CylinderSector can't have an aperture angle greater than 180°

[nplinden]

Bug Description

Hi,
I am trying to build a cylinder sector with an aperture angle higher than 180°. This seems to not be possible using the current implementation of the openmc.model.CylinderSector class.

Here are the result when using the default CylinderSector constructor with $\theta_1 = 0$ and $\theta_2 \in [10, 350]$:

And here are the results when using the CylinderSector.from_theta_alpha constructor with $\alpha = 45°$ and $\theta \in [10, 350]$:

It's seems that once the place defined by $\theta_2$ crosses the other plane, the boolean operations used to get the sector change and the current implementation fails.
Here's what I mean:

Steps to Reproduce

Here's the script I use to generate the gif:

import openmc
import matplotlib.pyplot as plt
import numpy as np
from pathlib import Path


def build_default(angle):
    openmc.reset_auto_ids()
    model = openmc.Model()
    fuel = openmc.Material()
    fuel.add_nuclide("Pu239", 1.)
    fuel.set_density("g/cm3", 10)
    coolant = openmc.Material()
    coolant.add_nuclide("Cl35", 1.)
    coolant.set_density("g/cm3", 2)
    model.materials = openmc.Materials(materials=[fuel, coolant])

    sector = openmc.model.CylinderSector(
        r1 = 1,
        r2 = 2,
        theta1=0,
        theta2=angle,
        center=(0, 0),
        axis="z"
    )
    cells = [
        openmc.Cell(region=-sector, fill=fuel),
        openmc.Cell(region=+sector, fill=coolant)
    ]
    model.geometry = openmc.Geometry(root=openmc.Universe(cells=cells))
    return model

def build_alpha(angle):
    openmc.reset_auto_ids()
    model = openmc.Model()
    fuel = openmc.Material()
    fuel.add_nuclide("Pu239", 1.)
    fuel.set_density("g/cm3", 10)
    coolant = openmc.Material()
    coolant.add_nuclide("Cl35", 1.)
    coolant.set_density("g/cm3", 2)
    model.materials = openmc.Materials(materials=[fuel, coolant])

    sector = openmc.model.CylinderSector.from_theta_alpha(
        r1 = 1,
        r2 = 2,
        theta=angle,
        alpha=45,
        center=(0, 0),
        axis="z"
    )
    cells = [
        openmc.Cell(region=-sector, fill=fuel),
        openmc.Cell(region=+sector, fill=coolant)
    ]
    model.geometry = openmc.Geometry(root=openmc.Universe(cells=cells))
    return model


Path("default").mkdir(exist_ok=True)
for i, angle in enumerate(np.arange(10, 360, 10)):
    fig, ax = plt.subplots(1, 1)
    model = build_default(angle)
    fig.suptitle("Default Constructor")
    print(i)
    print("built")
    model.plot(pixels=(700, 700), axes=ax)
    print("plotted")
    ax.set_title(r"$\theta_1 = %d \quad \theta_2 = %d$" % (0, angle))
    fig.savefig(f"default/{i:03d}.png")
    plt.close()

Path("alpha").mkdir(exist_ok=True)
for i, angle in enumerate(np.arange(10, 360, 10)):
    fig, ax = plt.subplots(1, 1)
    model = build_alpha(angle)
    fig.suptitle("theta_alpha Constructor")
    print(i)
    print("built")
    model.plot(pixels=(700, 700), axes=ax)
    print("plotted")
    ax.set_title(r"$\theta = %d \quad \alpha = %d$" % (angle, 45))
    fig.savefig(f"alpha/{i:03d}.png")
    plt.close()

Environment

I use the develop branch on Ubuntu 20.04

I have a new implementation ready but i'd love some feedback on this issue before making a PR.

Cheers