The SQUG program for resolution of USI A-46 — Status and implementation plans

In response to U.S. Nuclear Regulatory Commission (NRC) Unresolved Safety Issue (USI) A-46, “Seismic Qualification of Equipment and Operating Nuclear Power Plants”, the Seismic Qualification Utility Group (SQUG), with the support of the Electric Power Research Institute (EPRI), developed a comprehensive program to verify the seismic adequacy of equipment in operating nuclear power plants. The primary thrust of the program has been the development of procedures, criteria, and data to apply actual experience on the performance of equipment during earthquakes to the verification of seismic ruggedness of similar equipment in nuclear plants. While the use of such experience data continues to play a primary part in the SQUG program for resolution of USI A-46, the overall SQUG program includes a number of other significant elements which, taken together, provide a comprehensive approach for verification of the seismic adequacy of equipment in nuclear plants. These elements of the SQUG program include the assimilation and use of seismic shake table data in a generic way; the development of simplified analytical tools and criteria for evaluation of equipment anchorage, tanks, heat exchangers and cable trays; and the development of procedures for identifying and evaluating electrical relays, which are essential to plant shutdown in response to an earthquake. Procedures and data bases for performing and documenting the various seismic evaluations and plant walkdowns, and a program for training the large number of engineers who will be required to implement the SQUG methodology, have also been developed. This paper describes the main elements of the SQUG program for resolution of USI A-46 and provides a status report on the plans for their implementation in SQUG member plants.     

Severe accident management strategy verification for VVER-1000 (V320) reactor

Severe accident analysis of a reactor is an important aspect in evaluation of source term. This in turn helps in emergency planning and Severe Accident Management (SAM). The use of the Severe Accident Management Guideline (SAMG) is required for accident situation which is not handled adequately through the use of Emergency Operating Procedures (EOP), thus leading to a partial or a total core melt. Actions recommended in the SAMG aim at limiting the risk of radiologically significant radioactive releases in the short- and mid-term (a few hours to a few days). Initiation of SAMG for VVER-1000 is considered at two core exit temperatures viz. 650 °C as a desirable entry temperature and 980 °C as a backup action. Analyses have been carried out for VVER-1000 (V320) for verification of some of the strategies namely water injection in primary and secondary circuit. These strategies are analysed for a high and low pressure primary circuit transients. Station Black Out (SBO) is one such high pressure transient for which core heat can be removed by natural circulation of the primary circuit inventory by maintaining the secondary side inventory. This strategy has been verified where the feed water injection to secondary side of SG is considered from external power sources (e.g. mobile DG sets) as suggested in SAM guidelines. The second transient, a low pressure event is analysed for verification of the SG flooding and core flooding strategies. The analysis shows that SG flooding is not adequate to arrest the degradation of the core. In case of core flooding strategy, the analyses show that core flooding is not adequate to arrest the degradation of the core for the large break LOCA where as for small break LOCA the injections through available safety systems are adequate. The assessments are carried out with integral severe accident computer code ASTEC V1.3.     

Status and verification strategy for ITER neutronics

The paper summarizes the current status of neutronics at ITER and a first set of proposals for experimental programmes to be conducted in the early operational life-time of ITER are described for the more crucial areas. These include a TF coils heating benchmark, a streaming benchmark and streaming measurements by activation on ITER itself. Also on ITER the measurement of activated water from triton burn-up should be planned and performed. This will require the measurement of triton burn-up in DD phase. Measurements of neutron flux in the tokamak building during DD operations should also be carried out. The use of JET for verification of shut down dose rate estimates is desirable. Other facilities to examine the production and behaviour of activated corrosion products and the shielding properties of concretes to high energy (6 MeV) gamma-rays are recommended.     

Optimizing cell importances using an extension of the DSA — theory, implementation, preliminary results

Starting from the theoretical results of the extension of Dubi's Direct Statistical Approach (DSA) surface parameter model to a cell importance model, a computer code based on MCNP has been written that directly estimates the second moment and time functions. Two versions have been developed: one that estimates the exact functions and the other that estimates the point-surface approximation functions. Preliminary results obtained using the two versions are presented.     

