Document: NUREG-0800
Document ID: 26aca061-b0de-4983-bbca-3fccb00afc2f
Document Type: srp
Title: PRESSURE-TEMPERATURE LIMITS AND PRESSURIZED THERMAL SHOCK1
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070431.pdf
Revision Date: 2023-06
Chapter: 5
Section ID: 5.3.2
CFR Part: 
CFR Title: 

Content:
o 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 K caused by thermal stresses, as a function of wall thickness and I rate of temperature 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 50 F 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 bybe applied 59 to the K from thermal stress, but a factor of 2.0 is used on primary stresses. The I basic expression is then: K 2 K (membrane) + K (thermal) IRa I I 60 5.3.2-13 DRAFT Rev. 2 - April 1996 K (membrane) is calculated exactly as in the previous examples. K (thermal) for I I a 9-in. thick wall, at 50 F/hr is about 12,000 psi in. 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 M of m 2.87, the basic expression is given by K > (2)(24,000)(2.87) + 12,000 = 150,000 psi in. IRa 61 From the K curve, a temperature of RT + 158 F is required. With an IRa NDT 62 RT of 140 F (including irradiation effects), the