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Title: Study of the integrity of pressurized LEH window assemblies at cryogenic temperatures for NIF targets

Abstract

The National Ignition Facility (NIF) is a directorate of LLNL, a DOE Lab, and is home to the world’s largest laser. This laser shoots its 192 beams at a target about the size of a pencil eraser. Within the target are two main chambers; and depending on the type of shot, those chambers need to be pressurized to a certain point at a very low temperature (18 Kelvin). The component used for keeping the hohlraum at its designated pressure is a Laser Entrance Hole (LEH) window, made from a thin (0.5um) polyimide film and an aluminum washer attached with a miniscule amount of polymeric adhesive. One issue that has been known to happen is the chambers will leak, at very low rates (5.0E-7 mBar-liter/s and under). At higher pressures significantly larger leak rates have been observed.There are three proposed mechanisms by which the LEH windows are leaking. The first is that there is a small pinhole somewhere in the freestanding film. This is the most unlikely because before any film is shipped from Luxel, it must pass a 50-75 torr room temperature pressure test. The second is a tear in the film at the edge of the washer. This typemore » of damage suggests that the film is under additional stress at this edge portion and/or the edge of the washer itself is what is doing the damage. Lastly, it has been hypothesized that there are small channels under the window that do not get completely filled by the glue and, if they connect to the edge of the freestanding portion of the film, then the pressure can escape through them. These channels were the mechanism being most directly tested over the course of the experiments.« less

Authors:
 [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1297657
Report Number(s):
LLNL-TR-699859
TRN: US1601780
DOE Contract Number:
AC52-07NA27344
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; WINDOWS; US NATIONAL IGNITION FACILITY; FILMS; TEMPERATURE RANGE 0013-0065 K; LEAKS; IMIDES; PRESSURE RANGE KILO PA; TEMPERATURE RANGE 0000-0013 K

Citation Formats

Hamza, H. Study of the integrity of pressurized LEH window assemblies at cryogenic temperatures for NIF targets. United States: N. p., 2016. Web. doi:10.2172/1297657.
Hamza, H. Study of the integrity of pressurized LEH window assemblies at cryogenic temperatures for NIF targets. United States. doi:10.2172/1297657.
Hamza, H. Fri . "Study of the integrity of pressurized LEH window assemblies at cryogenic temperatures for NIF targets". United States. doi:10.2172/1297657. https://www.osti.gov/servlets/purl/1297657.
@article{osti_1297657,
title = {Study of the integrity of pressurized LEH window assemblies at cryogenic temperatures for NIF targets},
author = {Hamza, H.},
abstractNote = {The National Ignition Facility (NIF) is a directorate of LLNL, a DOE Lab, and is home to the world’s largest laser. This laser shoots its 192 beams at a target about the size of a pencil eraser. Within the target are two main chambers; and depending on the type of shot, those chambers need to be pressurized to a certain point at a very low temperature (18 Kelvin). The component used for keeping the hohlraum at its designated pressure is a Laser Entrance Hole (LEH) window, made from a thin (0.5um) polyimide film and an aluminum washer attached with a miniscule amount of polymeric adhesive. One issue that has been known to happen is the chambers will leak, at very low rates (5.0E-7 mBar-liter/s and under). At higher pressures significantly larger leak rates have been observed.There are three proposed mechanisms by which the LEH windows are leaking. The first is that there is a small pinhole somewhere in the freestanding film. This is the most unlikely because before any film is shipped from Luxel, it must pass a 50-75 torr room temperature pressure test. The second is a tear in the film at the edge of the washer. This type of damage suggests that the film is under additional stress at this edge portion and/or the edge of the washer itself is what is doing the damage. Lastly, it has been hypothesized that there are small channels under the window that do not get completely filled by the glue and, if they connect to the edge of the freestanding portion of the film, then the pressure can escape through them. These channels were the mechanism being most directly tested over the course of the experiments.},
doi = {10.2172/1297657},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Aug 05 00:00:00 EDT 2016},
month = {Fri Aug 05 00:00:00 EDT 2016}
}