Ion traps — recent applications and developments

Paul and Penning traps are now widely applied in chemistry and physics laboratories. They are used as storage devices, as tools for precision spectroscopy and metrology, and as mass spectrometers. Direct mass measurements of short-lived Rb, Sr, Cs, Ba, Fr and Ra isotopes were performed at the on-line mass separator ISOLDE at CERN, Geneva, by means of a tandem Penning trap system. The ions from ISOLDE are captured and cooled in a first trap and trasnferred to a second trap. Here the mass of the trapped ions is determined by measuring their cyclotron frequency. Resolving powers exceeding m/Δm (FWHM) = 10⁶ could be achieved. Mass values of about 60 isotopes have been determined with accuracies of typically δm/m = 10⁻⁷. For the first time in the history of mass spectrometry the isomeric and ground states of a nucleus have been resolved.     

Soil-structure interaction — an engineering evaluation

The two methods of analysis for soil-structure interaction, the impedance and the finite element methods, are reviewed with regard to their present capabilities to address the significant factors of the problem. The objective of the paper is to evaluate if an adequate engineering solution to the problem is provided by either approach. Questions related to the reduction of seismic motions with depth, scattering of incident waves, the three-dimensionality of the real problem, soil damping, strain dependency of soil properties and the uncertainties associated with all of the above are discussed in sufficient detail. All conclusions made are based on referenced material. It appears that, although both methods as presently practised have not yet completely solved the problem, the impedance approach has come closer to addressing the more significant issues. Because of this finding, in addition to its simplicity and low cost, the impedance approach is the preferred engineering method for soil-structure interaction.     

TTPIXAN — the 4th generation

During the past six years the computer code TTPIXAN [I. Orlić et al., NIMB 49 (1990) 166] went through many changes and developments. From its infant stage when it was developed for a simple quantitative broad beam PIXE analysis, through a more sophisticated version [K.K. Loh et al., NIMB 77 (1993) 132] suited for applications in Nuclear Microscopy (NM). At present, the program is finally reaching its mature stage or its 4th metamorphosis [S.C. Liew et al., NIMB 104 (1995) 222]. It is now capable of not only simulating NM elemental images but also performing quantitative analysis and reconstruction of a complex 3D elemental composition encountered in NM applications. From a given initial 3D elemental distributions the program calculates exact elemental maps, compares them with the corresponding measured maps and by using a very efficient iterative Maximum-Likelihood Expectation-Maximisation (MLEM) algorithm, it calculates a new 3D elemental distributions. Energy loss of the incident particles and attenuation of the X-ray photons are incorporated into the reconstruction algorithm by using the most up-to date data base. The reconstruction algorithm has been successfully tested on several samples such as thin tungsten wire coated with paint, integrated circuits, and single aerosol particles. The computer code is briefly described and future plans outlined.     

Turbine missile — a critical review

The turbine missile problem has been critically reviewed. A probabilistic approach to the problem seems to be most reasonable. However, United States Nuclear Regulatory Commission's guidelines on this subject may not be adequate. In this paper, some of the critical parameters in the turbine missile problem have been identified and their probabilistic characteristics have been discussed. Separation of high and low trajectory missiles in damage potential evaluation appears to be inappropriate. Definitions of targets from the engineer's point of view have also been suggested. In estimating the occurrence rate of external missiles the statistical approach using the Duane growth rate model seems to be more appealing than the systems reliability approach. However, the observed samples and durations may not be adequate for the Duane growth rate model. A probabilistic methodology to estimate the damage potential of turbine missiles is also developed considering various sources of uncertainty. The methodology is clarified with the help of an example. If the uncertainties in the contributing parameters are considered appropriately, the crude conservatism that has been introduced into the damage potential evaluation can be reduced with confidence.     

