Patent Number: 040640019
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a nuclear reactor 10 including a nuclear reactor pressure vessel 20 surrounded by biological shielding 34 and having an active core or fuel region 24 therein. Core 24 is supported in the reactor pressure vessel 20 in a well-known manner by core support barrel 22 which is suspended from a pressure vessel flange (not shown). The reactor coolant is circulated through the cold leg 16 by the reactor coolant pump 14. As best seen in FIG. 2, the cold coolant enters the reactor pressure vessel 20 and impinges upon the core support barrel 22. The flow of the coolant is then deflected downwardly to pass through the annular region 21 between the core support barrel 22 and the reactor pressure vessel 20 to the lower portions of the reactor pressure vessel where it is deflected upwardly to pass to the interior of the reactor core support barrel. Once on the interior of the reactor core support barrel, the coolant flows upwardly through the fuel assemblies (not shown) of the reactor core 24 and subsequently passes into the reactor plenum 25 immediately above the reactor core 24. From here the coolant is again deflected to pass out of the reactor pressure vessel 20 and into hot leg 18 by which means it is delivered to steam generator 12. During its passage through the steam generator 12, the coolant is cooled in a well-known manner by transferring its heat content to the secondary coolant system. After being cooled in the steam generator 12, the primary coolant is recirculated by the reactor coolant pump 14 and the cycle is repeated. Also shown in FIGS. 1 and 2 is a portion of the emergency core cooling system which includes storage tank 28 check valve 36 and delivery pipe 26. Storage tank 28 contains a large quantity of highly borated water. Check valve 36 is designed to permit the passage of the borated water contained in tank 28 to the primary coolant system by means of pipe 26 when the pressure in the primary coolant system drops below a predetermined pressure. Such a pressure drop occurs with a loss of coolant accident or LOCA. The borated water is then obliquely injected into the primary coolant system at penetration 27 in the cold leg 16. This borated emergency coolant is injected under a high pressure so that the coolant is caused to flow through the cold leg 16 into the reactor vessel 20, and down through the annulus 21 between the reactor vessel 20 and the core support barrel 22 to reflood the reactor core 24 from the bottom. As discussed above, this injection and reflooding technique is impeded if a substantial steam pressure is permitted to exist in the reactor plenum 25 above the reactor core 24. Accordingly, steam relief means 30 are provided to relieve the steam pressure from the reactor plenum 25. Steam relief means 30, which is external to the reactor vessel 20, is connected between the cold leg 16 (fluid coolant delivering means) and the hot leg 18 (fluid coolant removing means) for the purpose of relieving the excess pressure in the hot leg when the pressure in the hot leg exceeds the pressure in the cold leg. For the purposes of this disclosure, the "fluid coolant delivering means" shall include not only the hot leg pipe 16 but also that portion of reactor vessel 20 and the core support barrel 22 which forms the annular region 21 between the reactor pressure vessel 20 and the reactor core support barrel 22. Accordingly, an alternative embodiment of the present invention is illustrated in FIG. 3 in which the external reactor pressure relief means includes a pipe 31' connecting the hot leg 18 to the annular region 21 between the reactor pressure vessel 20 and the reactor core support barrel 22 by means of a penetration through the reactor pressure vessel 20. In all cases, the external reactor pressure relief means 30 includes a valve 32 which is responsive to the different pressure existing between the fluid coolant delivering means and the fluid coolant removing means. Valve 32 may consist of a conventional commercially available check valve, the particular construction of which does not form a part of the present invention.