Safety calculation

Table XII shows some margins of safety calculated by Dr. Sheldon Wagner of Oregon State University, for a set of common prescription medicines. These include caffeine when prescribed at the dose level for which it is prescribed as a medicine, antibiotics, tranquilizers, vitamins, and other drugs. Notice that the margins of safety range from 1/2 through 100, 200, and up to 1000.

These categories are of interest in themselves as an attempt to develop the ideas of parameter, system and human error as previously presented. However, in examining past failures and the likelihood of future failures, a more detailed set of statements which have direct relevance to the project under consideration is needed. To this end the author has presented a list of 25 questions, a sort of personal check list, which attempts to feature matters which are not immediately calculable and so are not normally taken into account in structural safety calculations. The questions are formulated in such a way that two answers are required when assessing a praticular project. Firstly the degree of confidence in the truth of the statement, and secondly the importance of it in the overall context. The questions are ... 

For criticality safety calculations, the isotopic composition differs from that used for radiation protection design Pu-239 in Pu-tot = 95% and Pu-240 in Pu-tot = 5%. Similarly the contents of Pu in different products applied are more conservative cf Table 3). 

Hauptmanns U (2008) The impact of reliability data on probabilistic safety calculations. J Loss Prev Process Ind 21 38-49... 

Staff members who perform and document analyses for the SAR and TSR are experienced nuclear engineers with advanced degrees (e.g., M.A., M.S., or Ph.D.). Likewise, the members of RCSC are familiar with nuclear facility operations and usually have advanced degrees in nuclear engineering or radiation protection. The committee membership includes personnel with extensive experience in performing criticality safety calculations or criticality experiments. 

The lack of data to support claims for failure rates is an issue which is widely investigated by data uncertainty analyses. For example, Hauptmanns, 2008 compares the use of reliability data stemming from different sources on probabilistic safety calculations, and tends to prove that results do not differ substantially. Wang, 2004 discusses and identifies the inputs that may lead to SIL estimation changes. Propagation of error, Monte Carlo, and Bayesian methods (Guerin, 2003) are quite common. Fuzzy set theory is also often used to handle data uncertainties, especially into fault tree analyses (Tanaka, 1983, Singer, 1990). Other approaches are based on evidence, possibihty, and interval analyses (Helton, 2004). 

Hauptmanns, U. 2008. The impact of reliability data on probabilistic safety calculations. Journal of Loss Prevention in the Process Industries 21 38-49 Helton, J.C. et al. 2004. An exploration of alternative approaches to the representation of uncertainty in model predictions. Reliability Engineering and System Safety 85 39-71... 

VII.13. It would be helpful to include a table that identifies all different material regions in the criticality safety calculational models. This table should list the following, as appropriate, for each region the material, the density of the material, the constituents of the material, the weight per cent and atom density of each constituent, the region mass represented by the model, and the actual mass of the region (consistent with the contents and packaging description discussed in paras VII.3-VII.6). 

The paper gives a short survey of st reactor activities in Germany. The st reactor activities of FZK are part of the Nuclear Safety Projects. The R D program include neutron physical and safety calculated, and post-irradiated examination of structui materials. The key issues and tasks of the program concerned safety and transmission of minor activities and fission products. 

These safety calculations for ADSs have since been complemented by a study of reactivity insertion accidents. For an assumed subcriticality of - 3, reactivity ramp rates of 170, 6, and 0.1 /s were introduced, leading to a total reactivity insertion of about + 3. These calculations showed an initially benign behaviour of the ADS (this important safety feature of an ADS had already been found earlier with simpler calculations). However, after tenths of seconds a limited steady state type overpower condition was predicted by the present calculations. In particular the slowest ramp led to a longer-term overpower condition of about 1.5 times nominal. If the accelerator is not switched off or the proton beam interrupted, this overpower will eventually lead to some pin ruptures and fuel sweepout which will stabilise the behaviour of the ADS at a low overpower. This core damage could be avoided by selecting a lower subcriticality of the ADS. 

All safety calculations and relief device sizings should become a permanent part of the project file. 