Component vibration of VVER-reactors — diagnostics and modelling

Flow induced vibrations of reactor pressure vessel (RPV) internals (control element and core barrel motions) at VVER-440 reactors have lead to the development of dedicated methods for on-line monitoring. These methods need a certain developed stage of the faults to be detected. To achieve a real sensitive early detection of mechanical faults of RPV internals, a theoretical vibration model was developed based on finite elements. The model comprises the whole primary circuit including the steam generators (SG). By means of that model all eigenfrequencies up to 30 Hz and the corresponding mode shapes were calculated for the normal vibration behaviour. Moreover the shift of eigenfrequencies and of amplitudes due to the degradation or to the failure of internal clamping and spring elements could be investigated, showing that a recognition of such degradations even inside the RPV is possible by pure excore vibration measurements. A true diagnostics, that is the identification of the failed component, might become possible because different faults influence different and well separated eigenfrequencies.     

The implementation of magnetics verification in EAST plasma control system

Experimental advanced superconducting tokamak (EAST) is an experimental device aiming at steady state plasma operation for fusion research. The values of many discharge parameters, such as plasma shape, position and current must be directly acquired or indirectly evaluated from the magnetic measurements, so the accuracy of magnetic measurements plays an important role in reliable plasma control performance. A method for verifying the key magnetic measurements in real time for each shot is described in this paper. Such magnetics verification will prevent the discharge from a key magnetic signal failure and ensure the quality of a successful discharge. The diagnostics verification algorithm has been implemented in the plasma control system for the EAST. The implementation details and its application in the recent experiment are presented in this paper.     

The nuclear safety project at KfK 1972–1986 — Objectives and results

In 1972 the light water reactor safety activities conducted at the Karlsruhe Nuclear Research Center (KfK) were combined under the Nuclear Safety Project (PNS). Its primary objective was to assess in quantifiable terms the safety reserves which are provided in nuclear power plant design in a conservative approach. While in the initial phase R&D work conducted under the project was largely characterized by investigations of the design basis accidents, mainly the loss-of-coolant accident, emphasis in the past decade has been shifted more and more towards severe core and core meltdown accident analysis. The activities comprise both theoretical studies and experimental investigations, often performed in adequate, large-scale facilities. All activities have been an essential part of the reactor safety research program of the Federal Ministry for Research and Technology (BMFT) and have been coordinated with a number of other programs conducted in Germany and abroad. This paper gives a broad overview of PNS contributions to LWR safety research in the past 15 years and summarizes the results, comparing them with the general goals defined. In conclusion, the attempt is made to give an outlook on remaining activities in LWR safety research being carried out by KfK.     

Seismic qualification of equipment — research needs

In general, industry has followed the Institute of Electric and Electronic Engineers' (IEEE) Recommended Practices for Seismic Qualification of Class 1E Equipment for Nuclear Power Stations (IEEE Standard 344-1975). However, the U.S. Nuclear Regulatory Commission Regulatory Guide 1.100 notes exceptions to a small part of the IEEE Standards.This paper describes research needed to reconcile the differencies between the IEEE Standard and the Regulatory Guide. In addition, the paper discusses the effects of shake table mass and stiffness on the dynamic response of equipment tested, and the effect attributable to the difference between methods of attaching to the shake table and the actual in-situ attachment method.     

NONSAP — A nonlinear structural analysis program

The current version of the computer program NONSAP for linear and nonlinear, static and dynamic finite element analysis is presented. The solution capabilities, the numerical techniques used, the finite element library, the logical construction of the program and storage allocations are discussed. The solutions of some sample problems considered during the development of the program are presented.     

INTOR — a first-generation tokamak experimental reactor

An intensive, year-long, international evaluation of the next major tokamak beyond the generation of large experiments currently under construction was carried out during 1979. This evaluation consisted of the definition of objectives an assessment of the physics and technology base and R&D needs and the identification of a set of parameters that physically characterize the machine.     

