INL/EXT-06-01183 Revision 1 Criticality Safety Basics for INL FMHs and CSOs April 2012 The INL is a U.S. Department of Energy National Laboratory operated by Battelle Energy Alliance DISCLAIMER This information was prepared as an account of work sponsored by an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness, of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. References herein to any specific commercial product, process, or service by trade name, trade mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof. INL/EXT-06-01183 Revision 1 Criticality Safety Basics for INL FMHs and CSOs April 2012 Idaho National Laboratory Criticality Safety Engineering Idaho Falls, Idaho 83415 http://www.inl.gov Prepared for the U.S. Department of Energy Office of Nuclear Energy Under DOE Idaho Operations Office Contract DE-AC07-05ID14517 FOREWORD Nuclear power is a valuable and efficient energy alternative in our energy- intensive society. However, material that can generate nuclear power has properties that require this material be handled with caution. If improperly handled, a criticality accident could result, which could severely harm workers. This document is a modular self-study guide about Criticality Safety Principles. This guide’s purpose it to help you work safely in areas where fissionable nuclear materials may be present, avoiding the severe radiological and programmatic impacts of a criticality accident. It is designed to stress the fundamental physical concepts behind criticality controls and the importance of criticality safety when handling fissionable materials outside nuclear reactors. This study guide was developed for fissionable-material-handler and criticality-safety-officer candidates to use with related web-based course 00INL189, BEA Criticality Safety Principles, and to help prepare for the course exams. These individuals must understand basic information presented here. This guide may also be useful to other Idaho National Laboratory personnel who must know criticality safety basics to perform their assignments safely or to design critically safe equipment or operations. This guide also includes additional information that will not be included in 00INL189 tests. The additional information is in appendices and paragraphs with headings that begin with “Did you know,” or with, “Been there. Done that!” Fissionable-material-handler and criticality-safety-officer candidates may review additional information at their own discretion. This guide is revised as needed to reflect program changes, user requests, and better information. Issued in 2006, Revision 0 established the basic text and integrated various programs from former contractors. Revision 1 incorporates operation and program changes implemented since 2006. It also incorporates suggestions, clarifications, and additional information from readers and from personnel who took course 00INL189. Revision 1 also completely reorganized the training to better emphasize physical concepts behind the criticality controls that fissionable material handlers and criticality safety officers must understand. The reorganization is based on and consistent with changes made to course 00INL189 due to a review of course exam results and to discussions with personnel who conduct area-specific training. iii The photographs on the cover and this page were taken on July 14, 2010 during receipt and repackaging of new fuel elements for the Neutron Radiography Reactor (NRAD). On the cover, a fissionable material handler (FMH) prepares to repackage an element. The TN-BGC-1 shipping container (birdcage) used to ship the elements from France to the Hot Fuels Examination Facility (HFEF) at the Materials and Fuels Complex (MFC). This type of container is often called a birdcage because the payload container is surrounded by a cage. The FMH inserts an element into a 55 gallon fuel The interior of the 55 gallon fuel storage drum with storage drum. a few of the new elements. iv CONTENTS MODULE 1 ATOMS & NEUTRONS ............................................................................................ 1 Introduction ................................................................................................................. 1 Objectives ................................................................................................................... 1 Topic 1.1 The Atom and Its Parts ................................................................................................ 2 1.1.1 Molecules and Atoms .................................................................................................. 2 1.1.2 Inside an Atomic Nucleus: Protons and Neutrons ...................................................... 2 1.1.3 Outside an Atomic Nucleus: Electrons ....................................................................... 2 1.1.4 Atomic Number........................................................................................................... 3 1.1.5 Isotopes ....................................................................................................................... 3 1.1.6 Mass Number .............................................................................................................. 4 Review Questions ....................................................................................................... 6 Review-Question Answers .......................................................................................... 8 Topic 1.2 Neutron Interactions .................................................................................................. 10 1.2.1 Neutron Scattering .................................................................................................... 11 1.2.2 Neutron Absorption................................................................................................... 12 Review Questions ..................................................................................................... 12 Review-Question Answers ........................................................................................ 14 MODULE 2 FISSION & CHAIN REACTIONS .......................................................................... 15 Introduction ............................................................................................................... 15 Objectives ................................................................................................................. 15 Topic 2.1 Nuclear Fission ......................................................................................................... 16 Topic 2.2 Fission Chain Reaction ............................................................................................. 17 Topic 2.3 Fissionable Material and Fissionable Isotopes .......................................................... 17 Topic 2.4 Types of Fission Chain Reactions ............................................................................. 18 2.4.1 Subcritical ................................................................................................................. 18 2.4.2 Critical ....................................................................................................................... 19 2.4.3 Supercritical .............................................................................................................. 19 2.4.4 Information for Criticality Safety Officers ............................................................... 20 Review Questions ..................................................................................................... 21 Review-Question Answers ........................................................................................ 22 MODULE 3 CRITICALITY CONTROL FACTORS ................................................................... 23 Introduction ............................................................................................................... 23 Objectives ................................................................................................................. 23 Topic 3.1 Mass .......................................................................................................................... 24 Topic 3.2 Enrichment ................................................................................................................ 26 Topic 3.3 Reflection .................................................................................................................. 27 Topic 3.4 Moderation ................................................................................................................ 29 Topic 3.5 Absorption (neutron capture) .................................................................................... 32 Topic 3.6 Interaction ................................................................................................................. 34 Topic 3.7 Density and Concentration ........................................................................................ 35 Topic 3.8