Reactor Primary Coolant System

ASYMMETRIC BLOWDOWN LOADS ON REACTOR PRIMARY COOLANT SYSTEMS... 

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 nuclear primary system is enclosed in a containment building strong enough to withstand the major pipe break in the reactor primary coolant system. 

In these closed test-loops components inserted in the reactor core, the coolant, instrumentation and heat transfer systems were completely separated fi om the main FFTF core, permitting the testing of fuels and materials over a wide range of temperatures in a controlled environment independent of the main reactor coolant system. The open loop test positions and integral components of the reactor core for testing large quantities of candidate fuel pins and assemblies were cooled by the reactor primary coolant system. 

N Demineralization plant Provided demineralized water for reactor primary coolant system. Reinforced concrete and structural steel, 82 X 78 X 40 ft high immediately west of 183-8 building with which it shares a common wall... 

Plow and pressure and temperature transients occurring in the ex reactor primary coolant system have been analysed from the viewpoint of stress and fatigue and effect on process Many conditions have been Studied ranging from the normal scram tranaienta to significant pipe rtgitures and lose of the heat removal eyacem ... 

When compared to stainless steel, carbon steel exhibits significantly improved resistance to both transient thexmal stresses and steady-state, thermally induced expansion stresses Thus, it Is concluded that carbon steel is a suitable choice for reactor primary coolant system material from a structural... 

The SLCS is a system for injecting borated water into the reactor primary coolant system. The neutron absorption by the boron causes shutdown of the reactor. Addition of this system was proposed by the Utility Group on ATWS for new plants (those receiving an operating license three years after the effective date of the final rule). Because of the vulnerability of BWR containments to ATWS sequences, the NRC determined that increased SLCS capacity was warranted. The preferred location for SLCS injection was into HPCS or HPCI lines, which provides significant improvement in mixing of... 

The reactor building and the general arrangement of components as coiiceix cd in the reference design are shown in Fig, 2.5-1. The reactor, primary coolant system, fuel system, and steam generator are enclosed in a gaslight steel containment shell. 

Two reports, "K-Reactor Primary Coolant Systems Integrity" (Reference 14), and "K-Reactbr Tank Integrity Status" (Reference 7) were issued in 1989. These reports document that significant evidence exists that the structural integrity.of the K-Reactor tank and the K-Reactor PWS is adequate for safe operation. This evidence was based on the results of visual examination an... 

To slow down and control the rate of reaction, a moderator is also required. Typically, the moderator is boric acid, graphite, or heavy water (D20) and is present in the high-purity water, which also serves as a primary coolant for the fuel and the reactor vessel. The tremendous heat generated by nuclear fission is transferred to this closed-loop coolant, which is contained within a reactor primary-coolant circulation system. The high-purity water coolant also contains a suitable pH buffer such as lithium hydroxide, which has the additional effect of limiting the corrosion of fuel-cladding and other components. 

Boric acid [B(OH)3] is employed in primary coolant systems as a soluble, core reactivity controlling agent (moderator). It has a high capture cross-section for neutrons and is typically present to the extent of perhaps 300 to 1,000 ppm (down from perhaps 500 to 2,500 ppm 25 years ago), depending on nuclear reactor plant design and the equilibrium concentration reached with lithium hydroxide. However, boric acid may be present to a maximum extent of 1,200 ppm product in hot power nuclear operations. 

LMFBR Design Principles. There are many design differences among the reactor designs, including (1) primary coolant system arrangement ... 

In the following paragraphs, three important aspects of LWRs are discussed fuel elements, the primary coolant system, and reactor containment. They each play an important role in providing multiple barriers that prevent radioactive fuel and fission products from being released to the environment. 

As anticipated, there have been occasional equipment failures involving reactors, but the safety systems have been sufficiently redundant so that one or more have always worked. Even in the Three Mile Island accident in 1979, the safety systems worked as designed. Much of the damage resulted from operator actions to override the safety systems. As concluded in the Reactor Safety Report, the limitations of the operator created and then seriously aggravated the Three Mile Island incident. Nevertheless, the features of the containment system prevented significant exposure to the plant personnel or any off-site individual, this despite failure of the barriers provided by the fuel cladding and the primary coolant system. 

Minimum pressurization-temperature (MPT) curves specify the temperature and pressure limitations for reactor plant operation. They are based on reactor vessel and head stress limitations and the need to preclude reactor vessel and head brittle fracture. Figure 4 shows some pressure-temperature operating curves for a pressurized water reactor (PWR) Primary Coolant System (PCS). 

Reactor vessel height / diameter Primary coolant systems Primary coolant sodium mass Inlet / outlet reactor temperature Primary coolant flow rate Primary coolant flow velocity Secondary coolant systems Secondary coolant sodium mass Inlet / outlet IHX temperature Secondary coolant flow rate Secondary coolant flow velocity Water - steam systems Feed water flow rate Steam temperature (turbine inlet) Steam pressure (turbine inlet) Type of steam generator Refueling system... 

Category I Equipment of primary importance, not redundant, not easily repairable or replaceable (reactor tank, primary coolant system piping). 

Returning to the Westinghouse AP reactor design, the primary coolant system water chemistry is selected to minimize corrosion. Routinely scheduled analyses of the coolant chemical composition are performed to verify that the reactor coolant chemistry meets the specifications. Other additions, such as those to reduce activity transport and deposition, may be added to the system. The CVCS provides a means for adding chemicals to the RCS. The chemicals perform the following functions ... 

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)...

IAEA TECDOC-667 Coolant Technology of Water Cooled Reactors. Vol. 2, Corrosion in the Primary Coolant Systems of Water Cooled Reactors. Vienna, 1992, p. 65—68 Asay, R. H., Naudin, O., Thiry, M., Lantes, B., Gouillardou, G., Saurin, R, Weber, C. (a) Effect of surface treatments on radiation buildup in steam generators. Vol. 1. Manway seal plate tests in the Chinon B1 PWR. Report EPRI TR-100059, Vol. 1 (1991)... 

For this experiment, the reactor core had been equipped with a central fuel module containing 100 pre-pressurized fuel rods, the UO2 fuel of which had been enriched to 9.7% and which had been pre-irradiated to a bumup of about 450 MWd/t U. The transient phase started with the reactor scram and was terminated about 30 minutes later when the external temperatiure on the surface of the shroud of the central fuel module reached 1517 K at this time, the highest measured cladding temperature reached 2100 K. When reflooding of the reactor core with emergency coolant was started, a rapid temperature excursion occurred within the central fuel module which was caused by the enhanced metal—water reaction. The transient was followed by a post-transient period of 44 days during which the reactor core was cooled by recirculating coolant and the concentrations of fission products deposited in the primary coolant system as well as their behavior in the blowdown suppression tank were measured. 

By far the most (about 96 per cent) of the heat generated In the reactor is removed ffom the reactor by the primary coolant system, transferred to the boiling water secondary system and dissipated to the Columbia River via condenser cooling water streams, failure of the primary coolant system to remove heat from the reactorat design power level will result In certain fuel melting unless the last-ditch backup cooling system functions. 

The primary coolant system removes more than 9d per cent of the heat generated in the reactor. This system is divided functionally into two portions a heat removal section in the 105 H Building and a heat dissipation system in the 109 N Building ... 

The heat picked up In the reactor hy the primary coolant system la transferred to the secondary system via the ten, parallel, steam generators. At design reactor power levels, this will result In the generation of a total of 13,900,000 pounds per hour of steam at 87 5 psla. 

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