Overcoming thermal shock problems in liquid targets

Journal Article · Sat Jul 01 04:00:00 EDT 2000 · Transactions of the American Nuclear Society

OSTI ID:20086961

Taleyarkhan, R P; Kim, S H

Short-pulse accelerator-driven neutron sources such as the Spallation Neutron Source (SNS) employ high-energy proton beam energy deposition in heavy metal (such as mercury) over microsecond time frames. The interaction of the energetic proton beam with the mercury target leads to very high heating rates in the target. Although the resulting temperature rise is relatively small (a few degrees centigrade), the rate of temperature rise is enormous ({approximately}10{sup 7} C/s) during the very brief beam pulse ({approximately}0.58 {micro}s). The resulting thermal shock-induced compression of the mercury leads to the production of large-amplitude pressure waves in the mercury that interact with the walls of the mercury target and the bulk flow field. Safety-related operational concerns exist in two main areas: (a) possible target enclosure failure from impact of thermal shocks on the wall due to its direct heating from the proton beam and the loads transferred from the mercury compression waves and (b) impact of the compression-cum-rarefaction wave-induced effects such as cavitation bubble emanation and fluid surging. Preliminary stress evaluations indicate stress levels approaching yielding conditions and beyond in select regions of the target. Also, the induction of cavitation (which could assist in attenuation) can also release gases that may accumulate at undesirable locations and impair heat transfer. Fortunately, powerful approaches also exist that if properly applied can conclusively mitigate thermal shock issues. The general philosophy being proposed for addressing thermal shock-related issues for SNS is intelligently designing their way out. To succeed in such a philosophy requires knowledge of one or more key phenomena or mechanisms that provide conclusive and compelling benefits that if properly harnessed into the design will automatically address several issues. The general approach is based on use of wave energy attenuation via use of appropriately configures scattering centers (such as gas-filled low-impedance cylinders/spheres, or gas injection) in the bulk or at liquid-structure interface regions. This paper provides a perspective overview of scoping assessments that demonstrate via simulation the degree of attenuation one may expect with introduction of scattering centers (SCs) modest void fractions in mercury. A companion paper presents experimental confirmation.

• Research Organization: Oak Ridge National Lab., TN (US)
• OSTI ID: 20086961
• Journal Information: Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Vol. 82; ISSN 0003-018X; ISSN TANSAO
• Country of Publication: United States
• Language: English

Related Subjects

07 ISOTOPE AND RADIATION SOURCES
43 PARTICLE ACCELERATORS
ACCELERATOR FACILITIES
ENERGY ABSORPTION
ENERGY LOSSES
LIQUID METALS
MERCURY
NEUTRON SOURCES
PROTON BEAMS
TARGETS
THERMAL SHOCK
VOID FRACTION