Hence, safety calculations on systems that are significant departures from uniformly spaced systems should be treated with caution. A conservative approach would be to assume that the smallest spacing of a three-dimensional system is also the spacing of the other dimensions. Criticality data from uniform systems could then be applied with confidence. 

The Monte Carlo Method as Applied to Nuclear Criticality Safety Calculations, G. E ... 

E. C. CRUME, Jr., "The Reliability of CriticaUty Safety Calculations Using the New Codes CSC and KENO," Y-KC-96, Union C arbide Corp., Nuclear Division, (AprU 1967). 

H. K. CLARK, Computer Codes for Nuclear Criticality Safety Calculations," DP-1121, Savannah River Laboratory (1967). 

R. M. WESTFALL, D. M. PLASTER, and W. E. FORD, m, Procedure for Determining Broad-Group Energy Structure for Criticality Safety Calculations," Trans, Am. Nucl. Soc., 22, 291. (1975). 

The performance of a broad-group neutron cross-section library being developed as a standard for criticality safety calculations ha.s been evaluated using several critical uranium systems. The primary effort was directed toward the evaluation of clean and borated water-moderated, iow-enriched lattices of uranium metal or uranium oxide > rods. A set of uranium solution experiments over a wide range of H to U ratios was also evaluated. 

Safety Calculations end Rehchmarking of PWR Fuel Storage Pool Studies, D. 

The JOSHUA system handles data (e.g., input parameters, cross sections, intermediate data, outyut parameters, etc.) in named records, which may be written or read by foe modules or by foe user at a terminal through a template. A template is simply a means of displaying foe data with labels to identify items. Such labels tend to help foe user avoid errors in supplying input. Modules in foe JOSHUA system may be executed in sequence during the course of a job. A driver module, K O, has been written to prepare specialized input for the different niodules used for criticality safety calculations and to execute them in specified sequences. 

Quality Assurance Plan for Criticality Safety Calculations at Rocky Flats, Deanne Pecora (Rockwell Int)... 

Pitfalls in Criticality Safety Calculations and Experiences in Operations, G. Chatbum (BNFL-Engiand)... 

In France, for criticality safety calculations we use primarily a Monte Carlo code called MORET and Hansen and Roach cross-section sets or cross sections elaborated by a code called APOLLO, especially in the case of regular lattices of fissile rods. These methods have been tested with experimental results when needed but it now... 

The need for increased storage c iacity in existing fissile-material storage vaults is a problem encountered by criticality safety specialists, Xlnfortunat y, construction of additional vault mace may be prohibitively expensive because of extensive security and safety standards. Criticality safety calculations indicate storage limits coidd be increased if a neutron absorber were used to isolate unusually massive units. 

Criticality safety calculations made concurrently proved to be a desirable factor in the design of the revised Rover dissolution system and the determination of safe limits. 

Brovchenkao, M. 2012. Preliminary Safety Calculations to Improve the Design of Molten Salt Fast Reactor. In PHYSOR 2011, BCnoxville, TN. 

One result of this is that there is a much higher uncertainty in fc-effective in criticality safety analyses, and this imcertainty does not really disappear with processing experience. That is, in almost all criticality safety analyses—in contrast with reactor analyses—there is almost no chance that the resulting predictions of the /c-effective of the process will ever be verified experimentally. This leads to a much higher dependence on the validation of criticality safety calculations with externally produced benchmark experiments. This has resulted in a tremendous industry-wide effort to document, evaluate, and distribute reliable information on available critical experiment benchmarks over a wide range of fuels, enrichments, involved materials, and geometries. 

Validation of neutron transport methods for nuclear criticahty safety calculations... 

Because the results of a particular criticality safety calculation are unlikely to be experimentally verifiable, it is important to have a formal validation of the computer methods—a term that formally includes the computer code itself and the data used by the code. The basic approach to this task is to compare the computational tool against as many experimental results that are "similar" to the system being analyzed as is possible again, the validation effort is consistent with our overall goal of the computation to assure ourselves that conditions predicted to be subcritical by the method would be actually expected to be subcritical in reality. There are two primary results of the validation process ... 

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