ATWS

A long evolving use of PSA was for Anticipated Transients without Scram (ATWS) which extended over 15 years to culminate in NUREG-0460 which was upset by the Salem failure-to-scram incident and the subsequent SECY Letter 83-28. Other special studies have been (a) value-impact analysis (VIA.) studies of alternative containment concepts (e.g., vented containment, NUREG/CR-0165), (b) auxiliary feedwater studies, (c) analysis of DC power requirements, (d) station blackout (NUREG/CR-3220), and (e) precursors to potential core-damage accident.s (NUREG/CR-2497), to name a few of the NRC sponsored studies. 

---

Fig. 4. Laboratory tubing model for supercoiling in closed-circular DNA (a) relaxed DNA, ALK = 0 (b) ALK = ATw -...

T Sients with Wlure of powef conversion system PCS) and safety / Injection 23% i ATWS 4%... 

This, more physical model that visualizes failure to result from random "shocks," was specialized from the more general model of Marshall and Olkin (1967) by Vesely (1977) for sparse data for the ATWS problem. It treats these shocks as binomially distributed with parameters m and p (equation 2.4-9). The BFR model like the MGL and BPM models distinguish the number of multiple unit failures in a system with more than two units, from the Beta Factor model,... 

F.xamples of initiating events considered in five PRAs are provided by Joksimovich et al. (lhS3) and presented as Table 6.3-5. The occurrence frequencies vary from a high of 3.7/yr for turbine and reactor trip at Zion to a low of lE-6/yr for a large steam line break outside of containment at Big Rock Point. Another low frequency is 2E-6/yr for ATWS from the loss of one feedwater pump, also at Big Rock Point. Surprisingly, these are less than a large LOCA (IE- 5/yr) at the same plant. Except for Big Rock Point, this table provides no information on externalities. 

Suppose that the RHR system in the example in Section 8.1.2 lost half of its heat removal capability after 90 s. When would it reach 2,3(X)" F (a temperature criterion once suggested by Steve Hanauer regarding ATWS) ... 

Transients (other than station hlaekouts and ATWS) Important contributor for most plants because of rcli.fiicc i>n sup wii sy- iems failure of such systems can defeat redundancy in front-line systems. Both plant-specific design IPii mcdeling assumptions contribute to variability in results ... 

ATWS -Revise training on bound control rnip, (hi -Install automatic ADS inhibit (b1 -Install alternate boron injection system i nj -(i apabllllv To remove power lo hiis m li p breaker failure (p) -Install Westinghouse ATWS mitigainni ipi... 

At 40 MW operation, the core damage frequency is 3.7E-04/y. The proportion of accident classes is LOCA, 50% beam tube rupture, 27% ATWS, 17% LOOP, 4% and other transients, 2 7. Three minutes of forced flow are not required and large LOCAs with break size smaller than 2.8 inches can be mitigated. 

Erdmann, R. C. et al., 1976, ATWS A Reappraisal Part If Evaluation of Societal Risks Due to Reactor Protection System Failure Vol IIBWR Risk Analysis EPRINP-265,. ugust. 

Kdly, J. E. et al 1976, ATWS, A Reappraisal Part II, Evaluation of Societal Risks due to Reactor Protection System Failure Vol.3 PWR Risk Analysis, EPRINP 265, August. 

Ixverenz, F. L. et al., 1978, ATWS A Reappraisal Part III Frequency of Anticipated Transients, EPRINP-801. 

Luckas, W. J. et al., A Human Reliability Analysis for the ATWS Accident Sequence at the Peach Bottom Atomic Power Station, BNL Technical Report A3272, May 1986. 

ATWS A Reappraisal, Part 3 Frequency of Unanticipated Transients Nuclear 200 pump failure events from Arkansas Nuclear Unit 1, Calvert Cliff Unit 1, and Indian Point Unit 3 nuclear plants Nuclear reactor coolant pump seals 102. 

ATWS A Reappraisal,Part 3 Frequency of Unanticipated Transients... 

Atw = Temperature rise of water, °F V = Volume of tank or system, cu ft V = Volume of vessel or system, liters V0 = Volume of pumping chambers, liters W or Wa = Flow rate, lbs/hr... 

The equilibrium equation for the first step is shown in Scheme 5-2. Introducing the equilibrium constant Kw of water (Kw = [H+][0H ]/[H20] leads to the equation shown in Scheme 5-3. ATW can be combined with the constant K (defined by Kx = K[KW) to give the equation of Scheme 5-4. In the same way, the second step can be expressed as in Scheme 5-5. 

US Environmental Protection Agency, http //www.epa.gov/ttn/atw/hlthef/ quinolin.html. 

The result of this effort was an ATW roadmap released by DOE just this week. It concluded that ATW would require a six-year, 281 million R D effort for open technical issues. ATW could complement geologic disposal, and any decision to pursue ATW would follow evaluation of technical, costs, and nonproliferation issues. Whether or not this effort leads to any ATW international collaboration, we are eager to expand international collaboration on nuclear waste issues in general. 

---