Document: NUREG-0800
Document ID: e2737d9a-8e56-46cb-a97d-aaf62a442c6c
Document Type: srp
Title: PRESSURE-TEMPERATURE LIMITS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340637.pdf
Revision Date: 2023-06
Chapter: 5
Section ID: 5.3.2
CFR Part: 
CFR Title: 

Content:
erature from cold shutdown conditions to full pressurization conditions. Reactor vendors have developed computer codes to perform the necessary calculations, because thermal stresses must be included, and hand calculations of even moderate sophistication are very time consuming. WRC Bulletin 175 includes a set of curves derived from computer programs that can be used to approximate the KI caused by thermal stresses, as a function of wall thickness and rate of tem- perature change. Pressure-temperature curves developed using these approximations agree fairly well with those determined using much more rigorous procedures, and can be used with confidence to evaluate the proposed operating limits given in Technical Specifications. These curves require the calculation of only 3 to 5 points. Either allowable pressure at a given temperature, or allowable temperature at a given pressure can be calculated. It is usually more convenient to calculate allowable minimum temperature, so this method will be used in the example. Using the same reactor vessel as in the previous example, and a rate of temperature change of 500F per hour, calculations of required temperatures for several pressures are illustrated. The curves for thermal effects given in WRC Bulletin 175 are very conservative, thus no additional margin need by applied to the K1 from thermal stress, but a factor of 2.0 is used on primary stresses. The basic expression is then: KIR > 2 K,(membrane) + K, (thermal) KI(membrane) is calculated exactly as in the previous examples. K,(thermal) for a 9-in. thick wall, at 500/hr is about 12,000 psi 4Tin from Figure 4-5, WRC Bulletin 175 (reproduced here as Fig. 3). Thus, for a pressure of 2250 psig, a membrane stress of 24,000 psi, and Mm of 2.87, the basic expression is given by KIR > (2)(24,000)(2.87) + 12,000 = 150,000 psi %ri4 From the KIR curve, a temperature of RTNDT + 1580F is required. With an RTNDT of 1400F (including irradiation effects), the temperature required for