SAFETY CONSIDERATIONS FOR SHIELDDOOR CONTROL SYSTEMS
H.A. Watkins†, W. Barkley, C. Hatch, D. Martinez, D. Rai, E. Simakov | Los Alamos National Lab

Abstract

The Accelerator Operations and Technology
division is upgrading the control system for a 33ton shield door that will be used when theCathodes and RF Interactions in Extremes(CARIE) accelerator begins operations. The door
was installed in the 1990’s but safety standards
such as ISO 13849-1 have since emerged which
provide safety requirements and guidance on theprinciples for the design and integration of safetyrelated parts of a control system. Applying thisstandard, a safety controller, safety relays and alight curtain barrier have been added to eliminate
injury and exposure of personnel to potential
hazards during door operations.

“HOW we do things is
as important as WHAT
we do.” – Thom Mason, Lab Director LANL
Overview of CARIE
Los Alamos National Lab (LANL) is starting
construction of a new C-band (5.712GHz)
accelerator test facility for cathode, accelerator,and material science studies. The new facility iscalled Cathode and RF Interactions in Extremes(CARIE). This accelerator will reside in a radiation
protection vault on the Los Alamos Neutron
Science Center (LANSCE) mesa. This location
will house a cryo-cooled copper RF photoinjector
with a high QE cathode and a high gradientaccelerator section with beam power up to 20kW.

What is Safety? What is Risk?
Control system engineers must incorporate safety
into designs to provide the protective measuresneeded to insure safe operations. Control systemsafety can be defined as “freedom of the operator
from unacceptable risk.” This infers that there isminimal level of risk involved even when a system
is considered safe.

Possibility of avoiding hazard
P1: Possible under specific conditions
P2: Scarcely possible

S1
F1

Risk = Severity of Harm x Probabilityof the Occurrence of Harm
Risk Assessment
Control system engineers should begin with a risk
assessment using the flow chart in figure 2 todetermine limits, hazards, risk and the protective
measures needed to mitigate exposure to thehazards. This risk assessment was completed forthe shield door project and resulted in a design tominimize operator exposure to identified hazards.
STARTDETERMINE THE
LIMITS OF THEMACHINEPROTECTIVE MEASURES
IMPLEMENTED BY
DESIGNERSIDENTIFY HAZARDSFrequency or exposure to hazard
F1: Seldom to less often
F2: Frequent to continuous

Severity of Injury
S1: Slight
S2: Serious

P1S2S

F1F2F

P1

P2P

P1P2P

F2F

P2P

P1P2P

Degreeof Risk
PLrabcde

Figure 4: Risk Estimation Flow Chart

Evaluate Risk and Implement Protective
Measures
Now that the hazard and PLr have been identified,
it is possible to implement measures to reduce theexposure to the hazard in the form of protectivemeasures.

Risk Analysis

Inherently Safe
Design Measures
ESTIMATE RISKEngineering Controls
Safeguarding
Measures

EVALUATE RISK

Administrative Controls••Motion
Risk Assessment

Warning signs
Warning signals

NO

RISK ADEQUATELYREDUCED?

Safety Logic andTesting

Figure 5: Light Barrier Safety Design (PLe rating)

YES
COMPLETE

Figure 2: Risk Assessment Flowchart

Determine Limits and Identify Hazards
The shield door project determined that the limitsof the shield door were based on the track
structure and the stroke of the hydraulic cylinder.
The shield doors specific mechanical hazard was
identified as crushing.

LightBarrier

Figure 1: Radiation Shield Vault

Shield Vault
CARIE will reside in a 12 by 25-foot interior vault
that uses 4-foot-thick magnetite blocks to shield
the exterior control and operations areas. A 33ton moveable shield door separates the vault fromthe control room. When closed during CARIE
operation, the door protects personnel fromneutron and bremsstrahlung radiation, activatedair, and ozone. The door is constructed of 12magnetite concrete blocks welded together on
their edges and welded to a reinforced concretebase. The door is mounted on four sets of Hilman
rollers and guided by tracks on the floor, the door
is opened and closed by a hydraulic piston.

Figure 6: Shield Door Opening and Existing Hydraulic System

Figure 3: Mechanical Safety Hazards

Estimate Risk
The risk estimation chart (see Fig. 4) allows anengineer to determine the degree of risk as aperformance level requirement (PLr) given theseverity of injury, frequency of exposure to thehazard and the possibility of avoiding the hazard.

Managed by Triad National Security, LLC, for the U.S. Department of Energy’s NNSA.

Conclusion
Engineered safety controls and administrative
controls were implemented to reduce the risk ofhazard exposure to a minimal level for operatorsof the shield door. Los Alamos National Lab has
instituted a new focus on disciplined operations.
This focus reminds employees to use the safe
conduct of research principals to cultivate aquestioning attitude about safety and reminds all
employees to maintain a healthy respect for what
can go wrong.
† hwatkins@lanl.gov
LA-UR-23-30122