A3 Test Stand Shielding Considerations and Dose Rate Analysis
The document discusses shielding considerations for the A3 Test Stand, covering radiation protection principles, dose rate responses, and calculation methods. It includes information on shielding scenarios, dose rate boundaries relative to NASA facilities during operations, using the MCNP6 code for analysis and validation against neutron and photon experiments. The results provide insights into dose rates from neutrons and gamma rays in various shielding scenarios, emphasizing the importance of time, distance, and shielding in radiation protection.
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Presentation Transcript
Shielding Considerations for A3 Test Stand ROM 27 June 2017 .1
Radiation Protection 10 CFR Part 20 Occupational dose limits 5 rem per year (whole body) Dose limits for members of the public 100 mrem per year 2 mrem per hour Basic Principles of Radiation Protection: Time, Distance, Shielding Source: https://www.nrc.gov/about-nrc/radiation/protects-you/protection-principles.html .2
Dose Rate Response After Shutdown For illustration: Dose rate decreases by a factor of 100 in 24 hours Similar response expected for 500MWt engine (with shorter burn time) Source: NERVA Program document, TID/SNA-1304, accessed at https://www.osti.gov/scitech/servlets/purl/4221346. .4
A3 Test Stand Shielding Considerations Calculation Method: MCNP6 (Monte Carlo N-Particle) radiation transport code used for shielding analysis: an industry standard for shielding calculations, developed and maintained by Los Alamos National Laboratory MCNP6 has been qualified for simulating safety-related components of the BWXT mPower Small Modular Reactor design program Validated against published neutron and photon shielding experiments Results (excluding gamma rays from neutron activation of test stand structures): Test capsule with clamshell shield Dose rate from neutrons and gamma rays from 500 MW LEU core (mrem/h) 500 ft 1.68E+07 4.26E+05 Shielding scenario 1000 ft 1.75E+06 3.36E+04 test cell only test cell with shielding clamshell* test cell, shielding clamshell, and 2ft concrete** test cell, shielding clamshell, and 4ft concrete test cell, no clamshell, and 4ft concrete test cell, shielding clamshell, and 5ft concrete test cell, shielding clamshell, and 6ft concrete *Clamshell consists of aluminum shell containing borated water (700 ppm) and lead liner **Concrete extends to ground level for all scenarios 1.20E+04 239.1 4.39E+03 34.9 ~8 1.94E+03 46.7 1.04E+03 7.3 ~1.4 Test capsule with concrete .5
A3 Test Stand Shielding Considerations Dose rate boundaries relative to NASA facilities during NTP operation: Distance from 4-ft concrete shield (ft) mrem/h 3000 ft 500 1000 2000 2500 3000 5000 239.1 46.7 11.7 7.5 5.2 1.9 2000 ft 1000 ft Combination of shielding and controlled area size will determine ROM impact. .6
A3 Test Stand Shielding Considerations mrem/h (500 ft) 1.6E+14 1.3E+12 1.0E+10 Doses from neutron scatter through clamshell and 4-ft concrete shield to ground level 8.4E+07 6.8E+05 5.5E+03 4.4E+01 3.6E-01 2.9E-03 2.3E-05 Note: A full length shield will be required to reduce scattering contributions to the dose rate. .7
Follow On Analyses Operational dose rates Shielded and unshielded Function of time after shutdown Function of distance Source: NERVA Program document, WANL-TNR-230, Technical Summary Report of NERVA Program, Phase I NRX & XE, Volume I, Engineering Design and Analysis Techniques and Development wording legibility not required for display of concept for information only Source: NERVA Program document, TID/SNA-1304, accessed at https://www.osti.gov/scitech/servlets/purl/4221346. .8