Thermochemical processes for water splitting — Status and outlook

In this paper we discuss the proposals for processes which have already been realised in form of bench scale units or which have been planned, as well as those which have a high degree of development potential. A part of these cycles have in common the splitting of sulfuric acids which causes corrosion problems unsolved up to now. The essential part of the metal/metal hydride-processes is a hydrogen permeable membrane which separates the hydrogen acceptor from the water containing electrolyte melt. Actually we are intending to build up a lab cycle using a TiNi-basis membrane. The metal membranes offer a number of further interesting applications, such as (1) hydrogen production from gas mixtures at high temperatures, and (2) tritium separation from the helium of the HTR primary cooling circuit. A further promising process is the hydrocarbon hybrid cycle, in which the reduction of methanol to methane and oxygen is the key reaction. Till now we can detect a methane yield of up to 50%. An interesting combined procedure for the production of hydrogen and electricity is proposed, where sulphuric acid is decomposed by means of coal. The detailed mass and energy balance shows an efficiency of up to 57%. Thermodynamic analysis for the watersplitting cycles indicates efficiencies of up to 50%. Further research and development work is necessary in order to solve material problems and to demonstrate the suitability and availablity of the techniques using larger scale laboratory and prototype units.     

Computer codes for shielding calculations — 1969

An extensive library of computer codes useful for radiation transport or shielding calculations is available from the Radiation Shielding Information Center at Oak Ridge National Laboratory. In addition to the point kernel, Monte Carlo, and discrete ordinates codes used for neutron and gamma-ray transport calculations, the collection includes cross-section libraries and codes for processing cross sections, calculating fission product inventories, proton penetration of spacecraft, electron-photon transport, and analyzing neutron activation detector data to determine spectra. A list of the most current codes is given and essential information for each is included.     

Failure analysis following decontamination — laboratory and case studies

Based on the laboratory decontamination results, three failed type 321 stainless steel bellows expansion joints were decontaminated to reduce the radiation dose level below LLD (low limit of detection) and to investigate the cause of failure in laboratory. The corrosion test showed that, apart from 316L and Alloy 600, the corrosion rate of materials increased proportionally with both the temperature and the concentration of chemical cleaning reagents. Importantly, creviced coupons on which heavily localized corrosion was observed showed a higher corrosion rate than rod specimens. Analyses of the decontaminated broken bellows revealed flat-face fractures (produced by high longitudinal stresses) along the upper convolution, where the failure initiated. Rough and fibrous surfaces were observed where the general fracture direction was at 45 degrees to the main tensile load. No detrimental species such as sulfur or chlorine were detected at the crack tips by energy dispersive spectroscopy (EDS). The failure of the bellows was attributed to mechanical fatigue.     

Equations of state and spinodal lines — a review

Modern thermal processes in the power industry involve ever increasing heat fluxes and rapid transients. Simulating such processes requires accurate thermodynamic properties and correlations that encompass stable as well as metastable states. Here we review the development of cubic equations of state that can be made to yield very accurate thermodynamic properties of liquids in saturation and metastable (superheated) states. These cubic equations enable us to develop predictions and correlations for a number of other quantities which are either useful in themselves or for application to boiling and two-phase flow. Examples of such results include predictions of the saturation pressure, the limiting liquid superheat, the destructive energy available to a superheated liquid, the surface tension of a saturated fluid and the approach of the specific heat at constant pressure to infinity at the spinodal point. These topics are described and discussed, and it emerges that these seemingly separate topics can be unified by the use of cubic equations of state. We pay particular attention to the issue of a possible connection between the limit of liquid superheat and the liquid spinodal line.     

Systems reliability/structural reliability — Interaction and differences in approach

The question of reliability technology using quantified techniques is considered for systems and structures. Systems reliability analysis has progressed to a viable and proven methodology whereas this has yet to be fully achieved for large scale structures.Structural loading variants over the life-time of the plant are considered to be more difficult to analyse than for systems, even though a relatively crude model may be a necessary starting point. Various reliability characteristics and environmental conditions are considered which enter this problem.The rare event situation is briefly mentioned together with aspects of proof testing and normal and upset loading conditions.