Sunil S. Chirayath

• PhD
• Director at Texas A&M University

It is important to understand the different types of insiders and the need for insider threat mitigation. Protecting against insider threats is an inherently difficult challenge because of the insider’s access to, authority over, and knowledge of the facility. Several strategies and best practices for insider threat mitigation implemented at differ...

Human Reliability Programs (HRP) addresses the needs of sensitive or high-risk industries to employ the best possible workforce. Trustworthiness is essential to safety because it can help ensure compliance with procedures and works in accordance with other safety measures to reduce human error. An HRP can also mitigate the greatest security threat...

The Human Reliability Program (HRP) is a security and safety reliability program designed to ensure that individuals who occupy positions affording access to certain materials, facilities, and programs meet the highest standards of reliability and physical and mental suitability. In this chapter, we summarize the steps to implementing a sustainable...

Human Reliability Program (HRP) is a set of procedures, protocols, and the corresponding performance of activities to support and sustain the secure and safe operation of a facility. Our review indicated that HRP is referred to by various names, such as, Personnel Reliability Program (PRP), Trustworthiness Program, and Fitness for Duty Program, wit...

We demonstrate the ability to obtain the direction of the gamma rays using a standard coaxial high purity germanium (HPGe) detector using the direction-sensitive information embedded in the shape of the pre-amplified HPGe signals. We deduced the complex relationship between the shape of the signal and the direction from which the gamma-ray enters t...

Dry casks will be a prevalent spent nuclear fuel (SNF) storage option until solutions for long-term storage or disposal are deployed. A dry cask storing 32 pressurized water reactor fuel assemblies will likely contain about 20 significant quantities of plutonium, so these structures require effective safeguards monitoring. An external remote monito...

It has become a common practice to store sufficiently cooled spent nuclear fuel (SNF) assemblies in interim storage dry casks with passive cooling. These dry casks require nuclear safeguards monitoring because they contain plutonium. Past studies on dry cask modeling and simulations have shown that a remote monitoring system (RMS) situated inside t...

Traditional nuclear forensics methods aim to ascertain key pieces of information regarding material provenance using material characteristics. In 2018, a novel nuclear forensics methodology for source discrimination of separated plutonium was developed, which utilizes a maximum likelihood formulation and intra-element isotope ratios to identify the...

Proliferation resistance (PR) evaluations of discharged fuel from a pebble bed reactor (PBR) that employs one-batch, single-pass, and multi-pass refueling schemes were performed. Four attributes (heat load, radiation dose rate, spontaneous fission neutron rate, and Rossi-α) of 8-kg plutonium (Pu) were used for the PR evaluations. Neutronics simulat...

A nuclear forensics technique, based on the maximum likelihood method, for the attribution of reactor type, fuel burnup, and time since irradiation (TSI) of separated pure plutonium (Pu) samples was previously developed at Texas A&M University. The method utilized measured values of ten intra-elemental isotope ratios in the Pu sample and a large da...

The objective of this work is to determine if coherent-elastic-neutrino-nucleus scatter (CEνNS) in natural germanium detectors can be used to detect antineutrinos from an AP1000-type fission reactor. In this work, we first modeled the AP1000 core using Monte Carlo N-Particle Transport Code 6.2 (MCNP) to estimate the number of fissions from each fis...

A study is carried out to assess the proliferation resistance (PR) of pebble bed reactor (PBR) fuel using two methods. The Proliferation Resistance Analysis and Evaluation Tool for Observed Risk (PRAETOR) code is the first method, which employs 68 attributes (intrinsic and extrinsic) to assess the overall PR. Forty-six uranium and plutonium diversi...

Understanding radiation effects on avalanche photodiodes (APDs) is important because they are used in several applications involving harsh radiation environments. APDs are used as photosensors in applications where speed and detection efficiency are critical. Proton irradiation experiments on a commercial off-the-shelf APD demonstrated that the irr...

A nuclear energy facility is one of the most critical facilities to be safely protected during and after operation because the physical destruction of its barriers by an external attack could release radioactivity into the environment and can cause harmful effects. The barrier walls of nuclear energy facilities should be sufficiently robust to prot...

