderator coolant system vlll remove some heat from the reactor In the event of the complete failure of the primary coolant loop While this vlll probably not prevent some fuel melt from occur-rlngi It vlll minimize the extent of the melting ... 

To condense part (120 Ibs/sec) of the steam released from a break In the primary coolant loop during steam venting This decreases the time that the steam vents must remain open ... 

Radioactive effluents and wastes were generated in a variety of process systems. These radioactive wastes included reactor primary coolant water, spent fuel storage basin cooling water, reactor periphery systems cooling water, reactor primary-coolant-loop decontamination and rinse solution, and miscellaneous drainage from reactor support facilities (WHC 1987a). 

Reactor Primary Coolant Loop Decontamination System... 

The radioactive effluent piped from the 116-N-2 storage tank was internal decontamination solution from cleaning the primary coolant loop in N Reactor and various waste decontamination solutions from small decontamination Jobs. The primary loop was decontaminated every 3 to 5 years. The radioactive wastewater resulting from this procedure contained phosphoric acid and diethyl thiourea. The wastewater was neutralized in the 116-N-2 facility. 

In addition there are French studies on a leak before break (LBB) approach, similar to the American ones (GDC 4). This concept LBB is used in the German-French project EPR for the main primary coolant loops and for the short section of main secondary loop between the external side of containment and the main steam isolation valves. 

Which parameter in the primary coolant loop results in energizing the primary pump running light ... 

The primary, secondary and tertiary heat transfer system, and the emergency core cooling system were set to 400°C isothermal, the primary coolant loop dampers to minimum opening and the main pumps with the pony motors to 5% nominal speed. The flow-rate in the emergency core cooling rtused by means of the electromagnetic pumps to 100%,... 

Pressure in the primary coolant system is maintained by the on-line, boiling-water pressurizer. Water temperature, and hence steam pressure, is regulated by electric immersion heater batiks and by a spray of water from the cold leg of the primary coolant system A control bank of heaters will ordinarily operate continuoi sly and the sprays intermittently Larger capacity heaters and spray units are available as backups for control during the more severe transients A vent system Is provided to prevent accumulation of non-condensable gases which would adversely affect the ability to control pressures The pressurizer is hydraulically connected to the remainder of the primary coolant loop at the outlet manifold located in the 109-N Building Pipe Gallery ... 

The use of Zlrcaloy-2 for fuel cladding does not constitute a nuclear ha,2sard beyond the probable occurrence of occasional fuel element failures. Such fallurcrs may Involve release of a fraction of the uranium and fission product of the fuel into the primary coolant loop. No release to the environs would be expected, except via the bleed stream, which will be adequately controlled. 

Advanced, modular loop type designs with the reduced piping and physical connections between the primary coolant loop and auxiliary circuits (MARS, VBER-300), for the enhanced prevention of loss of coolant accidents. 

Extensive in-shop pre-manufacturing of components (including main, large components of the primary coolant loop). 

A drastic reduction in the number of physical connections between the primary coolant loop and auxiliary circuits. 

For Large LOCA mitigation, the proposed system is connected to the primary loop through the same connection used by the low pressure injection system. Water is directly injected in the primary coolant loop vessel by gravity. 

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