Technical Report:

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  • In this report we finalize our conclusions concerning the issues that determine the feasibility of a low-inventory NIF target filling system: 1) calculation of the basic physical (thermodynamic, thermal flow, strength, etc.) characteristics; 2) choice of the optimum technological sequence; 3) choice of the principal design. To make discussion easier, in this report we present more or less detailed sketches of the filling system assembly inexplicit form. Since some of the already available important physical-engineering solutions (for instance, the design of the capsule removal device) are not know to us, we left certain engineering questions open for further discussion andmore » detalization. Summing up very briefly, we show that a very low-inventory filling system is undoubtedly feasible, notwithstanding some lingering ambiguities (for example, choice of the auxiliary capacity design, pressure gauge principle, etc.). Our previous evaluation [1] of the general concept of the low-inventory filling system was based on calculations for normal D{sub 2}. The recalculation to the 50-50% D{sub 2}-T{sub 2} mixture, reported here, does not change much in either final figures, or conclusions. We do not formulate anew the overall concept but refer to Part III of Agreement. We either omit some of our previous reasonings and evaluations, referring the reader to 1st Quarterly Report [1].« less
  • A novel methodology to detect diversion of spent fuel from Pressurized Water Reactors (PWR) has been developed in order to address a long unsolved safeguards verification problem for international safeguards community such as International Atomic Energy Agency (IAEA) or European Atomic Energy Community (EURATOM). The concept involves inserting tiny neutron and gamma detectors into the guide tubes of a spent fuel assembly and measuring the signals. The guide tubes form a quadrant symmetric pattern in the various PWR fuel product lines and the neutron and gamma signals from these various locations are processed to obtain a unique signature for anmore » undisturbed fuel assembly. Signatures based on the neutron and gamma signals individually or in a combination can be developed. Removal of fuel pins from the assembly will cause the signatures to be visibly perturbed thus enabling the detection of diversion. All of the required signal processing to obtain signatures can be performed on standard laptop computers. Monte Carlo simulation studies and a set of controlled experiments with actual commercial PWR spent fuel assemblies were performed and validated this novel methodology. Based on the simulation studies and benchmarking measurements, the methodology developed promises to be a powerful and practical way to detect partial defects that constitute 10% or more of the total active fuel pins. This far exceeds the detection threshold of 50% missing pins from a spent fuel assembly, a threshold defined by the IAEA Safeguards Criteria. The methodology does not rely on any operator provided data like burnup or cooling time and does not require movement of the fuel assembly from the storage rack in the spent fuel pool. A concept was developed to build a practical field device, Partial Defect Detector (PDET), which will be completely portable and will use standard radiation measuring devices already in use at the IAEA. The use of the device will not require any information provided by the operator or any prior knowledge of the spent fuel assembly. The device can also be operated without any movement of the spent fuel from its storage position. Based on parametric studies conducted via computer simulation, the device should be able to detect diversion of as low as ten percent of the missing or replaced fuel from an assembly regardless of the location of the missing fuel within the assembly, of the cooling time, initial fuel enrichment or burnup levels. Conditions in the spent fuel pool such as clarity of the water or boron content are also not issues for this device. The shape of the base signature is principally dependent on the layout of the guide tubes in the various types of PWR fuel assemblies and perturbations in the form of replaced fuel pins will distort this signature. These features of PDET are all unique and overcome limitation and disadvantages presented by currently used devices such as the Fork detector or the Cerenkov Viewing Device. Thus, this device when developed and tested could fill an important need in the safeguards area for partial defect detection, a technology that the IAEA has been seeking for the past few decades.« less
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  • The initial NIF Cryogenic Target Systems (NCTS) major milestone for FY03 was to complete the conceptual design and a Conceptual Design Report (CDR). Due to actual FY03 NCTS funds available, this milestone has been postponed to FY2004. Some effort toward the CDR and related development activities did continue in the area of methods for fuel-filling of both beryllium and polymer ignition capsules. This work was performed mainly at General Atomics in collaboration with LANL and LLNL.