Radiation effects studies on a commercial beveled-edge avalanche photodiode (APD) showed that applying reverse bias to the device during irradiation enhanced the severity of apparent damage. Proton microbeam irradiations were made using a proton beam energy of 2 MeV and fluence ranging from 2.0 × 10¹⁰ to 5.1 × 10¹² cm⁻². Charge collection measureme...

Monte Carlo (MC) neutronics codes are used widely for academic and industrial needs. Several schemes of coupling MC neutronics code with isotope generation and depletion code exist, which are used for performing nuclear fuel depletion simulations. These simulations can estimate the inventory of isotopes in neutron irradiated nuclear reactor fuel. H...

Until a long-term solution is finalized, interim storage of sufficiently cooled spent nuclear fuel (SNF) assemblies in dry casks is the predominant practice. Since these dry casks can contain approximately 160 kg of reactor-grade plutonium, they require safeguards monitoring. Results of a simulation study conducted on the design development and ana...

The X-10 nuclear reactor was built at the Clinton Engineering Works in Oak Ridge, Tennessee, USA, as the world’s first Pu production reactor. Operation commenced in November 1943, producing Pu on the gram-scale for the first time. A 61.1 mg sample of 239Pu has been identified at Los Alamos National Laboratory containing multiple forensic signatures...

Researchers at Texas A&M University (TAMU) have designed the radiation integrated circuit (RIC) for deployment as a new radiation detection system. Most integrated circuits are susceptible to radiation-induced failures, and decades of research have gone into solving this problem. Research at TAMU has led to a novel integrated circuit design that ut...

The Monte Carlo N-particle radiation transport code (MCNP) is used widely in nuclear fuel burnup simulation (FBS). In the FBS, MCNP predicts various neutron reaction rates and the associated stochastic relative error (SRE). The SRE is due to the nature of the statistical methods used in MCNP. These SREs for neutron reaction rates and fluxes are rep...

A chemical methodology has been selected to isolate and concentrate select trace fission product (FP) elements from separated Pu for nuclear forensics. The methodology employs several different resins and eluents to chromatographically separate U and the FP elements of interest into their own fractions. The U, rare-earth element, Cs, and Ba fractio...

The long-term sustainability of nuclear energy requires a closed fuel cycle in which used fuel is reprocessed and recycled. Unlike the PUREX process, which produces a pure plutonium product, pyro-processing produces a depleted uranium ingot and a mixed ingot of depleted uranium and transuranic elements (neptunium, plutonium, americium, and curium)...

The proliferation resistance (PR) of an inert matrix fuel (IMF) in the transuranic nuclear fuel cycle (NFC) of a high temperature gas cooled reactor is evaluated relative to the uranium and plutonium mixed-oxide (MOX) NFC of a light water reactor using PRAETOR code and sixty-eight input attributes. The objective is to determine the impacts of chemi...

The axial variation of Pu quality ([Pu-239 + Pu-241]/Pu) in used nuclear fuel is analyzed using MCNP simulations. The Pu quality ratio variation is found to be due to the differences in axial neutron flux and neutron interaction cross-sections of U and Pu isotopes. The Pu axial non-uniformity is found to be larger for isotopes with smaller neutron...

The correlation of the amount of Pu produced in spent nuclear fuel to burnup (BU), cooling time (CT), initial U-235 enrichment (IE), and axial location (AX) is investigated by the Support Vector Regression (SVR) method. The AX parameter is a new one compared to the other studies reported in the literature. The regression coefficient (R²) and root m...

We present a new stochastic computational tool, Multi-path Analysis of Physical Protection Systems (MAPPS) useful for Physical Protection System (PPS) effectiveness analysis. MAPPS tool can perform multi-path (adversary paths) analysis using an Adversary Sequence Diagram (ASD) and can determine the Most Vulnerable Path (MVP). The MVP determination...

There is a shortage of reliable information on the highly enriched uranium (HEU) stockpile, production capabilities, and natural uranium reserves of the Democratic People's Republic of Korea (DPRK or North Korea). It is, however, possible to estimate DPRK’s nuclear material reserves using the data in the open literature and considering various scen...

The Monte Carlo N-Particle (MCNP6) radiation transport code is widely used to perform material transmutation and depletion calculations using the embedded module CINDER90. CINDER90 is capable of obtaining fission product and transuranic nuclide concentrations with a high level of accuracy in irradiated nuclear fuel. This information is very useful...

Monte Carlo n-Particle (MCNP) simulations are conducted to study the effect of different fill materials on a spent nuclear fuel (SNF) multi-purpose canister (MPC). Surface gamma and neutron dose rates and neutron multiplication were recorded for vacuum, Portland concrete, sand, borosilicate glass, and water fills for MPCs filled with 3-year cooled...

The nuclear proliferation challenges posed by Iran alleviated considerably when the Joint Comprehensive Plan of Action (JCPOA) between Iran and the E3/EU+3 countries (Germany, France, the U.K./European Union+U.S., China, and Russia), came into force in January 16, 2016 [1]. However, the unilateral withdrawal announcement of the United States from t...

As part of an experimental validation of a nuclear forensics methodology for Pu source reactor-type discrimination, destructive analysis has been performed on two irradiated UO 2 pellets with different irradiation histories. Analysis has focused on measuring key Sm fission product isotope ratios used in a previously published maximum likelihood met...

A recently published nuclear forensics methodology for source discrimination of separated weapons-grade plutonium utilizes intra-element isotope ratios and a maximum likelihood formulation to identify the most likely source reactor-type, fuel burnup and time since irradiation of unknown material. Sensitivity studies performed here on the effects of...

The lack of an operational deep geological repository in the U.S. has left the nuclear power plant operators with the option of storing the more than five years water cooled spent nuclear fuel (SNF) assemblies in dry casks as an interim solution. A single dry cask that typically stores 32 pressurized water reactor (PWR) SNF assemblies can contain u...

An experimental validation of a nuclear forensics methodology for the source reactor-type discrimination of separated weapons-useable plutonium is presented. The methodology uses measured values of intra-element isotope ratios of plutonium and fission product contaminants. MCNP radiation transport codes were used for various reactor core modeling a...

New methodologies for rationally safeguarding a nuclear system in terms of economics have been developed based on the Bayesian decision theory and the risk management approach. Two methodologies are formulated and presented. In the first method, the two terms in which the cost for an error (Type-I or Type-II error) event is multiplied by the probab...

A new methodology to analyze the nuclear material accountability for pyroprocessing system is developed. The Pu-to-244Cm ratio quantification is one of the methods for Pu accountancy in pyroprocessing. However, an uncertainty in the Pu-to-244Cm ratio due to the non-uniform composition in used fuel assemblies can affect the accountancy of Pu. A rand...

Under normal operating conditions, a pyroprocessing facility removes highly radioactive and nonradioactive fission product waste from used nuclear reactor fuel to recycle the remaining uranium (U), plutonium (Pu), and other actinides contained in it. The products from this facility are separate ingots of U and mixed transuranic elements (TRUs)–uran...

Destruction of critical nuclear infrastructure would have a debilitating effect on national public health, safety, national economy and security. For this reason, analysts perform safety risk analyses on the performance of the nuclear system to quantify and understand the nature of unwanted events. Since the world has gone through many changes afte...

The growing nuclear threat has amplified the need for developing diverse and accurate nuclear forensics analysis techniques to strengthen nuclear security measures. The work presented here is part of a research effort focused on developing a methodology for reactor-type discrimination of weapons-grade plutonium. To verify the developed methodology,...

An analysis of a pyroprocessing safeguards methodology employing the Pu-to- includes characterization of representative used nuclear fuel assemblies with respect to computed nuclide composition. The nuclide composition data computationally generated is appropriately reformatted to correspond 244 with the material conditions after each step in the h...

A nuclear forensics methodology has been developed that is capable of source attribution of separated weapons-grade plutonium in case of an interdiction. The methodology utilizes plutonium and contaminant fission product isotopes within the separated plutonium sample to determine the characteristics (reactor parameters) of the interdicted material....

A multi-physics computational methodology to analyze xenon induced power oscillations in a nuclear reactor is developed and presented. The methodology development takes into account both neutron transport and thermal hydraulics behaviors and their inter-dependent feedbacks in a nuclear power reactor as a function of fuel burn-up. The methodology us...

A terrorist attack using an improvised nuclear device is one of the most serious dangers facing the United States. The work presented here is part of an effort to improve nuclear deterrence by developing a methodology to attribute weapons-grade plutonium to a source reactor by measuring the intrinsic physical characteristics of the interdicted plut...

Experimental investigations to determine fission product separation from actinides (U and Pu) while employing the Plutonium Uranium Recovery by Extraction (PUREX) process to purify plutonium produced in a fast neutron irradiated depleted uranium dioxide (DUO2) target were conducted. The sample was a DUO2 pellet (0.256 wt% ²³⁵U) irradiated to a low-...

The small modular reactor (SMR) offers many feasible pathways for the construction of more nuclear power plants. A physics model of a near term deployable SMR of the integral pressurized water reactor (IPWR) design is developed. Fuel depletion simulations are performed to optimize the active fuel length, fuel enrichment and core loading pattern in...

Radioiodine thyroid ablation therapy is a common method for treatment of felines exhibiting hyperthyroidism. Due to the high gamma-ray emission rate of radioiodine (I), patients following treatment must be held in isolation for several days before release to prevent unnecessary dose to owners and members of the public. Dose rate measurement on the...

A systematic and strategic nuclear power reactor deployment roadmap has been developed for South Africa within the national strategic plan, utilizing thorium-based fuel. The roadmap was developed through analysis of economical, strategic and historical aspects. The accumulated advantages of thorium-based fuels are summarized, which could form the i...

The objective of this paper is to analyze the uncertainty in radiation dose rate estimates outside of a used nuclear fuel (UNF) dry cask storage unit due to the parametric variability of concrete compositions and densities. This requires the selection of a limited number of concrete compositions from a standardized database and the development of a...

The growing concern about nuclear terrorism threats has enhanced the need to develop fast and accurate nuclear forensics analysis techniques for nuclear material source attribution and to create a credible nuclear deterrence. Plutonium produced as a by-product in nuclear reactor fuel, especially in fuel discharged at low burn-up (1 to 2 MWd/kg), is...

Analysis of a thorium fuelled gas cooled fast breeder reactor (TGFBR) concept has been done to demonstrate the self-sustainability, breeding capability, actinide recycling ability, and thorium fuel feasibility. Simultaneous use of 232Th and used fuel from light water reactor in the core has been considered. Results obtained confirm the core neutron...

Korea Hydro and Nuclear Power has built a new modular type of CANDU spent fuel bundle dry storage facility, MACSTOR KN-400, at the Wolsong reactor site in the Republic of Korea. Four CANDU reactors operate at the Wolsong site, and the MACSTOR KN-400 has the capacity to store up to 24000 CANDU spent fuel bundles. The International Atomic Energy Agen...

In recent years, the United States, along with many other countries, has significantly increased its detection and defense mechanisms against terrorist attacks. A potential attack with a nuclear weapon, using nuclear materials smuggled into the country, has been identified as a particularly grave threat. The system for detecting illicit nuclear mat...

This paper proposes a layered container inspection system for detecting illicit nuclear materials using radiography information. We argue that the current inspection system, relying heavily on the Automated Targeting System (ATS) and passive radiation detectors, is inherently incapable of reliably detecting shielded radioactive materials, especiall...

Computational core physics analysis carried out for a typical fast breeder reactor (FBR) core design is presented through two case studies; one using only (PuO2–UO2) MOX fuel and another that replaces ∼41% of (PuO2–UO2) MOX with (PuO2–ThO2) MOX while conserving the total Pu content. The basic computational framework employed uses the MONTEBURNS2 PE...

Validation studies based on the analysis of theoretical benchmarks play a key role in the identification of deficiencies in the reactor physics design computational codes and the associated nuclear data libraries. Implementation of improvements, if any, in theoretical models and the choice of appropriate nuclear data libraries help in enhancing the...

Utilization of Mixed Uranium–Plutonium Oxide (MOX) fuel in VVER-1000 reactors envisages the core physics analysis using computational methods and validation of the related computer codes. Towards this objective, an international experts group has been established at OECD/NEA. The experts group facilitates sharing of existing information on physics...

Monte Carlo modeling of the Kalpakkam Mini reactor (KAMINI) had been made earlier by us for the first time using Monte Carlo code (MCNP4A) and ENDF/B-VI.2 data in the year 2004. KAMINI has been accepted as a part of the International Criticality Safety Benchmark Evaluation Project (ICSBEP) recently and its detailed configuration is available for an...

Inclusion of intrinsic safeguards in fast reactor systems could lower one of the barriers to a closed fuel cycle. This project aims to locate and evaluate the proliferation concerns in a generic fast reactor fuel cycle: plutonium driver fuel from LWR or CANDU spent fuel with a depleted uranium blanket and PUREX reprocessing. Proliferation Resistanc...

A pool type 500 MWe Prototype Fast Breeder Reactor (PFBR) is under construction in India. It is well known that the neutron flux monitoring system in a pool type fast breeder reactor is a very challenging issue, which involves high complexity. The use of external neutron source subassemblies of Sb-Be type has been explored as a possibility to obtai...

Continuous-energy Monte Carlo code, MCNP along with its cross section data library in ACE format based on ENDF/B-V &VI has been used to analyze a new computational benchmark circulated by LANL (LA-UR-06-2968) on Doppler coefficient for different types UO 2 . Doppler coefficient has been computed by calculating the eigen values of some selected idea...

As per TG-43 dose calculation formalism, it is essential to obtain various dosimetric parameters such as the air-kerma strength, dose rate constant, radial dose function, and anisotropy function, as they account for accurate determination of dose rate distribution around brachytherapy sources. Most of the available reported Monte Carlo simulations...

An analysis of Ir-192 source distribution using the Monte Carlo method and radiochromic film experiments for endovascular brachytherapy is presented. Three different source possibilities, namely, mHDR Ir-192 sources with 5 mm and 2.5 mm step sizes and Ir-192 seed sources with 1 mm air gap are investigated to obtain uniform radial dose distribution...

The present work is primarily focused on the estimation of relative dose distribution and effective transmission around a shielded vaginal cylinder with an 192Ir source using the Monte Carlo technique. The MCNP4B code was used to evaluate the dose distribution around a tungsten shielded vaginal cylinder as a function of thickness and angular shield...

The analysis of the x-ray spectrum obtained in electron cyclotron resonance (ECR) x-ray source is carried out. Assuming single-particle motion, the electron acceleration and its final energy are calculated for TE111 cylindrical cavity field and uniform external dc magnetic field. In the calculation, initial coordinates of 40 000 electrons were unif...

Monte Carlo modeling of the Kalpakkam Mini Reactor (KAMINI) has been carried out for the first time by using Monte Carlo code (MCNP4A) and continuous energy cross-sections. The safety control plate (SCP) drop experiment is simulated and the computed integral worth of the SCPs is compared with the measured value. The measured axial neutron flux prof...

KAMINI is the Kalpakkam Mini Reactor and its main purpose is to cater to the experimental needs and for neutron radiography. It is a water-cooled reactor with 233U as the fissile material. The reactor has three neutron beam ports for experimental needs, which are made of graded cylindrical aluminium channel. All the beam ports start from the core,...

A graphical user-friendly interface is developed in Visual Basic (VB)-6 to view the variation of neutron and photon interaction cross-sections of different isotopes as a function of energy. VB subroutines developed read the binary data files of cross-sections created in MCNP-ACE (Briesmeister, J.F., 1993. MCNP- a general purpose Monte Carlo N-Parti...

KAMINI is the Kalpakkam Mini Reactor, and its main purpose is to cater to experimental needs and for neutron radiography. It is a water-cooled reactor with ²³³U as the fissile material. Using the Monte Carlo n-particle transport code MCNP, shielding optimization calculations are carried out for the south beam port tube, which is meant for neutro...

The Nuclear Security Science and Policy Institute (NSSPI) has established a Nuclear Nonproliferation specialization for the Master of Science degree within the Nuclear Engineering Department at Texas A&M University (TAMU). Since 2004, twenty-eight students have received MS degrees in this area and over 200 (technical and policy) students have taken...